Solid oxide fuel cell (SOFC) energy system waste heat multi-stage utilization structure and optimization method

Abstract

The invention belongs to the technical field of SOFC waste heat utilization, and particularly discloses an SOFC energy system waste heat multi-stage utilization structure and an optimization method. The waste heat multi-stage utilization structure is designed on the basis of improvement of an existing triple-effect absorption refrigerator, switching of three efficiency modes is achieved through the valve and the waste gas branch which are additionally arranged, and on one hand, it is guaranteed that refrigeration output can be achieved when an SOFC energy system operates at low power or the heat power of absorbable waste gas is low; and on the other hand, when the SOFC energy system operates at high power or rated power, refrigeration output can still be conducted in a high-COP multi-effect mode. The COP is not reduced, the power interval of refrigeration output is improved, the defect that a multi-effect absorption refrigerator cannot refrigerate when the heat grade of waste gas is low is overcome, and the performance of the combined cooling heating and power system with the SOFC as the energy core is improved.

Description

Technical Field

[0001] This application belongs to the field of SOFC waste heat utilization technology, and more specifically, relates to a multi-stage utilization structure and optimization method for SOFC energy system waste heat. Background Technology

[0002] High-temperature solid oxide fuel cells (SOFCs) are a competitive option for facilitating the transition of human energy structure from fossil fuels to fully renewable energy electricity production. Unlike low-temperature proton exchange membrane fuel cells, SOFCs can directly use hydrocarbons such as natural gas as fuel, eliminating the need for expensive pure hydrogen. SOFCs not only have significantly higher power generation efficiency than traditional gas turbines, but also produce very high exhaust gas temperatures, allowing for the cascade utilization of heat and cold by incorporating high-grade waste heat recovery cycles and absorption chillers.

[0003] Due to the high temperature of the exhaust gas, waste heat refrigeration equipment typically employs double- or triple-effect lithium bromide absorption chillers with high coefficients of performance (COP) for cooling output. While more effects result in higher cooling capacity, they also place higher demands on the exhaust gas temperature. To ensure the chiller can absorb sufficient heat for normal operation, the minimum starting thermal power of multi-effect chillers is usually also higher. Therefore, when an SOFC energy system operates at low power, the exhaust gas flow rate and temperature are low, and the waste heat may not be sufficient to expel water vapor from the generator, thus failing to generate cooling capacity. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to provide a multi-stage waste heat utilization structure and optimization method for SOFC energy systems, which aims to solve the technical problem that multi-effect absorption chillers cannot utilize low-temperature waste heat when SOFCs are operating at low power.

[0005] The first aspect of this application relates to a multi-stage waste heat utilization structure for an SOFC energy system, comprising: A triple-effect absorption chiller is used to refrigerate the exhaust gas discharged from an SOFC energy system. The medium-temperature exhaust gas branch is used to guide the heat of the exhaust gas into the medium-pressure generator of the triple-effect absorption chiller; the low-temperature exhaust gas branch is used to guide the heat of the exhaust gas into the low-pressure generator of the triple-effect absorption chiller. The zero two-way valve is used to control the direct discharge of the exhaust gas; the first two-way valve is used to control the exhaust gas to pass through the high-pressure generator of the triple-effect absorption chiller; the second two-way valve is used to control the exhaust gas to pass through the medium-pressure generator; the third two-way valve is used to control the exhaust gas to pass through the low-pressure generator; the fourth two-way valve is used to control the gaseous refrigerant in the high-pressure generator to enter the low-pressure generator; the fifth two-way valve is used to control the gaseous refrigerant in the high-pressure generator and the medium-pressure generator to enter the condenser of the triple-effect absorption chiller; the sixth two-way valve is used to control the working fluid pair in the high-pressure generator to enter the medium-pressure generator; and the seventh two-way valve is used to control the working fluid pair in the medium-pressure generator to enter the low-pressure generator. The first three-way valve is used to control the working fluid pair in the absorber of the triple-effect absorption chiller to enter the high-pressure generator or the medium-pressure generator; the second three-way valve is used to control the working fluid pair in the absorber to enter the first three-way valve or the low-pressure generator. The control unit is used to control each two-way valve and three-way valve to realize the single-effect mode, double-effect mode or triple-effect mode of the SOFC energy system waste heat multi-stage utilization structure.

[0006] Preferably, in the single-effect mode, the zero two-way valve, the first two-way valve, the second two-way valve, the fourth two-way valve, the fifth two-way valve, the sixth two-way valve, and the seventh two-way valve are closed, the third two-way valve is open, the first three-way valve is closed in all three directions, and the second three-way valve controls the working fluid in the absorber to enter the low-pressure generator.

[0007] Preferably, in the dual-effect mode, the zero two-way valve, the first two-way valve, the third two-way valve, the fourth two-way valve, and the sixth two-way valve are closed, while the second two-way valve, the fifth two-way valve, and the seventh two-way valve are open; the first three-way valve controls the working fluid pair in the absorber to enter the medium-pressure generator; and the second three-way valve controls the working fluid pair in the absorber to enter the first three-way valve.

[0008] Preferably, in the triple-effect mode, the zero two-way valve, the second two-way valve, and the third two-way valve are closed, and the first two-way valve, the fourth two-way valve, the fifth two-way valve, the sixth two-way valve, and the seventh two-way valve are open. The first three-way valve controls the working fluid pair in the absorber to enter the high-pressure generator, and the second three-way valve controls the working fluid pair in the absorber to enter the first three-way valve.

[0009] Preferably, the control unit is used to derive the absorbable heat power in the single-effect mode, double-effect mode and triple-effect mode; If the absorbable heat power in the triple-effect mode is greater than the preset triple-effect mode start-up threshold, then control each two-way valve and three-way valve to achieve the triple-effect mode; otherwise, continue to determine if the absorbable heat power in the double-effect mode is greater than the preset double-effect mode start-up threshold. If so, control each two-way valve and three-way valve to achieve the double-effect mode; otherwise, continue to determine if the absorbable heat power in the single-effect mode is greater than the preset single-effect mode start-up threshold. If so, control each two-way valve and three-way valve to achieve the single-effect mode; otherwise, open the zeroth two-way valve, close all two-way valves except the zeroth two-way valve, and close all three-way valves.

[0010] Preferably, the absorbable heat power in the single-effect mode is specifically: ; The absorbable heat power in the dual-effect mode is specifically as follows: ; The absorbable heat power in the triple-effect mode is specifically as follows: ; in, The specific heat capacity of the exhaust gas. The flow rate of the exhaust gas. The temperature of the exhaust gas, To minimize the heat exchange temperature difference, This refers to the minimum operating temperature of the high-voltage generator. This is the minimum operating temperature of the medium-pressure generator. This is the minimum operating temperature of the low-pressure generator.

[0011] Preferably, one end of the medium-temperature exhaust gas branch is connected to the exhaust gas discharge passage, and the other end passes through the medium-pressure generator and connects to the outside; one end of the low-temperature exhaust gas branch is connected to the exhaust gas discharge passage, and the other end passes through the medium-pressure generator and connects to the outside.

[0012] Preferably, the first three-way valve and the second three-way valve are located on the working fluid pair passage from the absorber to the high-pressure generator. The first end of the first three-way valve is connected to the medium-pressure generator, the second end is connected to the high-pressure generator, and the third end is connected to the second three-way valve. The first end of the second three-way valve is connected to the low-pressure generator, the second end is connected to the first three-way valve, and the third end is connected to the absorber.

[0013] The second aspect of this application relates to an optimization method for a multi-stage waste heat utilization structure of an SOFC energy system, the optimization method being based on any of the multi-stage waste heat utilization structures of the SOFC energy system described in the first aspect, and comprising the following steps: (1) Derive the absorbable heat power in the single-effect mode, double-effect mode and triple-effect mode; (2) Determine whether the absorbable heat power in the triple-effect mode is greater than the preset triple-effect mode start-up threshold. If so, control each two-way valve and three-way valve to realize the triple-effect mode; otherwise, proceed to step (3). (3) Determine whether the absorbable heat power in the dual-effect mode is greater than the preset dual-effect mode start-up threshold. If so, control each two-way valve and three-way valve to realize the dual-effect mode; otherwise, proceed to step (4). (4) Determine whether the absorbable heat power in the single-effect mode is greater than the preset single-effect mode start-up threshold. If so, control each two-way valve and three-way valve to realize the single-effect mode; otherwise, proceed to step (5). (5) Open the zero-second valve, close all two-way valves except the zero-second valve, and close all three-way valves.

[0014] Preferably, the absorbable heat power in the single-effect mode is specifically: ; The absorbable heat power in the dual-effect mode is specifically as follows: ; The absorbable heat power in the triple-effect mode is specifically as follows: ; in, The specific heat capacity of the exhaust gas. The flow rate of the exhaust gas. The temperature of the exhaust gas, To minimize the heat exchange temperature difference, This refers to the minimum operating temperature of the high-voltage generator. This is the minimum operating temperature of the medium-pressure generator. This is the minimum operating temperature of the low-pressure generator.

[0015] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: This application modifies an existing triple-effect absorption chiller to design a multi-stage waste heat utilization structure. This structure achieves switching between three efficiency modes through additional valves and waste gas branches. On the one hand, it ensures cooling output even when the SOFC energy system operates at low power or when the absorbable waste gas heat quality is low. On the other hand, when the SOFC energy system operates at high power or rated power, it can still output cooling in a high-COP multi-effect mode. While ensuring that the COP does not decrease, it expands the power range of cooling output, compensating for the limitation of multi-effect absorption chillers in failing to cool when the waste gas heat quality is low, thus improving the performance of the combined cooling, heating, and power system with SOFC as its energy core. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structural composition of a multi-stage waste heat utilization structure for an SOFC energy system provided in an embodiment of this application.

[0017] Figure 2 This is a schematic diagram of an optimization method for a multi-stage waste heat utilization structure of an SOFC energy system provided in an embodiment of this application.

[0018] Figure 3 This is a schematic diagram of the COP and start-up threshold of the structure of this application under the single-effect mode, double-effect mode, and triple-effect mode provided in the embodiments of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] In this application, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order of objects. For example, "first two-way valve" and "second two-way valve," etc., are used to distinguish different two-way valves, not to describe a specific order of two-way valves.

[0021] In this application, the term "electrical connection" can refer to a direct circuit connection or a signal transmission via a communication protocol.

[0022] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0023] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0024] The embodiments of this application are described below with reference to the accompanying drawings.

[0025] like Figure 1As shown, a multi-stage waste heat utilization structure for an SOFC energy system includes: a control unit, a triple-effect absorption chiller, a medium-temperature waste gas branch, a low-temperature waste gas branch, a zero two-way valve V0, a ​​first two-way valve V1, a second two-way valve V2, a third two-way valve V3, a fourth two-way valve V4, a fifth two-way valve V5, a sixth two-way valve V6, a seventh two-way valve V7, a first three-way valve VT1, and a second three-way valve VT2.

[0026] The triple-effect absorption chiller in this application adopts a conventional structure, including: High-pressure generator, medium-pressure generator, low-pressure generator, high-temperature heat exchanger, medium-temperature heat exchanger, low-temperature heat exchanger, condenser, throttle valve, evaporator, absorber, working fluid pump, cooling water pump, cooling tower, cooling water pump.

[0027] In this embodiment, the circulating working fluid of the triple-effect absorption chiller is a lithium bromide solution. The triple-effect absorption chiller is divided into three parts: high-pressure high-temperature effect (composed of a high-pressure generator and a high-temperature heat exchanger), medium-pressure medium-temperature effect (composed of a medium-pressure generator and a medium-temperature heat exchanger), and low-temperature low-pressure effect (composed of a low-pressure generator and a low-temperature heat exchanger).

[0028] Absorption refrigeration is driven by thermal energy. It uses lithium bromide solution to absorb and release water vapor, and uses the heat absorbed by the evaporation of water under low pressure to produce cooling capacity.

[0029] The following explains the operating principle of a triple-effect absorption chiller: The exhaust gas generated during the operation of the SOFC energy system passes through a high-pressure generator, where it releases heat into a lithium bromide solution. The exhaust gas is then cooled before being discharged. Under high pressure, the lithium bromide solution absorbs heat, and water vapor is released from the solution, serving as a heat source for the medium-pressure generator. The increased concentration of the lithium bromide solution then releases heat through a high-temperature heat exchanger before entering the medium-pressure generator. In the medium-pressure generator, the lithium bromide solution absorbs heat and further releases water vapor, increasing its concentration further. The water vapor released from the high-pressure and medium-pressure generators combines to form a heat source for the low-pressure generator. The even more concentrated lithium bromide solution releases heat in a medium-temperature heat exchanger before entering the low-pressure generator.

[0030] All the water vapor precipitated in the high-pressure, medium-pressure, and low-pressure generators converges and flows into the condenser, where it is cooled and liquefied by circulating cooling water. It is then throttled to a lower pressure by a throttling valve and enters the evaporator. In the evaporator, the water absorbs heat from the chilled water and evaporates. The chilled water temperature decreases, allowing it to provide cooling. Subsequently, the water vapor is absorbed by the lithium bromide solution in the absorber, and the heat generated by the phase change is carried away by the cooling water. The lithium bromide solution reformed in the absorber is pumped through high-temperature, medium-temperature, and low-temperature heat exchangers, absorbing heat before returning to the high-pressure generator, completing the cycle.

[0031] In an embodiment of this application, a multi-stage waste heat utilization structure for an SOFC energy system is described: The medium-temperature exhaust gas branch is used to guide the heat of the exhaust gas into the medium-pressure generator of the triple-effect absorption chiller; the low-temperature exhaust gas branch is used to guide the heat of the exhaust gas into the low-pressure generator of the triple-effect absorption chiller; one end of the medium-temperature exhaust gas branch is connected to the exhaust gas discharge passage, and the other end passes through the medium-pressure generator and connects to the outside; one end of the low-temperature exhaust gas branch is connected to the exhaust gas discharge passage, and the other end passes through the medium-pressure generator and connects to the outside.

[0032] In an embodiment of this application, a multi-stage waste heat utilization structure for an SOFC energy system is described: The zero-two-way valve V0 is used to control the direct discharge of the exhaust gas; the first two-way valve V1 is used to control the exhaust gas to pass through the high-pressure generator of the triple-effect absorption chiller; the second two-way valve V2 is used to control the exhaust gas to pass through the medium-pressure generator; the third two-way valve V3 is used to control the exhaust gas to pass through the low-pressure generator; the fourth two-way valve V4 is used to control the gaseous refrigerant in the high-pressure generator to enter the low-pressure generator; the fifth two-way valve V5 is used to control the gaseous refrigerant in the high-pressure generator and the medium-pressure generator to enter the condenser of the triple-effect absorption chiller; the sixth two-way valve V6 is used to control the working fluid pair in the high-pressure generator to enter the medium-pressure generator; and the seventh two-way valve V7 is used to control the working fluid pair in the medium-pressure generator to enter the low-pressure generator.

[0033] The first three-way valve VT1 is used to control the working fluid pair in the absorber of the triple-effect absorption chiller to enter the high-pressure generator or the medium-pressure generator; the second three-way valve VT2 is used to control the working fluid pair in the absorber to enter the first three-way valve VT1 or the low-pressure generator; the first three-way valve VT1 and the second three-way valve VT2 are located on the working fluid pair passage from the absorber to the high-pressure generator, the first end 1 of the first three-way valve VT1 is connected to the medium-pressure generator, the second end 2 is connected to the high-pressure generator, and the third end 3 is connected to the second three-way valve VT2; the first end 1 of the second three-way valve VT2 is connected to the low-pressure generator, the second end 2 is connected to the first three-way valve VT1, and the third end 3 is connected to the absorber.

[0034] The types of two-way valves and three-way valves are not limited in this application. In this embodiment, both the two-way valve and the three-way valve are solenoid valves.

[0035] The SOFC energy system waste heat multi-stage utilization structure described in this application determines whether the three generators (high-pressure generator, medium-pressure generator, and low-pressure generator) of the triple-effect absorption chiller participate in the cooling of the waste gas by opening and closing various valves, thus obtaining three different operating modes: Triple-effect mode: High-pressure generator, medium-pressure generator, low-pressure generator, high-temperature heat exchanger, medium-temperature heat exchanger, and low-temperature heat exchanger are all in operation. Dual-effect mode: Medium-pressure generator, low-pressure generator, medium-temperature heat exchanger, and low-temperature heat exchanger are in operation; Single-effect mode: Low-pressure generator and low-temperature heat exchanger are in operation.

[0036] In an embodiment of this application, a multi-stage waste heat utilization structure for an SOFC energy system is described: The control unit is used to control each two-way valve and three-way valve to realize the single-effect mode, double-effect mode or triple-effect mode of the SOFC energy system waste heat multi-stage utilization structure.

[0037] To achieve the above objectives, the control logic of the control unit is as follows, specifically as follows: Figure 2 As shown: S1. Collect the temperature and flow rate of the exhaust gas discharged from the current SOFC power generation system.

[0038] S2. Calculate the absorbable heat power in single-effect, double-effect, and triple-effect modes, referring to the following formula: The absorbable heat power in the single-effect mode is specifically as follows: ; The absorbable heat power in the dual-effect mode is specifically as follows: ; The absorbable heat power in the triple-effect mode is specifically as follows: ; in, The specific heat capacity of the exhaust gas. The flow rate of the exhaust gas. The temperature of the exhaust gas, To minimize the heat exchange temperature difference, This refers to the minimum operating temperature of the high-voltage generator. This is the minimum operating temperature of the medium-pressure generator. This is the minimum operating temperature of the low-pressure generator.

[0039] According to the second law of thermodynamics, the temperature of the exhaust gas leaving the generator must be higher than the internal temperature of the generator; therefore, a minimum heat exchange temperature difference is set. Furthermore, the thermal power start-up threshold and minimum operating temperature of each stage of the generator are determined by the inherent characteristics of the triple-effect absorption chiller.

[0040] S3. Compare the absorbable heat power and the start-up threshold under different operating modes sequentially. If the absorbable heat power in the current mode is greater than the start-up threshold, the chiller will operate in that mode or shut down. Specifically: S31. Determine whether the absorbable heat power in the triple-effect mode is greater than the preset triple-effect mode start-up threshold. If so, control each two-way valve and three-way valve to realize the triple-effect mode; otherwise, proceed to step S32.

[0041] S32. Determine whether the absorbable heat power in the dual-effect mode is greater than the preset dual-effect mode start-up threshold. If so, control each two-way valve and three-way valve to realize the dual-effect mode; otherwise, proceed to step S33.

[0042] S33. Determine whether the absorbable heat power in the single-effect mode is greater than the preset single-effect mode start-up threshold. If so, control each two-way valve and three-way valve to realize the single-effect mode; otherwise, proceed to step S34.

[0043] S34. The triple-effect absorption chiller stops, meaning that the absorbable heat power in different operating modes does not meet the start-up threshold, and all exhaust gas is discharged. The valve status is: the zero-second valve V0 is open, all two-way valves except the zero-second valve V0 are closed, and all three-way valves are closed.

[0044] In triple-effect mode, the control unit controls the zero two-way valve V0, the second two-way valve V2, and the third two-way valve V3 to close, and the first two-way valve V1, the fourth two-way valve V4, the fifth two-way valve V5, the sixth two-way valve V6, and the seventh two-way valve V7 to open; port 1 of the first three-way valve VT1 is closed, and ports 2 and 3 are open, controlling the working fluid in the absorber to enter the high-pressure generator; port 1 of the second three-way valve VT2 is closed, and ports 2 and 3 are open, controlling the working fluid in the absorber to enter the first three-way valve.

[0045] In dual-effect mode, the control unit controls the zero two-way valve V0, the first two-way valve V1, the third two-way valve V3, the fourth two-way valve V4, and the sixth two-way valve V6 to close, while the second two-way valve V2, the fifth two-way valve V5, and the seventh two-way valve V7 are opened; the second three-way valve VT1 has its port 2 closed and its ports 1 and 3 open, controlling the working fluid in the absorber to enter the medium-pressure generator; the second three-way valve VT2 has its port 1 closed and its ports 2 and 3 open, controlling the working fluid in the absorber to enter the first three-way valve.

[0046] In single-effect mode, the control unit controls the zero two-way valve V0, the first two-way valve V1, the second two-way valve V2, the fourth two-way valve V4, the fifth two-way valve V5, the sixth two-way valve V6, and the seventh two-way valve V7 to close, and the third two-way valve V3 to open; the first three-way valve VT1 is closed in all three directions; the second three-way valve VT2 has its port 2 closed and its ports 1 and 3 open, controlling the working fluid in the absorber to enter the low-pressure generator.

[0047] S4. At the next moment, return to step S1 to perform the above data collection and calculation.

[0048] The technical solution of this application will now be further illustrated through an embodiment: In this embodiment, the flow rate of the dilute lithium bromide solution leaving the absorber is set to 0.26 kg / s, with a mass fraction of 50%. The mass fraction of the concentrated lithium bromide solution entering the absorber is 60%. The operating pressures of the high-pressure generator, medium-pressure generator, and low-pressure generator are 93.3 kPa, 64.8 kPa, and 7.8 kPa, respectively.

[0049] like Figure 3 As shown in the illustration, this embodiment of the application continuously increases the absorbable heat power by gradually increasing the operating power of the SOFC energy system. The corresponding generators can only start operating and cause refrigerant water vapor to be released when the absorbable heat power flowing through the high-pressure generator, medium-pressure generator, and low-pressure generator exceeds 16.1kW, 13.3kW, and 9.4kW, respectively. With increasing heat power input, the COP is highest in the triple-effect mode, followed by the double-effect mode, and lowest in the single-effect mode. At a heat power input of 50kW, the COPs are 1.94, 1.37, and 0.74, respectively.

[0050] It is clear that if a traditional double-effect or triple-effect absorption chiller is used, the traditional triple-effect absorption chiller will not be able to operate when the absorbable heat power is less than 13.3kW and 16.1kW, respectively. However, in the multi-stage utilization structure of this application, when the absorbable heat power is 9.4kW-13.3kW, it operates in single-effect mode; when the absorbable heat power is 13.3kW-16.1kW, it operates in double-effect mode; and when the absorbable heat power is greater than 16.1kW, it operates in triple-effect mode. This expands the cooling output range downwards without affecting the chiller's cooling performance at the corresponding number of effects.

[0051] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0052] Furthermore, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0053] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. "Fixed connection" refers to a connection where the relative positional relationship remains unchanged after connection. "Rotary connection" refers to a connection where the components can rotate relative to each other after connection. "Sliding connection" refers to a connection where the components can slide relative to each other after connection. The directional terms mentioned in the embodiments of this application, such as "top," "bottom," "inner," "outer," "left," and "right," are only for reference to the directions in the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of this application, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0054] Furthermore, the mathematical concepts mentioned in the embodiments of this application, such as symmetry, equality, parallelism, and perpendicularity, are limitations specific to the current technological level, rather than absolute and strict mathematical definitions. Slight deviations are permissible; approximations of symmetry, equality, parallelism, and perpendicularity are all acceptable. For example, "A and B are parallel" means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. "A and B are perpendicular" means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0055] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology 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-stage utilization structure of waste heat of a SOFC energy system, characterized in that, The application relates to a three-effect absorption refrigerator for refrigeration by using the exhaust gas of a SOFC energy system. A medium-temperature exhaust gas branch for guiding the heat of the exhaust gas into a medium-pressure generator of the three-effect absorption refrigerator; a low-temperature exhaust gas branch for guiding the heat of the exhaust gas into a low-pressure generator of the three-effect absorption refrigerator; A zeroth two-way valve for controlling the direct discharge of the exhaust gas; a first two-way valve for controlling the exhaust gas through a high-pressure generator of the three-effect absorption refrigerator; a second two-way valve for controlling the exhaust gas through the medium-pressure generator; a third two-way valve for controlling the exhaust gas through the low-pressure generator; a fourth two-way valve for controlling the gaseous refrigerant in the high-pressure generator into the low-pressure generator; A fifth two-way valve for controlling the gaseous refrigerant in the high-pressure generator and the medium-pressure generator into a condenser of the three-effect absorption refrigerator; a sixth two-way valve for controlling the working medium pair in the high-pressure generator into the medium-pressure generator; a seventh two-way valve for controlling the working medium pair in the medium-pressure generator into the low-pressure generator; A first three-way valve for controlling the working medium pair in an absorber of the three-effect absorption refrigerator into the high-pressure generator or the medium-pressure generator; A second three-way valve for controlling the working medium pair in the absorber into the first three-way valve or the low-pressure generator; The control unit is used for controlling the two-way valves and the three-way valves to realize a single-effect mode, a double-effect mode or a three-effect mode of the SOFC energy system waste heat multi-stage utilization structure. In the single-effect mode, the zeroth two-way valve, the first two-way valve, the second two-way valve, the fourth two-way valve, the fifth two-way valve, the sixth two-way valve and the seventh two-way valve are closed, the third two-way valve is opened, the first three-way valve is three-way closed, and the second three-way valve controls the working medium pair in the absorber into the low-pressure generator.

2. The multi-stage waste heat utilization structure of SOFC energy system according to claim 1, characterized in that, In the double-effect mode, the zeroth two-way valve, the first two-way valve, the third two-way valve, the fourth two-way valve and the sixth two-way valve are closed, the second two-way valve, the fifth two-way valve and the seventh two-way valve are opened, the first three-way valve controls the working medium pair in the absorber into the medium-pressure generator, and the second three-way valve controls the working medium pair in the absorber into the first three-way valve.

3. The multi-stage waste heat utilization structure of SOFC energy system according to claim 1, characterized in that, In the three-effect mode, the zeroth two-way valve, the second two-way valve and the third two-way valve are closed, the first two-way valve, the fourth two-way valve, the fifth two-way valve, the sixth two-way valve and the seventh two-way valve are opened, the first three-way valve controls the working medium pair in the absorber into the high-pressure generator, and the second three-way valve controls the working medium pair in the absorber into the first three-way valve.

4. The multi-stage waste heat utilization structure of SOFC energy system according to claim 1, characterized in that, The control unit is used for deriving the absorbable heat power in the single-effect mode, the double-effect mode and the three-effect mode.

5. The multi-stage waste heat utilization structure of SOFC energy system according to claim 1, characterized in that, ​ determining whether the absorbable heat power in the triple-effect mode is greater than a preset triple-effect mode starting threshold, if yes, controlling each two-way valve and three-way valve to realize the triple-effect mode; otherwise, determining whether the absorbable heat power in the double-effect mode is greater than a preset double-effect mode starting threshold, if yes, controlling each two-way valve and three-way valve to realize the double-effect mode; otherwise, determining whether the absorbable heat power in the single-effect mode is greater than a preset single-effect mode starting threshold, if yes, controlling each two-way valve and three-way valve to realize the single-effect mode; otherwise, opening the zeroth two-way valve, closing all two-way valves except the zeroth two-way valve, and closing all three-way valves.

6. The multi-stage waste heat utilization structure of SOFC energy system according to claim 5, characterized in that, The absorbable heat power in the single-effect mode is specifically: ； The absorbable heat power in the double-effect mode is specifically: ； The absorbable heat power in the triple-effect mode is specifically: ； wherein is the specific heat capacity of the exhaust gas, is the flow rate of the exhaust gas, is the temperature of the exhaust gas, is the minimum temperature difference of heat exchange, is the minimum operating temperature of the high-pressure generator, is the minimum operating temperature of the medium-pressure generator, is the minimum operating temperature of the low-pressure generator.

7. The multi-stage waste heat utilization structure of SOFC energy system according to claim 1, characterized in that, One end of the medium-temperature exhaust gas branch is connected to the exhaust gas discharge passage, and the other end is connected to the outside after passing through the medium-pressure generator; one end of the low-temperature exhaust gas branch is connected to the exhaust gas discharge passage, and the other end is connected to the outside after passing through the medium-pressure generator.

8. The multi-stage waste heat utilization structure of SOFC energy system according to claim 1, characterized in that, The first three-way valve and the second three-way valve are located on the working medium pair passage from the absorber to the high-pressure generator, the first end of the first three-way valve is connected to the medium-pressure generator, the second end is connected to the high-pressure generator, and the third end is connected to the second three-way valve; the first end of the second three-way valve is connected to the low-pressure generator, the second end is connected to the first three-way valve, and the third end is connected to the absorber.

9. An optimization method for a multi-stage waste heat utilization structure of a SOFC energy system, characterized in that, The optimization method is based on the SOFC energy system waste heat multi-stage utilization structure of any one of claims 1-8, comprising the following steps: (1) deriving the absorbable heat power in the single-effect mode, double-effect mode and triple-effect mode; (2) determining whether the absorbable heat power in the triple-effect mode is greater than a preset triple-effect mode starting threshold, if yes, controlling each two-way valve and three-way valve to realize the triple-effect mode; otherwise, entering step (3); (3) determining whether the absorbable heat power in the double-effect mode is greater than a preset double-effect mode starting threshold, if yes, controlling each two-way valve and three-way valve to realize the double-effect mode; otherwise, entering step (4); (4) determining whether the absorbable heat power in the single-effect mode is greater than a preset single-effect mode starting threshold, if yes, controlling each two-way valve and three-way valve to realize the single-effect mode; otherwise, entering step (5); (5) opening the zeroth two-way valve, closing all two-way valves except the zeroth two-way valve, and closing all three-way valves.

10. The method of Claim 9, wherein the SOFC energy system waste heat multi-stage utilization structure is optimized by, The absorbable heat power in the single-effect mode is specifically: ； The absorbable heat power in the double-effect mode is specifically: ； The absorbable heat power in the triple-effect mode is specifically: ； wherein is the specific heat capacity of the exhaust gas, is the flow rate of the exhaust gas, is the temperature of the exhaust gas, is the minimum temperature difference for heat exchange, is the minimum operating temperature of the high-pressure generator, is the minimum operating temperature of the medium-pressure generator, is the minimum operating temperature of the low-pressure generator.

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