Normal-pressure SOFC and GT combined hybrid power generation system

Abstract

The invention provides a normal-pressure SOFC and GT combined hybrid power generation system, which belongs to the field of energy conversion and storage in renewable energy sources, and comprises a flat plate type SOFC system and a GT system, the connection between the flat-plate SOFC system and the GT system is divided into direct connection and indirect connection; the direct connection is that tail gas of the flat plate type SOFC system is mixed with fuel gas in the GT system, and the mixture is introduced into a compressor of the GT system, so that direct connection of the flat plate type SOFC system and the GT system is realized; the indirect connection is that tail gas heat of the SOFC system is transmitted to a heat exchanger in the GT system, and indirect connection of the flat plate type SOFC system and the GT system is achieved; the two connection modes are freely switched by a valve; and tail gas energy and tail gas of the flat plate type SOFC system are directly or indirectly introduced into the GT system for power generation. According to the invention, the whole hybrid power generation system can always operate under the highest efficiency.

Description

Technical Field

[0001] The present application belongs to the field of energy conversion and storage in renewable energy, and more specifically, to a hybrid power generation system combining normal pressure SOFC and GT. Background Art

[0002] Solid oxide fuel cells use solid metal oxides as electrolytes and operate at medium to high temperatures. They have the advantages of high energy conversion efficiency, low noise, stable operation and long service life. They are not limited by the Carnot cycle and can form a combined power generation system with gas turbines (GT), steam turbines, etc.

[0003] SOFC is divided into tubular SOFC and flat SOFC structures. Among them, tubular SOFC (Solid Oxide Fuel Cell) has good pressure resistance and can work under several atmospheres of pressure. The gas has been pressurized before entering the SOFC. Under pressurized conditions, the performance of SOFC will be improved. The exhaust gas at the SOFC outlet contains huge mechanical energy and thermal energy. Passing the gas into the gas turbine GT cycle can make full use of this energy, thereby improving the overall power generation power and efficiency of the system.

[0004] However, the most widely used and most promising commercial application is the flat-plate SOFC. The structure of the flat-plate SOFC determines that it cannot operate under high pressure, that is, the gas should be kept slightly higher than the atmospheric pressure before entering the SOFC for gas driving force. If the pressure is too high, it is easy to cause cracks and ruptures in the ceramic structure inside the SOFC. Therefore, it is difficult to use the flat-plate SOFC in combination with the GT cycle hybrid power generation system. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of this application is to provide a hybrid power generation system combining normal-pressure SOFC and GT, aiming to solve the problem that it is difficult to generate power under the conditions of normal-pressure operation of flat-plate SOFC and pressurized operation of GT.

[0006] To achieve the above-mentioned purpose, the present application provides a hybrid power generation system combining atmospheric pressure SOFC and GT, including: a flat-plate SOFC system and a GT system; the connection between the flat-plate SOFC system and the GT system is divided into direct connection and indirect connection;

[0007] Direct connection is to mix the tail gas of the flat-plate SOFC system with the fuel gas in the GT system and pass it into the compressor of the GT system to realize the direct connection between the flat-plate SOFC system and the GT system; indirect connection is to transfer the tail gas heat of the SOFC system to the heat exchanger between the compressor and the second burner in the GT system to realize the indirect connection between the flat-plate SOFC system and the GT system; the two connection methods are freely switched by switching valves;

[0008] Among them, the fuel gas is not pressurized before entering the flat-plate SOFC system, and the tail gas energy of the flat-plate SOFC system and the tail gas are used to directly or indirectly enter the GT system for power generation, thereby realizing the cascade utilization of the tail gas energy of the flat-plate SOFC system.

[0009] Further preferably, the flat-plate SOFC system comprises: a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a reformer, a SOFC stack and a burner;

[0010] The first output end of the first heat exchanger is connected to the cathode of the SOFC stack; the first output end of the third heat exchanger and the first output end of the fourth heat exchanger are connected to the reformer; the output end of the reformer is connected to the first input end of the second heat exchanger; the first output end of the second heat exchanger is connected to the anode of the SOFC stack; the output end of the SOFC stack is connected to the input end of the first burner; the output end of the first burner is connected to the second input end of the first heat exchanger; the second output end of the first heat exchanger is connected to the second input end of the second heat exchanger; the second output end of the second heat exchanger is connected to the second input end of the third heat exchanger; the second output end of the third heat exchanger is connected to the second input end of the fourth heat exchanger; the output end of the fourth heat exchanger is connected to the compressor input side of the GT system or the heat exchanger between the compressor and the second burner in the GT system;

[0011] The first heat exchanger is used to allow air at normal pressure to enter the cathode of the SOFC stack from the first input end; the fourth heat exchanger is used to allow fuel gas to enter the reformer through the first input end, and the third heat exchanger is used to allow water to enter the reformer through the first input end; the reformer is used to allow the output gas to enter the anode of the SOFC stack through the second heat exchanger; the first burner is used to transmit the output exhaust gas and exhaust gas energy to the GT system through the first heat exchanger, the second heat exchanger, the third heat exchanger and the fourth heat exchanger in sequence.

[0012] Further preferably, the GT system comprises a multi-way valve, a compressor, a fifth heat exchanger, a second burner and a turbine;

[0013] The output end of the compressor is connected to the first input end of the fifth heat exchanger; the first output end of the fifth heat exchanger is connected to the input end of the second burner; the output end of the second burner is connected to the turbine; the output end of the turbine is connected to the second input end of the fifth heat exchanger; the second output end of the fifth heat exchanger is used to discharge the exhaust gas;

[0014] The multi-way valve is provided with at least two paths, one path is used to mix the exhaust gas in the fourth heat exchanger with the fuel gas input from the compressor side and then enter the compressor, and the other path is used to allow the exhaust gas heat in the fourth heat exchanger to enter the second burner through the fifth heat exchanger.

[0015] Further preferably, direct connection and indirect connection are judged by power and efficiency curves, and valves are used for free switching.

[0016] Further preferably, the fuel gas is hydrogen fuel or hydrocarbon fuel, and the hydrocarbon fuel includes methane and methanol.

[0017] Further preferably, the multi-way valve is a three-way valve.

[0018] Further preferably, the first burner is arranged adjacent to the reformer and is located in the same heat box to provide the required heat for the reformer.

[0019] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art:

[0020] The flat-plate SOFC tail gas is mixed with the fuel gas in the GT system and then enters the compressor, and the energy of the flat-plate SOFC tail gas is input into the front heat exchanger of the second burner. Compared with the existing tail gas output by the first burner directly entering the turbine, this application can solve the overall design problem of the atmospheric pressure SOFC-GT combined power generation system. At the same time, the flat-plate SOFC tail gas is directly or indirectly introduced into the GT system for power generation, completing the hybrid power generation of the flat-plate SOFC and GT systems. That is, by directly or indirectly utilizing the heat of the tail gas at the outlet of the fourth heat exchanger to drive the GT cycle, the utilization efficiency of the tail gas is improved. In addition, the direct connection and indirect connection between the flat-plate SOFC system and the GT system have different maximum efficiencies in different power ranges. By flexibly switching the system mode, the entire hybrid power generation system can always operate at the highest efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of a hybrid power generation system combining atmospheric pressure SOFC and GT provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0023] like Figure 1 The figure shows a hybrid power generation system diagram of SOFC and GT under normal pressure. There are direct GT and indirect GT modes. The function of the flat-plate SOFC system is to convert the chemical energy in the fuel into electrical energy through electrochemical reactions. The function of the GT system is to compress the gas through the compressor, and after the burner burns, the gas containing huge thermal energy and mechanical energy is passed into the turbine for expansion to generate electricity. The latter can make full use of the thermal energy in the exhaust gas of the former to generate electricity, thereby improving the overall efficiency of the system.

[0024] More specifically, the present application provides a switchable direct or indirect SOFC and GT hybrid power generation system. In the two modes of direct connection between SOFC and GT or indirect connection between SOFC and GT, the SOFC cycle remains unchanged, air and fuel gas enter the SOFC at normal pressure for electrochemical reaction and power generation, and the SOFC exhaust gas is burned in the burner and used to preheat the intake air. After preheating, the exhaust gas still contains a large amount of unutilized heat energy, and at this time there is a difference between the indirect and direct GT cycles; in the direct connection between SOFC and GT, the GT directly utilizes the gas at the outlet of the fourth heat exchanger in the SOFC cycle, moderates it with the fuel gas of the GT cycle, and then introduces it into the compressor for GT cycle; in the indirect connection between SOFC and GT, the GT cycle does not directly utilize the gas at the outlet of the fourth heat exchanger in the SOFC cycle, but utilizes the exhaust gas heat through the fifth heat exchanger to improve the GT cycle efficiency.

[0025] It should be pointed out here that the air and fuel gas are not pressurized before entering the SOFC, and are almost at normal pressure (slightly higher than atmospheric pressure for other drives). By utilizing the tail gas heat and unreacted components in the SOFC, GT is used for energy cascade utilization;

[0026] It should be noted here that the direct connection between SOFC and GT and the indirect connection between SOFC and GT are judged by the power-efficiency curve and can be switched freely.

[0027] The following is a detailed description of the atmospheric pressure SOFC and GT combined hybrid power generation system provided by the present application:

[0028] In the top-level loop:

[0029] The fuel (methane) is connected to the inlet of the fourth heat exchanger, and the water is connected to the inlet of the third heat exchanger; the fuel outlet of the fourth heat exchanger and the water outlet of the third heat exchanger are connected to the inlet of the reformer;

[0030] The reformed gas is passed into the second heat exchanger, and the fuel gas outlet of the second heat exchanger is connected to the anode of the SOFC stack;

[0031] The air is connected to the inlet of the first heat exchanger, and the first heat exchanger is connected to the cathode inlet of the SOFC;

[0032] The outlets of the cathode and anode of the SOFC stack are mixed through a three-way valve and connected to the first burner; the first burner is arranged adjacent to the reformer and located in the same heat box to provide the required heat for the reformer; in addition, the outlet of the first burner is connected to the inlet of the hot end of the first heat exchanger, the outlet of the hot end of the first heat exchanger is connected to the inlet of the hot end of the second heat exchanger, the outlet of the hot end of the second heat exchanger is connected to the inlet of the hot end of the third heat exchanger, the outlet of the hot end of the third heat exchanger is connected to the inlet of the hot end of the fourth heat exchanger; the outlet of the hot end of the fourth heat exchanger is connected to the inlet of the GT system;

[0033] In direct SOFC-GT mode:

[0034] The gas at the hot end outlet of the fourth heat exchanger is directly mixed with air and methane through a three-way valve and then connected to the compressor inlet, and the compressor outlet is connected to the inlet of the fifth heat exchanger;

[0035] The gas outlet of the fifth heat exchanger is connected to the second burner, the outlet of the second burner is connected to the turbine for expansion, the outlet of the turbine is connected to the inlet of the hot end of the fifth heat exchanger, and the outlet of the hot end of the fifth heat exchanger is discharged into the atmosphere.

[0036] In the indirect SOFC-GT mode:

[0037] The hot end outlet of the fourth heat exchanger is connected to the hot end inlet of the fifth heat exchanger. At this time, the three-way valve is disconnected, and the methane is mixed with the air and connected to the compressor inlet through the three-way valve, and the compressor outlet is connected to the inlet of the fifth heat exchanger; the fifth heat exchanger outlet is connected to the second burner inlet, the second burner outlet is connected to the turbine inlet, the turbine outlet is connected to the hot end inlet of the fifth heat exchanger, and finally discharged into the atmosphere through the hot end outlet of the fifth heat exchanger.

[0038] It should be noted that in this system, the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger and the fifth heat exchanger are used to transfer heat from the high-temperature gas to the low-temperature gas, the reformer is used to reform methane to produce hydrogen; the first burner and the second burner are used to burn the gas.

[0039] In summary, compared with the prior art, the present application has the following advantages:

[0040] The flat-plate SOFC tail gas is mixed with the fuel gas in the GT system and then enters the compressor, and the energy of the flat-plate SOFC tail gas is input into the front heat exchanger of the second burner. Compared with the existing tail gas output by the first burner directly entering the turbine, this application can solve the overall design problem of the atmospheric pressure SOFC-GT combined power generation system. At the same time, the flat-plate SOFC tail gas is directly or indirectly introduced into the GT system for power generation, completing the hybrid power generation of the flat-plate SOFC and GT systems. That is, by directly or indirectly utilizing the heat of the tail gas at the outlet of the fourth heat exchanger to drive the GT cycle, the utilization efficiency of the tail gas is improved. In addition, the direct connection and indirect connection between the flat-plate SOFC system and the GT system have different maximum efficiencies in different power ranges. By flexibly switching the system mode, the entire hybrid power generation system can always operate at the highest efficiency.

[0041] It should be understood that expressions such as "including" and "may include" that may be used in the present 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 the present application, terms such as "including" and / or "having" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0042] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense.

[0043] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A hybrid power generation system combining atmospheric pressure SOFC and GT, characterized in that: It includes a flat-plate SOFC system and a GT system; the connection between the flat-plate SOFC system and the GT system is divided into direct connection and indirect connection; Direct connection is to mix the tail gas of the flat-plate SOFC system with the fuel gas in the GT system and pass it into the compressor of the GT system to realize the direct connection between the flat-plate SOFC system and the GT system; indirect connection is to transfer the tail gas heat of the SOFC system to the heat exchanger between the compressor and the second burner in the GT system to realize the indirect connection between the flat-plate SOFC system and the GT system; the two connection methods are freely switched by valves; Among them, the fuel gas is not pressurized before entering the flat-plate SOFC system, and the tail gas energy of the flat-plate SOFC system and the tail gas are used to directly or indirectly enter the GT system for power generation, thereby realizing the cascade utilization of the tail gas energy of the flat-plate SOFC system.

2. The hybrid power generation system according to claim 1, characterized in that: The flat-plate SOFC system includes: a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a reformer, a SOFC stack and a burner; The first output end of the first heat exchanger is connected to the cathode of the SOFC stack; the first output end of the third heat exchanger and the first output end of the fourth heat exchanger are connected to the reformer; the output end of the reformer is connected to the first input end of the second heat exchanger; the first output end of the second heat exchanger is connected to the anode of the SOFC stack; the output end of the SOFC stack is connected to the input end of the first burner; the output end of the first burner is connected to the second input end of the first heat exchanger; the second output end of the first heat exchanger is connected to the second input end of the second heat exchanger; the second output end of the second heat exchanger is connected to the second input end of the third heat exchanger; the second output end of the third heat exchanger is connected to the second input end of the fourth heat exchanger; the output end of the fourth heat exchanger is connected to the compressor input side of the GT system or the heat exchanger between the compressor and the second burner in the GT system; The first heat exchanger is used to allow air at normal pressure to enter the cathode of the SOFC stack from the first input end; the fourth heat exchanger is used to allow fuel gas to enter the reformer from the first input end, and the third heat exchanger is used to allow water to enter the reformer through the first input end; the reformer is used to allow the output gas to enter the anode of the SOFC stack through the second heat exchanger; the first burner is used to transmit the output exhaust gas and exhaust gas energy to the GT system through the first heat exchanger, the second heat exchanger, the third heat exchanger and the fourth heat exchanger in sequence.

3. The hybrid power generation system according to claim 1 or 2, characterized in that: The GT system includes a multi-port valve, a compressor, a fifth heat exchanger, a second burner, and a turbine; The output end of the compressor is connected to the first input end of the fifth heat exchanger; the first output end of the fifth heat exchanger is connected to the input end of the second burner; the output end of the second burner is connected to the turbine; the output end of the turbine is connected to the second input end of the fifth heat exchanger; the second output end of the fifth heat exchanger is used to discharge the exhaust gas; The multi-way valve is provided with at least two paths, one path is used to mix the exhaust gas in the fourth heat exchanger with the fuel gas input from the compressor side and then enter the compressor, and the other path is used to allow the exhaust gas heat in the fourth heat exchanger to enter the second burner through the fifth heat exchanger.

4. The hybrid power generation system according to any one of claims 1 to 3, characterized in that: Direct connection and indirect connection are determined by power and efficiency curves, and are switched freely using valves.

5. The hybrid power generation system according to any one of claims 1 to 3, characterized in that: The fuel gas in the planar SOFC system and the GT system is hydrogen fuel or hydrocarbon fuel, and the hydrocarbon fuel includes methane and methanol.

6. The hybrid power generation system according to claim 3, characterized in that: The multi-way valve is a three-way valve.

7. The hybrid power generation system according to claim 2, characterized in that: The first burner is arranged adjacent to the reformer and is located in the same heat box to provide the required heat for the reformer.

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