A system and method for utilizing off-gas based on combined power generation of fuel cells

Abstract

The present invention discloses a waste gas utilization system and method based on combined power generation of fuel cells, including a solid oxide fuel cell power generation subsystem and a supercritical carbon dioxide cycle power generation subsystem. The solid oxide fuel cell power generation subsystem includes a preheater, an air compressor, an air preheater, a solid oxide fuel cell, an inverter, a combustion chamber, and a waste heat boiler. The supercritical carbon dioxide cycle power generation subsystem includes a turbine, a recuperator, a precooler, a compressor, and a generator. The solid oxide fuel cell power generation subsystem converts the Gibbs free energy part of the chemical energy of the combustible gas in the waste gas into electric energy. The unreacted combustible gas is burned and then used for power generation through a supercritical carbon dioxide Brayton cycle. The tail gas is used to preheat the waste gas and air. This system can achieve efficient utilization of the waste gas.

Description

Technical Field

[0001] The present invention relates to the technical field of utilization of purge gas, and particularly to a purge gas utilization system and method based on combined power generation of fuel cells. Background Art

[0002] Purge gas is the gas that does not participate in the reaction in chemical production or cannot be utilized due to too low grade, and accumulates in chemical equipment or pipelines. Since purge gas affects the heat transfer effect of equipment, the reaction speed and progress, and reduces production efficiency, etc., purge gas must be discharged regularly. Purge gas generally contains the raw material gas for chemical production, and most of them are combustible gases. There are generally three treatment methods for purge gas. One is to use pressure swing adsorption or membrane separation to extract the raw material gas components in the purge gas, and continue chemical production after extraction, with a complex process. The second is to directly burn it as fuel gas to produce steam, etc., with low efficiency. The third is to vent it after treatment.

[0003] Solid oxide fuel cells have strong adaptability to fuels, can operate under a variety of fuels including carbon-based fuels, can provide high-quality waste heat, realize combined heat and power generation, have a high fuel utilization rate, and the energy utilization rate is as high as about 80%.

[0004] Currently, there is no report on the efficient utilization of purge gas by using solid oxide fuel cells. Summary of the Invention

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a purge gas utilization system and method based on combined power generation of fuel cells, which can realize the efficient utilization of purge gas.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A purge gas utilization system based on combined power generation of fuel cells includes a solid oxide fuel cell power generation subsystem and a supercritical carbon dioxide cycle power generation subsystem;

[0008] The described solid oxide fuel cell power generation system includes a preheater 1 and an air compressor 2. The cold-side outlet of the preheater 1 is connected to the anode inlet of the solid oxide fuel cell 4. The anode outlet of the solid oxide fuel cell 4 is connected to the combustion chamber 6. The outlet of the air compressor 2 is connected to the cold-side inlet of the air preheater 3. The cold-side outlet of the air preheater 3 is connected to the cathode inlet of the solid oxide fuel cell 4 and enters. The cathode outlet of the solid oxide fuel cell 4 is connected to the combustion chamber 6. The outlet of the combustion chamber 6 is connected to the hot-side inlet of the waste heat boiler 7. The hot-side outlet of the waste heat boiler 7 is connected to the hot-side inlet of the preheater 1. The hot-side outlet of the preheater 1 is connected to the hot-side inlet of the air preheater 3. The anode electrode and the cathode electrode of the solid oxide fuel cell 4 are connected to the inverter 5;

[0009] The described supercritical carbon dioxide cycle power generation system includes a turbine 8. The cold-side outlet of the waste heat boiler 7 is connected to the inlet of the turbine 8. The outlet of the turbine 8 is connected to the hot-side inlet of the recuperator 9. The hot-side outlet of the recuperator 9 is connected to the hot-side inlet of the precooler 10. The hot-side outlet of the precooler 10 is connected to the inlet of the compressor 11. The outlet of the compressor 11 is connected to the cold-side inlet of the recuperator 9. The cold-side outlet of the recuperator 9 is connected to the cold-side inlet of the waste heat boiler 7. The turbine 8 is connected to the compressor 11 and the generator 12 through a coupling.

[0010] The cold-side outlet of the preheater 1 is connected to the inlet of the combustion chamber 6.

[0011] The cooling medium of the precooler 10 is circulating cooling water.

[0012] The air entering the air compressor 2 is in excess relative to the flue gas entering the preheater 1.

[0013] The turbine 8 drives the compressor 11 and the generator 12 to rotate through a coupling. The compressor 11 compresses carbon dioxide, and the generator 12 outputs electric power.

[0014] A method for utilizing flue gas in a fuel cell combined power generation includes the following steps;

[0015] After the off-gas is preheated on the cold side of the preheater 1, it enters the anode of the solid oxide fuel cell 4. After the air is pressurized by the air compressor 2 and preheated by the air preheater 3, it enters the cathode of the solid oxide fuel cell 4. The off-gas and the air react in the solid oxide fuel cell 4, and the reacted gas enters the combustion chamber 6 for combustion. If the content of combustible gas in the reacted off-gas is too low to support combustion, a part of the off-gas directly enters the burner 6 after the cold side of the preheater 1 to ensure stable combustion in the burner 6. The cathode electrode and the anode electrode of the solid oxide fuel cell 4 output electricity to the inverter 5. The flue gas after combustion enters the hot side of the waste heat boiler 7 to heat the carbon dioxide on the cold side. The flue gas after heat exchange enters the preheater 1 to preheat the off-gas, then enters the air preheater 3 to preheat the air, and then goes to tail gas treatment;

[0016] The carbon dioxide on the cold side of the waste heat boiler 7 is heated and then enters the turbine 8 to drive the turbine 8 to rotate and do work. The carbon dioxide after doing work enters the hot side of the recuperator 9 and exchanges heat with the carbon dioxide on the cold side, and then enters the hot side of the precooler 10 for further cooling. The cooled carbon dioxide enters the compressor 11 for pressurization. The pressurized carbon dioxide enters the cold side of the recuperator 9 and exchanges heat with the carbon dioxide on the hot side. The carbon dioxide after being heated enters the cold side of the waste heat boiler 7 for further heating. The heated carbon dioxide enters the turbine 8 to complete the cycle.

[0017] The off-gas described above is preheated to 500 °C by the preheater 1, and the air is pressurized to 5 MPa by the air compressor 2 and preheated to 500 °C by the air preheater 3.

[0018] Advantages of the present invention:

[0019] When the off-gas utilization system and method based on fuel cell combined power generation of the present invention are specifically operated, since the solid oxide fuel cell converts the Gibbs free energy part of the chemical energy of the combustible gas in the off-gas into electric energy through an electrochemical reaction and is not restricted by the Carnot cycle effect, the efficiency is high; after the unreacted combustible gas in the off-gas is burned, power generation is carried out through a supercritical carbon dioxide Brayton cycle. When the combustible gas is insufficient, the off-gas can be introduced from the back of the cold side of the preheater to the combustion chamber to ensure combustion. The tail gas is used to preheat the off-gas and the air, and the off-gas is fully utilized. Description of the drawings

[0020] Figure 1 It is a structural schematic diagram of the present invention.

[0021] Among them, 1 is the preheater, 2 is the air compressor, 3 is the air preheater, 4 is the solid oxide fuel cell, 5 is the inverter, 6 is the combustion chamber, 7 is the waste heat boiler, 8 is the turbine, 9 is the recuperator, 10 is the precooler, 11 is the compressor, and 12 is the generator. Detailed Embodiments

[0022] The present invention will be further described in detail below in conjunction with embodiments.

[0023] As Figure 1 shown, the synthetic methanol purge gas, with a pressure of 5 MPa and a temperature of 50°C, contains combustible gases such as hydrogen and methane. It is preheated to 500°C in the preheater 1 and then enters the anode of the solid oxide fuel cell 4. Air is pressurized to 5 MPa by the air compressor 2 and preheated to 500°C in the air preheater 3, and then enters the cathode of the solid oxide fuel cell 4. The purge gas and air react in the solid oxide fuel cell 4, and the anode electrode and cathode electrode deliver electricity to the inverter 5. There is still a certain amount of combustible gas in the reacted purge gas, and there is still a certain amount of oxygen in the reacted air. The reacted purge gas and air enter the combustion chamber 6. The purge gas burns and releases heat in the combustion chamber 6. If the content of combustible gas in the reacted purge gas is too low to support combustion, a part of the purge gas directly enters the burner 6 from the cold side of the preheater 1 to ensure stable combustion in the burner 6. The flue gas after combustion enters the hot side of the waste heat boiler 7 to heat the carbon dioxide on the cold side. The flue gas after heat exchange enters the preheater 1 to preheat the purge gas. After preheating the purge gas, it enters the air preheater 3 to preheat the air, and then goes to tail gas treatment.

[0024] After the carbon dioxide on the cold side of the waste heat boiler 7 is heated, it enters the turbine 8, driving the turbine 8 to rotate and do work. The turbine 8 drives the compressor 11 and the generator 12 to rotate through a coupling. The compressor 11 compresses the carbon dioxide, and the generator 12 outputs electricity. The carbon dioxide after doing work enters the hot side of the recuperator 9 to exchange heat with the carbon dioxide on the cold side. The carbon dioxide on the hot side enters the hot side of the precooler 10 for further cooling, exchanging heat with the circulating cooling water on the cold side. The cooled carbon dioxide enters the compressor 11 for pressurization. The pressurized carbon dioxide enters the cold side of the recuperator 9 to exchange heat with the carbon dioxide on the hot side. The carbon dioxide after being heated enters the cold side of the waste heat boiler 7 for further heating. The heated carbon dioxide enters the turbine 8 to complete the cycle. The turbine 8 drives the compressor 11 and the generator 12 to rotate through a coupling. The compressor 11 compresses the carbon dioxide, and the generator 12 outputs electricity.

Claims

1. A waste gas utilization system based on combined power generation of fuel cells, characterized in that, It includes a solid oxide fuel cell power generation system and a supercritical carbon dioxide cycle power generation system; The solid oxide fuel cell power generation system includes a preheater (1) and an air compressor (2). The cold-side outlet of the preheater (1) is connected to the anode inlet of the solid oxide fuel cell (4). The anode outlet of the solid oxide fuel cell (4) is connected to the combustion chamber (6). The outlet of the air compressor (2) is connected to the cold-side inlet of the air preheater (3). The cold-side outlet of the air preheater (3) is connected to the cathode inlet of the solid oxide fuel cell (4) and enters. The cathode outlet of the solid oxide fuel cell (4) is connected to the combustion chamber (6). The outlet of the combustion chamber (6) is connected to the hot-side inlet of the waste heat boiler (7). The hot-side outlet of the waste heat boiler (7) is connected to the hot-side inlet of the preheater (1). The hot-side outlet of the preheater (1) is connected to the hot-side inlet of the air preheater (3). The anode electrode and the cathode electrode of the solid oxide fuel cell (4) are connected to the inverter (5); The supercritical carbon dioxide cycle power generation system includes a turbine (8). The cold-side outlet of the waste heat boiler (7) is connected to the inlet of the turbine (8). The outlet of the turbine (8) is connected to the hot-side inlet of the recuperator (9). The hot-side outlet of the recuperator (9) is connected to the hot-side inlet of the precooler (10). The hot-side outlet of the precooler (10) is connected to the inlet of the compressor (11). The outlet of the compressor (11) is connected to the cold-side inlet of the recuperator (9). The cold-side outlet of the recuperator (9) is connected to the cold-side inlet of the waste heat boiler (7). The turbine (8) is connected to the compressor (11) and the generator (12) through a coupling; The air entering the air compressor (2) is in excess relative to the flue gas entering the preheater (1); The turbine (8) drives the compressor (11) and the generator (12) to rotate through a coupling. The compressor (11) compresses carbon dioxide, and the generator (12) outputs electricity; The cold-side outlet of the preheater (1) is connected to the inlet of the combustion chamber (6).

2. The utilization system for off-gas based on combined power generation of fuel cells according to claim 1, characterized in that, The cooling medium of the precooler (10) is circulating cooling water.

3. A method for using a waste gas utilization system based on fuel cell combined power generation according to claim 1, characterized in that, It includes the following steps; After the flue gas is preheated on the cold side of the preheater (1), it enters the anode of the solid oxide fuel cell (4). After the air is pressurized by the air compressor (2) and preheated by the air preheater (3), it enters the cathode of the solid oxide fuel cell (4). The flue gas and the air react in the solid oxide fuel cell (4). The reacted gas enters the combustion chamber (6) for combustion. If the content of combustible gas in the reacted flue gas is too low to support combustion, a part of the flue gas directly enters the combustion chamber (6) from the back of the cold side of the preheater (1) to ensure stable combustion in the combustion chamber (6). The cathode electrode and the anode electrode of the solid oxide fuel cell (4) output electricity to the inverter (5). The flue gas after combustion enters the hot side of the waste heat boiler (7) to heat the carbon dioxide on the cold side. The flue gas after heat exchange enters the preheater (1) to preheat the flue gas, and then enters the air preheater (3) to preheat the air, and then goes to tail gas treatment; The carbon dioxide on the cold side of the waste heat boiler (7) is heated and then enters the turbine (8), driving the rotation of the turbine (8) to do work. After doing work, the carbon dioxide enters the hot side of the recuperator (9), exchanges heat with the carbon dioxide on the cold side, and then enters the hot side of the precooler (10) for further cooling. The cooled carbon dioxide enters the compressor (11) for pressurization. The pressurized carbon dioxide enters the cold side of the recuperator (9), exchanges heat with the carbon dioxide on the hot side, and the heated carbon dioxide enters the cold side of the waste heat boiler (7) for further heating. The heated carbon dioxide enters the turbine (8) to complete the cycle.

4. The usage method of a waste gas utilization system based on combined power generation of fuel cells according to claim 3, characterized in that The described blowdown gas is preheated to 500 °C by the preheater (1), the air is pressurized to 5 MPa by the air compressor (2), and is preheated to 500 °C by the air preheater (3).

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