Biomass gas semi-closed supercritical CO2 circulation alcohol-electricity co-production system and method

Abstract

According to the biomass gas semi-closed supercritical CO2 circulation alcohol-electricity co-production system and method, synthesis gas obtained after biomass gasification and oxygen are subjected to oxygen-enriched combustion to obtain high-temperature and high-pressure supercritical carbon dioxide and smoke of water vapor, and the smoke enters a gas turbine to expand to do work and drive a power generator to generate power. One part of electric power generated by the generator supplies energy to the electrolytic cell to decompose water into oxygen and hydrogen, and the other part is sent to the power grid. After the expanded flue gas is cooled, water is separated out of the system, and the separated water is used as a gasifying agent required by biomass gasification. Pure carbon dioxide is liquefied after being further compressed and cooled, most carbon dioxide is discharged out of the system, and a small part is used for controlling the temperature of the combustion chamber and the gas turbine. And performing catalytic reaction on carbon dioxide discharged from the system and hydrogen produced by electrolysis to obtain methanol. In the whole process, the carbon neutral fuel is used, and the captured carbon dioxide and hydrogen are used for synthesizing methanol which is easy to store, so that the environmental pollution is reduced, the energy utilization efficiency is improved, and the aim of carbon negative emission of the whole system is fulfilled.

Description

Technical Field

[0001] This invention belongs to the field of renewable energy utilization, and specifically relates to a biomass gas semi-closed supercritical CO2 cycle alcohol cogeneration system and method. Background Technology

[0002] Currently, biomass energy utilization mainly relies on direct combustion or gasification power generation, which generally suffers from low energy conversion efficiency (typically below 30%), low CO2 concentration in flue gas (<20%), and insufficient pressure. This leads to the need for high-energy-consuming and high-cost auxiliary devices such as chemical absorption for subsequent carbon capture, resulting in poor economic viability. Although some studies have attempted to introduce semi-closed supercritical CO2 cycles into biomass systems to obtain high-concentration, high-pressure CO2 flue gas through oxygen-enriched combustion to facilitate carbon capture, this approach still requires external air separation equipment to provide oxygen, increasing system complexity and energy consumption. Furthermore, if the captured CO2 is only used for storage, there is a lack of economic incentive, making sustainable operation difficult. On the other hand, while green hydrogen has clean advantages, its storage and transportation costs are high, and safety challenges are significant, necessitating its conversion into an easily stored and transportable energy carrier. Synthesizing methanol from CO2 and H2 is an ideal route, but existing processes largely rely on fossil-derived raw materials, failing to achieve end-to-end decarbonization.

[0003] To address the aforementioned issues, this invention aims to construct a highly efficient, self-sustaining, and carbon-negative biomass energy comprehensive utilization system, focusing on solving four key technical challenges: First, achieving oxygen self-sufficiency—utilizing the system's self-generated electricity to drive water electrolysis, providing the necessary oxygen for oxygen-enriched combustion, thus eliminating dependence on external air separation units; second, achieving high-value utilization of CO2—using high-purity CO2 obtained through simple condensation and separation after combustion, combined with green hydrogen generated from electrolysis, to catalytically synthesize methanol in situ within the system, turning waste into treasure; third, improving overall energy efficiency—recovering the cooling heat of syngas and waste heat from flue gas to heat the methanol synthesis reaction, achieving cascaded energy utilization; and fourth, achieving carbon-negative emissions—using carbon-neutral biomass as raw material, combined with CO2 resource sequestration in methanol products, resulting in a net negative carbon emission for the system. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a semi-closed supercritical CO2 cycle methanol cogeneration system and method based on biomass gas, which significantly improves energy utilization efficiency and simultaneously produces electricity and green methanol, thus having both environmental benefits and economic feasibility.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A semi-closed supercritical CO2 cycle methanol-electricity cogeneration system based on biomass gasification includes a biomass gasification unit, an oxygen-enriched combustion-power generation unit, a flue gas treatment and CO2 separation unit, an electrolysis hydrogen production unit, and a methanol synthesis unit. The biomass gasification unit outputs syngas which is then fed into an oxygen-enriched combustion-power generation unit for combustion, driving a gas turbine to generate electricity. The generator supplies power to the electrolysis hydrogen production unit to produce hydrogen and oxygen by electrolyzing water. The flue gas treatment and CO2 separation unit cools, separates water and gas, and liquefies CO2 in the flue gas discharged from the gas turbine. Part of the liquefied CO2 is catalytically synthesized into methanol in the methanol synthesis unit with hydrogen obtained from electrolysis, and the other part is pressurized and returned to the oxygen-enriched combustion-power generation unit as a circulating working fluid for combustion dilution and temperature control.

[0006] Preferably, the biomass gasification unit includes a gasification chamber, a syngas cooler, a syngas compressor, and a syngas heat exchanger; The outlet of the gasification chamber is connected to the inlet of the syngas cooler, the outlet of the syngas cooler is connected to the inlet of the syngas compressor, the outlet of the syngas compressor is connected to the inlet of the first flow channel of the syngas heat exchanger, and the outlet of the first flow channel of the syngas heat exchanger is connected to the combustion chamber.

[0007] Preferably, the oxygen-enriched combustion power generation unit includes a combustion chamber, a gas turbine, a generator, and a heat exchanger; The combustion chamber outlet is connected to the gas turbine inlet, the gas turbine is coaxially connected to the generator, and the gas turbine exhaust port is connected to the hot side inlet of the heat exchanger.

[0008] Preferably, the flue gas treatment and CO2 separation unit includes a cooler, a separator, a water separator, a carbon dioxide compressor, a condenser, a distributor, a pump, and a carbon dioxide distributor. The hot-side outlet of the heat exchanger is connected in sequence to the cooler and the separator; the liquid phase outlet of the separator is connected to the water splitter, and the gas phase outlet is connected to the carbon dioxide compressor; the outlet of the carbon dioxide compressor is connected to the condenser, and the outlet of the condenser is connected to the splitter.

[0009] Preferably, the first outlet of the water splitter is connected to the second flow channel inlet of the syngas heat exchanger, and the second outlet is the system drain outlet; the first outlet of the splitter is connected to the reaction chamber, and the second outlet is connected to the pump inlet; the pump outlet is connected to the carbon dioxide splitter inlet.

[0010] Preferably, the first outlet of the carbon dioxide splitter is connected to the cold side inlet of the heat exchanger, and after heat exchange, it is directly injected into the gas turbine for temperature control; the second outlet is connected to the first inlet of the mixer.

[0011] Preferably, the electrolytic hydrogen production unit includes an electrolyzer, an oxygen storage tank, a hydrogen storage tank, an oxygen compressor, a hydrogen compressor, a first valve, and a second valve; The oxygen outlet of the electrolyzer is connected to an oxygen storage tank, and after passing through a first valve and an oxygen compressor, it is connected to the second inlet of the mixer; the hydrogen outlet is connected to a hydrogen storage tank, and after passing through a second valve and a hydrogen compressor, it is connected to the reaction chamber.

[0012] Preferably, the outlet of the mixer is connected to the inlet of the other cold side flow channel of the heat exchanger, and after heat exchange, it is sent into the combustion chamber as an oxidant component.

[0013] Preferably, the methanol synthesis unit includes a reaction chamber and a methanol storage tank; the reaction chamber receives liquid CO2 from the distributor and high-pressure H2 from the hydrogen compressor, and synthesizes methanol under the action of a catalyst, and the product is sent to the methanol storage tank; the heat required for the reaction is provided by the synthesis gas cooler and the waste heat of the cooler.

[0014] A method for operating a semi-closed supercritical CO2 cycle alcohol-electricity cogeneration system using biomass gas, comprising the following steps: (1) Biomass reacts with water vapor in the gasification chamber to generate syngas, which is then cooled, compressed, and heat-exchanged before being sent into the combustion chamber; (2) The electrolyzer uses the electricity generated by the generator to electrolyze water. The resulting oxygen is compressed and mixed with circulating CO2 and sent into the combustion chamber. The hydrogen is compressed and sent into the reaction chamber. (3) Syngas and oxygen-enriched gas are combusted in the combustion chamber to generate high-temperature and high-pressure supercritical CO2 flue gas, which drives the gas turbine to generate electricity; (4) The exhaust gas from the gas turbine is heat exchanged, cooled and separated to obtain water and high-purity CO2; part of the water is recycled as a gasification agent, and the CO2 is liquefied and used to synthesize methanol in one part and pressurized to supercritical state and returned to the system for circulation. (5) CO2 and H2 are catalytically synthesized into methanol in the reaction chamber, and the heat of reaction is supplied by the waste heat of the system.

[0015] The present invention can achieve the following beneficial effects: 1. This system uses biomass as fuel, which absorbs atmospheric CO2 during its growth process, making it a carbon-neutral feedstock. Simultaneously, the high-purity CO2 produced after combustion is completely captured and synthesized into methanol with green hydrogen (obtained by electrolyzing water using the system's own electricity), thus achieving the resource utilization of CO2. The entire process not only does not generate new carbon emissions, but also achieves a system-level carbon-negative emission target by fixing atmospheric carbon and storing it long-term in the methanol product.

[0016] 2. The semi-closed supercritical CO2 cycle is used as the power cycle, which has the advantages of high thermal efficiency, high working fluid energy density and compact equipment. At the same time, the waste heat in many parts of the system (such as the syngas cooler and flue gas cooler) is recovered and used for heating the methanol synthesis reaction, which significantly improves the overall energy utilization efficiency.

[0017] 3. This system synchronously outputs stable electrical energy (partially for internal electrolysis, the remainder connected to the grid) and liquid methanol. Methanol, as a high-energy-density, easily stored and transported liquid fuel or chemical feedstock, solves the problems of high cost and poor safety of hydrogen energy storage and transportation, realizing the efficient conversion and long-term storage of renewable energy.

[0018] 4. The main components of the flue gas after supercritical CO2 recycling combustion are CO2 and H2O. High-purity CO2 can be obtained by simple condensation and separation, without the need for complex carbon capture devices. The captured CO2 can be directly used to synthesize methanol, turning waste into treasure and reducing carbon treatment costs.

[0019] 5. A portion of the water separated from the flue gas cooling process is reused as a gasifying agent in the biomass gasification process, forming an internal water cycle, reducing the system's demand for external fresh water sources, and improving sustainability. By organically coupling units such as biomass gasification, supercritical CO2 power generation, water electrolysis for hydrogen production, CO2 capture, and methanol synthesis, an integrated cogeneration system is constructed, reducing losses in intermediate links and enhancing the synergy and stability of the energy conversion chain. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a system structure diagram of the present invention.

[0021] In the diagram: 1. Gasification chamber, 2. Syngas cooler, 3. Syngas compressor, 4. Syngas heat exchanger, 5. Combustion chamber, 6. Gas turbine, 7. Generator, 8. Heat exchanger, 9. Cooler, 10. Separator, 11. Water distributor, 12. Carbon dioxide compressor, 13. Condenser, 14. Flow divider, 15. Pump, 16. Carbon dioxide flow divider, 17. Mixer, 18. Oxygen compressor, 19. First valve, 20. Oxygen storage tank, 21. Electrolyzer, 22. Hydrogen storage tank, 23. Second valve, 24. Hydrogen compressor, 25. Reaction chamber, 26. Methanol storage tank. Detailed Implementation

[0022] Preferred solutions include Figure 1 As shown, a semi-closed supercritical CO2 cycle methanol-electricity cogeneration system and method using biomass gas includes a gasification chamber 1, a syngas cooler 2, a syngas compressor 3, a syngas heat exchanger 4, a combustion chamber 5, a gas turbine 6, a generator 7, a heat exchanger 8, a cooler 9, a separator 10, a water separator 11, a carbon dioxide compressor 12, a condenser 13, a distributor 14, a pump 15, a carbon dioxide distributor 16, a mixer 17, an oxygen compressor 18, a first valve 19, an oxygen storage tank 20, an electrolyzer 21, a hydrogen storage tank 22, a second valve 23, a hydrogen compressor 24, a reaction chamber 25, and a methanol storage tank 26.

[0023] The gasification chamber 1 uses biomass as raw material and water vapor as the gasifying agent to convert biomass into syngas containing hydrogen, carbon monoxide, methane, and other components under certain temperature and pressure. The syngas is cooled by the syngas cooler 2 and then compressed to the working pressure of the combustion chamber 5 by the syngas compressor 3. The high-pressure syngas enters the syngas heat exchanger 4, where the heat of compression heats the separated water into a gaseous state, providing the gasifying agent for the gasification process. The heat-exchanged syngas then enters the combustion chamber 5.

[0024] The electrolyzer 21 is powered by the generator 7. The electrolyzer 21 electrolyzes water into oxygen and hydrogen, which are stored in the oxygen storage tank 20 and hydrogen storage tank 22, respectively. The first valve 19 controls the flow rate of oxygen into the oxygen compressor 18. The oxygen compressor 18 pressurizes the oxygen to the reaction pressure in the combustion chamber 5 and mixes it with carbon dioxide. The mixture is then sent to the combustion chamber 5 after heat exchange in the heat exchanger 8. The second valve 23 controls the flow rate of hydrogen into the hydrogen compressor 24. The hydrogen compressor 24 pressurizes the hydrogen to the working pressure in the reaction chamber 25 and sends it into the reaction chamber 25.

[0025] The combustion chamber 5 is connected to the syngas heat exchanger 4 and heat exchanger 8 via pipelines. Syngas and oxygen react in the combustion chamber 5 to generate high-temperature and high-pressure fuel gas.

[0026] The gas turbine 6 is connected to the generator 7 and the heat exchanger 8. The high-temperature and high-pressure gas enters the gas turbine 6, expands, and performs work, driving the generator 7 to generate electricity. The expanded flue gas enters the heat exchanger 8 to exchange heat with the mixed gas and carbon dioxide stream.

[0027] The cooler 9 is connected to the separator 10, and the flue gas after heat exchange enters the cooler 9 for further cooling. The cooled flue gas separates water in the separator 10. The separated water enters the water separator 11 and is divided into two streams. One stream is heated and vaporized by the synthesis gas heat exchanger 4 and enters the vaporization chamber 1 as a vaporizing agent. The other stream is discharged from the system.

[0028] The carbon dioxide compressor 12 is connected to the separator 10 and the condenser 13. The gaseous carbon dioxide from the separator 10 enters the carbon dioxide compressor 12, is compressed, and then enters the condenser 13 to be cooled into a liquid state. The liquid carbon dioxide is divided into two streams by the distributor 14, one stream is sent to the reaction chamber 25, and the other stream is sent to the pump 15.

[0029] The reaction chamber 25 is connected to the methanol storage tank 26. In the reaction chamber 25, carbon dioxide and hydrogen are synthesized into methanol under certain temperature and pressure. The heat required for the reaction comes from the synthesis gas cooler 2 and cooler 9. The synthesized methanol is stored in the methanol storage tank 26 through pipelines.

[0030] The pump 15 is connected to the carbon dioxide splitter 16. The pump 15 pressurizes the carbon dioxide to a supercritical state. The supercritical carbon dioxide enters the carbon dioxide splitter 16 and is divided into two streams. One stream enters the heat exchanger 8 for heat exchange and is then directly fed into the gas turbine 6 to control the temperature of the gas turbine 6. The other stream enters the mixer 17 to mix with oxygen, then enters the heat exchanger 8 for heat exchange, and is then fed into the combustion chamber 5 through a pipeline to burn with the syngas.

[0031] The operating principle of this system: Biomass fuel reacts with a gasifying agent in the gasification chamber to produce syngas. The syngas exiting the gasification chamber is cooled by a syngas cooler and then pressurized to combustion pressure by a syngas compressor. The syngas exiting the compressor enters a syngas heat exchanger, where the heat of compression heats the water separated from the flue gas into a gaseous state, providing a gasifying agent for the biomass gasification process. The syngas exiting the heat exchanger enters the combustion chamber and burns with an oxygen / carbon dioxide mixture. The resulting flue gas enters a gas turbine, expands, and performs work, driving a generator to produce electricity. The expanded flue gas exchanges heat with the oxygen / carbon dioxide mixture stream and the carbon dioxide stream in a heat exchanger, then enters a cooler for further cooling. The flue gas exiting the cooler enters a separator to separate water and carbon dioxide. The separated water enters a water separator and is divided into two streams; one stream is gasified in a heat exchanger and used as a gasifying agent, while the remaining water is discharged from the system. The carbon dioxide exiting the separator enters a carbon dioxide compressor and is pressurized to near its critical pressure, then condensed into a liquid state by a condenser. Liquid carbon dioxide is split into two streams in a splitter. One stream enters the reaction chamber, and the other is pressurized to combustion pressure by a pump. The pressurized carbon dioxide is then split into two streams in a carbon dioxide splitter. One stream, after heat exchange in a heat exchanger, is directly sent to the gas turbine to regulate its temperature. The other stream mixes with oxygen pressurized to combustion pressure by an oxygen compressor in a mixer, and then enters a heat exchanger to exchange heat with the expanded flue gas. The preheated mixture enters the combustion chamber to participate in the combustion reaction. A portion of the electricity generated by the generator powers the electrolyzer, and the remainder is fed into the power grid. The oxygen and hydrogen produced after water electrolysis in the electrolyzer are stored in oxygen and hydrogen storage tanks, respectively. A first valve controls the oxygen flow rate to the oxygen compressor. A second valve controls the flow rate from the hydrogen storage tank to the hydrogen compressor. The hydrogen compressor pressurizes the hydrogen to the working pressure of the reaction chamber, and the hydrogen enters the reaction chamber to synthesize methanol with carbon dioxide. A synthesis gas cooler and a chiller provide heat to the reaction chamber. The synthesized methanol is stored in a methanol storage tank.

[0032] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system, characterized in that, It includes a biomass gasification unit, an oxygen-enriched combustion-power generation unit, a flue gas treatment and CO2 separation unit, an electrolysis hydrogen production unit, and a methanol synthesis unit; The biomass gasification unit outputs syngas which is then fed into an oxygen-enriched combustion-power generation unit for combustion, driving a gas turbine to generate electricity. The generator supplies power to the electrolysis hydrogen production unit to produce hydrogen and oxygen by electrolyzing water. The flue gas treatment and CO2 separation unit cools, separates water and gas, and liquefies CO2 in the flue gas discharged from the gas turbine. Part of the liquefied CO2 is catalytically synthesized into methanol in the methanol synthesis unit with hydrogen obtained from electrolysis, and the other part is pressurized and returned to the oxygen-enriched combustion-power generation unit as a circulating working fluid for combustion dilution and temperature control.

2. The biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to claim 1, characterized in that: The biomass gasification unit includes a gasification chamber (1), a syngas cooler (2), a syngas compressor (3), and a syngas heat exchanger (4). The outlet of the gasification chamber (1) is connected to the inlet of the syngas cooler (2), the outlet of the syngas cooler (2) is connected to the inlet of the syngas compressor (3), the outlet of the syngas compressor (3) is connected to the inlet of the first flow channel of the syngas heat exchanger (4), and the outlet of the first flow channel of the syngas heat exchanger (4) is connected to the combustion chamber (5).

3. The biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to claim 2, characterized in that: The oxygen-enriched combustion-power generation unit includes a combustion chamber (5), a gas turbine (6), a generator (7), and a heat exchanger (8). The combustion chamber (5) outlet is connected to the gas turbine (6) inlet, the gas turbine (6) is coaxially connected to the generator (7), and the gas turbine (6) exhaust port is connected to the hot side inlet of the heat exchanger (8).

4. The biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to claim 3, characterized in that: The flue gas treatment and CO2 separation unit includes a cooler (9), a separator (10), a water splitter (11), a carbon dioxide compressor (12), a condenser (13), a splitter (14), a pump (15), and a carbon dioxide splitter (16). The hot side outlet of the heat exchanger (8) is connected to the cooler (9) and the separator (10) in sequence; the liquid phase outlet of the separator (10) is connected to the water splitter (11), and the gas phase outlet is connected to the carbon dioxide compressor (12); the outlet of the carbon dioxide compressor (12) is connected to the condenser (13), and the outlet of the condenser (13) is connected to the splitter (14).

5. The biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to claim 4, characterized in that: The first outlet of the water splitter (11) is connected to the second flow channel inlet of the syngas heat exchanger (4), and the second outlet is the system drain outlet; the first outlet of the splitter (14) is connected to the reaction chamber (25), and the second outlet is connected to the pump (15) inlet; the pump (15) outlet is connected to the carbon dioxide splitter (16) inlet.

6. The biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to claim 5, characterized in that: The first outlet of the carbon dioxide splitter (16) is connected to the cold side inlet of the heat exchanger (8), and after heat exchange, it is directly injected into the gas turbine (6) for temperature control; the second outlet is connected to the first inlet of the mixer (17).

7. The biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to claim 1, characterized in that: The electrolytic hydrogen production unit includes an electrolyzer (21), an oxygen storage tank (20), a hydrogen storage tank (22), an oxygen compressor (18), a hydrogen compressor (24), a first valve (19), and a second valve (23). The oxygen outlet of the electrolyzer (21) is connected to the oxygen storage tank (20), and after passing through the first valve (19) and the oxygen compressor (18), it is connected to the second inlet of the mixer (17); the hydrogen outlet is connected to the hydrogen storage tank (22), and after passing through the second valve (23) and the hydrogen compressor (24), it is connected to the reaction chamber (25).

8. A biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to claim 6 or 7, characterized in that: The outlet of the mixer (17) is connected to the inlet of the other cold side flow channel of the heat exchanger (8), and after heat exchange, it is sent into the combustion chamber (5) as an oxidant component.

9. The biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to claim 1, characterized in that: The methanol synthesis unit includes a reaction chamber (25) and a methanol storage tank (26); the reaction chamber (25) receives liquid CO2 from the splitter (14) and high-pressure H2 from the hydrogen compressor (24) to synthesize methanol under the action of a catalyst, and the product is sent to the methanol storage tank (26); the heat required for the reaction is provided by the waste heat of the synthesis gas cooler (2) and the cooler (9).

10. The operating method of a biomass gas semi-closed supercritical CO2 cycle power and methanol synthesis combined system according to any one of claims 1-9, characterized in that, Includes the following steps: Biomass reacts with water vapor in the gasification chamber (1) to generate syngas, which is then cooled, compressed, and heat-exchanged before being sent into the combustion chamber (5). The electrolyzer (21) uses the electricity generated by the generator (7) to electrolyze water. The resulting oxygen is compressed and mixed with circulating CO2 and sent into the combustion chamber (5). The hydrogen is compressed and sent into the reaction chamber (25). Syngas and oxygen-enriched gas are combusted in combustion chamber (5) to generate high-temperature and high-pressure supercritical CO2 flue gas, which drives gas turbine (6) to generate electricity; The exhaust gas from the gas turbine (6) is heat exchanged, cooled, and separated to obtain water and high-purity CO2; part of the water is recycled as a gasification agent, and the CO2 is liquefied and used to synthesize methanol in one part and pressurized to a supercritical state to return to the system for circulation; CO2 and H2 are catalytically synthesized into methanol in reaction chamber (25), and the heat of reaction is supplied by the waste heat of the system.

Images