System for synthesizing green alkanes by SOEC and synthesis method thereof

Abstract

This invention discloses a system for synthesizing green alkanes using SOEC, comprising a co-electrolysis system and a methanol synthesis system. The co-electrolysis system includes an SOEC stack. The outlet side of the fuel electrode of the SOEC stack is connected sequentially to a first cooling device and a first gas-liquid separation device via pipelines. The gas outlet of the first gas-liquid separation device is connected sequentially to a first separation device and a first mixing device via pipelines. The outlet end of the first separation device is connected to the methanol synthesis system. This invention utilizes renewable electricity to drive a solid oxide electrolyzer to achieve the synergistic electrolysis of H2O and CO2 to generate syngas. The composition of the resulting syngas satisfies the molar ratio required for methanol synthesis: (H2–CO2) / (CO2+CO)≈2. This method effectively improves system energy efficiency through thermoelectric synergy and a gas circulation strategy. This invention also provides a synthesis method for the system of synthesizing green alkanes using SOEC.

Description

Technical Field

[0001] This invention belongs to the field of solid oxide electrolytic cell co-electrolysis technology, and relates to a system for synthesizing green alkanes using a solid oxide electrolytic cell (SOEC). This invention also relates to a synthesis method of the above-mentioned system for synthesizing green alkanes using SOEC and green alkanes. Background Technology

[0002] Industrially, methanol synthesis primarily utilizes the syngas (hydrogen H2, carbon monoxide CO, carbon dioxide CO2) route, which has been in use for over a century. The catalyst systems, reactor designs, process flows, and industrial foundation are all relatively mature. From the perspective of technological stability and industrial feasibility, the syngas route exhibits high maturity and significant advantages. However, using green hydrogen and carbon dioxide to synthesize methanol presents challenges in terms of lower energy efficiency and difficulty in scaling up production. Summary of the Invention

[0003] The purpose of this invention is to provide a system for synthesizing green alkanes using SOEC, which features high energy efficiency and high methane yield, and can achieve efficient conversion of green electricity into methane.

[0004] A second objective of this invention is to provide a systematic method for synthesizing green alkanes using SOEC.

[0005] The technical solution adopted in this invention is a system for synthesizing green alkanes using SOEC, including a co-electrolysis system and a methanol synthesis system. The co-electrolysis system includes an SOEC stack. The outlet side of the fuel electrode of the SOEC stack is connected in sequence to a first cooling device and a first gas-liquid separation device via pipelines. The gas outlet of the first gas-liquid separation device is connected in sequence to a first separation device and a first mixing device via pipelines. The outlet end of the first separation device is connected to the methanol synthesis system.

[0006] The invention is further characterized by: The co-electrolysis system also includes a water pump and an air compressor. Liquid water is connected to the inlet of the water pump, and the outlet of the water pump is connected to a steam generator and a first heating device in sequence through a pipe. The outlet of the first heating device is connected to the fuel electrode of the SOEC stack through a pipe, and the outlet of the first mixing device is connected to the steam generator through a pipe. Air is introduced into the air compressor inlet, and the outlet is connected to the inlet of the second heating device through a pipe. The outlet of the second heating device is connected to the oxygen electrode of the SOEC stack through a pipe, and the outlet side of the oxygen electrode of the SOEC stack is connected to the second cooling device.

[0007] The methanol synthesis system includes a second mixing unit. The inlet of the second mixing unit is connected to the outlet of the first separation unit via a pipeline. The outlet of the second mixing unit is connected in sequence via a pipeline to a first compressor, a third cooling unit, a second compressor, a third heating unit, and the third mixing unit. The outlet of the third mixing unit is connected to a methanol reactor via a pipeline. The outlet of the methanol reactor is connected in sequence via a fourth cooling unit, a first pressure reducing valve, and a second gas-liquid separator via a pipeline. The gas outlet of the second gas-liquid separator is connected to the inlet of the second separation unit via a pipeline. The outlet of the second separation unit is connected to the third compressor. The outlet of the third compressor is connected to the inlet of the fourth heating unit via a pipeline. The outlet of the fourth heating unit is connected to the inlet of the third mixing unit via a pipeline.

[0008] The liquid outlet of the second gas-liquid separator is connected in sequence to the second pressure reducing valve, the fifth heating device, and the distillation unit via pipelines. The top outlet of the distillation unit is connected to the sixth heating device, and the bottom outlet of the distillation unit is connected to the sixth cooling device.

[0009] The other outlet of the second separation device is connected to the combustion chamber via a pipe. The inlet of the combustion chamber is also connected to the outlet of the second cooling device. The outlet of the combustion chamber is connected to the fifth cooling device via a pipe.

[0010] The second technical solution adopted in this invention is a synthesis method using a system for synthesizing green alkanes via SOEC, specifically including the following steps: Step 1: The mixed gas is preheated and then co-electrolyzed by an SOEC stack to produce syngas; Step 2: The synthesis gas is separated by the first separation device of the co-electrolysis system, and a portion of it enters the methanol synthesis system; Step 3: The synthesis gas entering the methanol synthesis system is separated by the second gas-liquid separator to obtain gas and liquid phases; Step 4: The liquid phase obtained in Step 3 is purified by distillation to obtain high-purity methanol.

[0011] The second technical solution of the present invention is further characterized by: In step 1, liquid water at room temperature is pumped into the steam generator, and CO2 gas is introduced into the steam generator through the first mixing device. The temperature in the steam generator is 110-150℃. A CO2-H2O mixed gas is formed in the steam generator and input into the first heating device. The heating temperature of the first heating device is 650-850℃. The heated mixed gas is then introduced into the fuel electrode of the SOEC stack. Outside air enters the second heating device through an air compressor. The heating temperature of the second heating device is 650-850℃, and the purge air flow rate is 0.4-1.0 liters / min / 100cm². The preheated air is then introduced into the oxygen electrode of the SOEC stack. Syngas is generated by co-electrolysis using an SOEC stack.

[0012] In step 2, the cooling temperature of the first cooling device is 30-80℃; Syngas with a volume ratio of 20%-100% is fed into the methanol synthesis system through the outlet of the first separation unit; syngas with a volume ratio of 0%-80% is circulated to the steam generator through the other outlet of the first separation unit, and then fed into the fuel electrode of the SOEC stack through the first heating unit. The volume ratio of reducing gas H2 to CO in the SOEC stack fuel electrode feed is 10%-50%. The H2O and CO2 flow rates are adjusted in steps of 0.1 standard liters per minute (SLM) per cell, while the SOEC stack operating current is adjusted in steps of 5 amps (A).

[0013] In step 3, the pressure of the synthesis gas after being pressurized by the second compressor is 50-100 bar, the third heating device heats the synthesis gas to 200-300℃, and the cooling temperature of the fourth cooling device is 30-50℃; The second gas-liquid separation device separates methanol and aqueous solution into liquid phase and unreacted syngas into gas phase. 95%-99% of the unreacted syngas is recycled back to the methanol reactor to continue participating in the reaction, while 1%-5% of the unreacted syngas is output as tail gas.

[0014] In step 4, the liquid phase is sequentially fed into the distillation unit through the second pressure reducing valve and the fifth heating device 28, and the reflux ratio and distillation ratio are controlled to obtain high-purity methanol and circulating aqueous solution. The pressure of the liquid phase drops to 0.3-0.6 MPa after passing through the second pressure reducing valve, and the temperature of the distillation unit is 200-400℃. The concentrations of both high-purity methanol and circulating aqueous solution are not less than 98%.

[0015] The beneficial effects of this invention are: This invention provides a system and method for synthesizing green alkanes using SOEC. The system utilizes renewable electricity to drive a solid oxide electrolyzer (SOEC) to achieve the synergistic electrolysis of H2O and CO2 to generate syngas (H2, CO, CO2). The resulting syngas composition satisfies the molar ratio required for methanol synthesis: (H2–CO2) / (CO2+CO)≈2. This method effectively improves system energy efficiency through thermoelectric synergy and gas circulation strategies. Under the condition of achieving the same methanol yield, it has a significant efficiency advantage compared to the traditional water electrolysis-to-hydrogen coupled CO2 hydrogenation route. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the co-electrolysis system of the present invention; Figure 2 This is a schematic diagram of the methanol synthesis system of the present invention; Figure 3 This is a comparison chart of the overall composite curves of the co-electrolysis preparation of syngas and the methanol synthesis route by electrolysis of H2O and CO2 in Example 5 of the present invention. Figure 4 This is the overall composite curve of the methanol synthesis system under different SOEC co-electrolysis thermal neutral conditions in Example 6 of the present invention; Figure 5 This is a graph showing the relationship between the system efficiency and methanol yield of the methanol synthesis system under different SOEC co-electrolysis thermal neutral conditions in Example 6 of the present invention.

[0017] In the diagram, 1. Water pump, 2. Steam generator, 3. First heating device, 4. SOEC fuel cell stack, 5. First cooling device, 6. First gas-liquid separator, 7. First separator, 8. First mixing device, 9. Air compressor, 10. Second heating device, 11. Second cooling device, 12. Second mixing device, 13. First compressor, 14. Third cooling device, 15. Second compressor, 16. Third heating device, 17. Third mixing device, 18. Methanol reactor, 19. Fourth cooling device, 20. First pressure reducing valve, 21. Second gas-liquid separator, 22. Second separator, 23. Third compressor, 24. Combustion chamber, 25. Fourth heating device, 26. Fifth cooling device, 27. Second pressure reducing valve, 28. Fifth heating device, 29. Distillation unit, 30. Sixth heating device, 31. Sixth cooling device. Detailed Implementation

[0018] The following detailed description is provided in conjunction with specific implementation methods.

[0019] like Figure 1As shown, the system for synthesizing green alkanes using SOEC includes a co-electrolysis system and a methanol synthesis system. The co-electrolysis system includes a water pump 1, with liquid water connected to its inlet. The outlet of the water pump 1 is connected in sequence to a steam generator 2 and a first heating device 3 via pipelines. The outlet of the first heating device 3 is connected to the fuel electrode of the SOEC stack 4 via a pipeline. The outlet of the fuel electrode of the SOEC stack 4 is connected in sequence to a first cooling device 5 and a first gas-liquid separator 6 via pipelines. The liquid outlet of the first gas-liquid separator 6 discharges circulating water, and the gas outlet of the first gas-liquid separator 6 is connected in sequence to a first separation device 7 and a first mixing device 8 via pipelines. The outlet of the first mixing device 8 is connected to the steam generator 2 via a pipeline. The outlet of the first separation device 7 is connected to the methanol synthesis system.

[0020] Air is fed into the air compressor 9, and its outlet is connected to the inlet of the second heating device 10 via a pipe. The outlet of the second heating device 10 is connected to the oxygen electrode of the SOEC fuel cell stack 4 via a pipe. The outlet side of the oxygen electrode of the SOEC fuel cell stack 4 is connected to the second cooling device 11, and the outlet of the second cooling device 11 outputs oxygen-enriched air.

[0021] like Figure 2 As shown, the methanol synthesis system includes a second mixing unit 12. The inlet of the second mixing unit 12 is connected to the outlet of the first separation unit 7 via a pipeline. The outlet of the second mixing unit 12 is connected in sequence via a pipeline to a first compressor 13, a third cooling unit 14, a second compressor 15, a third heating unit 16, and a third mixing unit 17. The outlet of the third mixing unit 17 is connected to a methanol reactor 18 via a pipeline. The outlet of the methanol reactor 18 is connected in sequence via a fourth cooling unit 19, a first pressure reducing valve 20, and a second gas-liquid separator 21 via a pipeline.

[0022] When the gas output from the outlet of the first separation device 7 contains only hydrogen, CO2 gas is introduced into the other inlet of the second mixing device 12.

[0023] The gas outlet of the second gas-liquid separator 21 is connected to the inlet of the second separator 22 via a pipe. The two outlets of the second separator 22 are respectively connected to the third compressor 23 and the combustion chamber 24. The outlet of the third compressor 23 is connected to the inlet of the fourth heating device 25 via a pipe, and the outlet of the fourth heating device 25 is connected to the inlet of the third mixing device 17 via a pipe. The inlet of the combustion chamber 24 is also connected to the outlet of the second cooling device 11, and the outlet of the combustion chamber 24 is connected to the fifth cooling device 26 via a pipe. The outlet of the fifth cooling device 26 outputs combustion exhaust gas.

[0024] The liquid outlet of the second gas-liquid separator 21 is connected in sequence to the second pressure reducing valve 27, the fifth heating device 28, and the distillation unit 29 via pipelines. The top outlet of the distillation unit 29 is connected to the sixth heating device 30 via a pipeline, outputting circulating water; the bottom outlet of the distillation unit 29 is connected to the sixth cooling device 31 via a pipeline, outputting methanol.

[0025] During the synthesis process, the mixed gas is first preheated in the co-electrolysis system, and then produced as syngas through co-electrolysis of the SOEC stack. The syngas is then separated by the first separation unit 7 of the co-electrolysis system, with a portion entering the methanol synthesis system. The specific process is as follows: Liquid water at room temperature is pumped into steam generator 2 via water pump 1, while CO2 gas is simultaneously introduced into steam generator 2 via first mixing device 8. The liquid water is converted into superheated steam in steam generator 2 at a temperature of 110-150℃. The steam and CO2 gas are mixed uniformly to form a CO2-H2O mixture. This CO2-H2O mixture is then further heated to the operating temperature of SOEC stack 4, which is 650-850℃, via first heating device 3.

[0026] Outside air enters the second heating device 10 through the air compressor 9 and is preheated to the operating temperature of the SOEC stack 4, wherein the operating temperature is 650-850℃ and the purge air flow rate is 0.4-1.0L / min / 100cm².

[0027] A CO2-H2O mixed gas is introduced into the fuel electrode of SOEC stack 4. Preheated air is introduced into the oxygen electrode of SOEC stack 4 and then co-electrolyzed to generate syngas, which consists of H2, CO and CO2.

[0028] The gas from the SOEC stack 4 fuel electrode outlet is cooled to 30-80°C by the first cooling device 5 and then separated into gas and liquid by the first gas-liquid separator 6, where circulating water is discharged from the liquid outlet. The remaining H2+CO+CO2 synthesis gas is rich in reducing gases. After entering the first separator 7, 20%-100% of the synthesis gas by volume is fed into the methanol synthesis system through the outlet of the first separator 7. 0%-80% of the synthesis gas by volume is returned to the steam generator 2 through the other outlet of the first separator 7 and the first mixing device 8, where it, together with H2O and CO2 in the steam, constitutes the electrolysis feed. The volume ratio of reducing gases (H2+CO) in the SOEC stack 4 fuel electrode feed is 10%-50% to suppress Ni oxidation in the fuel electrode.

[0029] The air output from the oxygen electrode outlet side of the SOEC fuel cell stack 4 is cooled by the second cooling device 11, resulting in oxygen-enriched air. The outlet end of the second cooling device 11 is connected to the inlet end of the combustion chamber 24, meaning that oxygen-enriched air is input into the combustion chamber 24.

[0030] The H2O and CO2 flow rates are adjusted in steps of 0.1 SLM per unit, while the SOEC stack 4 operating current is adjusted in steps of 5 A. This ensures that the SOEC stack 4 operates under thermal neutral voltage conditions and guarantees that the product gas meets the feed requirements of the subsequent methanol synthesis reactor.

[0031] In the methanol synthesis system, the synthesis gas entering the system is separated by the second gas-liquid separator 21 to obtain a gas phase and a liquid phase. The liquid phase is then purified by distillation to obtain high-purity methanol. The specific process is as follows: Syngas with a volume fraction of 20%-100% is output through the first separation unit 7 and sequentially passes through the second mixing unit 12, the first compressor 13, the third cooling unit 14, and the second compressor 15, i.e., it is pressurized through a multi-stage compressor to a pressure of 50-100 bar. After pressurization, the syngas then passes through the third heating unit 16, where it is heated to the methanol synthesis temperature of 200-300°C. The heated syngas is then output to the third mixing unit 17.

[0032] Syngas exits through the outlet of the third mixing unit 17 and enters the methanol reactor 18. Due to chemical equilibrium limitations, the reaction is incomplete, and the outlet gas of the methanol reactor 18 contains methanol, water, and unreacted gas. The outlet gas of the methanol reactor 18 is cooled to 30-50°C by the fourth cooling unit 19, and then enters the second gas-liquid separator 21 through the first pressure reducing valve 20, separating the gas and liquid phases. The liquid phase is mainly a methanol-water solution; the gas phase contains unreacted syngas. The gas phase passes through the second separation unit 22, where 95%-99% by volume of the unreacted syngas is recycled to the third mixing unit 17 after passing through the third compressor 23 and the fourth heating unit 25. After mixing in the third mixing unit 17, it returns to the methanol reactor 18 to continue participating in the reaction, avoiding resource waste. The remaining 1%-5% by volume of the unreacted syngas is output as tail gas, mixed with oxygen-enriched air from the SOEC oxygen electrode side, and sent to the combustion chamber 24 for combustion, generating heat for other system heat requirements. The combustion chamber 24 outlet is connected to the fifth cooling device 26, which outputs combustion exhaust gas. This exhaust gas diversion design avoids the accumulation of inert gas and improves methanol yield.

[0033] The liquid phase (methanol-water solution) separated by the second gas-liquid separator 21 is sequentially fed into the distillation unit 29 through the second pressure reducing valve 27 and the fifth heating device 28. The reflux ratio and distillation ratio are controlled to obtain high-purity methanol and circulating water solution. The pressure of the liquid phase drops to 0.3-0.6 MPa after passing through the second pressure reducing valve 27, and the temperature of the distillation unit is 200-400℃. The concentrations of both high-purity methanol and circulating water solution are not less than 98%.

[0034] SOEC electrolysis systems can be powered by green electricity to achieve carbon-neutral methanol production.

[0035] The SOEC electrolysis system and downstream methanol synthesis process of this invention are applicable not only to the CO2–H2O co-electrolysis route but also to the H2O electrolysis to hydrogen production–CO2 hydrogenation to methanol route. During the H2O electrolysis to hydrogen production–CO2 hydrogenation process, the SOEC electrolysis system feeds only high-purity water vapor, without introducing CO2. The electrolysis product is high-purity H2, meaning the CO2 inlet of the first mixing device 8 is closed, and the first separation device 7 outputs high-purity H2. At this time, the output gas of the co-electrolysis system is only H2. Subsequently, the second mixing device 12 is opened, and CO2 enters the second mixing device 12 to mix with H2. The resulting H2 and CO2 are mixed at a molar ratio of H2 / CO2 = 4 to form the synthesis gas required for methanol synthesis, which is then introduced into the methanol reactor 18 for catalytic conversion.

[0036] This invention can also thermally couple the heat load of the co-electrolysis system with the exothermic process of the methanol synthesis reactor, and improve the overall energy utilization efficiency by tapping the internal thermal integration potential of the system through pinch analysis.

[0037] A synthetic method for synthesizing green alkanes using SOEC, specifically including the following steps: Step 1: The mixed gas is preheated and then co-electrolyzed by an SOEC stack to produce syngas.

[0038] Liquid water at room temperature is pumped into steam generator 2 via water pump 1, and CO2 gas is input into steam generator 2 via first mixing device 8.

[0039] The temperature in the steam generator 2 is 110-150℃, and a CO2-H2O mixed gas is formed in the steam generator 2. This mixed gas is then fed into the first heating device 3, which has a heating temperature of 650-850℃. The heated mixed gas is then fed into the fuel electrode of the SOEC stack 4.

[0040] Outside air enters the second heating device 10 through the air compressor 9, with a heating temperature of 650-850℃ and a purge air flow rate of 0.4-1.0L / min / 100cm². The preheated air is then introduced into the oxygen electrode of the SOEC stack 4.

[0041] Syngas is generated through co-electrolysis using SOEC stack 4.

[0042] Step 2: The synthesis gas is separated by the first separation device 7 of the co-electrolysis system, and part of it enters the methanol synthesis system.

[0043] The first cooling device 5 has a cooling temperature of 30-80℃; Syngas with a volume ratio of 20%-100% is fed into the methanol synthesis system through the outlet of the first separation device 7; syngas with a volume ratio of 0%-80% is circulated to the steam generator 2 through the other outlet of the first separation device 7, and then fed into the fuel electrode of the SOEC stack 4 through the first heating device 3. The volume ratio of reducing gas H2 to CO in the feed to the fuel electrode of the SOEC stack 4 is 10%-50%. The H2O and CO2 flow rates are adjusted in steps of 0.1 SLM per unit, while the SOEC stack 4's operating current is adjusted in steps of 5 A.

[0044] Step 3: The synthesis gas entering the methanol synthesis system is separated by the second gas-liquid separation device 21 to obtain gas phase and liquid phase.

[0045] The pressure of the synthesis gas after being pressurized by the second compressor 15 is 50-100 bar. The third heating device 16 heats the synthesis gas to 200-300℃. The cooling temperature of the fourth cooling device 19 is 30-50℃. The liquid phase separated by the second gas-liquid separation device 21 includes methanol-water solution, and the gas phase separated includes unreacted synthesis gas. 95%-99% of the unreacted synthesis gas is recycled back to the methanol reactor 18 through the second separation device 22 to continue participating in the reaction, and 1%-5% of the unreacted synthesis gas is output as tail gas.

[0046] Step 4: The liquid phase obtained in Step 3 is purified by distillation to obtain high-purity methanol, i.e., green alkane.

[0047] The liquid phase is sequentially fed into the distillation unit 29 through the second pressure reducing valve 27 and the fifth heating device 28 to obtain high-purity methanol and a circulating aqueous solution. After passing through the second pressure reducing valve 27, the pressure of the liquid phase drops to 0.3-0.6 MPa, and the temperature of the distillation unit is 200-400℃. The concentrations of both the high-purity methanol and the circulating aqueous solution are not less than 98%.

[0048] Example 1 The system for synthesizing green alkanes using SOEC includes a co-electrolysis system and a methanol synthesis system. The co-electrolysis system includes an SOEC stack 4. The outlet side of the fuel electrode of the SOEC stack 4 is connected in sequence to a first cooling device 5 and a first gas-liquid separation device 6 via pipelines. The gas outlet of the first gas-liquid separation device 6 is connected in sequence to a first separation device 7 and a first mixing device 8 via pipelines. The outlet end of the first separation device 7 is connected to the methanol synthesis system.

[0049] Example 2 The system for synthesizing green alkanes using SOEC includes a co-electrolysis system and a methanol synthesis system. The co-electrolysis system includes an SOEC stack 4. The outlet side of the fuel electrode of the SOEC stack 4 is connected in sequence to a first cooling device 5 and a first gas-liquid separation device 6 via pipelines. The gas outlet of the first gas-liquid separation device 6 is connected in sequence to a first separation device 7 and a first mixing device 8 via pipelines. The outlet end of the first separation device 7 is connected to the methanol synthesis system.

[0050] The co-electrolysis system also includes a water pump 1 and an air compressor 9. The inlet of the water pump 1 is connected to liquid water, and the outlet of the water pump 1 is connected to a steam generator 2 and a first heating device 3 in sequence through a pipe. The outlet of the first heating device 3 is connected to the fuel electrode of the SOEC stack 4 through a pipe, and the outlet of the first mixing device 8 is connected to the steam generator 2 through a pipe. Air is introduced into the inlet of the air compressor 9, and the outlet is connected to the inlet of the second heating device 10 through a pipe. The outlet of the second heating device 10 is connected to the oxygen electrode of the SOEC stack 4 through a pipe. The outlet side of the oxygen electrode of the SOEC stack 4 is connected to the second cooling device 11.

[0051] Example 3 The system for synthesizing green alkanes using SOEC includes a co-electrolysis system and a methanol synthesis system. The co-electrolysis system includes an SOEC stack 4. The outlet side of the fuel electrode of the SOEC stack 4 is connected in sequence to a first cooling device 5 and a first gas-liquid separation device 6 via pipelines. The gas outlet of the first gas-liquid separation device 6 is connected in sequence to a first separation device 7 and a first mixing device 8 via pipelines. The outlet end of the first separation device 7 is connected to the methanol synthesis system.

[0052] The co-electrolysis system also includes a water pump 1 and an air compressor 9. The inlet of the water pump 1 is connected to liquid water, and the outlet of the water pump 1 is connected to a steam generator 2 and a first heating device 3 in sequence through a pipe. The outlet of the first heating device 3 is connected to the fuel electrode of the SOEC stack 4 through a pipe, and the outlet of the first mixing device 8 is connected to the steam generator 2 through a pipe. Air is introduced into the inlet of the air compressor 9, and the outlet is connected to the inlet of the second heating device 10 through a pipe. The outlet of the second heating device 10 is connected to the oxygen electrode of the SOEC stack 4 through a pipe. The outlet side of the oxygen electrode of the SOEC stack 4 is connected to the second cooling device 11.

[0053] The methanol synthesis system includes a second mixing unit 12. The inlet of the second mixing unit 12 is connected to the outlet of the first separation unit 7 via a pipeline. The outlet of the second mixing unit 12 is connected in sequence via a pipeline to a first compressor 13, a third cooling unit 14, a second compressor 15, a third heating unit 16, and a third mixing unit 17. The outlet of the third mixing unit 17 is connected to a methanol reactor 18 via a pipeline. The outlet of the methanol reactor 18 is connected in sequence via a fourth cooling unit 19, a first pressure reducing valve 20, and a second gas-liquid separator 21 via a pipeline. The gas outlet of the second gas-liquid separator 21 is connected to the inlet of the second separation unit 22 via a pipeline. The outlet of the second separation unit 22 is connected to a third compressor 23. The outlet of the third compressor 23 is connected to the inlet of the fourth heating unit 25 via a pipeline. The outlet of the fourth heating unit 25 is connected to the inlet of the third mixing unit 17 via a pipeline.

[0054] Example 4 The system for synthesizing green alkanes using SOEC includes a co-electrolysis system and a methanol synthesis system. The co-electrolysis system includes an SOEC stack 4. The outlet side of the fuel electrode of the SOEC stack 4 is connected in sequence to a first cooling device 5 and a first gas-liquid separation device 6 via pipelines. The gas outlet of the first gas-liquid separation device 6 is connected in sequence to a first separation device 7 and a first mixing device 8 via pipelines. The outlet end of the first separation device 7 is connected to the methanol synthesis system.

[0055] The co-electrolysis system also includes a water pump 1 and an air compressor 9. The inlet of the water pump 1 is connected to liquid water, and the outlet of the water pump 1 is connected to a steam generator 2 and a first heating device 3 in sequence through a pipe. The outlet of the first heating device 3 is connected to the fuel electrode of the SOEC stack 4 through a pipe, and the outlet of the first mixing device 8 is connected to the steam generator 2 through a pipe. Air is introduced into the inlet of the air compressor 9, and the outlet is connected to the inlet of the second heating device 10 through a pipe. The outlet of the second heating device 10 is connected to the oxygen electrode of the SOEC stack 4 through a pipe. The outlet side of the oxygen electrode of the SOEC stack 4 is connected to the second cooling device 11.

[0056] The methanol synthesis system includes a second mixing unit 12. The inlet of the second mixing unit 12 is connected to the outlet of the first separation unit 7 via a pipeline. The outlet of the second mixing unit 12 is connected in sequence via a pipeline to a first compressor 13, a third cooling unit 14, a second compressor 15, a third heating unit 16, and a third mixing unit 17. The outlet of the third mixing unit 17 is connected to a methanol reactor 18 via a pipeline. The outlet of the methanol reactor 18 is connected in sequence via a fourth cooling unit 19, a first pressure reducing valve 20, and a second gas-liquid separator 21 via a pipeline. The gas outlet of the second gas-liquid separator 21 is connected to the inlet of the second separation unit 22 via a pipeline. The outlet of the second separation unit 22 is connected to a third compressor 23. The outlet of the third compressor 23 is connected to the inlet of the fourth heating unit 25 via a pipeline. The outlet of the fourth heating unit 25 is connected to the inlet of the third mixing unit 17 via a pipeline.

[0057] The liquid outlet of the second gas-liquid separation device 21 is connected in sequence to the second pressure reducing valve 27, the fifth heating device 28 and the distillation device 29 via pipelines. The top outlet of the distillation device 29 is connected to the sixth heating device 30, and the bottom outlet of the distillation device 29 is connected to the sixth cooling device 31.

[0058] Example 5 A synthetic method for synthesizing green alkanes using SOEC, specifically including the following steps: Step 1: The mixed gas is preheated and then co-electrolyzed by an SOEC stack to produce syngas; Step 2: The synthesis gas is separated by the first separation device 7 of the co-electrolysis system, and part of it enters the methanol synthesis system; Step 3: The synthesis gas entering the methanol synthesis system is separated by the second gas-liquid separator 21 to obtain gas and liquid phases; Step 4: The liquid phase obtained in Step 3 is purified by distillation to obtain high-purity methanol, i.e., green alkane.

[0059] In this embodiment, in order to achieve a closed-loop energy system, it is assumed that there is a constant temperature heat source of 1000°C as a thermal common engineering system and cooling water of 15°C as a cold common engineering system, and the minimum heat exchange temperature difference between the hot and cold flows is set to 10°C.

[0060] by Figure 3 Taking the 20 kW SOEC scale system shown as an example, we compare two routes: SOEC co-electrolysis to produce syngas for methanol synthesis and SOEC electrolysis of H2O plus CO2 for methanol synthesis. Both routes maintain SOEC operating in a thermally neutral state, assuming methanol synthesis conditions of 250℃, 50 bar, and a methanol yield of 2.6 kg / h.

[0061] The system efficiency is calculated as follows: (1) Table 1 compares the system performance of different synthesis routes. The specific system performance calculations are as follows: Table 1. Performance Comparison of Different Synthetic Routes

[0062] Therefore, the co-electrolysis route can effectively reduce the external heat load of the system and has higher system efficiency.

[0063] Example 6 A synthetic method for synthesizing green alkanes using SOEC, specifically including the following steps: Step 1: The mixed gas is preheated and then co-electrolyzed by an SOEC stack to produce syngas; Step 2: The synthesis gas is separated by the first separation device 7 of the co-electrolysis system, and part of it enters the methanol synthesis system; Step 3: The synthesis gas entering the methanol synthesis system is separated by the second gas-liquid separator 21 to obtain gas and liquid phases; Step 4: The liquid phase obtained in Step 3 is purified by distillation to obtain high-purity methanol, i.e., green alkane.

[0064] To achieve a closed-loop energy system, it is assumed that there is a constant-temperature heat source at 1000°C as a thermal common engineering system and cooling water at 15°C as a cold common engineering system, and the minimum heat exchange temperature difference between the hot and cold flows is set to 10°C.

[0065] This embodiment demonstrates the performance variations of the co-electrolysis system at different thermally neutral operating points. Operating parameters and SOEC subsystem conversion rates are shown in Table 2. Table 2 Operating parameters of SOEC co-electrolysis at different thermal neutral operating points

[0066] Depend on Figure 4 It is evident that there is always room for thermal coupling optimization in the system, and the heat required for methanol synthesis can partially meet the heat demand for H2O evaporation in the SOEC electrolysis subsystem. However, as the SOEC conversion rate decreases, the system pinch-point temperature stabilizes at 98℃, and the heat released from the reactor and tail gas combustion cannot fully meet the heat required for H2O evaporation, necessitating an external heat source to assist in evaporation. Simultaneously, the demand for external heat sources and cooling water increases with decreasing conversion rate.

[0067] Depend on Figure 5 As can be seen, the system efficiency is maintained between 71% and 78%. After selecting a suitable operating point, the overall system efficiency of green electricity to methanol can reach about 75%.

[0068] In summary, this invention presents a system and method for synthesizing green alkanes using SOEC. Compared with the traditional H2O electrolysis route, this scheme has advantages in terms of operating efficiency and thermal management; under reasonable operating conditions, the system efficiency can be stabilized at over 70%, and the methanol yield remains at a high level, achieving efficient utilization of green energy.

Claims

1. A system for synthesizing green alkanes using SOEC, characterized in that, The system includes a co-electrolysis system and a methanol synthesis system. The co-electrolysis system includes an SOEC stack (4). The outlet side of the fuel electrode of the SOEC stack (4) is connected to a first cooling device (5) and a first gas-liquid separation device (6) in sequence through pipes. The gas outlet of the first gas-liquid separation device (6) is connected to a first separation device (7) and a first mixing device (8) in sequence through pipes. The outlet end of the first separation device (7) is connected to the methanol synthesis system.

2. The system for synthesizing green alkanes using SOEC according to claim 1, characterized in that, The co-electrolysis system also includes a water pump (1) and an air compressor (9). The inlet of the water pump (1) is connected to liquid water, and the outlet of the water pump (1) is connected to a steam generator (2) and a first heating device (3) in sequence through a pipe. The outlet of the first heating device (3) is connected to the fuel electrode of the SOEC stack (4) through a pipe, and the outlet of the first mixing device (8) is connected to the steam generator (2) through a pipe. The air compressor (9) is connected to the air inlet and the outlet is connected to the inlet of the second heating device (10) through a pipe. The outlet of the second heating device (10) is connected to the oxygen electrode of the SOEC stack (4) through a pipe. The outlet side of the oxygen electrode of the SOEC stack (4) is connected to the second cooling device (11).

3. The system for synthesizing green alkanes using SOEC according to claim 2, characterized in that, The methanol synthesis system includes a second mixing device (12), the inlet of which is connected to the outlet of a first separation device (7) via a pipe, and the outlet of the second mixing device (12) is connected in sequence to a first compressor (13), a third cooling device (14), a second compressor (15), a third heating device (16), and a third mixing device (17) via pipes; the outlet of the third mixing device (17) is connected to a methanol reactor (18) via a pipe, and the outlet of the methanol reactor (18) is connected in sequence to a fourth cooling device (19), a first pressure reducing valve (20), and a second gas-liquid separator (21) via pipes; the gas outlet of the second gas-liquid separator (21) is connected to the inlet of a second separation device (22) via a pipe, and the outlet of the second separation device (22) is connected to a third compressor (23); the outlet of the third compressor (23) is connected to the inlet of a fourth heating device (25) via a pipe, and the outlet of the fourth heating device (25) is connected to the inlet of the third mixing device (17) via a pipe.

4. The system for synthesizing green alkanes using SOEC according to claim 3, characterized in that, The liquid outlet of the second gas-liquid separation device (21) is connected in sequence to the second pressure reducing valve (27), the fifth heating device (28) and the distillation device (29) through a pipeline. The top outlet of the distillation device (29) is connected to the sixth heating device (30), and the bottom outlet of the distillation device (29) is connected to the sixth cooling device (31).

5. The system for synthesizing green alkanes using SOEC according to claim 3, characterized in that, The other outlet of the second separation device (22) is connected to the combustion chamber (24) via a pipe. The inlet of the combustion chamber (24) is also connected to the outlet of the second cooling device (11). The outlet of the combustion chamber (24) is connected to the fifth cooling device (26) via a pipe.

6. A synthetic method for synthesizing green alkanes using SOEC, employing the system for synthesizing green alkanes using SOEC as described in claims 4-5, specifically comprising the following steps: Step 1: The mixed gas is preheated and then co-electrolyzed by an SOEC stack to produce syngas; Step 2: The synthesis gas is separated by the first separation device (7) of the co-electrolysis system, and part of it enters the methanol synthesis system; Step 3: The synthesis gas entering the methanol synthesis system is separated by the second gas-liquid separator (21) to obtain gas and liquid phases; Step 4: The liquid phase obtained in Step 3 is purified by distillation to obtain high-purity methanol.

7. The system for synthesizing green alkanes using SOEC according to claim 6, characterized in that, In step 1, liquid water at room temperature is pumped into the steam generator (2) through a water pump (1), and CO2 gas is input into the steam generator (2) through a first mixing device (8). The temperature in the steam generator (2) is 110-150℃. A CO2-H2O mixed gas is formed in the steam generator (2) and input into the first heating device (3). The heating temperature of the first heating device (3) is 650-850℃. The heated mixed gas is introduced into the fuel electrode of the SOEC stack (4). Outside air enters the second heating device (10) through the air compressor (9). The heating temperature of the second heating device (10) is 650-850℃, and the purge air flow rate is 0.4-1.0L / min / 100cm². The preheated air is then introduced into the oxygen electrode of the SOEC stack (4). Syngas is generated after co-electrolysis via SOEC stack (4).

8. The system for synthesizing green alkanes using SOEC according to claim 6, characterized in that, In step 2, the cooling temperature of the first cooling device (5) is 30-80℃; Synthesis gas with a volume ratio of 20%-100% is fed into the methanol synthesis system through the outlet of the first separation device (7); synthesis gas with a volume ratio of 0%-80% is circulated to the steam generator (2) through the other outlet of the first separation device (7), and then fed into the fuel electrode of the SOEC stack (4) through the first heating device (3). The volume ratio of reducing gas H2 to CO in the feed to the fuel electrode of the SOEC stack (4) is 10%-50%. The H2O and CO2 flow rate are adjusted in steps of 0.1 SLM per unit, and the SOEC stack (4) operating current is adjusted in steps of 5 A.

9. The system for synthesizing green alkanes using SOEC according to claim 6, characterized in that, In step 3, the pressure of the synthesis gas after being pressurized by the second compressor (15) is 50-100 bar, the third heating device (16) heats the synthesis gas to 200-300°C, and the cooling temperature of the fourth cooling device (19) is 30-50°C. The second gas-liquid separation device (21) separates the liquid phase including methanol and aqueous solution, and the separated gas phase includes unreacted synthesis gas. The second separation device (22) recycles 95%-99% of the unreacted synthesis gas back to the methanol reactor (18) to continue participating in the reaction, and outputs 1%-5% of the unreacted synthesis gas as tail gas.

10. The system for synthesizing green alkanes using SOEC according to claim 6, characterized in that, In step 4, the liquid phase is sequentially fed into the distillation unit (29) through the second pressure reducing valve (27) and the fifth heating device 28, and the reflux ratio and distillation ratio are controlled to obtain high-purity methanol and circulating aqueous solution; The pressure of the liquid phase drops to 0.3-0.6 MPa after passing through the second pressure reducing valve (27), and the temperature of the distillation unit is 200-400℃; the concentration of both high-purity methanol and circulating aqueous solution is not less than 98%.

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