Method and system for energy-saving synthesis of green methanol from low-concentration mine gas

Abstract

The invention discloses a method and a system for energy-saving synthesis of green methanol from low-concentration mine gas, and the method comprises the following steps: carrying out internal reforming reaction on low-concentration mine gas raw material gas to generate high-temperature synthesis gas; carrying out heat exchange on the high-temperature synthesis gas and the low-concentration mine gas raw material gas before internal reforming to obtain low-temperature synthesis gas; supplementing hydrogen into the low-temperature synthesis gas, mixing and pressurizing to form methanol synthesis raw material gas; feeding the methanol synthesis raw material gas to a methanol synthesis process to prepare crude methanol; and rectifying the crude methanol to obtain high-purity methanol. According to the invention, energy-saving and green conversion from low-concentration mine gas to a methanol product is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of methanol production, and in particular to a method and system for energy-saving synthesis of green methanol from low-concentration mine gas. Background Art

[0002] Coal mining is accompanied by the release of mine gas, a mixture of gases typically consisting of methane, water vapor, or carbon dioxide. Depending on the methane concentration, mine gas with a methane concentration of 30% or greater is considered high-concentration mine gas, while mine gas with a methane concentration of less than 30% is considered low-concentration mine gas.

[0003] High-concentration mine gas can be used directly as fuel or the methane can be purified and utilized. Since methane gas has high transportation costs and is flammable, explosive, and difficult to store, it is usually converted into high-value chemicals that are easy to transport and store. For example, it is converted into methanol (CH3OH), one of the four basic chemicals. Methanol (CH3OH) has outstanding advantages such as high calorific value and low pollution, and is easy to store and transport. At present, industrial methanol production usually adopts the indirect synthesis of methanol from methane, that is, methane is first reformed with water vapor or carbon dioxide to produce synthesis gas, and then methanol is synthesized at a high temperature exceeding 1073K. The specific chemical reaction formula is as follows:

[0004] CH4+H2O=CO+3H2; CH4+CO2=2CO+2H2; CO+2H2=CH3OH.

[0005] This process has at least the following disadvantages. On the one hand, methane is purified from high-concentration mine gas. On the other hand, it requires the additional introduction of water vapor and / or carbon dioxide gas. The generation of water vapor requires a lot of energy consumption, and carbon dioxide also requires the addition of a carbon capture unit.

[0006] Unlike high-concentration mine gas, which is highly utilised, low-concentration mine gas is often released directly into the atmosphere. Low-concentration mine gas accounts for a significant portion of total mine gas production, resulting in a significant waste of energy. Furthermore, because methane has a greenhouse effect 25 times greater than carbon dioxide, direct atmospheric emissions exacerbate global warming.

[0007] The main reasons why low-concentration mine gas is usually discharged directly are: the concentration range of methane in low-concentration mine gas is in the flammable and explosive concentration range, which is difficult to transmit and cannot burn stably; the proportion of methane in low-concentration mine gas is low, and it is mixed with a large amount of air (nitrogen, oxygen) and other impurities (such as carbon dioxide, water vapor), which makes the separation cost extremely high and difficult to purify and utilize.

[0008] The information disclosed in this background section is only intended to enhance understanding of the overall background of the invention and should not be considered as an admission or any form of suggestion that the information constitutes the prior art already known to a person of ordinary skill in the art. Summary of the Invention

[0009] Purpose of the invention: The technical problem to be solved by the present invention is to address the deficiencies of the existing technology and provide a method and system for energy-saving synthesis of green methanol from low-concentration mine gas, which can solve the technical problems that traditional reforming requires additional introduction of water vapor and / or carbon dioxide to proceed and that the raw gas for synthesizing methanol requires a higher hydrogen content to meet its reaction needs.

[0010] In order to solve the above technical problems, the first aspect of the present invention discloses a method for energy-saving synthesis of green methanol from low-concentration mine gas, the method comprising:

[0011] The low-concentration mine gas raw gas is subjected to an internal reforming reaction to generate a high-temperature synthesis gas; the low-concentration mine gas raw gas contains a methane mole fraction of 1% to 10%;

[0012] exchanging heat between the high-temperature synthesis gas and the low-concentration mine gas raw gas before internal reforming to obtain low-temperature synthesis gas;

[0013] adding hydrogen to the low-temperature synthesis gas, mixing and pressurizing the mixture to form methanol synthesis feed gas;

[0014] sending the methanol synthesis raw gas to a methanol synthesis process to produce crude methanol;

[0015] The crude methanol is distilled to obtain high-purity methanol.

[0016] Preferably, the heat required for the internal reforming reaction is at least partially supplemented by molten salt photothermal method.

[0017] Preferably, the hydrogen is produced by electrolyzing water using green electricity in the mining area; the green electricity in the mining area is provided by one or a combination of wind farms and photovoltaic power stations.

[0018] Specifically, the methanol synthesis process includes: performing a methanol synthesis reaction on the methanol synthesis raw gas to obtain methanol product gas; decompressing and cooling the methanol product gas to form a gas-liquid mixture containing liquid methanol; performing gas-liquid separation on the gas-liquid mixture containing liquid methanol to obtain the crude methanol; the pressure of the gas-liquid mixture containing liquid methanol formed by decompressing and cooling is 10-14 bar, preferably 12 bar; the temperature of the gas-liquid mixture containing liquid methanol formed by decompressing and cooling is 50-70°C, preferably 60°C.

[0019] Specifically, the internal reforming reaction refers to the reaction of carbon dioxide, water vapor and methane in the low-concentration mine gas raw gas to generate the high-temperature synthesis gas; the reaction conditions are: reaction temperature of 750-900°C and pressure of 10-16 bar.

[0020] Specifically, the methanol synthesis feed gas includes hydrogen and carbon oxides, and the carbon oxides are a combination of carbon monoxide and carbon dioxide; the added amount of the hydrogen is controlled so that the molar ratio of hydrogen to carbon oxides in the methanol synthesis feed gas is 1.50-2.30.

[0021] Specifically, the temperature of the low-temperature synthesis gas obtained by heat exchange is 200-280°C, preferably 280°C.

[0022] Specifically, the pressure of the methanol synthesis raw gas formed by mixing and pressurizing is 40-55 bar, preferably 45-50 bar.

[0023] A second aspect of the present invention discloses a system for energy-saving synthesis of green methanol from low-concentration mine gas, the system comprising:

[0024] Gas internal reforming reactor, used to carry out internal reforming reaction on low-concentration mine gas raw gas to generate high-temperature synthesis gas;

[0025] a heat exchanger for exchanging heat between the high-temperature synthesis gas discharged from the gas internal reforming reactor and the low-concentration mine gas feed gas before entering the gas internal reforming reactor to obtain low-temperature synthesis gas;

[0026] A hydrogen generation unit, configured to generate hydrogen;

[0027] a mixing and pressurizing unit, configured to add hydrogen discharged from the hydrogen generating unit to the low-temperature synthesis gas discharged from the heat exchanger, mix and pressurize the mixture, and form a methanol synthesis feed gas;

[0028] A methanol synthesis unit, used to produce crude methanol from the methanol synthesis feed gas discharged from the mixing and pressurizing unit;

[0029] and a distillation tower for distilling the crude methanol discharged from the methanol synthesis unit to obtain high-purity methanol.

[0030] Furthermore, it also includes a molten salt heat supplement unit, and the heat required for the internal reforming reaction in the gas internal reforming reactor is at least partially supplemented by the molten salt heat supplement unit; the molten salt heat supplement unit includes a solar trough collector, a hot molten salt storage tank and a cold molten salt storage tank, and the solar trough collector, the hot molten salt storage tank, the gas internal reforming reactor and the cold molten salt storage tank are connected in sequence through pipelines to form a molten salt circulation loop; a first circulation pump is provided on the pipeline connecting the solar trough collector and the hot molten salt storage tank, a second circulation pump is provided on the pipeline connecting the hot molten salt storage tank and the gas internal reforming reactor, a third circulation pump is provided on the pipeline connecting the gas internal reforming reactor and the cold molten salt storage tank, and a fourth circulation pump is provided on the pipeline connecting the cold molten salt storage tank and the solar trough collector;

[0031] The hydrogen generation unit is a unit for producing hydrogen by electrolyzing water using renewable energy power, and the renewable energy power is one or a combination of a wind farm and a photovoltaic power station.

[0032] Specifically, the gas internal reforming reactor has an inlet for receiving the low-concentration mine gas raw gas and an outlet for discharging the high-temperature synthesis gas;

[0033] The heat exchanger has a heat release side inlet, a heat release side outlet, a heat absorption side inlet and a heat absorption side outlet;

[0034] The hydrogen generating unit is provided with an outlet for discharging hydrogen;

[0035] The mixing and pressurizing unit has an inlet for receiving the low-temperature synthesis gas and the hydrogen and an outlet for discharging the methanol synthesis raw gas;

[0036] The methanol synthesis unit is provided with an inlet for receiving the methanol synthesis raw gas and an outlet for discharging the crude methanol;

[0037] The distillation column is provided with an inlet for receiving the crude methanol;

[0038] The heat-absorbing side inlet of the heat exchanger is connected to the low-concentration mine gas raw gas inlet pipeline, the heat-absorbing side outlet of the heat exchanger is connected to the inlet of the gas internal reforming reactor, the outlet of the gas internal reforming reactor is connected to the heat-releasing side inlet of the heat exchanger, the heat-releasing side outlet of the heat exchanger and the outlet of the hydrogen generation unit are respectively connected to the inlet of the mixing and pressurizing unit, the outlet of the mixing and pressurizing unit is connected to the inlet of the methanol synthesis unit, and the outlet of the methanol synthesis unit is connected to the inlet of the distillation tower;

[0039] The mixing and pressurizing unit includes a mixer, a mixed gas regulating valve, and a compressor. The inlet of the mixer serves as the inlet of the mixing and pressurizing unit. The heat release side outlet of the heat exchanger and the outlet of the hydrogen generating unit are respectively connected to the inlet of the mixer, so that the heat release side outlet of the heat exchanger and the outlet of the hydrogen generating unit are respectively connected to the inlet of the mixing and pressurizing unit. The outlet of the mixer is connected to the inlet of the mixed gas regulating valve, and the outlet of the mixed gas regulating valve is connected to the inlet of the compressor. The outlet of the compressor serves as the outlet of the mixing and pressurizing unit.

[0040] The methanol synthesis unit includes a methanol reactor, a methanol regulating valve, a condenser and a gas-liquid separator. The bottom inlet of the methanol reactor serves as the inlet of the methanol synthesis unit and is connected to the outlet of the compressor to achieve the connection between the outlet of the mixing and pressurizing unit and the inlet of the methanol synthesis unit; the top outlet of the methanol reactor is connected to the inlet of the methanol regulating valve, the outlet of the methanol regulating valve is connected to the inlet of the condenser, and the outlet of the condenser is connected to the inlet of the gas-liquid separator; the middle outlet of the gas-liquid separator serves as the outlet of the methanol synthesis unit and is connected to the inlet of the distillation tower to achieve the connection between the outlet of the methanol synthesis unit and the inlet of the distillation tower;

[0041] It also includes a raw gas regulating valve, a high-temperature synthesis gas regulating valve, a methanol storage tank and a water storage tank. The raw gas regulating valve is arranged on the low-concentration mine gas raw gas inlet pipeline; the high-temperature synthesis gas regulating valve is arranged on the pipeline connecting the outlet of the gas internal reforming reactor and the heat release side inlet of the heat exchanger; the methanol storage tank is connected to the top extraction of the distillation tower; and the water storage tank is connected to the bottom extraction of the distillation tower.

[0042] Beneficial effects:

[0043] 1. Compared with the existing technology of directly discharging low-concentration mine gas into the atmosphere, the present invention converts low-concentration mine gas into methanol, realizing the energy utilization of low-concentration mine gas and avoiding energy waste. At the same time, it reduces the emission of methane and carbon dioxide in mine gas into the atmosphere, which is more environmentally friendly.

[0044] 2. Compared with traditional mine gas reforming, the internal reforming reaction of the present invention does not require the introduction of additional carbon dioxide and water vapor. Instead, it combines the characteristics of the components of low-concentration mine gas itself, that is, it contains carbon dioxide, water vapor and methane at the same time, and uses its own components carbon dioxide and water vapor to convert methane.

[0045] 3. The internal reforming reaction of low-concentration mine gas is a highly endothermic reaction, which requires the combustion of fossil fuels to provide a large amount of heat to meet the needs of the internal reforming reaction. The present invention can utilize the natural photothermal conditions in the area where the mine is located to provide heat to the internal reforming reaction in the form of molten salt photothermal technology to reduce fuel consumption.

[0046] 4. The present invention utilizes the abundant wind and solar energy in the mine area to decompose water to produce hydrogen, and adds hydrogen to the methanol synthesis raw gas to meet the needs of methanol synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0048] Figure 1 A schematic structural diagram of a system for energy-saving synthesis of green methanol from low-concentration mine gas provided in one embodiment of the present invention.

[0049] Figure 2 for Figure 1 A partial enlarged view of the mine gas reforming and molten salt heating unit in the system shown.

[0050] Figure 3 for Figure 1 A partially enlarged view of the solar and wind energy water electrolysis hydrogen production unit in the system shown.

[0051] Figure 4 for Figure 1 An enlarged diagram of the connection relationship between the mixing and pressurizing unit, methanol synthesis unit and distillation unit in the system is shown.

[0052] Description of the accompanying drawings:

[0053] 1. Gas internal reforming reactor; 2. Heat exchanger; 3. Feed gas regulating valve; 4. Low-temperature synthesis gas regulating valve; 5. Mixer; 6. Circulating gas regulating valve; 7. Compressor; 8. Circulating gas pressurizing device; 9. Purge gas regulating valve; 10. Purge gas device; 11. Condenser; 12. Gas-liquid separator; 13. Distillation tower; 14. Water storage tank; 15. Methanol storage tank; 16. Oxygen storage tank; 17. Oxygen separator; 18. Steam regulating valve; 19. Water supply regulating valve; 20. Water mixer; 21. Electrolyzer; 22. Electrochemical storage tank Energy device; 23. Solid-state hydrogen storage device; 24. Photovoltaic power station; 25. Solar trough collector; 26. Hot molten salt storage tank; 271. First circulation pump; 272. Second circulation pump; 273. Third circulation pump; 274. Fourth circulation pump; 28. High-temperature synthesis gas regulating valve; 29. ​​Hydrogen regulating valve; 30. Mixed gas regulating valve; 31. Methanol regulating valve; 32. Hydrogen storage regulating valve; 33. Oxygen regulating valve; 34. Oxygen storage regulating valve; 35. Wind farm; 36. Cold molten salt storage tank; 37. Methanol reactor; 38. Mine. DETAILED DESCRIPTION

[0054] Example 1

[0055] Mining at Mine 38 generates a large amount of low-concentration mine methane, which is typically released directly into the atmosphere. Low-concentration mine methane accounts for a significant portion of the total mine methane output, resulting in a significant waste of energy. Furthermore, because methane has a greenhouse effect 25 times greater than carbon dioxide, direct atmospheric emissions exacerbate global warming.

[0056] A first aspect of the present embodiment provides a method for energy-saving synthesis of green methanol from low-concentration mine gas, the method comprising:

[0057] The low-concentration mine gas raw gas is subjected to an internal reforming reaction to generate a high-temperature synthesis gas; the low-concentration mine gas raw gas contains a methane mole fraction of 1% to 10%;

[0058] The high-temperature synthesis gas is heat exchanged with the low-concentration mine gas raw gas before internal reforming to obtain low-temperature synthesis gas;

[0059] Adding hydrogen to the low-temperature synthesis gas, mixing and pressurizing to form methanol synthesis feed gas;

[0060] The methanol synthesis raw gas is sent to the methanol synthesis process to produce crude methanol;

[0061] The crude methanol is distilled to obtain high-purity methanol.

[0062] Compared with traditional mine gas reforming, the internal reforming reaction in the embodiment of the present invention does not require the introduction of additional carbon dioxide and water vapor. Instead, it combines the characteristics of the low-concentration mine gas components, namely, it contains carbon dioxide, water vapor and methane at the same time, and uses its own components carbon dioxide and water vapor to convert methane to obtain high-temperature synthesis gas including carbon monoxide, hydrogen and carbon dioxide.

[0063] Specifically, the heat required for the internal reforming reaction is at least partially supplemented by molten salt photothermal method.

[0064] Specifically, the internal reforming reaction refers to making full use of the CO2, H2O and CH4 in the low-concentration mine gas raw gas to react and generate high-temperature synthesis gas; the reaction conditions are: reaction temperature of 750-900℃ and pressure of 10-16bar.

[0065] Specifically, the methanol synthesis raw gas includes hydrogen and carbon oxides, and the carbon oxides are a combination of carbon monoxide and carbon dioxide; the amount of hydrogen added is controlled so that the molar ratio of hydrogen to carbon oxides in the methanol synthesis raw gas is 1.50-2.30.

[0066] Specifically, the temperature of the low-temperature synthesis gas obtained by heat exchange is 200°C-280°C, preferably 280°C.

[0067] Specifically, the methanol synthesis process includes: conducting a methanol synthesis reaction on methanol synthesis feed gas to produce methanol product gas; decompressing and cooling the methanol product gas to form a gas-liquid mixture containing liquid methanol; and performing gas-liquid separation on the gas-liquid mixture containing liquid methanol to produce crude methanol. More specifically, the pressure of the gas-liquid mixture containing liquid methanol formed by decompressing and cooling is 10-14 bar, preferably 12 bar; and the temperature of the gas-liquid mixture containing liquid methanol formed by decompressing and cooling is 50-70°C, preferably 60°C.

[0068] Specifically, hydrogen is produced by electrolyzing water using green electricity from the mining area, which is provided by wind farms and photovoltaic power plants, or a combination of both.

[0069] In order to implement the above method provided in this embodiment, Figures 1 to 4As shown, the second aspect of this embodiment provides a system for energy-saving synthesis of green methanol from low-concentration mine gas, including: a gas internal reforming reactor 1, used to perform internal reforming reaction on low-concentration mine gas raw gas to generate high-temperature synthesis gas; a heat exchanger 2, used to exchange heat with the high-temperature synthesis gas discharged from the gas internal reforming reactor 1 against the low-concentration mine gas raw gas before entering the gas internal reforming reactor 1, to obtain low-temperature synthesis gas; a hydrogen generation unit, used to generate hydrogen; a mixing and pressurizing unit, used to add hydrogen discharged from the hydrogen generation unit to the low-temperature synthesis gas discharged from the heat exchanger 2, mixed and pressurized to form methanol synthesis raw gas; a methanol synthesis unit, used to produce crude methanol from the methanol synthesis raw gas discharged from the mixing and pressurizing unit; and a distillation tower 13, used to distill the crude methanol discharged from the methanol synthesis unit to obtain high-purity methanol.

[0070] Specifically, the gas internal reforming reactor 1 has an inlet for receiving low-concentration mine gas feed gas and an outlet for discharging high-temperature synthesis gas. The heat exchanger 2 has an exothermic side inlet, an exothermic side outlet, an endothermic side inlet, and an endothermic side outlet. The hydrogen generation unit is provided with an outlet for discharging hydrogen. The mixing and pressurizing unit has an inlet for receiving low-temperature synthesis gas and hydrogen and an outlet for discharging methanol synthesis feed gas. The methanol synthesis unit is provided with an inlet for receiving methanol synthesis feed gas and an outlet for discharging crude methanol. The distillation tower 13 is provided with an inlet for receiving crude methanol. The endothermic side inlet of the heat exchanger 2 is connected to the mine 38 via a low-concentration mine gas feed gas inlet pipeline. The low-concentration mine gas feed gas generated by mining in the mine 38 flows into the endothermic side inlet of the heat exchanger 2 via the low-concentration mine gas feed gas inlet pipeline. The heat absorption side outlet of the heat exchanger 2 is connected to the inlet of the gas internal reforming reactor 1, the outlet of the gas internal reforming reactor 1 is connected to the heat release side inlet of the heat exchanger 2, the heat release side outlet of the heat exchanger 2 and the outlet of the hydrogen generation unit are respectively connected to the inlet of the mixing and pressurizing unit, the outlet of the mixing and pressurizing unit is connected to the inlet of the methanol synthesis unit, and the outlet of the methanol synthesis unit is connected to the inlet of the distillation tower 13.

[0071] In one embodiment, see Figure 2 The system also includes a raw gas regulating valve 3, which is arranged on the low-concentration mine gas raw gas inlet pipeline.

[0072] During use, the low-concentration mine gas raw gas in the low-concentration mine gas raw gas inlet pipeline enters the heat exchanger 2 through the raw gas regulating valve 3. The low-concentration mine gas raw gas after heat exchange and temperature increase in the heat exchanger 2 enters the gas internal reforming reactor 1 for internal reforming.

[0073] In this embodiment, the input amount of low-concentration mine gas raw gas is controlled by the raw gas regulating valve 3 to meet the amount of components required for the internal reforming reaction, thereby ensuring a high conversion rate of methane.

[0074] Further, see Figure 2 The system may further include a high-temperature synthesis gas regulating valve 28 , which is arranged on a pipeline connecting the outlet of the internal gas reforming reactor 1 and the heat release side inlet of the heat exchanger 2 .

[0075] In this embodiment, the high-temperature syngas generated in the internal gas reforming reactor 1 enters the heat exchanger 2 through the high-temperature syngas regulating valve 28, where it undergoes heat exchange with the low-concentration mine gas feed gas before entering the internal gas reforming reactor 1. This increases the temperature of the low-concentration mine gas feed gas before entering the internal gas reforming reactor 1, achieving preheating of the low-concentration mine gas feed gas before entering the internal gas reforming reactor 1. Simultaneously, the syngas temperature is reduced before entering the methanol synthesis unit, facilitating the balance of the exothermic reaction and increasing methanol yield. The low-temperature syngas enters the methanol synthesis unit as feed gas for subsequent methanol synthesis.

[0076] In one embodiment, see Figure 2 To reduce fuel consumption, the system also includes a molten salt heat supplementation unit, which is connected to the gas internal reforming reactor 1 via a pipeline to form a molten salt circulation loop. The molten salt heat supplementation unit is configured to at least partially supplement the heat required for the internal reforming reaction in the gas internal reforming reactor 1.

[0077] Specifically, the molten salt heat supplementation unit includes a solar trough collector 25, a hot molten salt storage tank 26, and a cold molten salt storage tank 36. The solar trough collector 25, the hot molten salt storage tank 26, the gas reforming reactor 1, and the cold molten salt storage tank 36 are sequentially connected by pipelines to form a molten salt circulation loop. A first circulation pump 271 is provided on the pipeline connecting the solar trough collector 25 and the hot molten salt storage tank 26, a second circulation pump 272 is provided on the pipeline connecting the hot molten salt storage tank 26 and the gas reforming reactor 1, a third circulation pump 273 is provided on the pipeline connecting the gas reforming reactor 1 and the cold molten salt storage tank 36, and a fourth circulation pump 274 is provided on the pipeline connecting the cold molten salt storage tank 36 and the solar trough collector 25.

[0078] In this embodiment, within the molten salt circulation loop, the solar trough collector 25 converts solar energy into molten salt heat, heating the cold molten salt to convert it into hot molten salt. The hot molten salt flows into the hot molten salt storage tank 26 under the pumping of the first circulation pump 271. The hot molten salt in the hot molten salt storage tank 26 is then pumped into the gas internal reforming reactor 1 under the pumping of the second circulation pump 272, continuously supplying heat. After heat exchange, the cold molten salt flows into the cold molten salt storage tank 36 under the pumping of the third circulation pump 273. The cold molten salt in the cold molten salt storage tank 36 is then pumped back into the solar trough collector 25 under the pumping of the fourth circulation pump 274, where it is heated and recycled. In this embodiment, the second circulation pump 272 is used to adjust the flow rate of the molten salt to adjust the heat supply to the gas internal reforming reactor 1 to meet the heat requirements of the internal reforming reaction.

[0079] It should be understood that a channel for the passage of molten salt is provided inside the gas internal reforming reactor 1 .

[0080] In a preferred embodiment of the hydrogen generation unit, the hydrogen generation unit is a unit for producing hydrogen by electrolysis of water using renewable energy power, wherein the renewable energy power is one or a combination of a wind farm and a photovoltaic power station.

[0081] Specifically, if Figure 3 As shown, the hydrogen generation unit includes an electrochemical energy storage device 22, a water supply regulating valve 19, a water mixer 20, an electrolyzer 21, an oxygen regulating valve 33, an oxygen separator 17, an oxygen storage regulating valve 34, an oxygen storage tank 16, a steam regulating valve 18, a hydrogen storage regulating valve 32 and a solid-state hydrogen storage device 23.

[0082] Electrochemical energy storage device 22 is used to store electricity generated by wind farm 35 and / or photovoltaic power station 24. The electricity generated by wind farm 35 and photovoltaic power station 24 is stored in electrochemical energy storage device 22 to power electrolyzer 21. The water required for electrolysis in electrolyzer 21 enters water mixer 20 through water supply regulating valve 19 for mixing before entering electrolyzer 21 for electrolysis. Oxygen generated at the anode of electrolyzer 21 passes through oxygen regulating valve 33 and enters oxygen separator 17 for separation. The separated oxygen passes through oxygen storage regulating valve 34 and is stored in oxygen storage tank 16. Separated water vapor passes through steam regulating valve 18 and enters water mixer 20 for mixing with supplemental water. Supplemental water refers to the water that enters water mixer 20 through water supply regulating valve 19. Hydrogen generated at the cathode of electrolyzer 21 enters solid-state hydrogen storage device 23 through hydrogen storage regulating valve 32. The outlet of solid-state hydrogen storage device 23 serves as the outlet of the hydrogen generation unit.

[0083] In one embodiment, the system further includes a low-temperature syngas regulating valve 4 and a hydrogen regulating valve 29. The low-temperature syngas regulating valve 4 connects the heat release outlet of the heat exchanger 2 to the inlet of the mixing and pressurizing unit to supply low-temperature syngas to the mixing and pressurizing unit. The hydrogen regulating valve 29 connects the outlet of the solid hydrogen storage device 23 to the inlet of the mixing and pressurizing unit to supply hydrogen to the mixing and pressurizing unit.

[0084] The ratio between the low-temperature synthesis gas and hydrogen is adjusted by the combined regulation of the low-temperature synthesis gas regulating valve 4 and the hydrogen regulating valve 29, thereby ensuring the amount of raw gas required for methanol synthesis.

[0085] Figure 4 The structure and connection relationship of the mixing and pressurizing unit, the methanol synthesis unit and the distillation tower 13 provided in this embodiment are shown.

[0086] See also Figure 4The mixing and pressurizing unit includes a mixer 5, a mixed gas regulating valve 30, and a compressor 7. The inlet of the mixer 5 serves as the inlet of the mixing and pressurizing unit. The heat release side outlet of the heat exchanger 2 and the outlet of the hydrogen generating unit are respectively connected to the inlet of the mixer 5, so that the heat release side outlet of the heat exchanger 2 and the outlet of the hydrogen generating unit are respectively connected to the inlet of the mixing and pressurizing unit. The outlet of the mixer 5 is connected to the inlet of the mixed gas regulating valve 30, and the outlet of the mixed gas regulating valve 30 is connected to the inlet of the compressor 7. The outlet of the compressor 7 serves as the outlet of the mixing and pressurizing unit.

[0087] Specifically, the low-temperature synthesis gas discharged from the heat-release outlet of heat exchanger 2 is mixed with hydrogen produced by electrolysis of water using renewable energy power through mixer 5. The resulting mixed gas passes through mixed gas regulating valve 30 and is then pressurized through compressor 7 through a pipeline to form high-pressure methanol synthesis feed gas. The high-pressure methanol synthesis feed gas is then delivered to the inlet of the methanol synthesis unit.

[0088] In this embodiment, the mixed gas flow rate entering the compressor 7 is regulated by the mixed gas regulating valve 30. The mixed gas regulating valve 30 can reduce process instability caused by component fluctuations by adjusting the flow rate in real time, thereby ensuring the continuity and safety of the production process.

[0089] See also Figure 4 The methanol synthesis unit includes a methanol reactor 37, a methanol regulating valve 31, a condenser 11, and a gas-liquid separator 12. The bottom inlet of the methanol reactor 37 serves as the inlet of the methanol synthesis unit and is connected to the outlet of the compressor 7 to connect the outlet of the mixing and pressurizing unit with the inlet of the methanol synthesis unit. The top outlet of the methanol reactor 37 is connected to the inlet of the methanol regulating valve 31, the outlet of the methanol regulating valve 31 is connected to the inlet of the condenser 11, and the outlet of the condenser 11 is connected to the inlet of the gas-liquid separator 12. The middle outlet of the gas-liquid separator 12 serves as the outlet of the methanol synthesis unit and is connected to the inlet of the distillation tower 13 to connect the outlet of the methanol synthesis unit with the inlet of the distillation tower 13.

[0090] Specifically, the methanol synthesis feed gas discharged from the mixing and pressurizing unit enters the methanol reactor 37 to produce methanol product gas. The methanol product gas is then depressurized by the methanol regulating valve 31 and cooled by condenser 11, resulting in a gas-liquid mixture containing liquid methanol. This gas-liquid mixture enters the gas-liquid separator 12 for gas-liquid separation, producing crude methanol. The crude methanol separated by the gas-liquid separator 12 is extracted from the central portion and then distilled in the distillation tower 13 to produce high-purity methanol.

[0091] Further, see Figure 4 The system also includes a methanol storage tank 15 and a water storage tank 14. The methanol storage tank 15 is connected to the top extraction of the distillation tower 13, and the water storage tank 14 is connected to the bottom extraction of the distillation tower 13.

[0092] High-purity methanol is extracted from the top of the distillation tower 13 and flows into the methanol storage tank 15 , while water extracted from the bottom of the distillation tower 13 flows into the water storage tank 14 .

[0093] Furthermore, in order to effectively prevent excessive accumulation of inert gas in the system to maintain the stability and efficiency of the methanol synthesis reaction, see Figure 4 The system also includes a relaxation gas device 10, a circulation boosting device 8, a circulation gas regulating valve 6 and a relaxation gas regulating valve 9. The bottom outlet of the gas-liquid separator 12 is connected to the inlet of the relaxation gas device 10, the first outlet of the relaxation gas device 10 is connected to the inlet of the relaxation gas regulating valve 9, the outlet of the relaxation gas regulating valve 9 is connected to the outside world, the second outlet of the relaxation gas device 10 is connected to the inlet of the circulation boosting device 8, the outlet of the circulation boosting device 8 is connected to the inlet of the circulation gas regulating valve 6, and the outlet of the circulation gas regulating valve 6 is connected to the inlet of the mixer 5.

[0094] In this embodiment, the gas separated by the gas-liquid separator 12 is extracted and flows out from the bottom thereof, and a certain proportion of the purge gas is drawn out through the purge gas device 10, and the extraction ratio of the purge gas is controlled by the purge gas regulating valve 9. The drawn purge gas is pressurized by the circulation boosting device 8 and the circulation gas regulating valve 6, and then enters the mixer 5 for circulation.

[0095] The following demonstrates the methanol production results of the energy-efficient green methanol synthesis system from mine gas, as simulated using Aspen Plus under different process conditions. The simulated system includes a molten salt heating unit, and the hydrogen generation unit is a renewable energy-powered water electrolysis unit. The methanol reactor is a conventional plug flow reactor.

[0096] Table 1 shows the parameter settings of the main unit equipment in the first process condition of the present invention, Table 2 shows the parameter settings of the input stream and the simulation results of the output stream in the first process condition of the present invention, Table 3 shows the parameter settings of the main unit equipment in the second process condition of the present invention, and Table 4 shows the parameter settings of the input stream and the simulation results of the output stream in the second process condition of the present invention. As shown in Table 2, when the internal reforming temperature is 850℃ and the pressure is 10 bar, the methane conversion rate in the gas is 99.50%. By supplementing the flow rate of 280m 3 / h of hydrogen, the methanol yield reached 59.36%, and the purity of the methanol product after final distillation was 99.5%; From Table 4, it can be seen that when the internal reforming temperature was 875℃ and the pressure was 11bar, the methane conversion rate in the gas was 99.68%. 3 / h of green hydrogen, the methanol yield reaches 59.12%, and the purity of the methanol product after final distillation is 99.5%.

[0097] In addition, since the pipes of the solar trough collector 25 can withstand a temperature of up to 580°C, the temperature of the cold molten salt after heat exchange is selected as 290°C, and the temperature of the hot molten salt is selected as 550°C in this embodiment. The temperature of the low-concentration mine gas raw gas before heat exchange is 25°C, and the temperature of the low-concentration mine gas raw gas after heat exchange is 400°C. It is calculated that the molten salt heat supplement is 379.98kW, which can effectively replace 45.45% of the heat required for the internal reforming reaction. The calculation process of molten salt heat supplement is as follows: the heat required to heat the low-concentration mine gas raw gas from 25°C to 400°C using molten salt heat exchange is Q1, and the heat required to heat the low-concentration mine gas raw gas from 25°C to the reaction temperature of 850°C, that is, the heat required for the internal reforming reaction, is Q2. According to the heat calculation formula: Q=CMΔT, it can be obtained that Q1 / Q2=ΔT1 / ΔT2=(400°C-25°C) / (850°C-25°C)=0.4545. The heat required for the internal reforming reaction simulated by Aspen Plus simulation software is 836.0396kW. The heat supplemented to the internal reforming reaction by molten salt photothermal method is 836.0396*0.4545=379.98kW, which greatly reduces the demand for traditional fuel for the internal reforming reaction.

[0098] Regarding green electricity consumption, the power consumption per cubic meter of hydrogen is 3-4.5kWh. When the power consumption per cubic meter of hydrogen is 3.596kWh, the green electricity consumption is 3.596*280kWh=1006.88kWh.

[0099] Table 1 Parameter settings of main unit equipment in the first process condition of the present invention

[0100]

[0101] Table 2 Parameter settings of input streams and simulation results of output streams in the first process condition of the present invention

[0102]

[0103] Table 3 Parameter settings of main unit equipment in the second process condition of the present invention

[0104]

[0105] Table 4 Parameter settings of input streams and simulation results of output streams in the second process condition of the present invention

[0106]

[0107]

[0108] The present invention provides a method and system for energy-saving green methanol synthesis from low-concentration mine gas. Numerous methods and approaches exist for implementing this technical solution. The foregoing are merely preferred embodiments of the present invention. It should be noted that those skilled in the art may make improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for energy-saving synthesis of green methanol from low-concentration mine gas, characterized in that: include: The low-concentration mine gas raw gas is subjected to internal reforming reaction to generate high-temperature synthesis gas; The molar fraction of methane contained in the low-concentration mine gas raw gas is 1%-10%; exchanging heat between the high-temperature synthesis gas and the low-concentration mine gas raw gas before internal reforming to obtain low-temperature synthesis gas; adding hydrogen to the low-temperature synthesis gas, mixing and pressurizing the mixture to form methanol synthesis feed gas; sending the methanol synthesis raw gas to a methanol synthesis process to produce crude methanol; The crude methanol is distilled to obtain high-purity methanol.

2. The method according to claim 1, characterized in that The heat required for the internal reforming reaction is at least partially supplemented by molten salt photothermal method.

3. The method according to claim 1, characterized in that The hydrogen is produced by electrolyzing water using green electricity in the mining area; the green electricity in the mining area is provided by one or a combination of wind farms and photovoltaic power stations.

4. The method according to claim 1, wherein The methanol synthesis process includes: performing a methanol synthesis reaction on the methanol synthesis raw gas to obtain methanol product gas; decompressing and cooling the methanol product gas to form a gas-liquid mixture containing liquid methanol; performing gas-liquid separation on the gas-liquid mixture containing liquid methanol to obtain the crude methanol; the pressure of the gas-liquid mixture containing liquid methanol formed by decompressing and cooling is 10-14 bar, preferably 12 bar; the temperature of the gas-liquid mixture containing liquid methanol formed by decompressing and cooling is 50-70°C, preferably 60°C.

5. The method according to claim 1, wherein The internal reforming reaction refers to the reaction of carbon dioxide, water vapor and methane in the low-concentration mine gas raw gas to generate the high-temperature synthesis gas; the reaction conditions are: reaction temperature of 750-900°C and pressure of 10-16 bar.

6. The method according to claim 1, characterized in that The methanol synthesis raw gas includes hydrogen and carbon oxides, and the carbon oxides are a combination of carbon monoxide and carbon dioxide; the amount of hydrogen added is controlled so that the molar ratio of hydrogen to carbon oxides in the methanol synthesis raw gas is 1.50-2.

30.

7. The method according to claim 6, characterized in that The temperature of the low-temperature synthesis gas obtained by heat exchange is 200-280°C, preferably 280°C; The pressure of the methanol synthesis raw gas formed by mixing and pressurizing is 40-55 bar, preferably 45-50 bar.

8. A system for energy-saving synthesis of green methanol from low-concentration mine gas, characterized in that: include: A gas internal reforming reactor (1) is used to carry out an internal reforming reaction on low-concentration mine gas raw gas to generate high-temperature synthesis gas; The heat exchanger (2) is used to exchange heat between the high-temperature synthesis gas discharged from the gas internal reforming reactor (1) and the low-concentration mine gas raw gas before entering the gas internal reforming reactor (1), thereby obtaining low-temperature synthesis gas; A hydrogen generation unit, configured to generate hydrogen; A mixing and pressurizing unit, used for adding hydrogen discharged from the hydrogen generation unit to the low-temperature synthesis gas discharged from the heat exchanger (2), mixing and pressurizing, to form methanol synthesis raw gas; A methanol synthesis unit, used to produce crude methanol from the methanol synthesis feed gas discharged from the mixing and pressurizing unit; and a distillation tower (13) for distilling the crude methanol discharged from the methanol synthesis unit to obtain high-purity methanol.

9. The system according to claim 8, characterized in that The invention also includes a molten salt heat supplement unit, wherein the heat required for the internal reforming reaction in the gas internal reforming reactor (1) is at least partially supplemented by the molten salt heat supplement unit; the molten salt heat supplement unit includes a solar trough collector (25), a hot molten salt storage tank (26) and a cold molten salt storage tank (36); the solar trough collector (25), the hot molten salt storage tank (26), the gas internal reforming reactor (1) and the cold molten salt storage tank (36) are sequentially connected through pipelines to form a molten salt circulation loop; the solar trough collector (25), the hot molten salt storage tank (26), the gas internal reforming reactor (1) and the cold molten salt storage tank (36) are connected in sequence through pipelines to form a molten salt circulation loop; the solar trough collector (25) is connected to the hot molten salt storage tank (26) to form a molten salt circulation loop; the hot molten salt storage tank (26) is connected to the hot molten salt storage tank (3 ... A first circulation pump (271) is provided on the pipeline connecting the hot molten salt storage tank (26) and the gas internal reforming reactor (1), a second circulation pump (272) is provided on the pipeline connecting the gas internal reforming reactor (1) and the cold molten salt storage tank (36), and a fourth circulation pump (274) is provided on the pipeline connecting the cold molten salt storage tank (36) and the solar trough collector (25); The hydrogen generation unit is a unit for producing hydrogen by electrolyzing water using renewable energy power, and the renewable energy power is one or a combination of a wind farm and a photovoltaic power station.

10. The system according to claim 8, wherein: The gas internal reforming reactor (1) has an inlet for receiving the low-concentration mine gas raw gas and an outlet for discharging the high-temperature synthesis gas; The heat exchanger (2) has a heat release side inlet, a heat release side outlet, a heat absorption side inlet and a heat absorption side outlet; The hydrogen generating unit is provided with an outlet for discharging hydrogen; The mixing and pressurizing unit has an inlet for receiving the low-temperature synthesis gas and the hydrogen and an outlet for discharging the methanol synthesis raw gas; The methanol synthesis unit is provided with an inlet for receiving the methanol synthesis raw gas and an outlet for discharging the crude methanol; The distillation tower (13) is provided with an inlet for receiving the crude methanol; The heat-absorbing side inlet of the heat exchanger (2) is connected to the low-concentration mine gas raw gas inlet pipeline, the heat-absorbing side outlet of the heat exchanger (2) is connected to the inlet of the gas internal reforming reactor (1), the outlet of the gas internal reforming reactor (1) is connected to the heat-releasing side inlet of the heat exchanger (2), the heat-releasing side outlet of the heat exchanger (2) and the outlet of the hydrogen generation unit are respectively connected to the inlet of the mixing and pressurizing unit, the outlet of the mixing and pressurizing unit is connected to the inlet of the methanol synthesis unit, and the outlet of the methanol synthesis unit is connected to the inlet of the distillation tower (13); The mixing and pressurizing unit comprises a mixer (5), a mixed gas regulating valve (30) and a compressor (7); the inlet of the mixer (5) serves as the inlet of the mixing and pressurizing unit; the heat release side outlet of the heat exchanger (2) and the outlet of the hydrogen generating unit are respectively connected to the inlet of the mixer (5), so that the heat release side outlet of the heat exchanger (2) and the outlet of the hydrogen generating unit are respectively connected to the inlet of the mixing and pressurizing unit; the outlet of the mixer (5) is connected to the inlet of the mixed gas regulating valve (30), the outlet of the mixed gas regulating valve (30) is connected to the inlet of the compressor (7), and the outlet of the compressor (7) serves as the outlet of the mixing and pressurizing unit; The methanol synthesis unit comprises a methanol reactor (37), a methanol regulating valve (31), a condenser (11) and a gas-liquid separator (12); the bottom inlet of the methanol reactor (37) serves as the inlet of the methanol synthesis unit and is connected to the outlet of the compressor (7) to achieve the connection between the outlet of the mixing and pressurizing unit and the inlet of the methanol synthesis unit; the top outlet of the methanol reactor (37) is connected to the inlet of the methanol regulating valve (31), the outlet of the methanol regulating valve (31) is connected to the inlet of the condenser (11), and the outlet of the condenser (11) is connected to the inlet of the gas-liquid separator (12); the middle outlet of the gas-liquid separator (12) serves as the outlet of the methanol synthesis unit and is connected to the inlet of the distillation tower (13) to achieve the connection between the outlet of the methanol synthesis unit and the inlet of the distillation tower (13); The invention also includes a raw gas regulating valve (3), a high-temperature synthesis gas regulating valve (28), a methanol storage tank (15) and a water storage tank (14), wherein the raw gas regulating valve (3) is arranged on the low-concentration mine gas raw gas inlet pipeline; the high-temperature synthesis gas regulating valve (28) is arranged on a pipeline connecting the outlet of the gas internal reforming reactor (1) and the heat release side inlet of the heat exchanger (2); the methanol storage tank (15) is connected to the top extraction of the distillation tower (13); and the water storage tank (14) is connected to the bottom extraction of the distillation tower (13).

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