CO2-rich synthesis gas methanol synthesis system

Abstract

The CO2-rich synthesis gas methanol synthesis system comprises a hydrogen storage unit, a synthesis gas decarbonization unit, a synthesis gas compression unit, a synthesis unit, a gas / gas heat exchanger, a cooler, a high-pressure flash evaporator, a hydrogen recovery unit, a low-pressure flash evaporator and a low-pressure flash vapor compression unit, the hydrogen storage unit can receive volatilly supplied hydrogen and recycled hydrogen, and the hydrogen and the CO2-rich synthesis gas are jointly used as raw material gas for methanol synthesis after being cached by the hydrogen storage unit; the CO2-rich synthesis gas is formed by mixing synthesis gas generated by a synthesis gas decarbonization unit and low-pressure flash steam of a low-pressure flash steam compression unit; the synthesis gas decarburization unit can realize different CO2 removal rates according to requirements, so that the synthesis gas has wide CO2 concentration. According to the system, the CO2 removal rate of the synthesis gas decarbonization unit is adjusted according to the supply quantity of hydrogen, and H2 and CO2 in methanol synthesis tail gas are recycled, so that renewable energy fluctuation hydrogen production and flexible methanol synthesis by biomass synthesis gas are realized.

Description

Technical Field

[0001] The present invention relates to a methanol synthesis system for syngas rich in CO2, belonging to the technical field of green methanol preparation. Background Art

[0002] Methanol has the characteristics of high combustion efficiency, clean emissions, and renewability. It is a new type of clean energy known as "liquid sunshine". In terms of ship applications, only minor modifications to existing ships are required to use methanol as fuel, which can effectively save investment costs. Compared with liquefied natural gas that requires cryogenic liquefaction, methanol is in a liquid state at room temperature, making it more convenient for storage, transportation, and use. In the future, methanol will replace traditional high-carbon marine fuels and be widely used. Against the backdrop of global carbon emission reduction and carbon neutrality, shipping giants have all formulated plans to use green methanol to replace fuel oil as ship fuel to achieve carbon emission reduction. The demand for green methanol in the shipping industry will grow rapidly in the future, and the industry of preparing green methanol using clean and renewable energy will also enter the fast lane.

[0003] The coupling of biomass gasification and green hydrogen production to chemical products such as methanol and green aviation kerosene is an important way for the clean development of chemical fuels. As a renewable resource, biomass has the characteristics of rich resource output, wide geographical distribution, and stable energy reserves. The syngas produced by biomass gasification can be used as the raw material gas for methanol synthesis alone after adjusting the hydrogen-carbon ratio through conversion. However, the conversion system requires additional steam consumption and discharges some CO2, resulting in a reduction in the utilization rate of renewable carbon sources. With the increase in the installed capacity of renewable energy power generation in China, due to the disadvantage of unstable output of renewable energy, there has been a relatively serious problem of "abandoning wind and light". The problem of abandoned electricity in new energy power generation has become increasingly prominent, hindering the development and utilization of new energy. Using renewable energy power generation (such as wind power and photovoltaic) for electrolytic water hydrogen production, and coupling electrolytic water hydrogen production with biomass syngas to synthesize methanol is one of the effective ways to solve the problem of abandoned electricity in new energy power generation. At the same time, it can also improve the utilization rate of CO2 in biomass syngas and reduce the production cost of methanol.

[0004] In summary, there is an urgent need for a methanol synthesis system for syngas rich in CO2 to solve the problems of low utilization rate of renewable carbon (CO2) in biomass gasification to produce green methanol and the system adaptability problem of coupling biomass gasification with fluctuating green hydrogen to synthesize green methanol. Summary of the Invention

[0005] Currently, most of the hydrogen production by electrolyzing water on a large scale is for hydrogen production using new energy (wind power, photovoltaic) power generation. Due to the strong volatility and randomness of new energy power generation, the hydrogen provided by electrolyzing water for hydrogen production also has strong volatility. When hydrogen with strong volatility is used as a raw material for synthesizing green methanol, higher adaptability requirements are imposed on the methanol synthesis system. On the other hand, green methanol requires the source of carbon to be renewable carbon, such as carbon in biomass. At present, the traditional methanol synthesis technology has a low utilization efficiency of carbon. Renewable carbon is a precious resource that needs to be utilized as efficiently as possible.

[0006] The technical problems to be solved by the present invention are the low utilization rate of renewable carbon (CO2) in the synthesis of green methanol by biomass gasification and the system adaptability problem of coupling biomass gasification with volatile green hydrogen to synthesize green methanol.

[0007] To solve the above technical problems, the technical solution of the present invention is to provide a methanol synthesis system for syngas rich in CO2, and the technical solution is as follows: The system includes: a hydrogen storage unit, a syngas decarbonization unit, a syngas compression unit, a synthesis unit, a gas / gas heat exchanger, a cooler, a high-pressure flash drum, a hydrogen recovery unit, a low-pressure flash drum, and a low-pressure flash gas compression unit; The hydrogen storage unit can receive hydrogen supplied with volatility and hydrogen recovered by the hydrogen recovery unit. After being cached by the hydrogen storage unit, relatively stable hydrogen and syngas rich in CO2 are jointly used as the raw material gas for methanol synthesis; the syngas rich in CO2 is formed by mixing the syngas generated by the syngas decarbonization unit and the low-pressure flash gas obtained from the low-pressure flash drum; after hydrogen and syngas rich in CO2 are mixed, they enter the methanol synthesis loop. The hydrogen in the purge gas returns to the hydrogen storage unit for continued use, and the flash gas from the low-pressure flash also returns to the methanol synthesis loop for continued use.

[0008] Preferably, the hydrogen storage unit is for gaseous hydrogen storage, and the hydrogen storage pressure is 1.0 MPa to 8.0 MPa; Preferably, the syngas decarbonization unit can achieve different CO2 removal rates according to requirements, so that the syngas (202) has a wide range of CO2 concentrations, and the CO2 concentration is 3 mol% to 50 mol%; Preferably, the flash pressure of the low-pressure flash drum is 0.1 MPa to 1.0 MPa; the low-pressure flash gas returns to the methanol synthesis system for continued synthesis of methanol after being pressurized by the low-pressure flash gas compression unit; Preferably, the operating pressure of the hydrogen recovery unit is 0.3 MPa higher than the pressure of the hydrogen storage unit, and the recovered hydrogen is sent to the hydrogen storage unit; Preferably, the methanol synthesis loop is jointly composed of a syngas compression unit, a synthesis unit, a gas / gas heat exchanger, a cooler (600), and a high-pressure flash drum, and the operating pressure of the synthesis loop is 5 MPa to 10 MPa.

[0009] The present invention adapts to the volatility of green hydrogen by adjusting the CO2 content in the feed gas. When the supply of green hydrogen is at a peak, the CO2 removal rate of the syngas decarbonization unit is reduced to increase the CO2 content in the syngas entering the methanol synthesis loop. The excess hydrogen reacts with CO and a large amount of CO2 in the syngas simultaneously to produce green methanol. When the supply of green hydrogen is at a low valley, the CO2 removal rate of the syngas decarbonization unit is increased to reduce the CO2 content in the syngas entering the methanol synthesis loop. An appropriate amount of hydrogen reacts with CO and a small amount of CO2 in the syngas to produce green methanol.

[0010] A methanol synthesis system for syngas rich in CO2 provided by the present invention realizes the synthesis of green methanol by coupling volatile green hydrogen with high-concentration CO2 syngas. The system of the present invention operates stably and reliably, has a high utilization rate of renewable carbon (CO2), and can adapt to hydrogen with volatile supply. Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses green hydrogen with volatile supply to adjust the hydrogen-carbon ratio in the methanol synthesis feed gas, and eliminates the instability of volatile green hydrogen by setting up a hydrogen storage unit, realizing the stable operation of methanol synthesis. (2) Compared with a conventional methanol synthesis system, the present invention can convert a large amount of CO2 into methanol, improving the utilization rate of renewable carbon (CO2). BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of a methanol synthesis system for syngas rich in CO2 provided by the present invention.

[0013] 101 - Hydrogen with volatile supply; 100 - Hydrogen storage unit; 102 - Hydrogen; 200 - Syngas decarbonization unit; 201 - Biomass syngas; 202 / 203 - Syngas rich in CO2; 204 - CO2 gas; 300 - Syngas compression unit; 301 / 501 - Methanol synthesis feed gas; 400 - Methanol synthesis unit; 401 / 502 - Methanol synthesis product gas; 500 - Gas / gas heat exchanger; 600 - Methanol cooler; 601 - Methanol mixture gas; 700 - High-pressure flash drum; 701 - High-pressure flash gas; 702 - Recycle gas; 703 - Hydrogen recovery feed gas; 800 - Hydrogen recovery unit; 801 - Hydrogen; 802 - Purge gas; 704 / 901 - Crude methanol; 900 - Low-pressure flash drum; 902 / 1002 - Low-pressure flash gas; 1000 - Low-pressure flash gas compression unit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The present invention will be further described below in conjunction with specific embodiments.

[0015] Example: The object of the present invention is to make the best use of renewable carbon in biomass as much as possible, while solving the system adaptability problem of coupling biomass gasification with fluctuating green hydrogen synthesis of green methanol. To achieve the above object, the present invention provides a methanol synthesis system for syngas rich in CO2. To further clarify the present invention, a specific example of an annual green methanol production capacity of 100,000 tons is described. As Figure 1 shown, a methanol synthesis system for syngas rich in CO2 mainly includes a hydrogen storage unit, a syngas decarbonization unit, a syngas compression unit, a synthesis unit, a gas / gas heat exchanger, a cooler, a high-pressure flash tank, a hydrogen recovery unit, a low-pressure flash tank, and a low-pressure flash gas compression unit.

[0016] Designed for 8000 hours of annual operation, the methanol production is about 13 t / h. The supply pressure of hydrogen (102) is 1.5 MPa, the normal flow rate is 8000 Nm3 / h, and the flow rate variation range is 1000 Nm3 / h to 17600 Nm3 / h. The hydrogen storage pressure of the hydrogen storage unit (100) is 1.4 MPa, and the hydrogen storage capacity is 200,000 Nm3. The pressure of the biomass syngas (201) is 0.3 MPa, the normal composition of the syngas is 25 mol% CO, 30 mol% CO2, 35 mol% H2, and 10 mol% others, the normal flow rate is 34000 Nm3 / h, and the flow rate variation range is 13600 Nm3 / h to 34000 Nm3 / h; after passing through the decarbonization unit (200), the CO2 content of the syngas varies in the range of 2.6 mol% to 30 mol%. From the parameters of the above raw material gas, it can be seen that the variation range of hydrogen is 12.5% to 220% of the normal flow rate, and the flow rate variation range of the syngas is 40% to 100% of the normal flow rate. To adapt to the above fluctuation range, the present invention includes a special methanol synthesis catalyst, which is filled in the methanol synthesis unit (400). At the same time, to adapt to the change of load, the present invention also includes a special methanol synthesis reactor, which can adapt to the operation pressure range of 5 MPa to 10 MPa.

[0017] The present invention needs to switch and operate under different operating conditions. The operating conditions are shown in Table 1, and the descriptions are as follows. Table 1 is the operating condition parameter table

[0018] Condition 1: When the supply flow rate of hydrogen is 17600 Nm 3 / h, if the hydrogen storage unit is in a full-capacity state, hydrogen will directly enter the methanol synthesis loop at 26600 Nm3 / h until the stock in the hydrogen storage tank drops to the lowest value, and this process can be maintained for about 18 hours; in this process, it is not necessary to remove CO2 from the biomass syngas, and the methanol synthesis loop is at the upper limit of the operating pressure, and the carbon source (CO / CO2) can be efficiently utilized; Operating conditions 2 to 4: When the hydrogen supply flow rate is 17,600 Nm3 / h, if the hydrogen storage unit is in a full-capacity state but it is predicted that the hydrogen supply may decrease, then hydrogen directly enters the methanol synthesis loop at a rate of 10,600 Nm3 / h to 22,000 Nm3 / h until the inventory in the hydrogen storage tank decreases to the minimum value; this process requires reducing the syngas supply load to save raw material consumption. The methanol synthesis loop is at the upper limit of the operating pressure, and there is still no need to remove CO2 from the biomass syngas, and the carbon source (CO / CO2) can be efficiently utilized; Operating condition 5: When the hydrogen supply flow rate is 8,000 Nm3 / h, if the hydrogen storage unit is in a full-capacity state, then hydrogen directly enters the methanol synthesis loop at a rate of 11,000 Nm3 / h until the inventory in the hydrogen storage tank decreases to the minimum value, and the whole process can be maintained for about 80 hours; this process requires reducing the syngas supply to the minimum load. The methanol synthesis loop is at the intermediate value of the operating pressure, and there is no need to remove CO2 from the biomass syngas, and the carbon source (CO / CO2) can be efficiently utilized; Operating conditions 6 to 8: When the hydrogen supply flow rate is 8,000 Nm3 / h, it is determined whether it is necessary to increase the syngas supply load according to the annual methanol production demand. If so, the syngas supply load is gradually increased to increase methanol production. The methanol synthesis loop is at the intermediate value of the operating pressure, and at the same time, it is necessary to remove some CO2 from the syngas, and the utilization rate of the carbon source (CO2) is reduced; Operating conditions 9 to 10: When the hydrogen supply flow rate is less than 4,000 Nm3 / h, it is necessary to reduce the syngas supply load to 40%, and at the same time, it is necessary to remove most of the CO2 from the syngas. The methanol synthesis loop is at the lower limit of the operating pressure, and the utilization rate of the source (CO2) is further reduced at this time.

[0019] The above operating conditions are only limited examples for understanding the present invention. According to the hydrogen storage volume of the hydrogen storage unit and the predicted changes in hydrogen supply, different combinations can be made among several key indicators such as the hydrogen flow rate out of the hydrogen storage tank, the syngas supply load, the CO2 removal rate, and the operating pressure of the methanol synthesis loop to achieve the annual production target.

[0020] It can be seen from the above embodiments that through the innovative system design and reasonable process parameter setting of the present invention, new energy power generation is used to produce hydrogen to adjust the hydrogen-carbon ratio in the methanol synthesis raw material gas, and a hydrogen storage unit is set to provide relatively stable green hydrogen to the synthesis unit; by setting a syngas purification unit with adjustable CO2 removal rate, relatively stable operation of coupling biomass syngas with green hydrogen to produce green methanol is achieved; by using a special methanol synthesis catalyst and reactor, high-efficiency utilization of CO2 and high-elastic operation of methanol synthesis are realized, efficiently utilizing renewable carbon sources and hydrogen sources, and reducing the cost of green methanol preparation.

[0021] The above embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A methanol synthesis system for syngas rich in CO2, characterized in that, Comprising: A hydrogen storage unit (100), a syngas decarbonization unit (200), a syngas compression unit (300), a synthesis unit (400), a gas / gas heat exchanger (500), a cooler (600), a high-pressure flash drum (700), a hydrogen recovery unit (800), a low-pressure flash drum (900), and a low-pressure flash gas compression unit (1000); The hydrogen storage unit (100) can receive hydrogen (101) supplied with volatility and hydrogen (801) recovered by the hydrogen recovery unit (800). After being cached by the hydrogen storage unit (100), a relatively stable hydrogen (102) and a CO2-rich syngas (203) are formed and used together as the feed gas for methanol synthesis. The CO2-rich syngas (203) is formed by mixing the syngas (202) generated by the syngas decarbonization unit (200) and the low-pressure flash gas (902) obtained from the low-pressure flash drum (900) and the low-pressure flash gas (1002) pressurized by the low-pressure flash gas compression unit (1000). After the hydrogen (102) and the CO2-rich syngas (203) are mixed, they enter the methanol synthesis loop.

2. A CO2-rich syngas methanol synthesis system according to claim 1, wherein: The hydrogen storage unit (100) is for gaseous hydrogen storage, and the hydrogen storage pressure is 1.0 MPa to 8.0 MPa.

3. A CO2-rich syngas methanol synthesis system according to claim 2, wherein: The hydrogen storage pressure is 1.5 MPa to 3 MPa.

4. A CO2-rich syngas methanol synthesis system according to claim 1, wherein: The syngas decarbonization unit (200) can achieve different CO2 removal rates according to requirements, so that the syngas (202) has a wide range of CO2 concentrations, and the CO2 concentration is 1 mol% to 50 mol%.

5. A CO2-rich syngas methanol synthesis system according to claim 4, wherein: The CO2 concentration is 2 mol% to 30 mol%.

6. A CO2-rich syngas methanol synthesis system according to claim 1, wherein: The flash pressure of the low-pressure flash drum (900) is 0.1 MPa to 1.0 MPa; the low-pressure flash gas (902) returns to the methanol synthesis system to continue synthesizing methanol after being pressurized by the low-pressure flash gas compression unit (1000).

7. A CO2-rich syngas methanol synthesis system according to claim 6, wherein: The flash pressure of the low-pressure flash drum (900) is 0.3 MPa to 0.5 MPa.

8. A CO2-rich syngas methanol synthesis system according to claim 1, wherein: The operating pressure of the hydrogen recovery unit (800) is 0.3 MPa higher than the pressure of the hydrogen storage unit (100), and the recovered hydrogen (801) is sent to the hydrogen storage unit (100).

9. A CO2-rich syngas methanol synthesis system according to claim 1, wherein: The methanol synthesis loop is composed of a syngas compression unit (300), a synthesis unit (400), a gas / gas heat exchanger (500), a cooler (600), and a high-pressure flash drum (700). The operating pressure of the synthesis loop is 4 MPa to 12 MPa.

10. A CO2-rich syngas methanol synthesis system according to claim 1, wherein: The operating pressure of the synthesis loop is 5 MPa to 10 MPa.

Images