Methanol synthesis system with low recycle ratio and low energy consumption

Abstract

The utility model provides a methanol synthesis system with low recycle ratio and low energy consumption, and belongs to the technical field of methanol synthesis. According to the utility model, the two methanol synthesis units connected in series are adopted, and crude methanol and water generated by reaction are removed in time through the separation device, so that the degradation rate of a catalyst is reduced, and the overall operation stability is improved; meanwhile, gas obtained after crude methanol and water are separated by the first separation device enters the second synthesis device, so that the reaction impetus of the second synthesis device is improved, the conversion per pass is improved, and the recycle ratio is reduced. According to the methanol synthesis system disclosed by the utility model, gas connection and cyclic utilization are skillfully arranged, fresh synthesis gas and recycle gas are reasonably proportioned in the first synthesis device, and unreacted gas enters the second synthesis device for continuous reaction after being separated, so that the conversion per pass is remarkably improved, and the recycle ratio is reduced; meanwhile, unreacted hydrogen is enriched through the hydrogen recovery device and is returned to the system for reuse, so that an efficient circulating system is formed, and energy consumption is greatly reduced while raw material waste is reduced.

Description

Technical Field

[0001] This utility model relates to the field of methanol synthesis technology, specifically to a methanol synthesis system with low cycle ratio and low energy consumption. Background Technology

[0002] Methanol is an important organic chemical raw material, solvent, and high-quality fuel, widely used in organic synthesis, pharmaceuticals, pesticides, coatings, dyes, plastics, automobiles, and defense industries. In recent years, the application of methanol in emerging fields has been continuously expanding, such as methanol-to-olefins (MTO) and methanol-to-aromatics (MTO) using MTO-grade methanol as feedstock. Market demand for these products has surged, and the current growth rate of methanol production capacity is insufficient to meet the ever-increasing market demand. In China, MTO-grade methanol-to-olefins is the largest downstream demand scenario for methanol, accounting for approximately 60% of China's total methanol consumption. Furthermore, to achieve the "dual carbon" goal (carbon reduction and emission reduction), my country has issued a series of incentive policies for the production and application of green methanol. Supported by low-carbon policies, green methanol has a huge potential market in automotive fuel, fuel cells, marine fuel, and organic additives.

[0003] However, existing methanol production technologies face numerous unresolved problems, severely hindering the further development of the methanol industry. Existing methanol production technologies generally suffer from low reaction conversion rates and large recycle gas volumes. Regarding reaction conversion rates, current technologies fail to achieve efficient conversion, resulting in insufficient conversion of raw materials into the target product. This not only wastes raw materials but also increases the complexity and cost of subsequent processing. The large recycle gas volume places a heavy burden on the operation of the plant. Currently, the recycle ratio of large-scale methanol plants is generally between 1.6 and 3.5, ultimately leading to high energy consumption. High recycle ratios also bring a series of other negative impacts. Due to the large recycle gas volume, equipment within the synthesis zone needs to withstand greater pressure and flow rates. To meet these requirements, the equipment size is often designed to be too large, increasing manufacturing difficulty and cost, and significantly increasing the overall plant footprint. Currently, newly built methanol plants generally have a scale of over 2 million tons / year. This trend towards larger plants exacerbates the aforementioned problems, severely restricting the development of methanol technology. The persistently high construction and operating costs of these plants also affect the widespread application of methanol and its downstream products.

[0004] In conclusion, there is an urgent need to optimize the methanol synthesis system, reduce the cycle ratio and energy consumption, decrease equipment investment, and improve reaction efficiency. Utility Model Content

[0005] To address the shortcomings of existing technologies, this utility model discloses a methanol synthesis system with low circulation ratio and low energy consumption. By optimizing the methanol synthesis system, the single-pass conversion rate is improved and the amount of circulating gas is reduced, thereby reducing operating costs and providing technical support for the green and efficient development of the methanol industry.

[0006] To achieve the above technical objectives, this utility model proposes a methanol synthesis system with low cycle ratio and low energy consumption, comprising two methanol synthesis units connected in series, wherein each methanol synthesis unit includes a synthesis device, a separation device, and a heat exchange device.

[0007] The inlet of the first synthesis unit is connected to the first branch pipeline of synthesis gas and the circulating gas pipeline; the outlet of the first synthesis unit is connected to the inlet of the first separation unit via the first heat exchanger; the outlet of the first separation unit and the second branch pipeline of synthesis gas are both connected to the inlet of the second synthesis unit; and the liquid outlet of the first separation unit is connected to the flash evaporator.

[0008] The outlet of the second synthesis unit is connected to the inlet of the second separation unit via the second heat exchanger. The outlet of the second separation unit is connected to the circulating gas pipeline and the hydrogen recovery unit. The outlet of the hydrogen recovery unit is connected to the hydrogen-rich gas pipeline. The hydrogen-rich gas pipeline and the fresh synthesis gas pipeline are connected to the synthesis gas pipeline. The liquid outlet of the second separation unit is connected to the flash evaporator.

[0009] The aforementioned methanol synthesis system comprises two methanol synthesis units connected in series. The crude methanol and water produced in each stage of the synthesis are separated by a separation device. This avoids the problem of significantly reduced lifespan of the lower catalyst bed in traditional methanol reactors due to long-term resistance to high-temperature, high-pressure steam. Furthermore, the two synthesis units are connected by a first separation device. The gas remaining after separating the crude methanol and water from the material in the first synthesis unit is used to produce methanol in the second synthesis unit. This results in a stronger driving force for the synthesis reaction in the second unit, a higher single-pass conversion rate, and a lower recycle ratio. In contrast, traditional two-stage synthesis reactions connected in series lack a methanol separator, leading to excessively high levels of reaction products entering the second-stage methanol synthesis tower. This results in insufficient internal thrust in the second-stage methanol synthesis tower and limitations imposed by chemical equilibrium, preventing a significant increase in conversion rate.

[0010] The methanol synthesis system described above features a clever layout for gas connection and recycling: the inlet of the first synthesis unit is connected to the first branch pipeline of syngas and the circulating gas pipeline, allowing fresh syngas and circulating gas to enter the first synthesis unit in a reasonable ratio. This ensures the supply of raw materials required for the reaction and improves the utilization rate of raw materials through the use of circulating gas. The outlet of the first separation unit is connected to the inlet of the second synthesis unit along with the second branch pipeline of syngas, introducing unreacted gases and some product gases from the first synthesis unit into the second synthesis unit for further reaction, further improving the reaction conversion rate and reducing raw material waste. The outlet of the second separation unit is connected to the circulating gas pipeline and the hydrogen recovery unit, realizing the recycling of unreacted gases and the recovery of hydrogen. The circulating gas pipeline reintroduces unreacted gases into the first synthesis unit, forming a circulating reaction system and reducing the recycling ratio; the hydrogen recovery unit recovers hydrogen and connects it to the syngas pipeline through a hydrogen-rich gas pipeline and the fresh syngas pipeline, realizing the reuse of hydrogen, improving resource utilization efficiency, and also reducing system energy consumption.

[0011] In this invention, the first synthesis unit and the second synthesis unit respectively adopt a primary methanol synthesis tower and a secondary methanol synthesis tower. During the operation of the unit, the hydrogen-to-carbon ratio of the inlet gas of the primary methanol synthesis tower is 2.5-5; and / or, the hydrogen-to-carbon ratio of the inlet gas of the secondary methanol synthesis tower is 4-10.

[0012] The ratio of syngas volume in the first branch pipeline to the second branch pipeline is (60-80):(20-40), preferably (80-90):(10-20);

[0013] In this invention, using the synthesis system and the optimized control parameters described above, the recycle ratio of the methanol synthesis process is 0.5-1.5, preferably 0.7-1.3, which is much lower than the recycle ratio of existing methanol synthesis devices, resulting in lower energy consumption. In this invention, the reaction pressure of the primary methanol synthesis tower and / or the secondary methanol synthesis tower is 7.0-9.5 MPaG, and the reaction temperature is 210-250℃.

[0014] As an alternative, the low-cycle-ratio, low-energy-consumption methanol synthesis system also includes an online analysis and monitoring device, which is used to monitor the inlet gas composition and / or hydrogen-to-carbon ratio of the first synthesis unit and / or the second synthesis unit.

[0015] Specifically, by monitoring the composition and hydrogen-to-carbon ratio of the inlet gas through an online analysis and monitoring device, the reaction load of the two-stage methanol synthesis unit within the methanol synthesis system can be adjusted accordingly during the early, middle, and late stages of the catalyst's lifespan. This maintains the catalyst's high efficiency throughout its entire life cycle, resulting in less unreacted recycle gas required to achieve the expected methanol yield. In other words, the recycle ratio of the methanol unit is low, ultimately achieving low energy consumption. Simultaneously, it avoids overheating of the catalyst bed in the first synthesis unit under low recycle ratio conditions during the initial catalyst stage, thus preventing inconsistent catalyst lifespans within the synthesis unit and ultimately affecting the stable operation of the entire system and achieving the specified methanol yield. As some optional parameters, the online analysis and monitoring device is located at the inlet of the synthesis unit.

[0016] As an alternative, a first flow regulating valve is installed on the hydrogen-rich gas pipeline, and / or a second flow regulating valve is installed on the second branch pipeline of the syngas.

[0017] Specifically, the hydrogen-to-carbon ratio (H-C ratio) of the inlet gas in the two-stage methanol synthesis unit of the methanol synthesis system can be adjusted by installing a first flow control valve on the hydrogen-rich gas pipeline and a second flow control valve on the second branch pipeline of the synthesis gas. This adjustment method involves the coordinated control of multiple streams, requiring precise calculation of the content and flow rate of each component in different streams, as well as their impact on the H-C ratio of the inlet gas. The H-C ratio is calculated using the flow rates of the pure components H2, CO, and CO2 in the synthesis gas, according to (H2-CO2) / (CO+CO2). When the H-C ratio of the inlet gas of the first synthesis unit is too high, the amount of hydrogen-rich gas recovered is reduced by controlling the first flow control valve; when the H-C ratio is too low, the amount of hydrogen-rich gas recovered is increased by controlling the first flow control valve. When the H-C ratio of the inlet gas of the second synthesis unit is too high, the amount of gas in the second branch pipeline of the synthesis gas is increased by controlling the second flow control valve; when the H-C ratio is too low, the amount of gas in the second branch pipeline of the synthesis gas is reduced by controlling the second flow control valve.

[0018] As a preferred embodiment, the methanol synthesis system of the present invention with low cycle ratio and low energy consumption further includes an MTO-level methanol stabilizer or a methanol distillation pre-tower, and the outlet of the first synthesis unit is connected to the reboiler of the MTO-level methanol stabilizer or methanol distillation pre-tower via a first heat exchange device.

[0019] As an alternative, the outlet of the second synthesis unit is connected via a second heat exchanger to a first preheater located at the feed inlet of the MTO-level methanol stabilization tower or methanol distillation pre-tower.

[0020] Specifically, since the methanol content in the gas exiting the first and second synthesis units is relatively high, the corresponding dew point temperature of the gas is also relatively high. This is very beneficial for the recovery and utilization of waste heat in this part. The waste heat generated after the reaction of the two-stage synthesis units can be fully utilized as the heat source for the MTO-level methanol stabilization tower or methanol distillation pre-tower, ultimately achieving the goal of reducing operating energy consumption and plant footprint.

[0021] Furthermore, the methanol synthesis unit also includes a methanol dewaxing and separation device. The outlet of the first synthesis device is connected to the inlet of the first methanol dewaxing and separation device via a first heat exchange device. The gas outlet of the first methanol dewaxing and separation device is connected to the inlet of the first separation device via a heat exchange device. The liquid outlet of the first methanol dewaxing and separation device is connected to a flash evaporator.

[0022] Furthermore, the outlet of the second synthesis unit is connected to the inlet of the second methanol dewaxing and separation unit via the second heat exchanger, the gas outlet of the second methanol dewaxing and separation unit is connected to the inlet of the second separation unit via the heat exchanger, and the liquid outlet of the second methanol dewaxing and separation unit is connected to the flash evaporator.

[0023] Specifically, the dewaxing and separation unit is rationally connected to the synthesis and separation units via heat exchange devices, forming a tight and efficient system. This connection method ensures smooth material flow between the units and improves the overall energy utilization efficiency of the system. The dewaxing process separates the wax byproduct generated during the reaction, preventing the wax from solidifying and adhering to the inner walls of downstream equipment and pipelines during subsequent cooling, thus reducing equipment maintenance costs and downtime. Simultaneously, it avoids equipment performance degradation and safety hazards caused by wax blockage, ensuring the stable operation of the entire methanol synthesis system.

[0024] Furthermore, it also includes a hydraulic turbine generator set, and the outlet of the separation device and / or methanol dewaxing separation device is connected to the flash evaporation device via the hydraulic turbine generator set.

[0025] Specifically, the crude methanol and water separated by the first separation unit and / or the second separation unit are fed into the crude methanol flash tank after the pressure energy is recovered by the hydraulic turbine generator set.

[0026] And / or, the crude methanol and water separated by the first methanol dewaxing separator and / or the second methanol dewaxing separator are fed into the crude methanol flash tank after the pressure energy is recovered by the hydraulic turbine generator set.

[0027] By recovering the pressure energy from high-pressure crude methanol using a hydraulic turbine generator set, the energy consumption for methanol production can be further reduced.

[0028] Furthermore, the methanol synthesis unit also includes a steam drum, with the first steam drum connected to the first synthesis unit, and / or the second steam drum connected to the second synthesis unit.

[0029] After the boiler water is preheated by the synthesis unit, medium-pressure steam is formed. This not only further recovers the heat of methanol synthesis reaction, but also regulates the temperature of the inlet gas of the two-stage synthesis unit, maximizing the recovery of its heat.

[0030] Using the synthesis system of this invention, both the first steam drum and the second steam drum can produce medium-pressure steam with a pressure of 2.5 to 3.0 MPaG.

[0031] Furthermore, the outlet of the flash evaporator is connected to the MTO-grade methanol stabilization tower or methanol distillation pre-tower via a preheater.

[0032] Specifically, the crude methanol discharged from the flash evaporator is at a relatively high temperature and possesses a certain amount of thermal energy. This thermal energy is then connected to the MTO-stage methanol stabilization tower or methanol distillation pre-tower via a preheater, enabling the recovery and utilization of waste heat from the crude methanol. Before entering the MTO-stage methanol stabilization tower or methanol distillation pre-tower, the waste heat of the flash evaporator itself preheats the incoming material or the material already in the tower, reducing the consumption of external heating energy and significantly improving the overall system's energy efficiency. Simultaneously, the preheated crude methanol entering the MTO-stage methanol stabilization tower or methanol distillation pre-tower has a temperature closer to the tower's operating temperature, reducing temperature fluctuations and heat imbalances caused by excessively low feed temperatures. This helps stabilize the operating conditions within the tower or pre-tower, improving separation efficiency and product quality.

[0033] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0034] (1) The utility model adopts two methanol synthesis units in series. The hydrogen-carbon ratio of the two-stage synthesis unit can be controlled by adjusting the gas flow rate of the first branch pipeline of synthesis gas, the second branch pipeline of synthesis gas and the hydrogen-rich gas pipeline. The crude methanol and water generated by the reaction are removed in time by the separation device, which reduces the catalyst degradation rate and improves the overall operational stability. At the same time, the gas after the crude methanol and water are separated by the first separation device enters the second synthesis unit, which increases the reaction driving force of the second synthesis unit, thereby improving the single-pass conversion rate and reducing the cycle ratio.

[0035] (2) The methanol synthesis system of this utility model has a clever layout for gas connection and recycling. Fresh synthesis gas and recycled gas are reasonably matched in the first synthesis unit. Unreacted gas is separated and then enters the second synthesis unit to continue the reaction, which significantly improves the single-pass conversion rate and reduces the recycling ratio. At the same time, unreacted hydrogen is enriched by the hydrogen recovery device and returned to the system for reuse, forming an efficient recycling system, which reduces raw material waste and significantly reduces energy consumption. Attached Figure Description

[0036] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings:

[0037] Figure 1 The methanol synthesis system of Example 1 is shown;

[0038] Figure 2 The methanol synthesis systems of Examples 2 and 3 are shown.

[0039] The above figures include the following reference numerals:

[0040] 1-First synthesis unit; 2-First branch pipeline of syngas; 3-Circulating gas pipeline; 4-First heat exchanger; 5-First separation unit; 6-Second branch pipeline of syngas; 7-Second synthesis unit; 8-Second heat exchanger; 9-Flash evaporator; 10-Second separation unit; 11-Hydrogen recovery unit; 12-Hydrogen-rich gas pipeline; 13-Fresh syngas pipeline; 14-Syngas pipeline; 15-First flow control valve; 16-Second flow control valve; 17-MTO-grade methanol stabilizer or methanol distillation pre-tower; 8-First reboiler in the tower bottom; 19-First methanol dewaxing separator; 20-Waste heat recovery heat exchanger; 21-Second methanol dewaxing separator; 22-First preheater; 23-First methanol water cooler; 24-First hydraulic turbine generator set; 25-Second hydraulic turbine generator set; 26-First steam drum; 27-Second steam drum; 28-Second preheater; 29-Top condenser; 30-Reflux tank; 31-Reflux pump; 32-Second reboiler in the tower bottom; 33-Transfer pump; 34-Second methanol water cooler. Detailed Implementation

[0041] To facilitate understanding of this utility model, a more comprehensive description of it will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the utility model in any way, i.e., not limiting the scope of protection of this utility model.

[0042] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which this invention pertains.

[0043] Example 1

[0044] A methanol synthesis system with low cycle ratio and low energy consumption, such as Figure 1 As shown, it includes two methanol synthesis units connected in series. Each methanol synthesis unit includes a synthesis unit, a separation unit, and a heat exchange unit.

[0045] The inlet of the first synthesis unit 1 is connected to the first branch pipeline of synthesis gas 2 and the circulating gas pipeline 3 via the first heat exchanger 4. The outlet of the first synthesis unit 1 is connected to the inlet of the first separation unit 5 via the first heat exchanger 4. The outlet of the first separation unit 5 and the second branch pipeline of synthesis gas are connected together via the second heat exchanger 8 to the inlet of the second synthesis unit 7. The outlet of the first separation unit 5 is connected to the flash evaporator 9.

[0046] The outlet of the second synthesis unit 7 is connected to the inlet of the second separation unit 10 via the second heat exchange unit 8. The outlet of the second separation unit 10 is connected to the circulating gas pipeline 3 and the hydrogen recovery unit 11. The outlet of the hydrogen recovery unit 11 is connected to the hydrogen-rich gas pipeline 12. The hydrogen-rich gas pipeline 12 and the fresh synthesis gas pipeline 13 are connected to the synthesis gas pipeline 14. The liquid outlet of the second separation unit 10 is connected to the flash evaporator 9.

[0047] As some optional parameters, the synthesis unit is a tubular water-cooled reactor, or the first synthesis unit adopts a tubular water-cooled reactor and the second synthesis unit adopts other forms of isothermal reactor. For example, other forms of isothermal reactor can be methanol synthesis reactors with gas flow in the axial-radial direction and catalyst packed in the shell side.

[0048] Furthermore, it also includes an online analysis and monitoring device, which is used to monitor the composition and hydrogen-to-carbon ratio of the inlet gas of the first synthesis unit 1 and the second synthesis unit 7.

[0049] Furthermore, a first flow regulating valve 15 is installed on the hydrogen-rich gas pipeline 12, and a second flow regulating valve 16 is installed on the second branch pipeline 6 of the syngas.

[0050] As some optional parameters, the hydrogen-rich gas pipeline 12 and the fresh syngas pipeline 13 are connected to the syngas pipeline 14 after passing through a compressor; the recirculated gas pipeline 3 is connected to the inlet of the first synthesis unit 1 together with the first branch pipeline 2 of the syngas after passing through a compressor.

[0051] As some optional parameters, the hydrogen recovery unit 11 includes a membrane separation unit or a PSA unit.

[0052] As some optional parameters, the online analysis and monitoring device is located at the entrance of the synthesis unit.

[0053] It should be noted that this utility model does not limit the specific structure of the separation device. Those skilled in the art can select a device to promote methanol separation as needed, without limiting the scope of protection of this utility model.

[0054] It should be noted that this utility model does not limit the specific structure of the heat exchange device. Those skilled in the art can select conventionally used heat exchange devices as needed, without limiting the scope of protection of this utility model.

[0055] Example 2

[0056] Based on the methanol synthesis system with low cycle ratio and low energy consumption shown in Example 1, such as Figure 2 As shown, it also includes an MTO-grade methanol stabilizer or methanol distillation pre-tower 17. The outlet of the first synthesis unit 1 is connected to the first reboiler 18 of the bottom of the MTO-grade methanol stabilizer or methanol distillation pre-tower 17 via a first heat exchanger 4. The outlet of the second synthesis unit 7 is connected to the inlet of the MTO-grade methanol stabilizer or methanol distillation pre-tower 17 via a second heat exchanger 8.

[0057] Furthermore, the methanol synthesis unit also includes a methanol dewaxing and separation device. The outlet of the first synthesis unit 1 is connected to the inlet of the first methanol dewaxing and separation device 19 via the first heat exchanger 4. The outlet of the first methanol dewaxing and separation device 19 is connected to the inlet of the first separation unit 5 via the waste heat recovery heat exchanger 20. The outlet of the first methanol dewaxing and separation device 19 is connected to the flash evaporator 9. The outlet of the second synthesis unit 7 is connected to the inlet of the second methanol dewaxing and separation device 21 via the second heat exchanger 8. The outlet of the second methanol dewaxing and separation device 21 is connected to the inlet of the second separation unit 10 via the first preheater 22 and the first methanol water cooler 23. The outlet of the second methanol dewaxing and separation device 21 is connected to the flash evaporator 9.

[0058] Furthermore, it also includes a hydraulic turbine generator set. The crude methanol and water separated by the first separation device 5 and the second separation device 10 are fed into the flash evaporation device 9 after the pressure energy is recovered by the first hydraulic turbine generator set 24. The crude methanol and water separated by the first methanol dewaxing separation device 19 and the second methanol dewaxing separation device 21 are fed into the flash evaporation device 9 after the pressure energy is recovered by the second hydraulic turbine generator set 25.

[0059] Furthermore, it also includes steam drums, with the first steam drum 26 connected to the first synthesis unit 1 and the second steam drum 27 connected to the second synthesis unit 7.

[0060] Furthermore, the outlet of the flash evaporator 9 is connected to the MTO-grade methanol stabilization tower or methanol distillation pre-tower 17 via the second preheater 28 and the first preheater 22.

[0061] As a further optional parameter, the top of the MTO methanol stabilizer or methanol distillation pre-tower 17 is equipped with a condensation system, including a top condenser 29, a reflux tank 30, and a reflux pump 31; the bottom of the MTO methanol stabilizer or methanol distillation pre-tower 17 is also equipped with a second reboiler 32. The MTO-grade methanol or crude methanol produced at the bottom of the MTO methanol stabilizer or methanol distillation pre-tower 17 is further cooled and sent out of the device via a transfer pump 33, a second preheater 28, and a second methanol water cooler 34.

[0062] Example 3

[0063] A methanol synthesis method with low cycle ratio and low energy consumption is described in this embodiment. Figure 2 The unit shown is in operation and its methanol production meets the requirement of 2.8 million tons / year of methanol (pure).

[0064] The molar composition of the fresh synthesis gas is: H2- 66.77%, CO- 30.19%, CO2- 2.38%, N2- 0.50%, AR- 0.05%, CH4- 0.11%, with a flow rate of 770134 Nm³. 3 / h. The molar composition of the hydrogen-rich gas is: H2- 82.05%, CO- 1.07%, CO2- 3.33%, N2- 10.40%, AR- 1.51%, CH4- 1.64%, with a flow rate of 8736 Nm³. 3 / h. Fresh syngas supplied by fresh syngas pipeline 13 is mixed with hydrogen-rich gas supplied by hydrogen-rich gas pipeline, and then pressurized by the compressor to the pressure required for the methanol synthesis reaction, 9.0 MPaG. Approximately 70% of the pressurized fresh syngas flows through the first branch pipeline 2 and is then combined with circulating gas from the circulating gas pipeline 3 and the circulating gas compressor, with a flow rate of 693123 Nm³. 3 After mixing, a first stream (hydrogen-to-carbon ratio adjustable between 2.5 and 5, preferably 3.82) is formed. The hydrogen-to-carbon ratio of the first stream can be adjusted by the first flow regulating valve 15. The first stream, at a temperature of 78°C, enters the first heat exchanger 4 and exchanges heat with the first synthesis gas exiting the first synthesis unit 1 at a temperature of 235°C to recover its heat. The preheated first synthesis gas, at a temperature of 215°C, enters the first synthesis unit 1 to react and produce methanol. Another portion, approximately 30% of the fresh synthesis gas, is mixed with the outlet gas of the first separation unit 5 through the second branch pipeline 6 to form a second stream (hydrogen-to-carbon ratio adjustable between 4 and 10, preferably 5.16). The hydrogen-to-carbon ratio of the second stream can be adjusted by the second flow regulating valve 16. The second stream enters the second heat exchanger 8 and exchanges heat with the second synthesis gas exiting the second synthesis unit 7 at a temperature of 235°C to recover its heat. The preheated second synthesis gas, at a temperature of 215°C, enters the second synthesis unit 7 to react and produce methanol.

[0065] The first synthesis gas from the outlet of the first synthesis unit 1 enters the first heat exchanger 4 at a temperature of 133°C. It is first sent to the second reboiler 18 in the reboiler as a heat source to recover heat, and then enters the first methanol dewaxing separator 19 to separate crude methanol. This portion of crude methanol enters the second hydraulic turbine generator set 25 to recover energy and is depressurized to 0.4 MPaG before being sent to the flash evaporator 9 to separate light component gases from the crude methanol. The remaining gas phase then enters the waste heat recovery heat exchanger 20 for further cooling to 60°C. The resulting stream is separated into crude methanol in the first separation unit 5. This portion of crude methanol enters the first hydraulic turbine generator set 24 to recover energy and is depressurized to 0.4 MPaG before being sent to the flash evaporator 9 to separate light component gases from the crude methanol. The gas separated by the first separation unit 5, as described above, mixes with the gas transported by the second branch pipeline of the synthesis gas to form the second stream. The second synthesis gas at the outlet of the second synthesis unit 7 has a temperature of 235℃. After heat recovery in the second heat exchanger 8, the temperature drops to 119℃. It first enters the second methanol dewaxing separator 21 to separate crude methanol. This crude methanol then enters the second hydraulic turbine generator set 25, where it is depressurized to 0.4 MPaG (recovering energy and generating approximately 600 kW of power) before being sent to the flash evaporator 9 to separate the light component gases from the crude methanol. The remaining gas phase then enters the first preheater to preheat the crude methanol for further heat recovery, followed by further cooling to 40℃ in the first methanol water cooler. This facilitates the separation of the reaction-generated methanol in the second separation unit 10. This crude methanol then enters the first hydraulic turbine generator set 24, where it is depressurized to 0.4 MPaG (recovering energy and generating approximately 500 kW of power), before entering the flash evaporator 9 again to separate the light component gases from the crude methanol and other components before being discharged. The power generated by this energy recovery is approximately 600 kW. A portion of the gas separated in the second separation unit is released as purge gas with a flow rate of 624 Nm³. 3 The gas is discharged from the synthesis ring at a rate of / h to the hydrogen recovery unit 11 to recover the hydrogen-rich gas. The remaining non-permeable gas is discharged from the unit, and another part is used as circulating gas with a flow rate of 693123 Nm. 3 / h returns to the methanol synthesis loop and enters the circulating gas compressor for recirculation reaction.

[0066] The flow rate of crude methanol delivered from flash evaporator 9 is 375.9 Nm³. 3The methanol content is 94.3 wt%. Before entering the MTO methanol stabilization tower or methanol distillation pre-tower 17, it is preheated sequentially by the second preheater 28 and the first preheater 22. After preheating, the temperature is about 80°C, which meets the bubble point feed requirements of the distillation tower. The top condensation system of the MTO methanol stabilization tower or methanol distillation pre-tower 17 includes a top condenser 29, a reflux tank 30, and a reflux pump 31. The bottom reboiling system includes a first reboiler 18 and a second reboiler 32, whose heat sources are the waste heat from the primary reaction and low-pressure steam (0.35~0.5 MPaG saturated), respectively. The MTO-grade methanol or crude methanol produced at the bottom of the MTO methanol stabilization tower or methanol distillation pre-tower 17 first recovers heat through a transfer pump 33 and the second preheater 28, and then is further cooled to 40°C by the second methanol water cooler before being sent out of the unit.

[0067] In the above embodiment, the catalyst loading of the first synthesis unit 1 is 164m³. 3 The catalyst loading of the second synthesis unit 7 is 110m³. 3 Both the first steam drum (26) and the second steam drum (27) produce 2.5 MPaG steam as a byproduct, with a steam output of 1.27 t / t methanol. The operating cycle ratio is 0.9–1.0. The methanol production meets the requirement of 2.8 million tons / year of methanol (pure), and the unit has an operating flexibility of 50–100% and an annual operating time of 8,000 hours.

[0068] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the present invention to these descriptions; the dimensional data in this embodiment do not necessarily limit the technical solution, but merely illustrate one specific working condition. For those skilled in the art to which this invention pertains, several simple improvements and modifications can be made without departing from the concept of the present invention, and all such improvements and modifications should be considered to fall within the scope of protection of the present invention.

Claims

1. A methanol synthesis system with low cycle ratio and low energy consumption, characterized in that, It includes two methanol synthesis units connected in series, each methanol synthesis unit comprising a synthesis device, a separation device, and a heat exchange device; The inlet of the first synthesis unit is connected to the first branch pipeline of synthesis gas and the circulating gas pipeline; the outlet of the first synthesis unit is connected to the inlet of the first separation unit via the first heat exchanger; the outlet of the first separation unit and the second branch pipeline of synthesis gas are both connected to the inlet of the second synthesis unit; and the liquid outlet of the first separation unit is connected to the flash evaporator. The outlet of the second synthesis unit is connected to the inlet of the second separation unit via the second heat exchanger. The outlet of the second separation unit is connected to the circulating gas pipeline and the hydrogen recovery unit. The outlet of the hydrogen recovery unit is connected to the hydrogen-rich gas pipeline. The hydrogen-rich gas pipeline and the fresh synthesis gas pipeline are connected to the synthesis gas pipeline. The liquid outlet of the second separation unit is connected to the flash evaporator.

2. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 1, characterized in that, It also includes an online analysis and monitoring device, which is used to monitor the composition and / or hydrogen-to-carbon ratio of the inlet gas of the first synthesis unit and / or the second synthesis unit.

3. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 1, characterized in that, A first flow regulating valve is installed on the hydrogen-rich gas pipeline, and / or a second flow regulating valve is installed on the second branch pipeline of the syngas.

4. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 1, characterized in that, It also includes an MTO-grade methanol stabilizer or a methanol distillation pre-tower, and the outlet of the first synthesis unit is connected to the reboiler of the MTO-grade methanol stabilizer or methanol distillation pre-tower via a first heat exchanger.

5. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 4, characterized in that, The outlet of the second synthesis unit is connected via a second heat exchanger to a first preheater located at the feed inlet of the MTO-level methanol stabilization tower or methanol distillation pre-tower.

6. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 1, characterized in that, The methanol synthesis unit further includes a methanol dewaxing and separation device. The outlet of the first synthesis device is connected to the inlet of the first methanol dewaxing and separation device via a first heat exchange device. The gas outlet of the first methanol dewaxing and separation device is connected to the inlet of the first separation device via a heat exchange device. The liquid outlet of the first methanol dewaxing and separation device is connected to a flash evaporator.

7. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 6, characterized in that, The outlet of the second synthesis unit is connected to the inlet of the second methanol dewaxing and separation unit via the second heat exchanger. The outlet of the second methanol dewaxing and separation unit is connected to the inlet of the second separation unit via the heat exchanger. The outlet of the second methanol dewaxing and separation unit is connected to the flash evaporator.

8. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 1 or any one of claims 6-7, characterized in that, It also includes a hydraulic turbine generator set, and the outlet of the separation device and / or methanol dewaxing separation device is connected to the flash evaporation device via the hydraulic turbine generator set.

9. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 1, characterized in that, The methanol synthesis unit further includes a steam drum, with the first steam drum connected to the first synthesis unit, and / or the second steam drum connected to the second synthesis unit.

10. The methanol synthesis system with low cycle ratio and low energy consumption according to claim 4, characterized in that, The outlet of the flash evaporator is connected to the MTO-grade methanol stabilizer or methanol distillation pre-tower via a preheater.

Images