System and method for preparing low-carbon olefin from methanol

Abstract

The invention provides a system and a method for preparing low-carbon olefin from methanol. The system comprises a low-carbon olefin reactor, a heat exchange unit, a dimethyl ether reactor, a process water purification unit and a hydrocarbon separation unit. The heat exchange unit is provided with the four stages of heat exchangers which are communicated in sequence, so that the waste heat of the low-carbon olefin product gas is further utilized, raw materials participating in the reaction and the process water purification unit can be primarily heated in the waste heat utilization process, and the low-carbon olefin product gas can be cooled. According to the methanol-to-low-carbon olefin system, waste heat generated in the heat exchange unit and the process water purification unit is reasonably utilized, so that the purpose of shortening the MTP process flow is achieved, the heat loads of a quenching system and a heating system are reduced, the power consumption of a compressor and the steam consumption are reduced, and the energy consumption of the whole methanol-to-low-carbon olefin system is reduced; meanwhile, the process operation difficulty is also reduced, and the equipment manufacturing cost and the device operation cost are finally reduced.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology, and in particular to a system and method for preparing low-carbon olefins from methanol. Background Art

[0002] In view of the increasingly prominent contradiction between oil supply and demand and the increasing dependence on imported oil in my country in recent years, it poses a serious threat to national energy security, stable economic operation and sustainable development. At the same time, the demand for low-carbon olefins such as propylene and ethylene as basic organic chemical raw materials continues to grow with the development of the national economy. Traditional propylene and ethylene production is highly dependent on oil resources, and the shortage of oil resources and dependence on imports have become a bottleneck restricting the development of my country's chemical industry.

[0003] As a new non-petroleum resource utilization method, coal-based methanol to low-carbon olefins (MTP) technology has received widespread attention in recent years. The process mainly includes three main steps: coal gasification to synthesis gas, synthesis gas to methanol and methanol to olefins. Among them, the two technologies of coal gasification to synthesis gas and synthesis gas to methanol are relatively mature and can adapt to the development of economies of scale. It is an important way to achieve clean and efficient use of coal, which helps to make up for the shortage of oil and gas resources and promote the diversification of raw materials in the petrochemical industry. In my country, this technology is of great significance for ensuring energy security and optimizing and upgrading the energy structure.

[0004] MTP technology is a process developed based on modified ZSM-5 catalyst to convert methanol into propylene and ethylene via dimethyl ether. In addition to the production of polymerization-grade propylene and ethylene, it also produces by-products such as liquefied petroleum gas, mixed aromatics, and fuel gas. The main process is: the refined methanol in the boundary zone is pressurized and then subjected to heat exchange and preheating before entering the DME reactor. A DME (dimethyl ether) mixed gas is generated under the action of the DME-1 catalyst. The mixed gas is cooled and then enters the MTP reactor together with the hydrocarbon mixture recycled from the distillation system. Under the action of the MTP catalyst, the DME / hydrocarbon mixture undergoes a chemical reaction to generate a hydrocarbon mixture mainly composed of propylene. The mixture also contains other compounds such as carbon monoxide, carbon dioxide, water and other by-products. The heat of the mixture at the outlet of the MTP reactor is recovered through the waste heat recovery system. After that, the water is removed by rapid cooling. The gas phase coming out from the top of the rapid cooling tower is compressed and separated and enters the debutanizer. After the hydrocarbon mixture is heated and separated, the C4 and C4 components below the low boiling point of the gas phase material at the top of the tower are extracted from the top of the tower and enter the depropanizer at the same time as the gas phase C4 and C4 components below from the hydrocarbon compressor. After the mixture is separated, the C3 and C3 components below the gas phase material at the top of the tower are extracted from the top of the tower to the deethanizer. Part of the C4 and C4 components above are extracted from the bottom of the tower as C4 circulating hydrocarbons and returned to the MTP reactor, and part of them are used as liquefied petroleum gas products to the boundary area. The C4 and C4 components above the debutanizer are extracted from the bottom of the tower and sent to the dehexanizer. Here, the C6 and C6 components are separated from the top of the tower, most of which are returned to the MTP reactor as C5 / C6 circulating hydrocarbons, and a small part enters the gasoline stabilization tower. The C7 and C7 heavy components are separated from the bottom of the tower as mixed aromatic products. The materials from the top of the dehexanizer are separated in the gasoline stabilization tower. The gas phase C4 is extracted from the top of the tower and mixed with C5 / C6 circulating hydrocarbons and returned to the MTP reactor. The C5 and above components at the bottom of the tower are extracted from the bottom of the tower as mixed aromatic products and mixed with the mixed aromatic components at the bottom of the dehexanizer and sent to the boundary area. The content of the C4 component is adjusted by the gasoline stabilization tower to meet the requirements of the mixed aromatic component oil product for this component. The C3 and below materials from the top of the depropanizer enter the deethanizer, where the gas phase materials C2 and below components at the top of the tower are extracted from the top of the tower to the demethanizer, and C3 (propane and propylene) are extracted from the bottom of the tower to the C3 separation tower. The C3 separation tower separates propylene from propane to obtain polymerization-grade propylene. The gas phase materials C2 and below components from the top of the deethanizer enter the demethanizer, where the gas phase CH4, H2, and CO at the top of the tower are sent to the boundary area as fuel gas, and the bottom product goes to the C2 separation tower. In the C2 separation tower, the bottom product is mixed with the gas produced from the top of the demethanizer tower and sent to the boundary area as fuel gas, and the material produced from the top of the tower is sent to the boundary area as a polymerization-grade ethylene product.

[0005] Although MTP technology has achieved certain industrial application results, there are still some technical bottlenecks, such as complex process flow, low waste heat utilization efficiency, large amount of circulating materials, high equipment manufacturing cost, etc. These problems limit the economic benefits and market competitiveness of MTP technology. It is an inevitable requirement to achieve green, low-carbon and sustainable development of the coal chemical industry by optimizing process flow and parameters, reducing energy consumption in the MTP process, reducing device operating costs and improving resource utilization efficiency.

[0006] In summary, by optimizing the reaction conditions, operating parameters and process flow in the MTP process, improving the propylene yield and resource utilization efficiency, reducing energy consumption and emissions; and strengthening the energy recovery and utilization in the MTP process, such as utilizing reaction heat, waste gas, waste water and other resources, to achieve efficient and cyclic utilization of energy, it has important scientific significance and practical value for the industrial production of low-carbon olefins. In order to further solve the above problems, the present invention is proposed. Summary of the invention

[0007] The main purpose of the present invention is to provide a methanol to low-carbon olefin system and method to solve the problems of complicated operation and increased maintenance cost caused by the long process of the MTP process technology in the prior art and the large number of equipment involved.

[0008] In order to solve the above problems, the present invention proposes a methanol to light olefin system, comprising: a light olefin reactor 10, having a light olefin product gas outlet; the light olefin reactor 10 is used to react a dimethyl ether / hydrocarbon mixture to obtain a light olefin product gas; a heat exchange unit 20, comprising a primary heat exchanger 21, a secondary heat exchanger 22, a tertiary heat exchanger 23 and a quaternary heat exchanger 24 connected in sequence by heat exchange medium channels, the heat exchange medium channel inlet of the primary heat exchanger 21 is connected to the light olefin product gas outlet, and the heat exchange material outlet of the primary heat exchanger 21 is connected to the inlet of the light olefin reactor 10; the heat exchange material inlet of the quaternary heat exchanger 24 is used to introduce refined methanol, and the heat exchange material outlet of the quaternary heat exchanger 24 is connected to the heat exchange material inlet of the secondary heat exchanger 22; a dimethyl ether reactor 30, having a methanol inlet and a dimethyl ether outlet, and the methanol inlet is connected to the secondary heat exchanger 22. The heat exchange material outlet of the fourth-stage heat exchanger 24 is connected, and the dimethyl ether outlet is connected to the heat exchange material inlet of the first-stage heat exchanger 21; the dimethyl ether reactor 30 is used to react methanol to obtain a dimethyl ether product; the process water purification unit 40 has a process water inlet, a light olefin product gas inlet, a gaseous hydrocarbon outlet 401, a recovered methanol outlet 402 and a recovered hydrocarbon outlet 403, the light olefin product gas inlet is connected to the heat exchange medium channel outlet of the fourth-stage heat exchanger 24, and the recovered methanol outlet 402 is connected to the heat exchange material inlet of the second-stage heat exchanger 22; the process water purification unit 40 is used to purify the light olefin product gas discharged from the fourth-stage heat exchanger 24 after heat exchange to obtain gaseous hydrocarbons, recover methanol and recover hydrocarbons; the hydrocarbon separation unit 50 is connected to the gaseous hydrocarbon outlet 401, and the hydrocarbon separation unit 50 is used to separate gaseous hydrocarbons to obtain aromatics, ethylene, propylene and liquefied petroleum gas.

[0009] Furthermore, the process water purification unit 40 includes: a flash tank 41, having a process water inlet, a low-carbon olefin product gas inlet, a gaseous hydrocarbon outlet 401, a recovered hydrocarbon inlet and a flash liquid phase outlet; the flash tank 41 is used to mix the low-carbon olefin product gas after heat exchange with process water and flash evaporate to obtain a flash liquid phase and gaseous hydrocarbons; a hydrocarbon-water separator 42, having a flash liquid phase inlet, a separated water phase outlet 404 and a separated oil phase outlet 405, the flash liquid phase inlet is connected to the flash liquid phase outlet, and the separated water phase outlet 404 is connected to the process water inlet of the flash tank 41; the hydrocarbon-water separator 42 is used to perform hydrocarbon-water separation treatment on the flash liquid phase to obtain a separated water phase and a separated oil phase; a first process water purification tower 43, having a separated water phase inlet 406, a methanol recovery outlet 402 and a methanol removal water phase outlet 407; the separated water phase inlet 406 is connected to the separated water phase outlet 404; the first process water purification tower 43 is used to remove methanol from the separated water phase to obtain recovered methanol and a methanol removal water phase; the second process water purification tower 44, having a methanol removal water phase inlet 408, a hydrocarbon recovery outlet 403 and a purified water outlet 409, the methanol removal water phase inlet 408 is connected to the methanol removal water phase outlet 407, and the hydrocarbon recovery outlet 403 is connected to the hydrocarbon recovery inlet of the flash tank 41; the second process water purification tower 44 is used to remove hydrocarbons from the methanol removal water phase to obtain recovered hydrocarbons and purified water.

[0010] Furthermore, the purified water outlet 409 is connected to the heat exchange material inlet of the tertiary heat exchanger 23; the process water purification unit 40 also includes: a first heater 45, which is connected to the heat exchange material outlet of the tertiary heat exchanger 23, and the first heater 45 is used to heat the purified water after heat exchange in the tertiary heat exchanger 23 to form process steam; a process steam tank 46, having a process steam inlet, a first process steam outlet and a second process steam outlet, and the process steam inlet is connected to the outlet of the first heater 45; a second heater 47 is connected to the first process steam outlet, and is used to further heat the process steam to the required temperature of the low-carbon olefin reactor 10, and the outlet of the second heater 47 is connected to the inlet of the low-carbon olefin reactor 10; a fifth heat exchanger 48 is arranged in the bottom of the first process water purification tower 43, and the inlet and outlet of its heat exchange material channel are respectively connected to the bottom outlet and the bottom reflux port of the first process water purification tower 43; the heat exchange medium channel of the fifth heat exchanger 48 is connected to the second process steam outlet.

[0011] Furthermore, the bottom of the second process water purification tower 44 also has a heat medium inlet, which is also connected to the second process steam outlet; a third heater 49 is also provided on the pipeline connecting the separated water phase outlet 404 and the process water inlet of the flash tank 41, and the separated water phase inlet 406 is connected to the pipe section located between the third heater 49 and the separated water phase outlet 404.

[0012] Furthermore, the hydrocarbon separation unit 50 includes: a buffer compression unit for buffering and compressing gaseous hydrocarbons and pre-separating them to form hydrocarbons to be distilled; a distillation unit for distilling and separating the hydrocarbons to be distilled to obtain aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas; preferably, the buffer compression unit includes: a buffer tank 51 having a gaseous hydrocarbon inlet, a buffer gas phase outlet and a buffer phase outlet, the gaseous hydrocarbon inlet is connected to the gaseous hydrocarbon outlet 401, the buffer tank 51 is used to buffer the gaseous hydrocarbons to obtain a buffer gas phase and a buffer phase; the hydrocarbon-water separator 42 also has a buffer phase inlet, the buffer phase outlet is connected to the buffer phase inlet; multi-stage compression separation units connected in sequence are used to perform multi-stage compression and separation on the buffer gas phase to obtain hydrocarbons to be distilled; preferably, the multi-stage compression separation unit includes four-stage compression separation units connected in sequence, and each stage of the compression separation unit 52 includes a compression unit 521, a cold unit 522 connected in sequence, Condensation unit 522 and separation tank 523; wherein, according to the material flow sequence, the buffer gas phase outlet is connected to the compression unit 521 in the first-stage compression separation unit 52; the separation tank 523 has a gas phase outlet, a condensed water phase outlet and a condensed oil phase outlet, and in two adjacent compression separation units 52, the gas phase outlet of the separation tank 523 located upstream is connected to the compression unit 521 located downstream; the condensed water phase outlet of the separation tank 523 in the first-stage compression separation unit 52 is connected to the buffer tank 51, and the condensed water phase outlets of the separation tanks 523 in the second, third and fourth-stage compression separation units 52 are all connected to the buffer phase inlet of the hydrocarbon-water separator 42; the condensed oil phase outlet of the separation tank 523 in the first-stage compression separation unit 52 is connected to the separation tank 523 in the second-stage compression separation unit 52; the condensed oil phase outlet of the separation tank 523 in the second, third and fourth-stage compression separation units 52 is connected to the distillation unit.

[0013] Furthermore, the hydrocarbons to be distilled include the condensed oil phases produced by the separation tanks 523 in the second, third and fourth stage compression and separation units 52, the gas phase produced by the separation tank 523 in the fourth stage compression and separation unit 52, and the separated oil phase produced by the separated oil phase outlet 405 of the hydrocarbon-water separator 42; the distillation unit includes: a C6 removal distillation tower 53, having a first distillation inlet, a first tower bottom outlet and a first tower top outlet, the first distillation inlet is connected to the condensed oil phase outlet of the separation tank 523 in the second stage compression and separation unit 52, and the first distillation inlet is also connected to the separated oil phase outlet 405 of the hydrocarbon-water separator 42; the C6 removal distillation tower 53 is used to distill and produce the first part of aromatics and light components below C5; the C3 removal distillation tower 54 has a second distillation inlet, a second tower bottom outlet and a second tower top outlet, the second distillation inlet is respectively connected to the separation tank 523 in the fourth stage compression and separation unit 52 The gas phase outlet is connected to the condensed oil phase outlet; the C3 removal distillation tower 54 is used for distilling and outputting light components below C3 and the first part of liquefied petroleum gas; the C2 removal distillation tower 55 has a third distillation inlet, a third tower bottom outlet and a third tower top outlet, the third distillation inlet is connected to the second tower top outlet, and the C2 removal distillation tower 55 is used for distilling and outputting heavy components above C3 and light components of C2 and below; the propylene distillation tower 56 has a fourth distillation inlet, a fourth tower bottom outlet and a fourth tower top outlet, the fourth distillation inlet is connected to the third tower bottom outlet, and the propylene distillation tower 56 is used for distilling product propylene and the second part of liquefied petroleum gas; the third tower bottom outlet is also connected to the heat exchange material inlet of the first-stage heat exchanger 21; the ethylene distillation tower 57 has a fifth distillation inlet, a fifth tower bottom outlet and a fifth tower top outlet, the fifth distillation inlet is connected to the fourth tower top outlet, and the ethylene distillation tower 57 is used for distilling and outputting ethylene.

[0014] Furthermore, the distillation unit further includes: a C5 removal distillation tower 58, having a sixth distillation inlet, a sixth tower bottom outlet and a sixth tower top outlet, the sixth distillation inlet is connected to the first tower top outlet, and the sixth tower top outlet is connected to the heat exchange material inlet of the primary heat exchanger 21; the C5 removal distillation tower 58 is used to distill and produce the second part of aromatic hydrocarbons and C5-C6 circulating hydrocarbons, and the sixth tower top outlet is used to return the C5-C6 circulating hydrocarbons to the heat exchange material inlet of the primary heat exchanger 21; a C4 removal distillation tower 59, having a seventh distillation inlet, a seventh tower bottom outlet and a seventh tower top outlet, the seventh distillation inlet is connected to the condensed oil phase outlet of the separation tank 523 in the third-stage compression separation unit 52, and the seventh tower bottom outlet is connected to the heat exchange material inlet of the first-stage heat exchanger 21; The outlet of the seventh tower kettle is connected to the sixth distillation inlet of the de-C5 distillation tower 58, and the seventh tower top outlet is connected to the second distillation inlet of the de-C3 distillation tower 54; the de-C4 distillation tower 59 is used to distill and output heavy components above C5 and light components below C4; a C2 and below light component condenser 60 is arranged on the flow path where the third tower top outlet of the de-C2 distillation tower 55 is located, and is used to condense C2 and below light components; a C2 and below light component buffer tank 61 has a gas phase outlet and a liquid phase outlet, and the C2 and below light component buffer tank 61 is connected to the outlet of the C2 and below light component condenser 60, and the C2 and below light component buffer tank 61 is used to condense the condensed C2 and The following light components are buffered to obtain a gas phase and a liquid phase; a C1 removal distillation tower 62 has an eighth distillation inlet, an eighth tower bottom outlet and an eighth tower top outlet, the eighth distillation inlet is connected to the liquid phase outlet, and the eighth tower bottom outlet is connected to the fifth distillation inlet of the ethylene distillation tower 57; a gas phase inlet is also provided at the top of the C1 removal distillation tower 62, and the gas phase outlet is respectively connected to the gas phase inlet and the heat exchange material inlet of the first-stage heat exchanger 21; the C1 removal distillation tower 62 is used to distill and output fuel gas and C2 heavy components; preferably, a reflux port is also provided in the middle of the C1 removal distillation tower 62, and the fifth tower bottom outlet of the ethylene distillation tower 57 is connected to the reflux port; the multi-stage compression separation unit also includes: a The sixth heat exchanger 63, whose heat exchange medium channel is arranged on the pipeline between the compression unit 521 and the condensing unit 522 in the third-stage compression and separation unit 52, and the heat exchange material channel is arranged on the pipeline between the condensed oil phase outlet of the separation tank 523 in the second-stage compression and separation unit 52 and the first distillation inlet of the de-C6 distillation tower 53; the seventh heat exchanger 64, whose heat exchange medium channel is arranged on the pipeline between the compression unit 521 and the condensing unit 522 in the fourth-stage compression and separation unit 52, and the heat exchange material channel is arranged on the pipeline between the condensed oil phase outlet of the separation tank 523 in the third-stage compression and separation unit 52 and the seventh distillation inlet of the de-C4 distillation tower 59.

[0015] According to another aspect of the present invention, a method for preparing light olefins from methanol is provided. The method adopts the system for preparing light olefins from methanol according to any one of claims 1 to 7, and the method comprises the following steps: reacting a dimethyl ether / hydrocarbon mixture in a light olefin reactor 10 to obtain a light olefin product gas; using the light olefin product gas as a heat exchange medium to perform four-stage heat exchange in a heat exchange unit 20 to obtain a light olefin product gas after heat exchange; performing process water purification treatment on the light olefin product gas after heat exchange in a process water purification unit 40 to obtain gaseous hydrocarbons, recover methanol and recover hydrocarbons; separating gaseous hydrocarbons by using a hydrocarbon separation unit 50 to obtain aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas; wherein the heat exchange unit 20 comprises a primary heat exchanger 21, a secondary heat exchanger 22, a tertiary heat exchanger 23 and a fourth heat exchanger 24 connected in sequence by heat exchange medium channels, and the method further comprises: passing refined methanol into the heat exchange material channel of the fourth heat exchanger 24 for heat exchange with the light olefin product gas, and then It is passed together with the recovered methanol into the heat exchange material channel of the secondary heat exchanger 22 for heat exchange with the light olefin product gas again to obtain a methanol feedstock; the methanol feedstock is passed into the dimethyl ether reactor 30 for reaction to obtain a dimethyl ether product; the dimethyl ether / hydrocarbon mixture formed by the dimethyl ether product and hydrocarbons is passed into the heat exchange material channel of the primary heat exchanger 21 for heat exchange with the light olefin product gas, and then passed into the light olefin reactor 10 for reaction; preferably, the process water purification step includes: mixing and flashing the light olefin product gas after heat exchange with process water in a flash tank 41 to obtain a flash liquid phase and gaseous hydrocarbons; subjecting the flash liquid phase to hydrocarbon-water separation in a hydrocarbon-water separator 42 to obtain a separated water phase and a separated oil phase; subjecting the separated water phase to methanol removal treatment in a first process water purification tower 43 to methanol removal treatment to obtain recovered methanol and a methanol-removed water phase; subjecting the methanol-removed water phase to hydrocarbon removal treatment in a second process water purification tower 44 to hydrocarbon removal treatment to obtain recovered hydrocarbons and purified water, and returning the recovered hydrocarbons to the flash tank 41.

[0016] Furthermore, the method further comprises: passing purified water into the heat exchange material channel of the three-stage heat exchanger 23 to exchange heat with the light olefin product gas, using the first heater 45 to heat the purified water after heat exchange to form process steam and send it to the process steam tank 46; further heating the first part of the process steam to the required temperature of the light olefin reactor 10, and then sending it to the light olefin reactor 10; exchanging heat between the second part of the process steam and the methanol-removing water phase in the fifth heat exchanger 48 to heat and reflux the methanol-removing water phase; preferably, passing the third part of the process steam as a heat medium into the second process water purification tower 44; preferably, heating a portion of the separated water phase in the third heater 49 and then returning it to the process steam tank 46; Return to the flash tank 41 as process water; preferably, the step of separating gaseous hydrocarbons by using the hydrocarbon separation unit 50 includes: using a buffer compression unit to buffer and compress the gaseous hydrocarbons and pre-separate them to form hydrocarbons to be distilled; using a distillation unit to distill and separate the hydrocarbons to be distilled to obtain aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas; preferably, the buffer compression unit includes: buffering the gaseous hydrocarbons in the buffer tank 51 to obtain a buffer gas phase and a buffer phase; passing the buffer phase into the hydrocarbon-water separator 42; performing multi-stage compression and separation on the buffer gas phase in a multi-stage compression and separation unit to obtain hydrocarbons to be distilled; more preferably, the multi-stage compression and separation unit includes four-stage compression and separation units 52 connected in sequence, and each stage of the compression and separation units 52 each includes a compression unit 521, a condensation unit 522 and a separation tank 523 connected in sequence; wherein the buffer gas phase is passed into the compression unit 521 in the first-stage compression and separation unit 52; in the adjacent two-stage compression and separation units 52, the gas phase separated by the separation tank 523 located upstream is passed into the compression unit 521 located downstream; the condensed water phase separated by the separation tank 523 in the first-stage compression and separation unit 52 is returned to the buffer tank 51, and the condensed water phase separated by the separation tank 523 in the second, third and fourth-stage compression and separation units 52 is returned to the hydrocarbon-water separator 42; the condensed oil phase separated by the separation tank 523 in the first-stage compression and separation unit 52 is sent to the second-stage compression In the separation tank 523 of the separation unit 52, the condensed oil phase separated by the separation tank 523 in the second, third and fourth stage compression separation units 52 is sent to the distillation unit; preferably, the hydrocarbons to be distilled include the condensed oil phases produced by the separation tanks 523 in the second, third and fourth stage compression separation units 52, the gas phase produced by the separation tank 523 in the fourth stage compression separation unit 52, and the separated oil phase produced by the separated oil phase outlet 405 of the hydrocarbon-water separator 42; the distillation separation step includes: sending the condensed oil phase produced by the separation tank 523 in the second stage compression separation unit 52 and the separated oil phase produced by the hydrocarbon-water separator 42 to the de-C6 distillation tower 53 for distillation treatment to obtain the first part of aromatics and light components below C5;The gas phase and condensed oil phase produced by the separation tank 523 in the fourth stage compression separation unit 52 are sent to the C3 removal distillation tower 54 for distillation treatment to obtain light components below C3 and the first part of liquefied petroleum gas; the light components below C3 are sent to the C2 removal distillation tower 55 for distillation treatment to obtain heavy components above C3 and light components of C2 and below; the heavy components above C3 are sent to the propylene distillation tower 56 for distillation treatment to obtain propylene and the second part of liquefied petroleum gas; a part of the liquefied petroleum gas is returned to the heat exchange material inlet of the first stage heat exchanger 21 as part of the hydrocarbons; the light components of C2 and below are sent to the ethylene distillation tower 57 for distillation treatment to obtain ethylene. ;

[0017] Furthermore, the distillation separation step also includes: sending the light components below C5 to the de-C5 distillation tower 58 for distillation treatment to obtain the second part of aromatic hydrocarbons and C5-C6 circulating hydrocarbons; returning the C5-C6 circulating hydrocarbons to the heat exchange material inlet of the first-stage heat exchanger 21; sending the condensed oil phase produced by the separation tank 523 in the third-stage compression separation unit 52 to the de-C4 distillation tower 59 for distillation treatment to obtain heavy components above C5 and light components below C4; returning the heavy components above C5 to the de-C5 distillation tower 58; sending the light components below C4 to the de-C3 distillation tower 54; before sending the light components C2 and below to the ethylene distillation tower 57, first condensing the light components C2 and below in the C2 and below light component condenser 60, and condensing the C2 and above The lower light components are buffered in the C2 and lower light component buffer tank 61 to obtain a gas phase and a liquid phase; the liquid phase is sent to the de-C1 distillation tower 62 for distillation treatment to obtain fuel gas and C2 heavy components; and a part of the gas phase is sent from the upper part of the de-C1 distillation tower 62 to the de-C1 distillation tower 62, and the other part of the gas phase is returned to the heat exchange material inlet of the primary heat exchanger 21; the C2 heavy components are sent to the ethylene distillation tower 57 for distillation treatment to obtain ethylene; preferably, the bottom material of the ethylene distillation tower 57 is refluxed to the de-C1 distillation tower 62; preferably, after the refined methanol is pressurized to 0.5-0.8MPa, it is passed into the fourth-stage heat exchanger 24 for heat exchange to 120-150°C; the refined methanol after heat exchange is combined with the recovered methanol in the secondary heat exchanger 22 The reaction pressure in the dimethyl ether reactor 30 is 0.5-0.8 MPa, the reaction temperature is 350-380°C, and the catalyst required for the reaction is a solid acid catalyst; preferably, the solid acid catalyst is at least one of a supported heteropoly acid solid acid catalyst, an alumina solid acid catalyst and a molecular sieve solid acid catalyst; preferably, the temperature of the light olefin product gas obtained by the reaction of the light olefin reactor 10 is 480-500°C, and the catalyst required for the reaction of the light olefin reactor 10 is a ZSM-5 zeolite molecular sieve; the temperature of the dimethyl ether / hydrocarbon mixture after heat exchange in the primary heat exchanger 21 is 450-460°C; the temperature of the purified water produced by the second process water purification tower 44 is 100-120°C, and the pressure is The temperature of the purified water after heat exchange in the three-stage heat exchanger 23 is 131-140°C; the temperature of the light olefin product gas after heat exchange in the first-stage heat exchanger 21 is 380-400°C, the temperature after heat exchange in the second-stage heat exchanger 22 is 350-360°C, the temperature after heat exchange in the third-stage heat exchanger 23 is 210-230°C, and the temperature after heat exchange in the fourth-stage heat exchanger 24 is 90-100°C; preferably, the temperature of the separated water phase produced in the hydrocarbon-water separator 42 is 60-75°C, and the temperature of the process steam entering the light olefin reactor 10 is 430-440°C; in the four-stage compression separation unit 52, the pressure of the first stage compression is 0.2-0.25MPa, and the pressure of the second stage compression is 0.4-0.7MPa, the third stage compression pressure is 0.9~1.2MPa, and the fourth stage compression pressure is 1.7~2.3MPa. .

[0018] The present invention provides a methanol to low-carbon olefin system and method, which includes a low-carbon olefin reactor, a heat exchange unit, a dimethyl ether reactor, a process water purification unit and a hydrocarbon separation unit. The present invention realizes further utilization of the waste heat of the carbon olefin product gas by setting a four-stage heat exchanger connected in sequence in the heat exchange unit. In the process of utilizing the waste heat, not only can the raw materials participating in the reaction and the process water purification unit be preliminarily heated, but also the purpose of cooling the low-carbon olefin product gas can be achieved. The methanol to low-carbon olefin system, through the rational utilization of the waste heat generated in the heat exchange unit and the process water purification unit, not only improves the waste heat utilization efficiency, but also shortens the MTP process flow. In addition, through the optimization of the above-mentioned MTP process flow, the heat load of the quenching system and the heating system is reduced, the power consumption of the compressor and the steam consumption are reduced, and the energy consumption of the entire methanol to low-carbon olefin system is reduced; at the same time, the difficulty of process operation is also reduced, and the purpose of reducing equipment manufacturing costs and device operating costs is finally achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0020] Figure 1 A structural schematic diagram of a methanol to light olefin system according to the present invention is shown.

[0021] The above drawings include the following reference numerals:

[0022] 10. Low carbon olefin reactor; 20. Heat exchange unit; 21. Primary heat exchanger; 22. Secondary heat exchanger; 23. Third stage heat exchanger; 24. Fourth stage heat exchanger; 30. Dimethyl ether reactor; 40. Process water purification unit; 41. Flash tank; 42. Hydrocarbon water separator; 43. First process water purification tower; 44. Second process water purification tower; 45. First heater; 46. Process steam tank; 47. Second heater; 48. Fifth heat exchanger; 49. Third heater; 401. Gaseous hydrocarbon outlet; 402. Recovered methanol outlet; 403. Recovered hydrocarbon outlet; 404. Separated water phase outlet; 405. Separated oil phase outlet; 406. Separation water phase inlet; 407, methanol removal water phase outlet; 408, methanol removal water phase inlet; 409, purified water outlet; 50, hydrocarbon separation unit; 51, buffer tank; 52, compression separation unit; 53, C6 removal distillation tower; 54, C3 removal distillation tower; 55, C2 removal distillation tower; 56, propylene distillation tower; 57, ethylene distillation tower; 58, C5 removal distillation tower; 59, C4 removal distillation tower; 60, C2 and below light component condenser; 61, C2 and below light component buffer tank; 62, C1 removal distillation tower; 63, sixth heat exchanger; 64, seventh heat exchanger; 521, compression unit; 522, condensation unit; 523, separation tank. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0025] As described in the background technology section, although MTP technology has achieved certain industrial application results, there are still some technical bottlenecks, such as complex process flow, low waste heat utilization efficiency, large amount of circulating materials, high equipment manufacturing cost, etc. These problems limit the economic benefits and market competitiveness of MTP technology. By optimizing the process flow and parameters, reducing the energy consumption in the MTP process, reducing the operating cost of the device and improving the efficiency of resource utilization, it is an inevitable requirement for achieving green, low-carbon and sustainable development in the coal chemical industry, and it has important scientific significance and practical value for the industrial production of low-carbon olefins.

[0026] In order to solve the above problems, the present invention proposes a methanol to light olefins system, such as Figure 1As shown, the methanol to light olefin system comprises: a light olefin reactor 10, having a light olefin product gas outlet; the light olefin reactor 10 is used to react a dimethyl ether / hydrocarbon mixture to obtain a light olefin product gas; a heat exchange unit 20, comprising a primary heat exchanger 21, a secondary heat exchanger 22, a tertiary heat exchanger 23 and a quaternary heat exchanger 24, the heat exchange medium channel of the primary heat exchanger 21 being connected in sequence to the light olefin product gas outlet, and the heat exchange material outlet of the primary heat exchanger 21 being connected to the inlet of the light olefin reactor 10; the heat exchange material inlet of the quaternary heat exchanger 24 being used to introduce refined methanol, and the heat exchange material outlet of the quaternary heat exchanger 24 being connected to the heat exchange material inlet of the secondary heat exchanger 22; a dimethyl ether reactor 30, having a methanol inlet and a dimethyl ether outlet, and the methanol inlet being connected to the heat exchange material outlet of the secondary heat exchanger 22 The dimethyl ether outlet is connected to the heat exchange material inlet of the first-stage heat exchanger 21; the dimethyl ether reactor 30 is used to react methanol to obtain a dimethyl ether product; the process water purification unit 40 has a process water inlet, a light olefin product gas inlet, a gaseous hydrocarbon outlet 401, a recovered methanol outlet 402 and a recovered hydrocarbon outlet 403, the light olefin product gas inlet is connected to the heat exchange medium channel outlet of the fourth-stage heat exchanger 24, and the recovered methanol outlet 402 is connected to the heat exchange material inlet of the second-stage heat exchanger 22; the process water purification unit 40 is used to purify the light olefin product gas discharged from the fourth-stage heat exchanger 24 after heat exchange to obtain gaseous hydrocarbons, recover methanol and recover hydrocarbons; the hydrocarbon separation unit 50 is connected to the gaseous hydrocarbon outlet 401, and the hydrocarbon separation unit 50 is used to separate gaseous hydrocarbons to obtain aromatics, ethylene, propylene and liquefied petroleum gas.

[0027] The methanol to light olefins system comprises: a light olefins reactor 10, a heat exchange unit 20, a dimethyl ether reactor 30, a process water purification unit 40 and a separation unit 50 for separating gaseous hydrocarbons. By connecting the light olefins reactor with the heat exchange unit, the dimethyl ether reactor, the process water purification unit and the hydrocarbon separation unit, an efficient methanol conversion and light olefins production system is formed.

[0028] In particular, the heat exchange system is optimized in the methanol to low-carbon olefin system of the present invention, and the heat exchange material inlet of the four-stage heat exchanger 24 is used to pass refined methanol. The heat exchange material outlet of the four-stage heat exchanger 24 is connected to the heat exchange material inlet of the secondary heat exchanger 22, and the waste heat generated in the low-carbon olefin reactor 10 can be used to heat the refined methanol through the four-stage heat exchanger 24 and the secondary heat exchanger 22, so that the methanol after heat exchange can reach the required reaction temperature when it passes from the outlet of the secondary heat exchanger 22 to the dimethyl ether reactor 30. The outlet of the dimethyl ether reactor 30 is connected to the heat exchange material inlet of the primary heat exchanger 21, so that the waste heat generated in the low-carbon olefin reactor 10 can pass through the primary heat exchanger 21 to further heat the substances generated in the dimethyl ether reactor 30, so that when it passes from the outlet of the primary heat exchanger 21 to the low-carbon olefin reactor 10, it can reach the reaction temperature. The above process can also achieve the purpose of further cooling the low-carbon olefin products in the low-carbon olefin reactor 10.

[0029] In short, through the above-mentioned device design in the methanol to low-carbon olefins system, not only the process flow is shortened, but also the utilization rate of the heat generated in the production process is improved, and the energy consumption in the methanol to low-carbon olefins process is effectively reduced.

[0030] In a preferred embodiment, the process water purification unit 40 includes: a flash tank 41, having a process water inlet, a light olefin product gas inlet, a gaseous hydrocarbon outlet 401, a recovered hydrocarbon inlet and a flash liquid phase outlet; the flash tank 41 is used to mix the light olefin product gas after heat exchange with process water and flash evaporate to obtain a flash liquid phase and gaseous hydrocarbons; a hydrocarbon-water separator 42, having a flash liquid phase inlet, a separated water phase outlet 404 and a separated oil phase outlet 405, the flash liquid phase inlet is connected to the flash liquid phase outlet, and the separated water phase outlet 404 is connected to the process water inlet of the flash tank 41; the hydrocarbon-water separator 42 is used to perform hydrocarbon-water separation treatment on the flash liquid phase to obtain a separated water phase and a separated oil phase; the first process water The purification tower 43 has an aqueous phase separation inlet 406, a methanol recovery outlet 402 and a methanol removal aqueous phase outlet 407; the aqueous phase separation inlet 406 is connected to the aqueous phase separation outlet 404; the first process water purification tower 43 is used to remove methanol from the aqueous phase to obtain recovered methanol and a methanol removal aqueous phase; the second process water purification tower 44 has an aqueous phase separation inlet 408, a hydrocarbon recovery outlet 403 and a purified water outlet 409; the aqueous phase separation inlet 408 is connected to the methanol removal aqueous phase outlet 407, and the hydrocarbon recovery outlet 403 is connected to the hydrocarbon recovery inlet of the flash tank 41; the second process water purification tower 44 is used to remove hydrocarbons from the methanol removal aqueous phase to obtain recovered hydrocarbons and purified water.

[0031] The light olefin product gas after heat exchange is passed through the flash tank 41 from the outlet of the heat exchange medium channel of the four-stage heat exchanger 24 and the process water to obtain a flash liquid phase and gaseous hydrocarbons. This process can preliminarily separate the by-products in the light olefin product gas. Then, through the hydrocarbon-water separator 42, the first process water purification tower 43 and the second process water purification tower 44, the light olefin product gas can be further separated from the process water, and the purified water, recovered hydrocarbons and methanol obtained by separation can be recycled and continued to participate in the reaction. This process not only improves the recovery rate of methanol raw materials, effectively reduces the loss of methanol in the production process, but also reduces the production cost and the impact on the environment through the purification and recycling of process water. At the same time, the production efficiency and economic benefits can be significantly improved, and the environmental protection goals of energy saving and emission reduction can be achieved. Preferably, a compression unit is also provided between the separated water phase inlet 406 and the separated water phase outlet 404, which can make the separation process cheaper.

[0032] In a preferred embodiment, the purified water outlet 409 is connected to the heat exchange material inlet of the tertiary heat exchanger 23; the process water purification unit 40 also includes: a first heater 45, which is connected to the heat exchange material outlet of the tertiary heat exchanger 23, and the first heater 45 is used to heat the purified water after heat exchange in the tertiary heat exchanger 23 to form process steam; a process steam tank 46, having a process steam inlet, a first process steam outlet and a second process steam outlet, and the process steam inlet is connected to the outlet of the first heater 45; a second heater 47 is connected to the first process steam outlet, and is used to further heat the process steam to the required temperature of the low-carbon olefin reactor 10, and the outlet of the second heater 47 is connected to the inlet of the low-carbon olefin reactor 10; a fifth heat exchanger 48 is arranged in the bottom of the first process water purification tower 43, and the inlet and outlet of its heat exchange material channel are respectively connected to the bottom outlet and the bottom reflux port of the first process water purification tower 43; the heat exchange medium channel of the fifth heat exchanger 48 is connected to the second process steam outlet.

[0033] Connecting the purified water outlet 409 to the heat exchange material channel of the tertiary heat exchanger 23 can realize further utilization of the waste heat generated in the low-carbon olefin reactor 10. After the purified water after heat exchange passes through the first heater 45 to form process steam, it can continue to pass into the process steam tank 46 for further separation. The setting of the heat exchange device in the process water purification unit 40 can further utilize the heat generated in the system, more effectively improve the thermal efficiency, and reduce the production cost. In addition, the above-mentioned connection method of the process water purification unit can make the process water separation and purification better, and the setting of the waste heat utilization system in the system can further reduce the energy consumption in the process of process water purification.

[0034] In a preferred embodiment, the bottom of the second process water purification tower 44 also has a heat medium inlet, which is also connected to the second process steam outlet; a third heater 49 is also provided on the pipeline connecting the separated water phase outlet 404 and the process water inlet of the flash tank 41, and the separated water phase inlet 406 is connected to the pipe section between the third heater 49 and the separated water phase outlet 404.

[0035] In a preferred embodiment, the hydrocarbon separation unit 50 includes: a buffer compression unit for buffering and compressing gaseous hydrocarbons and pre-separating them to form hydrocarbons to be distilled; a distillation unit for distilling and separating the hydrocarbons to be distilled to obtain aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas. The design of the hydrocarbon separation unit 50 not only stabilizes the supply of gaseous hydrocarbons and ensures the efficient operation of the distillation unit, but also obtains high-purity aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas through fine separation. The unit can further improve production efficiency, reduce production costs and improve product quality. Preferably, the buffer compression unit includes: a buffer tank 51 having a gaseous hydrocarbon inlet, a buffer gas phase outlet and a buffer phase outlet, the gaseous hydrocarbon inlet is connected to the gaseous hydrocarbon outlet 401, the buffer tank 51 is used to buffer the gaseous hydrocarbons to obtain a buffer gas phase and a buffer phase; the hydrocarbon-water separator 42 also has a buffer phase inlet, and the buffer phase outlet is connected to the buffer phase inlet; the multi-stage compression separation units connected in sequence are used to perform multi-stage compression and separation on the buffer gas phase to obtain hydrocarbons to be distilled. The buffer tank 51 and the hydrocarbon-water separator 42 are connected to each other, so that the buffer produced by the buffer tank 51 can be passed into the hydrocarbon-water separator 42 for further separation. The four-stage compression separation units connected in sequence in the hydrocarbon separation unit play different separation roles, and the purpose of completely separating the hydrocarbons to be distilled can be achieved by further separating the buffer gas phase separated from the buffer tank 51 for multiple times.

[0036] Preferably, the multi-stage compression and separation unit includes four-stage compression and separation units 52 connected in sequence, and each stage of the compression and separation unit 52 includes a compression unit 521, a condensation unit 522 and a separation tank 523 connected in sequence; wherein, in the order of material flow, the buffer gas phase outlet is connected to the compression unit 521 in the first stage of the compression and separation unit 52; the separation tank 523 has a gas phase outlet, a condensed water phase outlet and a condensed oil phase outlet, and in two adjacent stages of the compression and separation units 52, the gas phase outlet of the separation tank 523 located upstream and the gas phase outlet of the compression unit 521 located downstream are connected. The condensed water phase outlet of the separation tank 523 in the first-stage compression and separation unit 52 is connected to the buffer tank 51, and the condensed water phase outlets of the separation tanks 523 in the second, third and fourth-stage compression and separation units 52 are all connected to the buffer phase inlet of the hydrocarbon-water separator 42; the condensed oil phase outlet of the separation tank 523 in the first-stage compression and separation unit 52 is connected to the separation tank 523 in the second-stage compression and separation unit 52; the condensed oil phase outlets of the separation tanks 523 in the second, third and fourth-stage compression and separation units 52 are connected to the distillation unit.

[0037] In the present application, the condensed water phase outlet of the separation tank 523 in the first-stage compression separation unit 52 is connected to the buffer tank 51, and the condensed water phase outlets of the separation tanks 523 in the second, third and fourth-stage compression separation units 52 are connected to the buffer phase inlet of the hydrocarbon-water separator 42, so that the condensed water phase generated during the compression separation process can be further separated. Connecting the condensed oil phase outlets of the separation tanks 523 in the second, third and fourth-stage compression separation units 52 in the compression separation unit with the distillation unit can achieve separation and processing of the condensed oil phase during the compression separation process, effectively reducing the separation difficulty of the subsequent distillation unit and improving the separation efficiency.

[0038] Preferably, a compression unit is arranged between the buffer tank 51 and the hydrocarbon-water separator 42, between the separation tank 523 of the first-stage compression separation unit and the separation tank 523 of the second-stage compression separation unit, and between the condensed oil phase outlet of the separation tank 523 in the second and third-stage compression separation units 52 and the distillation unit. This connection arrangement can make the separation more thorough.

[0039] In a preferred embodiment, the hydrocarbons to be distilled include the condensed oil phases produced by the separation tanks 523 in the second, third and fourth stage compression and separation units 52, the gas phase produced by the separation tank 523 in the fourth stage compression and separation unit 52, and the separated oil phase produced by the separated oil phase outlet 405 of the hydrocarbon-water separator 42; the distillation unit includes: a C6 removal distillation tower 53, having a first distillation inlet, a first tower bottom outlet and a first tower top outlet, the first distillation inlet is connected to the condensed oil phase outlet of the separation tank 523 in the second stage compression and separation unit 52, and the first distillation inlet is also connected to the separated oil phase outlet 405 of the hydrocarbon-water separator 42; the C6 removal distillation tower 53 is used to distill and produce the first part of aromatics and light components below C5; the C3 removal distillation tower 54 has a second distillation inlet, a second tower bottom outlet and a second tower top outlet, and the second distillation inlet is respectively connected to the separation tanks 52 in the fourth stage compression and separation unit 52 The gas phase outlet of 523 is connected to the condensed oil phase outlet; the C3 removal distillation tower 54 is used for distilling and outputting light components below C3 and the first part of liquefied petroleum gas; the C2 removal distillation tower 55 has a third distillation inlet, a third tower bottom outlet and a third tower top outlet, the third distillation inlet is connected to the second tower top outlet, and the C2 removal distillation tower 55 is used for distilling and outputting heavy components above C3 and light components of C2 and below; the propylene distillation tower 56 has a fourth distillation inlet, a fourth tower bottom outlet and a fourth tower top outlet, the fourth distillation inlet is connected to the third tower bottom outlet, and the propylene distillation tower 56 is used for distilling product propylene and the second part of liquefied petroleum gas; the third tower bottom outlet is also connected to the heat exchange material inlet of the first-stage heat exchanger 21; the ethylene distillation tower 57 has a fifth distillation inlet, a fifth tower bottom outlet and a fifth tower top outlet, the fifth distillation inlet is connected to the fourth tower top outlet, and the ethylene distillation tower 57 is used for distilling and outputting ethylene.

[0040] In particular, the present invention connects the outlet of the condensed oil phase of the separation tank 523 in the second-stage compression separation unit 52 with the outlet of the first distillation inlet of the C6 removal distillation tower 53, so as to achieve the purpose of pre-separating the obtained condensed oil phase during the compression separation process. This process can separate the C6 heavy components in the C6 removal distillation tower 53. The above-mentioned pre-separation process can also make the subsequent separation process easier, make the entire separation process cleaner and more thorough, and reduce the energy loss caused by the subsequent separation, so as to further reduce the energy consumption. Then, the gas phase and condensed oil phase separated in the separation tank 523 in the fourth-stage compression separation unit 52 are introduced into the C3 removal distillation tower 54 to produce light components below C3 and the first part of liquefied petroleum gas; the gas phase produced by the C3 removal distillation tower 54 is used for distillation to produce heavy components above C3 and light components of C2 and below; the components separated by the C2 removal distillation tower 55 are further separated to produce ice-washed products and ethylene products, etc.

[0041] In a preferred embodiment, the distillation unit further includes: a C5 removal distillation tower 58 having a sixth distillation inlet, a sixth tower bottom outlet and a sixth tower top outlet, the sixth distillation inlet is connected to the first tower top outlet, and the sixth tower top outlet is connected to the heat exchange material inlet of the primary heat exchanger 21; the C5 removal distillation tower 58 is used to distill and produce a second portion of aromatic hydrocarbons and C5-C6 circulating hydrocarbons, and the sixth tower top outlet is used to return the C5-C6 circulating hydrocarbons to the heat exchange material inlet of the primary heat exchanger 21; a C4 removal distillation tower 59 having a seventh distillation inlet, a seventh tower bottom outlet and a seventh tower top outlet, the seventh distillation inlet is connected to the condensed oil phase outlet of the separation tank 523 in the third-stage compression separation unit 52, the seventh tower bottom outlet is connected to the sixth distillation inlet of the C5 removal distillation tower 58, and the seventh tower top outlet is connected to the second distillation inlet of the C3 removal distillation tower 54; the C4 removal distillation tower 59 is used to distill and produce heavy components above C5 and light components below C4 The de-C1 distillation tower 62 has an eighth distillation inlet, an eighth tower bottom outlet and an eighth tower top outlet, the eighth distillation inlet is connected to the liquid phase outlet, and the eighth tower bottom outlet is connected to the fifth distillation inlet of the ethylene distillation tower 57; the upper part of the de-C1 distillation tower 62 is also provided with a gas phase inlet, and the gas phase outlet is respectively connected to the gas phase inlet and the heat exchange material inlet of the first-stage heat exchanger 21; the de-C1 distillation tower 62 is used to distill and output fuel gas and C2 heavy components.

[0042] The present invention connects the condensed oil phase outlet of the separation tank 523 in the third-stage compression and separation unit 52 with the seventh distillation inlet of the de-C4 distillation tower 59, so that the condensed oil phase of the separation tank 523 in the third-stage compression and separation unit 52 can be pre-separated in the de-C4 distillation tower 59, which is beneficial to further reduce the difficulty of separating subsequent light components, and can also make the entire separation process better, which is beneficial to improving the separation quality and reducing the separation energy consumption.

[0043] Preferably, a reflux port is also provided in the middle of the de-C1 distillation tower 62, and the fifth tower bottom outlet of the ethylene distillation tower 57 is connected to the reflux port; the multi-stage compression and separation unit also includes: a sixth heat exchanger 63, whose heat exchange medium channel is arranged on the pipeline between the compression unit 521 and the condensation unit 522 in the third-stage compression and separation unit 52, and whose heat exchange material channel is arranged on the pipeline between the condensed oil phase outlet of the separation tank 523 in the second-stage compression and separation unit 52 and the first distillation inlet of the de-C6 distillation tower 53; a seventh heat exchanger 64, whose heat exchange medium channel is arranged on the pipeline between the compression unit 521 and the condensation unit 522 in the fourth-stage compression and separation unit 52, and whose heat exchange material channel is arranged on the pipeline between the condensed oil phase outlet of the separation tank 523 in the third-stage compression and separation unit 52 and the seventh distillation inlet of the de-C4 distillation tower 59.

[0044] The sixth heat exchanger 63 is provided so that the condensed oil phase of the separation tank 523 in the second-stage compression separation unit can be further heated by the sixth heat exchanger 63 and then directly passed through the first distillation inlet of the C6 removal distillation tower 53 to the C6 removal distillation tower 53. The seventh heat exchanger 64 is provided so that the condensed oil phase of the separation tank 523 in the third-stage compression separation unit 52 can be further heated by the seventh heat exchanger 64 and then directly passed through the C4 removal distillation tower 59. The above-mentioned arrangement can further utilize the heat generated by the compression separation unit.

[0045] According to another aspect of the present invention, a method for preparing low-carbon olefins from methanol is also provided. The preparation method adopts the above-mentioned system for preparing low-carbon olefins from methanol, and the method comprises the following steps: reacting a dimethyl ether / hydrocarbon mixture in a low-carbon olefin reactor 10 to obtain a low-carbon olefin product gas; using the low-carbon olefin product gas as a heat exchange medium to perform four-stage heat exchange in a heat exchange unit 20 to obtain a low-carbon olefin product gas after heat exchange; subjecting the low-carbon olefin product gas after heat exchange to process water purification in a process water purification unit 40 to obtain gaseous hydrocarbons, recover methanol and recover hydrocarbons; separating gaseous hydrocarbons using a hydrocarbon separation unit 50 to obtain aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas; wherein the heat exchange unit 20 comprises a plurality of heating units, a plurality of heating units, and a plurality of heating units. 20 includes a primary heat exchanger 21, a secondary heat exchanger 22, a tertiary heat exchanger 23 and a quaternary heat exchanger 24 connected in sequence by heat exchange medium channels, and the method further includes: passing refined methanol into the heat exchange material channel of the fourth-stage heat exchanger 24 for heat exchange with light olefin product gas, and then passing it together with recovered methanol into the heat exchange material channel of the secondary heat exchanger 22 for heat exchange with light olefin product gas again to obtain methanol feedstock; passing the methanol feedstock into the dimethyl ether reactor 30 for reaction to obtain dimethyl ether product; passing the dimethyl ether / hydrocarbon mixture formed by the dimethyl ether product and hydrocarbon into the heat exchange material channel of the primary heat exchanger 21 for heat exchange with light olefin product gas, and then passing it into the light olefin reactor 10 for reaction.

[0046] The above-mentioned preparation method further utilizes the heat of the light olefin product gas generated in the light olefin reactor 10 through the primary heat exchanger 21, the secondary heat exchanger 22, the tertiary heat exchanger 23 and the quaternary heat exchanger 24, thereby achieving the purpose of reducing energy efficiency and realizing efficient and cyclic utilization of energy. By utilizing the waste heat of the light olefin product gas, the methanol raw material is heated twice, and the dimethyl ether / hydrocarbon mixture formed by the dimethyl ether product and the hydrocarbon is heated. This method realizes the further utilization of the waste heat and also realizes the cooling process of the light olefin product gas, rationally utilizing the heat generated in the system, effectively saving the system energy consumption, and improving the overall production efficiency.

[0047] Preferably, the process water purification treatment step includes: mixing the low-carbon olefin product gas after heat exchange with process water in a flash tank 41 and flashing to obtain a flash liquid phase and gaseous hydrocarbons; subjecting the flash liquid phase to hydrocarbon-water separation in a hydrocarbon-water separator 42 to obtain a separated water phase and a separated oil phase; subjecting the separated water phase to methanol removal in a first process water purification tower 43 to obtain recovered methanol and a methanol-removed water phase; subjecting the methanol-removed water phase to hydrocarbon removal in a second process water purification tower 44 to hydrocarbon removal to obtain recovered hydrocarbons and purified water, and returning the recovered hydrocarbons to the flash tank 41. The above-mentioned treatment method can separate the water phase and the oil phase, and can also further recycle the recovered methanol, process water and hydrocarbon substances. In addition, purifying the low-carbon olefin product gas and process water in the above-mentioned manner can not only separate the hydrocarbon substances and water therein more thoroughly, but also further improve the separation efficiency.

[0048] In a preferred embodiment, the method further includes: passing purified water into the heat exchange material channel of the three-stage heat exchanger 23 to exchange heat with the light olefin product gas, using the first heater 45 to heat the purified water after heat exchange to form process steam and send it to the process steam tank 46; further heating the first part of the process steam to the required temperature of the light olefin reactor 10, and then sending it to the light olefin reactor 10; exchanging heat between the second part of the process steam and the methanol-removing water phase in the fifth heat exchanger 48 to heat and reflux the methanol-removing water phase; preferably, passing the third part of the process steam as a heat medium into the second process water purification tower 44; preferably, heating a part of the separated water phase in the third heater 49 and then returning it to the flash tank 41 as process water. The above-mentioned setting of the system can not only make further use of the heat generated in the light olefin reactor 10, but also realize further use of the heat generated in the process water purification unit, which can further reduce the energy consumption in the process.

[0049] Preferably, the step of separating gaseous hydrocarbons using the hydrocarbon separation unit 50 includes: using a buffer compression unit to buffer and pre-separate the gaseous hydrocarbons to form hydrocarbons to be distilled; using a distillation unit to distill and separate the hydrocarbons to be distilled to obtain aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas; preferably, the buffer compression unit includes: buffering the gaseous hydrocarbons in a buffer tank 51 to obtain a buffer gas phase and a buffer phase; passing the buffer phase into a hydrocarbon-water separator 42; and performing multi-stage compression and separation on the buffer gas phase in a multi-stage compression and separation unit to obtain hydrocarbons to be distilled.

[0050] More preferably, the multi-stage compression and separation unit includes four-stage compression and separation units 52 connected in sequence, and each stage of the compression and separation unit 52 includes a compression unit 521, a condensation unit 522 and a separation tank 523 connected in sequence; wherein the buffer gas phase is passed into the compression unit 521 in the first-stage compression and separation unit 52; in two adjacent stages of the compression and separation units 52, the gas phase separated by the separation tank 523 located upstream is passed into the compression unit 521 located downstream; the condensed water phase separated by the separation tank 523 in the first-stage compression and separation unit 52 is returned to the buffer tank 51, and the condensed water phase separated by the separation tank 523 in the second, third and fourth-stage compression and separation units 52 is returned to the hydrocarbon-water separator 42; the condensed oil phase separated by the separation tank 523 in the first-stage compression and separation unit 52 is sent to the separation tank 523 of the second-stage compression and separation unit 52, and the condensed oil phase separated by the separation tank 523 in the second, third and fourth-stage compression and separation units 52 is sent to the distillation unit.

[0051] Preferably, the hydrocarbons to be distilled include the condensed oil phases produced by the separation tanks 523 in the second, third and fourth stage compression and separation units 52, the gas phase produced by the separation tank 523 in the fourth stage compression and separation unit 52, and the separated oil phase produced by the separated oil phase outlet 405 of the hydrocarbon-water separator 42; the distillation and separation step includes: sending the condensed oil phase produced by the separation tank 523 in the second stage compression and separation unit 52 and the separated oil phase produced by the hydrocarbon-water separator 42 to the C6 removal distillation tower 53 for distillation treatment to obtain the first part of aromatics and light components below C5; sending the separation tank 523 in the fourth stage compression and separation unit 52 to the separation tank 5 The gas phase and condensed oil phase produced by 23 are sent to the de-C3 distillation tower 54 for distillation treatment to obtain light components below C3 and the first part of liquefied petroleum gas; the light components below C3 are sent to the de-C2 distillation tower 55 for distillation treatment to obtain heavy components above C3 and light components of C2 and below; the heavy components above C3 are sent to the propylene distillation tower 56 for distillation treatment to obtain propylene and the second part of liquefied petroleum gas; a part of the liquefied petroleum gas is returned to the heat exchange material inlet of the first heat exchanger 21 as part of the hydrocarbons; the light components of C2 and below are sent to the ethylene distillation tower 57 for distillation treatment to obtain ethylene.

[0052] The condensed oil phase produced by the separation tank 523 in the second-stage compression separation unit 52 and the separated oil phase produced by the hydrocarbon-water separator 42 are sent to the C6 removal distillation tower 53 for distillation treatment. This process can separate the C6 heavy components in the C6 removal distillation tower 53. The above-mentioned pre-separation process can also make the subsequent separation process easier, which can not only make the separation effect better, but also reduce the difficulty of the subsequent separation process, improve the separation efficiency, and reduce the separation energy consumption.

[0053] In a preferred embodiment, the distillation separation step further includes: sending the light components below C5 to a de-C5 distillation tower 58 for distillation treatment to obtain a second portion of aromatic hydrocarbons and C5-C6 circulating hydrocarbons; returning the C5-C6 circulating hydrocarbons to the heat exchange material inlet of the primary heat exchanger 21; sending the condensed oil phase produced by the separation tank 523 in the third-stage compression separation unit 52 to a de-C4 distillation tower 59 for distillation treatment to obtain heavy components above C5 and light components below C4; returning the heavy components above C5 to the de-C5 distillation tower 58; sending the light components below C4 to a de-C3 distillation tower 54; before sending the light components C2 and below to the ethylene distillation tower 57, first condensing the light components C2 and below in a C2 and below light component condenser 60, and condensing the condensed components The C2 and below light components are buffered in the C2 and below light component buffer tank 61 to obtain a gas phase and a liquid phase; the liquid phase is sent to the de-C1 distillation tower 62 for distillation treatment to obtain fuel gas and C2 heavy components; and a part of the gas phase is sent from the upper part of the de-C1 distillation tower 62 to the de-C1 distillation tower 62, and the other part of the gas phase is returned to the heat exchange material inlet of the primary heat exchanger 21; the C2 heavy components are sent to the ethylene distillation tower 57 for distillation treatment to obtain ethylene; preferably, the bottom material of the ethylene distillation tower 57 is refluxed to the de-C1 distillation tower 62; preferably, after the refined methanol is pressurized to 0.5-0.8MPa, it is passed into the fourth-stage heat exchanger 24 for heat exchange to 120-150°C; the refined methanol after heat exchange is combined with the recovered methanol in the secondary heat exchanger 22 is heat exchanged to 260-300°C; the reaction pressure in the dimethyl ether reactor 30 is 0.5-0.8MPa, the reaction temperature is 350-380°C, and the catalyst required for the reaction is a solid acid catalyst; preferably, the solid acid catalyst is at least one of a supported heteropolyacid solid acid catalyst, an alumina solid acid catalyst and a molecular sieve solid acid catalyst; preferably, the temperature of the light olefin product gas obtained by the reaction of the light olefin reactor 10 is 480-500°C, the catalyst required for the reaction of the light olefin reactor 10 is a ZSM-5 zeolite molecular sieve, and the reaction pressure of the light olefin reactor 10 is 0.03-0.15MPa; the temperature of the dimethyl ether / hydrocarbon mixture after heat exchange in the first heat exchanger 21 is 450-460°C; the second process The temperature of the purified water produced by the water purification tower 44 is 100-120°C, and the pressure is 0.3-0.5MPa. The temperature of the purified water after heat exchange in the three-stage heat exchanger 23 is 131-140°C; the temperature of the light olefin product gas after heat exchange in the first-stage heat exchanger 21 is 380-400°C, the temperature after heat exchange in the second-stage heat exchanger 22 is 350-360°C, the temperature after heat exchange in the third-stage heat exchanger 23 is 210-230°C, and the temperature after heat exchange in the fourth-stage heat exchanger 24 is 90-100°C; preferably, the temperature of the separated water phase produced in the hydrocarbon-water separator 42 is 60-75°C, and the temperature of the process steam entering the light olefin reactor 10 is 430-440°C; in the four-stage compression separation unit 52, the pressure of the first stage compression is 0.2~0.25MPa, the pressure of the second stage compression is 0.4~0.7MPa, the pressure of the third stage compression is 0.9~1.2MPa, and the pressure of the fourth stage compression is 1.7~2.3MPa. The reaction pressure in the low-carbon olefin reactor 10 of the present application is 0.03~0.15MPa, and the reaction pressure in the dimethyl ether reactor 30 is 0.5~0.8MPa. The above reaction pressure is much lower than the reaction pressure in the existing MTP process. The above reaction conditions can ensure the smooth reaction in the reaction system and reduce the energy consumption in the heat and mass transfer process. In addition, the low-pressure reaction pressure and feed pressure will prevent the nozzle and distributor from being damaged due to excessive temperature difference during the feeding process, thereby achieving the purpose of smoothly controlling the bed temperature and further reducing the cost required to maintain the system. .

[0054] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0055] Example 1

[0056] by Figure 1 The system shown is used to process methanol to produce low-carbon olefins. The specific method is as follows:

[0057] With refined methanol as raw material, the refined methanol is pressurized to 0.5-0.8 MPa, and is passed into the heat exchange material channel of the fourth-stage heat exchanger 24 for heat exchange with the light olefin product gas, and the 37-41°C refined methanol raw material is preheated to 120-150°C; then it is passed into the heat exchange material channel of the secondary heat exchanger 22 together with the recovered methanol for heat exchange with the light olefin product gas again, and the 120-150°C refined methanol raw material is further heated to 260-300°C; then it is passed into the dimethyl ether reactor 30, and reacted under the action of alumina solid acid catalyst, the reaction temperature is 350-380°C, the reaction pressure is 0.5-0.8 MPa, and dimethyl ether product is obtained.

[0058] The above-obtained 0.5-0.8MPa, 350-380°C dimethyl ether product and the 0.3-0.5MPa dimethyl ether / hydrocarbon mixture formed in the hydrocarbon separation unit 50 are introduced into the heat exchange material channel of the primary heat exchanger 21 for heat exchange with the light olefin product gas, and the reaction waste heat of 480°C of the light olefin product gas raises the temperature of the above mixture from 250-270°C to 450-460°C, and then it is introduced into the light olefin reactor 10 for reaction. Under the action of the ZSM-5 zeolite molecular sieve catalyst, a light olefin product gas mainly composed of propylene and including byproducts such as water is generated, wherein the reaction temperature is 480-500°C and the reaction pressure is 0.03-0.15MPa. The reaction waste heat of 480-500°C of the obtained light olefin product gas passes through the primary heat exchanger 21, the secondary heat exchanger 22, the tertiary heat exchanger 23 and the quaternary heat exchanger 24 in sequence. As described above, the primary heat exchanger 21, the secondary heat exchanger 22 and the quaternary heat exchanger 24 can respectively heat the dimethyl ether product obtained in the dimethyl ether reactor 30 and the dimethyl ether / hydrocarbon mixture formed in the hydrocarbon separation unit 50, preheat the refined methanol for the second time and preheat the refined methanol for the first time. The tertiary heat exchanger 23 can preheat the purified water, so that the purified water temperature of 0.3-0.5 MPa and 100-120° C. is raised to 131-140° C., and then the preheated purified water is passed through the first heater 45 to form process steam and sent to the process steam tank 46. The temperature of the reaction waste heat of the light olefin product gas at 480-500° C. after passing through the primary heat exchanger 21, the secondary heat exchanger 22, the tertiary heat exchanger 23 and the quaternary heat exchanger 24 is: 380-400° C., 350-360° C., 210-230° C., 90-100° C. respectively.

[0059] After the four-stage heat exchange, the temperature of the low-carbon olefin product gas is reduced from 480-500°C to 90-100°C, and then flows out from the outlet of the four-stage heat exchanger 24, mixes with 60-75°C process water in the flash tank 41 and flashes to obtain a flash liquid phase and gaseous hydrocarbons; the flash liquid phase is subjected to hydrocarbon-water separation treatment in the hydrocarbon-water separator 42 to obtain a separated water phase and a separated oil phase; the separated water phase is subjected to methanol removal treatment in the first process water purification tower 43 to obtain recovered methanol and a methanol-removed water phase; the methanol-removed water phase is subjected to hydrocarbon removal treatment in the second process water purification tower 44 to obtain recovered hydrocarbons and purified water, and the first part of the process steam with a pressure of 0.3-0.5MPa and a temperature of 200-220°C is further heated to 430-440°C through the second heater 47, and then fed into the low-carbon olefin reactor 10.

[0060] The gaseous hydrocarbon separated from the flash tank 41 is buffered in the buffer tank 51 to obtain a buffer gas phase and a buffer phase; the buffer phase is passed into the hydrocarbon-water separator 42 for further separation, and the buffer gas phase is subjected to multi-stage compression and separation in a multi-stage compression and separation unit. The buffer gas phase is first passed into the first-stage compression and separation unit, compressed to 0.2-0.25 MPa by the compression unit 521, and then passed into the separation tank 523 through the condensation unit 522. The condensed water phase separated by the separation tank 523 is returned to the buffer tank 51, and the separated gas phase is passed into the compression unit 521 in the second-stage compression and separation unit 52, and the removed liquid hydrocarbons enter the separation tank 523 of the second-stage compression and separation unit. The separated gas phase is compressed to 0.4-0.7 MPa by the compression unit 521 in the second-stage compression and separation unit 52, and then enters the separation tank 523 through the condensation unit 522. The condensed water phase separated by the separation tank 523 is returned to the hydrocarbon-water separator 42, and the separated gas phase is passed to the compression unit 521 in the third-stage compression and separation unit 52. The condensed oil phase produced by the condensation unit 522 in the second-stage compression and separation unit 52 is sent to the C6 removal distillation tower 53 for distillation treatment after heat exchange with the separated oil phase produced by the hydrocarbon-water separator 42 to obtain the first part of aromatics and light components below C5. The gas phase separated by the separation tank 523 of the second-stage compression separation unit is reduced to 0.9-1.2MPa by the compression unit 521 in the third-stage compression separation unit 52, and then enters the separation tank 523 after heat exchange and cooling and condensation unit 522. The condensed oil phase produced by the separation tank 523 of the third-stage compression separation unit is sent to the de-C4 distillation tower 59 for distillation treatment to obtain heavy components above C5 and light components below C4. The gas phase separated by the separation tank 523 of the third-stage compression separation unit is reduced to 1.7-2.3MPa by the compression unit 521 in the fourth-stage compression separation unit 52, and then enters the separation tank 523 after heat exchange and cooling and condensation. The gas phase and condensed oil phase produced by the separation tank 523 in the fourth-stage compression separation unit 52 are sent to the C3 removal distillation tower 54 for distillation treatment to obtain light components below C3 and the first part of liquefied petroleum gas; the light components below C3 are sent to the C2 removal distillation tower 55 for distillation treatment to obtain heavy components above C3 and light components of C2 and below; the heavy components above C3 are sent to the propylene distillation tower 56 for distillation treatment to obtain propylene and the second part of liquefied petroleum gas; a part of the liquefied petroleum gas is returned to the heat exchange material inlet of the first-stage heat exchanger 21 as part of the hydrocarbons; the light components of C2 and below are sent to the ethylene distillation tower 57 for distillation treatment to obtain ethylene.

[0061] The reaction liquid after the reaction in the low-carbon olefin reactor 10 in Example 1 was taken, and the components of the reaction liquid were analyzed and measured. The results are shown in Table 1.

[0062] Table 1

[0063]

[0064]

[0065] As shown in the results in Table 1, the methanol to low-carbon olefin system and method of the present invention, through the low-carbon olefin reactor unit, the dimethyl ether reactor unit, the heat exchange unit, the content of each component in the low-carbon olefin product gas prepared is within a reasonable range. It can be seen that the heat exchange unit of the present invention can realize the normal operation of the methanol to low-carbon olefin system while effectively saving energy consumption. In addition, the propylene product, ethylene product and other by-products prepared by the hydrocarbon separation unit also meet the standard process indicators: the propylene product produced is >99.60wt%, the ethylene product is ≥99.9vol.%, and the C3+C4 in the liquefied gas is ≥98v%. In addition, by pre-separation of the second-stage compression unit, the load of the third-stage compression unit can be reduced by 25%, by pre-separation of the second and third-stage compression units, the load of the fourth-stage compression unit can be reduced by 32%, and by pre-separation of the compression system, the total load of the de-C4 distillation tower and the de-C3 distillation tower can be reduced by 25%.

[0066] In summary, the present invention not only achieves the purpose of shortening the MTP process flow, but also reduces the heat load of the quenching system and the heating system, reduces the power consumption of the compressor and the steam consumption, and reduces the energy consumption of the entire methanol to low-carbon olefin system through the rational use of the waste heat generated in the heat exchange unit and the process water purification unit; it also reduces the difficulty of process operation, and ultimately achieves the purpose of reducing equipment manufacturing costs and device operating costs. In addition, under the above-mentioned energy-saving conditions, the content of each component in the low-carbon olefin product gas prepared by the reaction unit is within a reasonable range, and each separated product also meets the standard process indicators. The methanol to low-carbon olefin system and method described in the present invention are used for industrial production, which has great prospects.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A methanol to light olefins system, characterized in that: include: A light olefin reactor (10) having a light olefin product gas outlet; the light olefin reactor (10) is used to react a dimethyl ether / hydrocarbon mixture to obtain a light olefin product gas; A heat exchange unit (20) comprises a primary heat exchanger (21), a secondary heat exchanger (22), a tertiary heat exchanger (23) and a quaternary heat exchanger (24) connected in sequence by heat exchange medium channels, wherein the heat exchange medium channel inlet of the primary heat exchanger (21) is connected to the light olefin product gas outlet, and the heat exchange material outlet of the primary heat exchanger (21) is connected to the inlet of the light olefin reactor (10); the heat exchange material inlet of the quaternary heat exchanger (24) is used to introduce refined methanol, and the heat exchange material outlet of the quaternary heat exchanger (24) is connected to the heat exchange material inlet of the secondary heat exchanger (22); a dimethyl ether reactor (30) having a methanol inlet and a dimethyl ether outlet, wherein the methanol inlet is connected to the heat exchange material outlet of the secondary heat exchanger (22), and the dimethyl ether outlet is connected to the heat exchange material inlet of the primary heat exchanger (21); the dimethyl ether reactor (30) is used to react methanol to obtain a dimethyl ether product; A process water purification unit (40) having a process water inlet, a light olefin product gas inlet, a gaseous hydrocarbon outlet (401), a recovered methanol outlet (402) and a recovered hydrocarbon outlet (403), wherein the light olefin product gas inlet is connected to the heat exchange medium channel outlet of the four-stage heat exchanger (24), and the recovered methanol outlet (402) is connected to the heat exchange material inlet of the two-stage heat exchanger (22); the process water purification unit (40) is used to perform process water purification on the light olefin product gas discharged from the four-stage heat exchanger (24) after heat exchange to obtain gaseous hydrocarbons, recovered methanol and recovered hydrocarbons; A hydrocarbon separation unit (50) is connected to the gaseous hydrocarbon outlet (401), and the hydrocarbon separation unit (50) is used to separate the gaseous hydrocarbons to obtain aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas.

2. The methanol to light olefins system according to claim 1, characterized in that: The process water purification unit (40) comprises: The flash tank (41) has the process water inlet, the light olefin product gas inlet, the gaseous hydrocarbon outlet (401), the recovered hydrocarbon inlet and the flash liquid phase outlet; the flash tank (41) is used to mix the light olefin product gas after heat exchange with the process water and flash evaporate it to obtain a flash liquid phase and the gaseous hydrocarbon; The hydrocarbon-water separator (42) has a flash liquid phase inlet, a separated water phase outlet (404) and a separated oil phase outlet (405), wherein the flash liquid phase inlet is connected to the flash liquid phase outlet, and the separated water phase outlet (404) is connected to the process water inlet of the flash tank (41); the hydrocarbon-water separator (42) is used to perform hydrocarbon-water separation treatment on the flash liquid phase to obtain a separated water phase and a separated oil phase; The first process water purification tower (43) has a separated water phase inlet (406), the recovered methanol outlet (402) and a methanol-removed water phase outlet (407); the separated water phase inlet (406) is connected to the separated water phase outlet (404); the first process water purification tower (43) is used to remove methanol from the separated water phase to obtain the recovered methanol and the methanol-removed water phase; The second process water purification tower (44) has a methanol removal water phase inlet (408), the recovered hydrocarbons outlet (403) and a purified water outlet (409), wherein the methanol removal water phase inlet (408) is connected to the methanol removal water phase outlet (407), and the recovered hydrocarbons outlet (403) is connected to the recovered hydrocarbons inlet of the flash tank (41); the second process water purification tower (44) is used to remove hydrocarbons from the methanol removal water phase to obtain the recovered hydrocarbons and purified water.

3. The methanol to light olefins system according to claim 2, characterized in that: The purified water outlet (409) is in communication with the heat exchange material inlet of the three-stage heat exchanger (23); the process water purification unit (40) further comprises: a first heater (45), which is in communication with a heat exchange material outlet of the three-stage heat exchanger (23), and the first heater (45) is used to heat the purified water after heat exchange in the three-stage heat exchanger (23) to form process steam; a process steam tank (46) having a process steam inlet, a first process steam outlet and a second process steam outlet, wherein the process steam inlet is connected to the outlet of the first heater (45); a second heater (47), connected to the first process steam outlet, for further heating the process steam to a temperature required by the light olefin reactor (10), wherein the outlet of the second heater (47) is connected to the inlet of the light olefin reactor (10); The fifth heat exchanger (48) is arranged in the bottom of the first process water purification tower (43), and the inlet and outlet of the heat exchange material channel are respectively connected to the bottom outlet and the bottom reflux port of the first process water purification tower (43); the heat exchange medium channel of the fifth heat exchanger (48) is connected to the second process steam outlet.

4. The methanol to light olefins system according to claim 3, characterized in that: The bottom of the second process water purification tower (44) also has a heat medium inlet, which is also connected to the second process steam outlet; a third heater (49) is also provided on the pipeline connecting the separated water phase outlet (404) and the process water inlet of the flash tank (41); the separated water phase inlet (406) is connected to the pipe section located between the third heater (49) and the separated water phase outlet (404).

5. The methanol to light olefins system according to claim 2, characterized in that: The hydrocarbon separation unit (50) comprises: A buffer compression unit, used for buffering and compressing the gaseous hydrocarbons and pre-separating them to form hydrocarbons to be distilled; A distillation unit, used for distilling and separating the hydrocarbons to be distilled to obtain the aromatic hydrocarbons, the ethylene, the propylene and the liquefied petroleum gas; Preferably, the buffer compression unit comprises: A buffer tank (51) having a gaseous hydrocarbon inlet, a buffer gas phase outlet and a buffer phase outlet, wherein the gaseous hydrocarbon inlet is connected to the gaseous hydrocarbon outlet (401), and the buffer tank (51) is used to buffer the gaseous hydrocarbon to obtain a buffer gas phase and a buffer phase; the hydrocarbon-water separator (42) also has a buffer phase inlet, and the buffer phase outlet is connected to the buffer phase inlet; The multi-stage compression and separation units are connected in sequence and are used to perform multi-stage compression and separation on the buffer gas phase to obtain the hydrocarbon to be distilled; Preferably, the multi-stage compression and separation unit comprises four stages of compression and separation units (52) connected in sequence, and each stage of the compression and separation unit (52) comprises a compression unit (521), a condensation unit (522) and a separation tank (523) connected in sequence; wherein, in the order of material flow, The buffer gas phase outlet is connected to the compression unit (521) in the first-stage compression separation unit (52); The separation tank (523) has a gas phase outlet, a condensed water phase outlet and a condensed oil phase outlet, and in two adjacent stages of the compression separation units (52), the gas phase outlet of the separation tank (523) located upstream is connected to the compression unit (521) located downstream; The condensed water phase outlet of the separation tank (523) in the first-stage compression separation unit (52) is connected to the buffer tank (51), and the condensed water phase outlets of the separation tanks (523) in the second, third and fourth-stage compression separation units (52) are all connected to the buffer phase inlet of the hydrocarbon-water separator (42); The condensed oil phase outlet of the separation tank (523) in the first-stage compression separation unit (52) is connected to the separation tank (523) in the second-stage compression separation unit (52); the condensed oil phase outlet of the separation tank (523) in the second, third and fourth-stage compression separation units (52) is connected to the distillation unit.

6. The methanol to light olefins system according to claim 5, characterized in that: The hydrocarbon to be distilled includes the condensed oil phase produced by the separation tank (523) in the second, third and fourth stage compression separation units (52), the gas phase produced by the separation tank (523) in the fourth stage compression separation unit (52), and the separated oil phase produced by the separated oil phase outlet (405) of the hydrocarbon-water separator (42); the distillation unit includes: A C6-removing distillation tower (53) having a first distillation inlet, a first tower bottom outlet and a first tower top outlet, wherein the first distillation inlet is connected to the condensed oil phase outlet of the separation tank (523) in the second-stage compression separation unit (52), and the first distillation inlet is also connected to the separated oil phase outlet (405) of the hydrocarbon-water separator (42); the C6-removing distillation tower (53) is used for distilling and producing the first part of the aromatic hydrocarbons and light components below C5; A C3-removing distillation tower (54) having a second distillation inlet, a second tower bottom outlet and a second tower top outlet, wherein the second distillation inlet is respectively connected to the gas phase outlet and the condensed oil phase outlet of the separation tank (523) in the fourth-stage compression separation unit (52); the C3-removing distillation tower (54) is used for distilling and outputting light components below C3 and the first part of the liquefied petroleum gas; a C2-removing distillation tower (55) having a third distillation inlet, a third tower bottom outlet and a third tower top outlet, wherein the third distillation inlet is connected to the second tower top outlet, and the C2-removing distillation tower (55) is used for distilling and outputting heavy components above C3 and light components below C2; A propylene distillation tower (56) having a fourth distillation inlet, a fourth tower bottom outlet and a fourth tower top outlet, wherein the fourth distillation inlet is connected to the third tower bottom outlet, and the propylene distillation tower (56) is used for distilling the propylene and the second part of the liquefied petroleum gas; the third tower bottom outlet is also connected to the heat exchange material inlet of the primary heat exchanger (21); The ethylene distillation tower (57) has a fifth distillation inlet, a fifth tower bottom outlet and a fifth tower top outlet, wherein the fifth distillation inlet is connected to the fourth tower top outlet, and the ethylene distillation tower (57) is used for distilling and producing the ethylene.

7. The methanol to light olefins system according to claim 6, characterized in that: The distillation unit also includes: a C5-removing distillation tower (58) having a sixth distillation inlet, a sixth tower bottom outlet and a sixth tower top outlet, wherein the sixth distillation inlet is in communication with the first tower top outlet, and the sixth tower top outlet is in communication with the heat exchange material inlet of the primary heat exchanger (21); the C5-removing distillation tower (58) is used for distilling and producing the second part of the aromatic hydrocarbons and C5-C6 circulating hydrocarbons, and the sixth tower top outlet is used for returning the C5-C6 circulating hydrocarbons to the heat exchange material inlet of the primary heat exchanger (21); a C4 removal distillation tower (59) having a seventh distillation inlet, a seventh tower bottom outlet and a seventh tower top outlet, wherein the seventh distillation inlet is connected to the condensed oil phase outlet of the separation tank (523) in the third stage compression separation unit (52), the seventh tower bottom outlet is connected to the sixth distillation inlet of the C5 removal distillation tower (58), and the seventh tower top outlet is connected to the second distillation inlet of the C3 removal distillation tower (54); the C4 removal distillation tower (59) is used for distilling and outputting heavy components above C5 and light components below C4; A C2 and lower light component condenser (60), arranged on the flow path where the third tower top outlet of the de-C2 distillation tower (55) is located, for condensing the C2 and lower light components; A C2 and below light component buffer tank (61) having a gas phase outlet and a liquid phase outlet, wherein the C2 and below light component buffer tank (61) is connected to the outlet of the C2 and below light component condenser (60), and the C2 and below light component buffer tank (61) is used to buffer the condensed C2 and below light components to obtain a gas phase and a liquid phase; a C1-removing distillation tower (62) having an eighth distillation inlet, an eighth tower bottom outlet and an eighth tower top outlet, wherein the eighth distillation inlet is connected to the liquid phase outlet, and the eighth tower bottom outlet is connected to the fifth distillation inlet of the ethylene distillation tower (57); a gas phase inlet is also provided at the top of the C1-removing distillation tower (62), and the gas phase outlet is respectively connected to the gas phase inlet and the heat exchange material inlet of the primary heat exchanger (21); the C1-removing distillation tower (62) is used for distilling and producing fuel gas and C2 heavy components; Preferably, a reflux port is further provided in the middle of the C1 removal distillation tower (62), and the fifth bottom outlet of the ethylene distillation tower (57) is connected to the reflux port; The multi-stage compression separation unit also includes: A sixth heat exchanger (63), whose heat exchange medium channel is arranged on the pipeline between the compression unit (521) and the condensation unit (522) in the third-stage compression and separation unit (52), and whose heat exchange material channel is arranged on the pipeline between the condensed oil phase outlet of the separation tank (523) in the second-stage compression and separation unit (52) and the first distillation inlet of the C6 removal distillation tower (53); The seventh heat exchanger (64) has a heat exchange medium channel arranged on the pipeline between the compression unit (521) and the condensation unit (522) in the fourth-stage compression separation unit (52), and a heat exchange material channel arranged on the pipeline between the condensed oil phase outlet of the separation tank (523) in the third-stage compression separation unit (52) and the seventh distillation inlet of the de-C4 distillation tower (59).

8. A method for preparing light olefins from methanol, characterized in that: The methanol to light olefins system according to any one of claims 1 to 7, the method comprising the following steps: Reaction of a dimethyl ether / hydrocarbon mixture in a light olefin reactor (10) to obtain a light olefin product gas; In a heat exchange unit (20), the light olefin product gas is used as a heat exchange medium to perform four-stage heat exchange to obtain the light olefin product gas after heat exchange; The light olefin product gas after heat exchange is subjected to process water purification treatment in a process water purification unit (40) to obtain gaseous hydrocarbons, recover methanol and recover hydrocarbons; Separating the gaseous hydrocarbons by a hydrocarbon separation unit (50) to obtain aromatic hydrocarbons, ethylene, propylene and liquefied petroleum gas; The heat exchange unit (20) comprises a primary heat exchanger (21), a secondary heat exchanger (22), a tertiary heat exchanger (23) and a quaternary heat exchanger (24) which are sequentially connected by heat exchange medium channels, and the method further comprises: After passing the refined methanol into the heat exchange material channel of the fourth-stage heat exchanger (24) to exchange heat with the light olefin product gas, it is then passed together with the recovered methanol into the heat exchange material channel of the second-stage heat exchanger (22) to exchange heat with the light olefin product gas again to obtain a methanol feedstock; The methanol raw material is passed into a dimethyl ether reactor (30) for reaction to obtain a dimethyl ether product; a dimethyl ether / hydrocarbon mixture formed by the dimethyl ether product and hydrocarbon is passed into the heat exchange material channel of the primary heat exchanger (21) for heat exchange with the light olefin product gas, and then passed into the light olefin reactor (10) for reaction; Preferably, the process water purification step comprises: Mixing the light olefin product gas after heat exchange with process water in a flash tank (41) and flashing to obtain a flash liquid phase and the gaseous hydrocarbons; The flash liquid phase is subjected to hydrocarbon-water separation treatment in a hydrocarbon-water separator (42) to obtain a separated water phase and a separated oil phase; The separated aqueous phase is subjected to a methanol removal treatment in a first process water purification tower (43) to obtain the recovered methanol and the methanol-removed aqueous phase; The methanol-removed aqueous phase is treated to remove hydrocarbons in a second process water purification tower (44) to obtain the recovered hydrocarbons and purified water, and the recovered hydrocarbons are returned to the flash tank (41).

9. The method for preparing light olefins from methanol according to claim 8, characterized in that: The method further comprises: Passing the purified water into the heat exchange material channel of the three-stage heat exchanger (23) to exchange heat with the light olefin product gas, and heating the purified water after the heat exchange by using a first heater (45) to form process steam and send it to a process steam tank (46); further heating the first part of the process steam to a temperature required by the light olefin reactor (10), and then feeding the first part into the light olefin reactor (10); exchanging heat with the methanol-removed aqueous phase in the fifth heat exchanger (48) to heat and reflux the methanol-removed aqueous phase; Preferably, a third portion of the process steam is introduced into the second process water purification tower (44) as a heat medium; Preferably, a portion of the separated aqueous phase is heated in a third heater (49) and then returned to the flash tank (41) as the process water; Preferably, the step of separating the gaseous hydrocarbons using the hydrocarbon separation unit (50) comprises: The gaseous hydrocarbons are buffer-compressed and pre-separated by a buffer compression unit to form hydrocarbons to be rectified; the hydrocarbons to be rectified are rectified and separated by the rectifier unit to obtain the aromatic hydrocarbons, the ethylene, the propylene and the liquefied petroleum gas; Preferably, the buffer compression unit comprises: buffering the gaseous hydrocarbons in a buffer tank (51) to obtain a buffer gas phase and a buffer phase; passing the buffer phase into the hydrocarbon-water separator (42); performing multi-stage compression and separation on the buffer gas phase in a multi-stage compression and separation unit to obtain the hydrocarbons to be distilled; More preferably, the multi-stage compression separation unit comprises four stages of compression separation units (52) connected in sequence, and each stage of the compression separation unit (52) comprises a compression unit (521), a condensation unit (522) and a separation tank (523) connected in sequence; wherein the buffer gas phase is introduced into the compression unit (521) in the first stage of the compression separation unit (52); in the two adjacent stages of the compression separation units (52), the gas phase separated by the separation tank (523) located upstream is introduced into the compression unit (521) located downstream; the gas phase separated by the separation tank (523) in the first stage of the compression separation unit (52) is introduced into the compression unit (521) located downstream; The condensed water phase separated by the separation tank (523) is returned to the buffer tank (51), and the condensed water phase separated by the separation tanks (523) in the second, third and fourth stages of the compression separation unit (52) is returned to the hydrocarbon-water separator (42); the condensed oil phase separated by the separation tank (523) in the first stage of the compression separation unit (52) is sent to the separation tank (523) in the second stage of the compression separation unit (52), and the condensed oil phase separated by the separation tanks (523) in the second, third and fourth stages of the compression separation unit (52) is sent to the distillation unit; Preferably, the hydrocarbon to be distilled includes the condensed oil phase produced by the separation tank (523) in the second, third and fourth stage compression separation units (52), the gas phase produced by the separation tank (523) in the fourth stage compression separation unit (52), and the separated oil phase produced by the separated oil phase outlet (405) of the hydrocarbon-water separator (42); the distillation separation step includes: The condensed oil phase produced by the separation tank (523) in the second stage compression separation unit (52) and the separated oil phase produced by the hydrocarbon-water separator (42) are sent to a C6 removal distillation tower (53) for distillation treatment to obtain the first part of aromatic hydrocarbons and light components below C5; The gas phase and condensed oil phase produced by the separation tank (523) in the fourth stage compression separation unit (52) are sent to a C3 removal distillation tower (54) for distillation treatment to obtain light components below C3 and the first part of the liquefied petroleum gas; the light components below C3 are sent to a C2 removal distillation tower (55) for distillation treatment to obtain heavy components above C3 and light components of C2 and below; The C3 and above heavy components are sent to a propylene distillation tower (56) for distillation treatment to obtain the propylene and the second part of the liquefied petroleum gas; a part of the liquefied petroleum gas is returned to the heat exchange material inlet of the primary heat exchanger (21) as part of the hydrocarbon; The C2 and lower light components are sent to an ethylene distillation tower (57) for distillation to obtain the ethylene.

10. The method for preparing light olefins from methanol according to claim 9, characterized in that: The distillation separation step also includes: The light components below C5 are sent to a C5 removal distillation tower (58) for distillation treatment to obtain the second part of aromatic hydrocarbons and C5-C6 circulating hydrocarbons; the C5-C6 circulating hydrocarbons are returned to the heat exchange material inlet of the primary heat exchanger (21); The condensed oil phase produced by the separation tank (523) in the third stage compression separation unit (52) is sent to a C4 removal distillation tower (59) for distillation treatment to obtain heavy components above C5 and light components below C4; the heavy components above C5 are returned to the C5 removal distillation tower (58); and the light components below C4 are sent to the C3 removal distillation tower (54); Before the C2 and lower light components are fed into the ethylene distillation tower (57), the C2 and lower light components are first condensed in a C2 and lower light component condenser (60), and the condensed C2 and lower light components are buffered in a C2 and lower light component buffer tank (61) to obtain a gas phase and a liquid phase; the liquid phase is fed into a C1 removal distillation tower (62) for distillation to obtain fuel gas and C2 heavy components; and a portion of the gas phase is fed into the C1 removal distillation tower (62) from the upper portion of the C1 removal distillation tower (62), and another portion of the gas phase is returned to the heat exchange material inlet of the primary heat exchanger (21); the C2 heavy components are fed into the ethylene distillation tower (57) for distillation to obtain the ethylene; Preferably, the bottom material of the ethylene distillation tower (57) is refluxed into the C1 removal distillation tower (62); Preferably, after the refined methanol is pressurized to 0.5-0.8 MPa, it is introduced into the fourth-stage heat exchanger (24) for heat exchange to 120-150° C.; the refined methanol after heat exchange is heat exchanged to 260-300° C. together with the recovered methanol in the second-stage heat exchanger (22); the reaction pressure in the dimethyl ether reactor (30) is 0.5-0.8 MPa, the reaction temperature is 350-380° C., and the catalyst required for the reaction is a solid acid catalyst; preferably, the solid acid catalyst is at least one of a supported heteropoly acid solid acid catalyst, an alumina solid acid catalyst and a molecular sieve solid acid catalyst; Preferably, the temperature of the light olefin product gas obtained by the reaction of the light olefin reactor (10) is 480-500° C., the catalyst required for the reaction of the light olefin reactor (10) is ZSM-5 zeolite molecular sieve, and the reaction pressure of the light olefin reactor (10) is 0.03-0.15 MPa; the temperature of the dimethyl ether / hydrocarbon mixture after heat exchange in the primary heat exchanger (21) is 450-460° C.; the temperature of the purified water produced by the second process water purification tower (44) is 100 ~120℃, the pressure is 0.3~0.5MPa, the temperature of the purified water after heat exchange in the three-stage heat exchanger (23) is 131~140℃; the temperature of the low-carbon olefin product gas after heat exchange in the first-stage heat exchanger (21) is 380~400℃, the temperature after heat exchange in the second-stage heat exchanger (22) is 350~360℃, the temperature after heat exchange in the third-stage heat exchanger (23) is 210~230℃, and the temperature after heat exchange in the fourth-stage heat exchanger (24) is 90~100℃; Preferably, the temperature of the separated water phase produced in the hydrocarbon-water separator (42) is 60-75° C., and the temperature of the process steam entering the light olefin reactor (10) is 430-440° C.; In the four-stage compression and separation unit (52), the pressure of the first stage compression is 0.2-0.25 MPa, the pressure of the second stage compression is 0.4-0.7 MPa, the pressure of the third stage compression is 0.9-1.2 MPa, and the pressure of the fourth stage compression is 1.7-2.3 MPa.

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