阅读说明：本技术 一种氢气单膨胀循环丙烷脱氢混合气体低温分离装置及使用方法 (Hydrogen single-expansion-cycle propane dehydrogenation mixed gas low-temperature separation device and use method ) 是由 孙石桥 韩一松 秦燕 王定伟 张宽 许路军 叶文良 林彬彬 于 2020-12-31 设计创作，主要内容包括：一种氢气单膨胀循环丙烷脱氢混合气体低温分离装置,它包括三组板翅式换热器、两台气液分离器、一台闪蒸罐D1、一台膨胀机组ET1、一台液体泵P1和若干台阀门等组成的低温分离系统,所述两台气液分离器分别为一级气液分离器V1和二级气液分离器V2,本发明有效降低了氢烃比,裂解反应温度可以降低,可提高裂解反应的单程转化率,反应产物压力有效降低,反应产物进低温分离系统的压力为～1.0MPa(G),比目前运行的类似装置低0.2 MPa,REC压缩机能耗降低约～9%,工艺流程简单,相对于已投运的丙烷脱氢装置的低温分离系统采用的高低压串联膨胀工艺,该方法为单膨胀循环膨胀制冷工艺,投资成本低,操作维护简单。(A hydrogen single expansion cycle propane dehydrogenation mixed gas low-temperature separation device comprises a low-temperature separation system consisting of three groups of plate-fin heat exchangers, two gas-liquid separators, a flash tank D1, an expansion unit ET1, a liquid pump P1, a plurality of valves and the like, wherein the two gas-liquid separators are a primary gas-liquid separator V1 and a secondary gas-liquid separator V2 respectively, the hydrogen-hydrocarbon ratio is effectively reduced, the cracking reaction temperature can be reduced, the one-way conversion rate of the cracking reaction can be improved, the pressure of reaction products is effectively reduced, the pressure of the reaction products entering the low-temperature separation system is-1.0 MPa (G), the pressure is 0.2 MPa lower than that of a similar device operated at present, the energy consumption of an REC compressor is reduced by about-9 percent, the process flow is simple, and the method is a single expansion cycle expansion refrigeration process compared with a high-low pressure series expansion process adopted by a low-temperature separation system of a propane dehydrogenation device already put into, the investment cost is low, and the operation and maintenance are simple.)

1. A hydrogen single expansion circulation propane dehydrogenation mixed gas low-temperature separation device comprises three groups of plate-fin heat exchangers, two gas-liquid separators, a flash tank D1, an expander set ET1, a liquid pump P1, a low-temperature separation system composed of a plurality of valves and the like, and is characterized in that the three groups of plate-fin heat exchangers are respectively a first plate-fin heat exchanger E1, a second plate-fin heat exchanger E2 and a third plate-fin heat exchanger E3, the two gas-liquid separators are respectively a first-stage gas-liquid separator V1 and a second-stage gas-liquid separator V2, the first plate-fin heat exchanger E1, the second plate-fin heat exchanger E2 and the third plate-fin heat exchanger E3 are mutually connected through pipelines, a first-stage gas-liquid separator V1 is arranged between the first plate-fin heat exchanger E1 and the second plate-fin heat exchanger E2, the second plate-fin heat exchanger E2 is respectively connected with the second-stage gas-liquid separator V2 and the expander set ET1, the third plate-fin heat exchanger E3 is respectively connected with a liquid pump P1 and a flash tank D1.

2. The use method of the hydrogen single expansion cycle propane dehydrogenation mixed gas low-temperature separation device according to claim 1 comprises the following steps: the method is characterized by comprising the following steps:

the reaction product pressurized to 1.0MPa (G) is cooled to-25 to-27 ℃ by a first plate-fin heat exchanger E1 and then partially condensed to form a gas-liquid mixture flow, and the gas-liquid mixture flow enters a first-stage gas-liquid separator V1; the gas flow separated by the first-stage gas-liquid separator V1 enters a second plate-fin heat exchanger E2, is further cooled to the temperature of between-110 and-115 ℃ in a second plate-fin heat exchanger E2, and is partially condensed to form a gas-liquid mixture flow which enters a second-stage gas-liquid separator V2;

the gas material flow separated by the secondary gas-liquid separator V2 returns to the second plate-fin heat exchanger E2 for reheating to-100 to-105 ℃ for recovering cold; the superheated gas stream after reheating is expanded in an isentropic way by an expansion unit ET1, the pressure is expanded from 0.96MPa (G) to 0.55MPa (G), and the temperature of the expanded gas stream is-120 to-125 ℃; the expanded material flow is divided into three paths, one path of gas material flow and the other path of gas material flow;

the gas stream is throttled across a valve and depressurized to a first pressure (as low as possible depending on heat exchange balance) to form a gas stream; the liquid material flow separated by the secondary gas-liquid separator V2 is divided into two paths, namely one path of liquid material flow and the other path of liquid material flow, and the liquid material flows are throttled and decompressed to a first pressure (the pressure is as low as possible according to heat exchange balance) through a valve to form a liquid material flow;

the gas material flow and the liquid material flow are mixed under the first pressure to form a refrigerating material flow, the refrigerating material flow returns to the second plate-fin heat exchanger E2 to be reheated to-28 to-33 ℃, and the refrigerating material flow is led out to obtain a refrigerating material flow;

the gas stream is throttled by a valve and depressurized to a second pressure (determined by the on-way resistance according to the reaction pressure) to form recycle hydrogen; the gas material flow is reheated to-28 to-33 ℃ through a second plate-fin heat exchanger E2 to obtain a gas material flow, and then reheated to 35 to 40 ℃ through a first plate-fin heat exchanger E1 to be discharged from a low-temperature separation system to be used as a dry gas product for a downstream process; the liquid propane with the temperature of-40 ℃ is pre-cooled to-23 to-26 ℃ through a third plate-fin heat exchanger E3 to obtain further-cooled liquid propane, the liquid propane is divided into two paths, one path is a liquid material flow accounting for 90-93% of the total flow of the liquid propane, the other path is a liquid material flow accounting for 7-10% of the total flow of the liquid propane, the liquid material flow enters a second plate-fin heat exchanger E2 to be cooled to-110 to-115 ℃, the liquid material flow is led out to obtain a liquid material flow, the liquid material flow is throttled and decompressed to a second pressure (determined according to reaction pressure and along-path resistance), the decompressed liquid material flow is mixed with circulating hydrogen, a premixed combined feed material flow is formed after mixing, the premixed combined feed material flow returns to the second plate-fin heat exchanger E2 to be reheated to-28 to-33 ℃, cold energy is recycled, and the liquid material;

the liquid material flows through a valve for throttling and reducing pressure to a third pressure (determined according to reaction pressure and along-path resistance), then the liquid material flow is formed, the liquid material flow and the reheated material flow are mixed to form combined feed, the combined feed enters a first plate-fin heat exchanger E1 and is reheated to 35-40 ℃, the combined feed is discharged from a low-temperature separation system and serves as a combined feed heat removal combined heat exchange and cracking reaction unit to form a reaction product, and the reaction product is returned to the low-temperature separation system after being subjected to heat exchange by a heat combined heat exchanger and compressed to-1.0 MPa (G) by an REC compressor;

throttling and decompressing all liquid separated by the first-stage gas-liquid separator V1 to 0.3-0.37 MPa (G) through a valve to obtain a gas-liquid mixture flow, entering a flash tank D1, throttling and decompressing one path of liquid flow 15 separated by the second-stage gas-liquid separator V2 to 0.32-0.38 MPa (G) through a valve to obtain a liquid flow, reheating the liquid flow through a second plate-fin heat exchanger E2 to-28-33 ℃ to obtain a liquid flow, and entering the flash tank D1; liquid separated from the flash tank D1 at the temperature of minus 30 ℃ is pressurized to 3.9-4.1 MPa (G) by a liquid pump P1 to obtain a liquid product, the liquid product enters a third plate-fin heat exchanger E3 and is reheated to the temperature of 35-40 ℃, and the liquid product is discharged from a low-temperature separation system and is sent to a downstream process as a liquid product; in order to balance the heat loads of the first plate-fin heat exchanger E1 and the third plate-fin heat exchanger E3 and improve the adjustability of cold quantity distribution, the refrigeration material flow is divided into two paths, one path of material flow and the other path of material flow; reheating the material flow through a first plate-fin heat exchanger E1 to form a gas flow which flows out of the low-temperature separation system; the gas separated from the flash tank D1 is throttled by a valve and decompressed to fourth pressure (the pressure is as low as possible according to the pressure balance of the system) to obtain a gas material flow, the gas material flow and the material flow are mixed to form a gas material flow, the gas material flow enters a third plate-fin heat exchanger E3 and is reheated to 35-40 ℃ to form a gas material flow out of the low-temperature separation system, the gas material flow and the gas material flow are converged to form a flash material flow, the flash material flow and a reaction product are mixed to enter an REC compressor for compression and then return to the low-temperature separation system for circulating heat exchange and separation, and the flash material flow and the reaction product are compressed by the REC compressor and then return to the low-temperature.

Technical Field

The invention relates to the technical field of low-temperature separation of mixed gas after catalytic cracking reaction of low-carbon alkane, and is suitable for a low-temperature separation process for effectively separating reaction products in a device for preparing propylene by dehydrogenation of propane with low hydrogen-hydrocarbon ratio in a low-temperature environment.

Background

The invention is suitable for a device for preparing propylene by propane catalytic dehydrogenation (propane dehydrogenation for short), and the process for preparing propylene by propane dehydrogenation comprises catalytic cracking reaction, product compression, low-temperature separation, product refining and the like, wherein a low-temperature separation system is a key link for ensuring the normal operation of upstream and downstream product separation units and the product quality.

Main chemical reaction equation of propane dehydrogenation cracking reaction:

C₃H₈ (g)→C₃H₆(g)+H₂(g) + Q (irreversible, strongly endothermic chemical reaction)

The formula of the main chemical reaction of propane dehydrogenation is combined with the chemical reaction kinetics principle, and the hydrogen-hydrocarbon ratio of the reaction is required to be reduced in order to improve the per-pass conversion rate of the reaction as much as possible; to prolong the service life of the catalyst, the cracking reaction temperature needs to be reduced, and the hydrogen-hydrocarbon ratio of the reaction also needs to be reduced; therefore, the aim of continuously optimizing and perfecting the process of the propane dehydrogenation device is to effectively reduce the hydrogen-hydrocarbon ratio of the cracking reaction.

The low-temperature separation system mainly aims to separate the mixed gas after dehydrogenation reaction, and fully separate propane, propylene and hydrogen components by utilizing physical cooling to obtain propane and propylene liquid products, dry gas products and the like. The hydrogen-hydrocarbon ratio (molar ratio of hydrogen to propane) of a propane dehydrogenation device which is put into operation and similar to the process is not less than 0.5 at present, and the hydrogen-hydrocarbon ratio is influenced by a low-temperature separation method of a low-temperature separation system matched with the propane dehydrogenation device; but is not beneficial to improving the conversion per pass of the propane dehydrogenation cracking reaction, reducing the temperature of the cracking reaction and reducing the power consumption of the REC compressor. Through research and analysis, the mixed gas low-temperature separation method which can flexibly adjust and reduce the hydrogen-hydrocarbon ratio (less than or equal to 0.25 and can be adjusted according to reaction conditions), has low outlet pressure of an REC compressor (energy consumption is reduced by 9 percent), less equipment (hydrogen single expansion circulation), high refrigeration heat exchange efficiency and large adjustment margin is specially designed according to the principles of mixed cooling of hydrogen, propane and propylene and combination of the principle of reducing the hydrogen-hydrocarbon ratio and being favorable for catalytic cracking reaction.

Disclosure of Invention

The invention aims to provide the low-energy-consumption hydrogen single-expansion circulation propane dehydrogenation mixed gas low-temperature separation method which has the advantages of simple process flow, less unit equipment, low energy consumption, high refrigeration heat exchange efficiency, simple operation, convenient maintenance and less investment; in order to realize the high-efficiency preparation and reasonable distribution of the cold quantity and reduce the investment and the operation cost, the invention adopts the following technical scheme: a low-temperature separation device for a hydrogen single-expansion circulation propane dehydrogenation mixed gas comprises a low-temperature separation system consisting of three groups of plate-fin heat exchangers, two gas-liquid separators, a flash tank D1, an expander set ET1, a liquid pump P1, a plurality of valves and the like, wherein the three groups of plate-fin heat exchangers are respectively a first plate-fin heat exchanger E1, a second plate-fin heat exchanger E2 and a third plate-fin heat exchanger E3, the two gas-liquid separators are respectively a first-stage gas-liquid separator V1 and a second-stage gas-liquid separator V2, the first plate-fin heat exchanger E1, the second plate-fin heat exchanger E2 and the third plate-fin heat exchanger E3 are mutually connected through pipelines, a first-stage gas-liquid separator V1 is arranged between the first plate-fin heat exchanger E1 and the second plate-fin heat exchanger E2, the second plate-fin heat exchanger E2 is respectively connected with the second-stage gas-liquid separator V2 and the expander set ET1, the third plate-fin heat exchanger E3 is respectively connected with a liquid pump P1 and a flash tank D1.

A use method of a hydrogen single expansion cycle propane dehydrogenation mixed gas low-temperature separation device comprises the following steps: the method comprises the following steps:

the reaction product pressurized to 1.0MPa (G) is cooled to-25 to-27 ℃ by a first plate-fin heat exchanger E1 and then partially condensed to form a gas-liquid mixture flow, and the gas-liquid mixture flow enters a first-stage gas-liquid separator V1; the gas flow separated by the first-stage gas-liquid separator V1 enters a second plate-fin heat exchanger E2, is further cooled to the temperature of between-110 and-115 ℃ in a second plate-fin heat exchanger E2, and is partially condensed to form a gas-liquid mixture flow which enters a second-stage gas-liquid separator V2;

the gas stream 5 separated by the secondary gas-liquid separator V2 returns to the second plate-fin heat exchanger E2 for reheating to-100 to-105 ℃ for recovering cold; the superheated gas stream after reheating is expanded in an isentropic way by an expansion unit ET1, the pressure is expanded from 0.96MPa (G) to 0.55MPa (G), and the temperature of the expanded gas stream is-120 to-125 ℃; the expanded material flow is divided into three paths, one path of gas material flow and the other path of gas material flow;

the gas stream is throttled across a valve and depressurized to a first pressure (as low as possible depending on heat exchange balance) to form a gas stream; the liquid stream separated by the secondary gas-liquid separator V2 is divided into two streams, one liquid stream and one liquid stream, and the liquid stream is throttled by a valve and depressurized to a first pressure (the pressure is as low as possible according to the heat exchange balance) to form a liquid stream. The gas material flow and the liquid material flow are mixed under the first pressure to form a refrigerating material flow, the refrigerating material flow returns to the second plate-fin heat exchanger E2 to be reheated to-28 to-33 ℃, and the refrigerating material flow is led out to obtain a refrigerating material flow;

the gas stream is throttled by a valve and depressurized to a second pressure (determined by the on-way resistance according to the reaction pressure) to form recycle hydrogen; the gas material flow is reheated to-28 to-33 ℃ through a second plate-fin heat exchanger E2 to obtain a gas material flow, and then reheated to 35 to 40 ℃ through a first plate-fin heat exchanger E1 to be discharged from a low-temperature separation system to be used as a dry gas product for a downstream process;

the liquid propane with the temperature of-40 ℃ is pre-cooled to-23 to-26 ℃ through a third plate-fin heat exchanger E3 to obtain further-cooled liquid propane, the liquid propane is divided into two paths, one path is a liquid material flow accounting for 90-93% of the total flow of the liquid propane, the other path is a liquid material flow accounting for 7-10% of the total flow of the liquid propane, the liquid material flow enters a second plate-fin heat exchanger E2 to be cooled to-110 to-115 ℃, the liquid material flow is led out to obtain a liquid material flow, the liquid material flow is throttled and decompressed to a second pressure (determined according to reaction pressure and along-path resistance), the decompressed liquid material flow is mixed with circulating hydrogen, a premixed combined feed material flow is formed after mixing, the premixed combined feed material flow returns to the second plate-fin heat exchanger E2 to be reheated to-28 to-33 ℃, cold energy is recycled, and the liquid material;

the liquid material flows through a valve for throttling and reducing pressure to a third pressure (determined according to reaction pressure and along-path resistance), then the liquid material flow is formed, the liquid material flow and the reheated material flow are mixed to form combined feed, the combined feed enters a first plate-fin heat exchanger E1 and is reheated to 35-40 ℃, the combined feed is discharged from a low-temperature separation system and serves as a combined feed heat removal combined heat exchange and cracking reaction unit to form a reaction product, and the reaction product is returned to the low-temperature separation system after being subjected to heat exchange by a heat combined heat exchanger and compressed to-1.0 MPa (G) by an REC compressor;

throttling and decompressing all liquid separated by the first-stage gas-liquid separator V1 to 0.3-0.37 MPa (G) through a valve to obtain a gas-liquid mixture flow, entering a flash tank D1, throttling and decompressing one path of liquid separated by the second-stage gas-liquid separator V2 to 0.32-0.38 MPa (G) through the valve to obtain a liquid flow, reheating the liquid flow to-28-33 ℃ through a second plate-fin heat exchanger E2 to obtain a liquid flow, and entering the flash tank D1; liquid separated from the flash tank D1 at the temperature of minus 30 ℃ is pressurized to 3.9-4.1 MPa (G) by a liquid pump P1 to obtain a liquid product, the liquid product enters a third plate-fin heat exchanger E3 and is reheated to the temperature of 35-40 ℃, and the liquid product is discharged from a low-temperature separation system and is sent to a downstream process as a liquid product;

in order to balance the heat loads of the first plate-fin heat exchanger E1 and the third plate-fin heat exchanger E3 and improve the adjustability of cold quantity distribution, the refrigeration material flow is divided into two paths, one path of material flow and the other path of material flow; reheating the material flow through a first plate-fin heat exchanger E1 to form a gas flow which flows out of the low-temperature separation system;

the gas separated from the flash tank D1 is throttled by a valve and decompressed to fourth pressure (the pressure is as low as possible according to the pressure balance of the system) to obtain a gas material flow, the gas material flow and the material flow are mixed to form a gas material flow, the gas material flow enters a third plate-fin heat exchanger E3 and is reheated to 35-40 ℃ to form a gas material flow out of the low-temperature separation system, the gas material flow and the gas material flow are converged to form a flash material flow, the flash material flow and a reaction product are mixed to enter an REC compressor for compression and then return to the low-temperature separation system for circulating heat exchange and separation, and the flash material flow and the reaction product are compressed by the REC compressor and then return to the low-temperature.

The invention has the following application effects: the invention provides a low-temperature separation method for low-energy-consumption hydrogen single-expansion cycle propane dehydrogenation mixed gas, which has the following advantages compared with similar devices operated at present:

1. effectively reduces the hydrogen-hydrocarbon ratio (less than or equal to 0.25), can reduce the temperature of the cracking reaction, and can improve the conversion per pass of the cracking reaction.

2. The pressure of the reaction product is effectively reduced, the pressure of the reaction product entering a low-temperature separation system is-1.0 MPa (G), the pressure is 0.2 MPa lower than that of a similar device operated at present, and the energy consumption of an REC compressor is reduced by about-9%.

3. The process flow is simple: compared with a high-low pressure series expansion process adopted by a low-temperature separation system of a put-into-operation propane dehydrogenation device, the method is a single expansion circulation expansion refrigeration process, the investment cost is low, and the operation and maintenance are simple.

Drawings

FIG. 1 is a flow diagram of a low energy consumption hydrogen single expansion cycle cryogenic separation system of the present invention;

FIG. 2 is a flow diagram of another system for low energy consumption hydrogen single expansion cycle cryogenic separation according to the present invention;

fig. 3 is an upstream-downstream flow diagram associated with a low energy consumption hydrogen single expansion cycle cryogenic separation system of the present invention.

Detailed Description

The present invention will be described in further detail with reference to embodiments. A low-temperature separation device for a hydrogen single-expansion circulation propane dehydrogenation mixed gas comprises a low-temperature separation system consisting of three groups of plate-fin heat exchangers, two gas-liquid separators, a flash tank D1, an expander set ET1, a liquid pump P1, a plurality of valves and the like, wherein the three groups of plate-fin heat exchangers are respectively a first plate-fin heat exchanger E1, a second plate-fin heat exchanger E2 and a third plate-fin heat exchanger E3, the two gas-liquid separators are respectively a first-stage gas-liquid separator V1 and a second-stage gas-liquid separator V2, the first plate-fin heat exchanger E1, the second plate-fin heat exchanger E2 and the third plate-fin heat exchanger E3 are mutually connected through pipelines, a first-stage gas-liquid separator V1 is arranged between the first plate-fin heat exchanger E1 and the second plate-fin heat exchanger E2, the second plate-fin heat exchanger E2 is respectively connected with the second-stage gas-liquid separator V2 and the expander set ET1, the third plate-fin heat exchanger E3 is respectively connected with a liquid pump P1 and a flash tank D1, and a reaction unit and a compression unit in the propane dehydrogenation device are mutually associated and restricted with a low-temperature separation system; the so-called hydrogen to hydrocarbon ratio is: the molar ratio of hydrogen to propane in the combined feed from the cryogenic separation system to the reaction unit.

Precooling propane, carrying out deep cooling on part of propane, premixing propane with hydrogen, cooling and refrigerating, fully mixing propane with premixed material flow, cooling, gasifying and refrigerating; mixing propane/propylene with hydrogen, cooling, gasifying and refrigerating; and refrigerating in the process of hydrogen reheating expansion, and the like. The heat load is reasonably distributed, and the refrigeration and heat exchange process flow is optimized; the reaction product is sequentially subjected to primary heat exchange, cooling and separation and secondary heat exchange, cooling and separation; obtaining qualified gas and liquid products.

Specific example 1 (Dry gas product pressure meets downstream Process requirements, no pressurization is required), as shown in FIG. 1

The reaction product 1 with the pressure of 1.0MPa (G) and the temperature of 43 ℃ below zero is cooled to 27 ℃ below zero by a first plate-fin heat exchanger E1 and then partially condensed to form a gas-liquid mixture flow 2, the gas-liquid mixture flow 2 is separated to form a gas flow 3 by a first-stage gas-liquid separator V1, the gas flow 3 is further cooled to 113 ℃ below zero by a second plate-fin heat exchanger E2, and then partially condensed to form a gas-liquid mixture flow 4 which enters a second-stage gas-liquid separator V2.

The gas material flow 5 separated by the secondary gas-liquid separator V2 returns to the second plate-fin heat exchanger E2 for reheating to-100 ℃ and recovering cold energy; the superheated gas stream 6 after reheating is expanded in an isentropic way (the expansion work is recovered by a generator) through an expansion unit ET1, the pressure is expanded from 0.96MPa (G) to 0.55MPa (G), and the temperature of the expanded gas stream 7 is-120 ℃; the expanded stream 7 is divided into three paths, one path of gas stream 8, one path of gas stream 9 and one path of gas stream 10.

The gas stream 10 is throttled across a valve to a reduced pressure to a first pressure (as low as possible depending on the heat exchange balance) to form a gas stream 12; the liquid stream 13 separated by the secondary gas-liquid separator V2 is split into two streams, one stream 14 and one stream 15, the liquid stream 14 is throttled across a valve and reduced in pressure to a first pressure (as low as possible depending on the heat exchange balance) to form a liquid stream 16. The gas material flow 12 and the liquid material flow 16 are mixed to form a refrigerating material flow 25, the refrigerating material flow is returned to the second plate-fin heat exchanger E2 to be reheated to-30 ℃, and the refrigerating material flow 26 is obtained after being led out; the refrigeration stream 26 is divided into two paths, one path 27 and one path 34; stream 27 is reheated to-40 ℃ by a first plate-fin heat exchanger E1 to form a gas stream 28 which exits the cryogenic separation system.

The gas stream 8 is reheated to-30 ℃ by a second plate-fin heat exchanger E2 to obtain a gas stream 19, and then the gas stream is passed through a first plate-fin heat exchanger E1

Reheating to-40 ℃ and discharging from the low-temperature separation system as a dry gas product 20 to a downstream process. The gas stream 9 is throttled across a valve to a second pressure (determined by the on-way resistance based on the reaction pressure) to form recycle hydrogen 11.

After liquid propane 38 with the pressure of 2.1MPa (G) and the temperature of 41 ℃ below zero is pre-cooled to 24 ℃ below zero by a third plate-fin heat exchanger E3, further sub-cooled liquid propane 39 is obtained and divided into two paths, one path is a liquid material flow 43 accounting for 91 percent of the total flow of the liquid propane 39, the other path is a liquid material flow 40 accounting for 9 percent of the total flow of the liquid propane 39 and is cooled to 113 ℃ below zero by a second plate-fin heat exchanger E2, and the obtained liquid material flow 41 is led out to be throttled and decompressed to a second pressure (determined according to reaction pressure and along-path resistance) by a valve to form a liquid material flow 42; liquid stream 43 is reduced in pressure via a valve restriction to a third pressure (determined by the on-way resistance based on the reaction pressure) to form liquid stream 44.

And mixing the liquid material flow 42 with the circulating hydrogen 11 to form a refrigerating material flow 23, returning the refrigerating material flow to the second plate-fin heat exchanger E2 for reheating to-32 ℃ for gasification and cold recovery, and leading out to obtain a material flow 24. The liquid material flow 44 and the material flow 24 are mixed to form a combined feed 45, the combined feed enters a first plate-fin heat exchanger E1 to be reheated to 40 ℃ and then is discharged from the low-temperature separation system to be used as a combined feed 46 for heat removal combined heat exchange and cracking reaction to form a reaction product, and the reaction product is compressed to 1.0MPa (G) by a REC compressor and then returns to the low-temperature separation system.

Liquid 21 separated from the first-stage gas-liquid separator V1 is throttled and decompressed to 0.35MPa (G) by a valve to obtain a gas-liquid mixture flow 22 which enters a flash

Throttling and decompressing a liquid material flow 15 separated by the secondary gas-liquid separator V2 to 0.36MPa (G) through a valve to obtain a liquid material flow 17, reheating the liquid material flow 17 to-30 ℃ through a second plate-fin heat exchanger E2 to obtain a liquid material flow 18, and feeding the liquid material flow 18 into a flash tank D1; liquid 35 separated from the flash tank D1 at the temperature of minus 30 ℃ is pressurized to be 4.0MPa (G) by a liquid pump P1 to obtain a liquid product 36, and the liquid product 36 enters a third plate-fin heat exchanger E3 to be reheated to the temperature of minus 40 ℃ to be discharged from a low-temperature separation system as a liquid product 37 to be sent to a downstream process.

The gas 29 separated from the flash tank D1 is throttled by a valve and decompressed by a fourth pressure (the pressure is as low as possible according to the pressure balance of the system) to obtain a gas stream 30, the gas stream 30 and the stream 34 are mixed to form a gas stream 31, the gas stream 31 enters a second plate-fin heat exchanger E2 and is reheated to a temperature of-40 ℃ to exit a low-temperature separation system to form a gas stream 32, the gas stream 32 and the gas stream 28 are merged to form a flash stream 33, and the flash stream 33 and a reaction product are mixed to enter an REC compressor for pressurization and then return to the low-temperature separation system for circular separation.

Specific example 2 (dry gas product pressure does not meet downstream process requirements, needs pressurization), as shown in fig. 2:

the reaction product 1 with the pressure of 0.9MPa (G) and the temperature of 43 ℃ below zero is cooled to 26 ℃ below zero through a first plate-fin heat exchanger E1 and then partially condensed to form a gas-liquid mixture flow 2, the gas-liquid mixture flow 2 is separated to form a gas flow 3 through a first-stage gas-liquid separator V1, the gas flow 3 enters a second plate-fin heat exchanger E2 and is further cooled to 112 ℃ below zero, and the gas flow 3 is partially condensed to form a gas-liquid mixture flow 4 and enters a second-stage gas-liquid separator V2.

The gas material flow 5 separated by the secondary gas-liquid separator V2 returns to the second plate-fin heat exchanger E2 for reheating to-102 ℃ for recovering cold; the superheated gas stream 6 after reheating is expanded in an isentropic way (the expansion work is recovered by a booster) by an expander set ET1, the pressure is expanded from 0.86MPa (G) to 0.40MPa (G), and the temperature of the expanded gas stream 7 is-124 ℃; the expanded stream 7 is divided into three paths, one path of gas stream 8, one path of gas stream 9 and one path of gas stream 10.

The gas stream 10 is throttled across a valve to a reduced pressure to a first pressure (as low as possible depending on the heat exchange balance) to form a gas stream 12; the liquid stream 13 separated by the secondary gas-liquid separator V2 is split into two streams, one stream 14 and one stream 15, the liquid stream 14 is throttled across a valve and reduced in pressure to a first pressure (as low as possible depending on the heat exchange balance) to form a liquid stream 16. The gas material flow 12 and the liquid material flow 16 are mixed to form a refrigerating material flow 25, the refrigerating material flow is returned to the second plate-fin heat exchanger E2 to be reheated to-30 ℃, and the refrigerating material flow 26 is obtained after being led out; the refrigeration stream 26 is divided into two paths, one path 27 and one path 34; stream 27 is reheated to-40 ℃ by a first plate-fin heat exchanger E1 to form a gas stream 28 which exits the cryogenic separation system.

The gas stream 8 is reheated to-30 ℃ by a second plate-fin heat exchanger E2 to obtain a gas stream 19, and then the gas stream is passed through a first plate-fin heat exchanger E1

Reheating to 40 ℃ below zero, discharging the dry gas product 20 out of the low-temperature separation system, introducing the dry gas product 20 to a supercharging end of a supercharging turboexpander set to be supercharged to 0.6 MPa (G), and delivering the supercharged dry gas product to a downstream process. The gas stream 9 is valved to form recycle hydrogen 11.

After liquid propane 38 with the pressure of 2.1MPa (G) and the temperature of 41 ℃ below zero is pre-cooled to 24 ℃ below zero by a third plate-fin heat exchanger E3, further sub-cooled liquid propane 39 is obtained and divided into two paths, one path is a liquid material flow 43 accounting for 90 percent of the total flow of the liquid propane 39, the other path is a liquid material flow 40 accounting for 10 percent of the total flow of the liquid propane 39 and is cooled to 112 ℃ below zero by a second plate-fin heat exchanger E2, and the obtained liquid material flow 41 is led out to be throttled and decompressed to a second pressure (determined according to reaction pressure and along-path resistance) by a valve to form a liquid material flow 42; liquid stream 43 is reduced in pressure via a valve restriction to a third pressure (determined by the on-way resistance based on the reaction pressure) to form liquid stream 44.

And mixing the liquid material flow 42 with the circulating hydrogen 11 to form a refrigerating material flow 23, returning the refrigerating material flow to the second plate-fin heat exchanger E2 for reheating to-32 ℃ for gasification and cold recovery, and leading out to obtain a material flow 24. The liquid material flow 44 and the material flow 24 are mixed to form a combined feed 45, the combined feed enters a first plate-fin heat exchanger E1 to be reheated to 40 ℃ and then is discharged from the low-temperature separation system to be used as a combined feed 46 for heat removal combined heat exchange and cracking reaction to form a reaction product, and the reaction product is compressed to 0.9MPa (G) through a heat combined heat exchange and REC compressor and then returns to the low-temperature separation system.

Liquid 21 separated from the first-stage gas-liquid separator V1 is throttled and decompressed to 0.35MPa (G) by a valve to obtain a gas-liquid mixture flow 22 which enters a flash

Throttling and decompressing a liquid material flow 15 separated by the secondary gas-liquid separator V2 to 0.36MPa (G) through a valve to obtain a liquid material flow 17, reheating the liquid material flow 17 to-30 ℃ through a second plate-fin heat exchanger E2 to obtain a liquid material flow 18, and feeding the liquid material flow 18 into a flash tank D1; liquid 35 separated from the flash tank D1 at the temperature of minus 30 ℃ is pressurized to be 4.0MPa (G) by a liquid pump P1 to obtain a liquid product 36, and the liquid product 36 enters a third plate-fin heat exchanger E3 to be reheated to the temperature of minus 40 ℃ to be discharged from a low-temperature separation system as a liquid product 37 to be sent to a downstream process.

The gas 29 separated from the flash tank D1 is throttled by a valve and decompressed by a fourth pressure (the pressure is as low as possible according to the pressure balance of the system) to obtain a gas stream 30, the gas stream 30 and the stream 34 are mixed to form a gas stream 31, the gas stream 31 enters a second plate-fin heat exchanger E2 and is reheated to a temperature of-40 ℃ to exit a low-temperature separation system to form a gas stream 32, the gas stream 32 and the gas stream 28 are merged to form a flash stream 33, and the flash stream 33 and a reaction product are mixed to enter an REC compressor for pressurization and then return to the low-temperature separation system for circular separation.

FIG. 3 is a schematic diagram for auxiliary explanation of the process flow of the separation upstream and downstream of the cryogenic separation system, and the main process thereof is as follows:

the temperature is-40 ℃, the combined feed is discharged from a low-temperature separation system 46, the temperature is firstly heated to-610 ℃ by a heat combined heat exchanger (determined according to the reaction process), the temperature enters a catalytic cracking reaction furnace for dehydrogenation reaction, and the reaction product after dehydrogenation is cooled to-43 ℃ by the heat combined heat exchanger; the flash evaporation material flow 33 with the temperature of 40 ℃ below zero flows out of the low-temperature separation system and directly enters the inlet of the REC compressor; the reaction product after dehydrogenation is mixed with the flash stream 33, the mixture is compressed to 1.0 (0.9) MPa (G) by a compressor to form a reaction product 1, and the reaction product 1 is sent to a low-temperature separation system to realize heat exchange, cooling and separation.