Propane dehydrogenation reaction solvent absorption and separation method and system

Abstract

The invention provides a propane dehydrogenation reaction solvent absorption and separation method and system.The method comprises the steps that product gas of a propane dehydrogenation reaction is compressed and subjected to three-phase separation through shallow cooling, and a water-phase product, an oil-phase product and a gas-phase product are obtained; and treating the water-phase product as wastewater, drying the oil-phase product, then carrying out rectification separation, drying the gas-phase product, and then carrying out separation by a solvent absorbent. The system comprises a compression shallow cooling unit, a three-phase separation tank, an oil phase rectification separation unit and a gas phase solvent absorption separation unit. The novel separation system for separating and recovering propane and propylene in propane dehydrogenation reaction gas by adopting a shallow cooling and solvent absorption technology reduces a reaction gas cryogenic section and a cryogenic refrigeration system, and has the advantages of high propane and propylene recovery rate, small absorbent loss, short process flow, low energy consumption and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to a propane dehydrogenation reaction solvent absorption and separation method and system. Background Art

[0002] Propylene is an important organic chemical raw material, widely used in various industries such as polymer materials and medicine, with broad prospects and large market demand. In recent years, with the rapid development of various industries, the demand for propylene has continued to rise, and different propylene production facilities have been built and put into production to increase propylene production capacity to meet market demand. Compared with traditional petrochemical and coal chemical propylene production technologies, the propane dehydrogenation process (PDH) has the characteristics of low project investment and high product yield, and has become a popular propylene synthesis process.

[0003] The absorption process uses C3-C4 low-carbon hydrocarbons or C5-C12 light gasoline as absorbents, and absorbs and separates low-carbon hydrocarbons in the reaction gas according to the different solubility of different gases in the absorbent. The absorption process can be divided into shallow cold oil absorption, medium cold oil absorption and deep cold oil absorption according to the different absorbent feed temperatures. Among them, medium cold oil absorption and deep cold oil absorption require the absorbent to be refined and then deep-cooled to -20-40℃ and -70-80℃ respectively for absorption and separation. Therefore, it has the disadvantages of low absorbent operating temperature, high energy consumption and high equipment investment. In the shallow cold oil absorption technology, the absorbent temperature is about -5-15℃, which has the advantages of less low-temperature cooling consumption and less equipment investment. For refinery dry gas, Sinopec Chemical Research Institute has developed shallow cold oil absorption technology, which uses C4 as absorbent to absorb and separate C2 and above components such as ethane, ethylene, propane, and propylene in dry gas. In the separation of propane dehydrogenation reaction gas, Hu Zhiyan et al. also used ether-containing carbon four as absorbent to conduct separation research on propane dehydrogenation reaction gas.

[0004] In a certain propane dehydrogenation process unit currently in operation, the separation technology of propane dehydrogenation reaction gas mainly adopts compression cooling first, drying and then entering the cold box system for cryogenic separation. The propane and propylene crude liquid recovered by cryogenic separation are distilled in a distillation tower to obtain propylene. In this separation process, the reaction gas needs to be cryogenically separated in a cold box. The cryogenic temperature is low and an additional cryogenic refrigeration system is required. This has the disadvantages of complex process flow, large number of equipment and high equipment investment.

[0005] Patent CN108713052B uses benzene as an absorbent to separate C3 hydrocarbons from a gas phase mixture of C1-C3 hydrocarbons. The required absorbent circulation amount is extremely large, and the energy consumption of the desorption tower is relatively high. Patents CN109574786A and 108456128A use the propane-rich liquid of the device's own propane-propylene separation tower or the separated carbon four components as absorbents. No cooling and recovery system is set at the top of the absorption tower, and the absorbent loss is large. Patent 113372189A provides a low-carbon alkane dehydrogenation separation olefin production device and process, the solvent recovery tower has a high operating pressure, and the bottom of the tower uses fuel gas or medium-pressure steam as the heat source of the solvent removal tower, and the total energy consumption is relatively high. At the same time, the invention does not carry out intermediate cooling recovery of propane and propylene, and the C3 loss rate is large.

[0006] Therefore, there is an urgent need for a solvent absorption and separation system for a propane dehydrogenation unit with a simple process flow and low energy consumption. Summary of the invention

[0007] In order to solve the above problems in the prior art, the present invention proposes a propane dehydrogenation reaction solvent absorption separation method and system.

[0008] In a first aspect, the present invention provides a propane dehydrogenation reaction solvent absorption separation method, the method comprising shallow cold separation and solvent absorption; comprising the following steps:

[0009] S1: compressing the product gas of propane dehydrogenation reaction, and performing three-phase separation by shallow cooling to obtain water phase product, oil phase product and gas phase product;

[0010] S2: The aqueous phase product is treated as wastewater, the oil phase product is dried and separated by distillation, and the gas phase product is dried and separated by a solvent absorbent.

[0011] As a specific implementation of the present invention, in the step S1, the product gas is compressed to 1.0-4.0 MpaG; the shallow cooling temperature is -20-20°C.

[0012] As a specific embodiment of the present invention, in step S2, the solvent absorbent includes at least one or a combination of C4 to C9 hydrocarbons, and the mass ratio of the solvent absorbent to the product gas is (1 to 8): 1; the separation temperature of the solvent absorbent is -30 to 10°C.

[0013] In a second aspect, the present invention provides a propane dehydrogenation reaction solvent absorption and separation system, the system comprising: a compression shallow cooling unit, a three-phase separation tank, an oil phase distillation separation unit and a gas phase solvent absorption and separation unit;

[0014] The compression shallow cooling unit comprises a compression device, a circulating water cooler and a low temperature cooler connected in sequence;

[0015] The three-phase separation separates the product gas compressed and cooled by the cryocooler into three phases;

[0016] The oil phase rectification and separation unit comprises a lightness removal tower;

[0017] The gas phase solvent absorption and separation unit comprises an absorption tower and a desorption tower which are connected in sequence.

[0018] As a specific embodiment of the present invention, the system also includes an absorption tower multi-stage condensation unit and a desorption tower multi-stage condensation unit, wherein the multi-stage condensation units are independently configured with one or more condensation stages, preferably 2-5 stages, and the condensation temperatures are independently -35 to 25°C;

[0019] The multi-stage condensation unit of the absorption tower is connected to the top of the absorption tower, and the multi-stage condensation unit of the desorption tower is connected to the top of the desorption tower.

[0020] Specifically, the product gas of the propane dehydrogenation reaction unit is compressed by the product gas compression unit, cooled by a circulating water cooler and a low-temperature cooler, and then sent to a liquid separator for three-phase separation. The water phase is sent to a wastewater treatment system as wastewater, the oil phase is sent to a subsequent separation system for separation after passing through a liquid phase drying bed, and the gas phase is sent to an absorption tower for absorption separation after passing through a gas phase drying bed. Most of the logistics in the propane dehydrogenation product gas are condensed and recovered through the compression unit and the shallow cooling separation unit to reduce the product gas processing volume in the subsequent absorption process.

[0021] The product gas compression and shallow cooling unit compresses the product gas from the propane dehydrogenation reaction unit, cools it in a circulating water cooler and a low-temperature cooler, and then sends it to a liquid separator for three-phase separation. The water phase is sent to the wastewater treatment system as wastewater, the oil phase is sent to the subsequent separation system for separation after passing through the liquid phase drying bed, and the gas phase is sent to the absorption tower for absorption separation after passing through the gas phase drying bed. Through compression and shallow cooling separation, most of the logistics in the propane dehydrogenation product gas are condensed and recovered to reduce the product gas processing volume in the subsequent absorption process.

[0022] The compression stages of the product gas compression system include but are not limited to three to five stages, and the pressure after compression includes but is not limited to 1.0-4.0 MPaG.

[0023] The product gas shallow cold separation temperature includes but is not limited to -20 to 20°C

[0024] As a specific embodiment of the present invention, the system also includes a drying device, which includes a liquid phase drying bed and a gas phase drying bed; the liquid phase drying bed is located at the front end of the light removal tower, and the gas phase drying bed is located at the front end of the absorption tower.

[0025] As a specific embodiment of the present invention, the system also includes a recovery unit, and the recovery unit includes a recovery tower; the recovery tower is connected to the top of the light removal tower, and the propane and propylene are deep-cold recovered in the recovery tower. The recovery tower is used to further distill and recover the propane and propylene in the gas phase at the top of the light removal tower, and the ethane-rich tail gas obtained at the top of the tower is used as fuel gas after heat recovery in the cold box, and the propane and propylene recovery liquid obtained at the bottom of the tower is returned to the light removal tower.

[0026] As a specific embodiment of the present invention, propane and propylene products are obtained at the bottom of the light-removal tower, and the gas phase at the top of the tower is connected to a recovery tower.

[0027] As a specific embodiment of the present invention, the system also includes an expander, which is connected to the multi-stage condensation unit at the top of the absorption tower to expand the cooled tail gas to generate electricity. The expander system refers to expanding the tail gas after multi-stage cooling at the top of the absorption tower to generate electricity, and using the expanded low-temperature tail gas as the cold source for the gas phase condensation at the top of the absorption tower and the condenser at the top of the recovery tower, thereby improving the low-temperature energy utilization efficiency.

[0028] As a specific embodiment of the present invention, a solvent absorbent is arranged in the absorption tower, and the absorption tower is connected to a low temperature cooler; the top of the tower is connected to a multi-stage condensation recovery system of the absorption tower, and the bottom of the tower is connected to a desorption tower.

[0029] Specifically, the absorption tower uses an absorbent to absorb and separate the product gas after shallow cold separation. The product gas after shallow cold separation enters from the bottom of the tower, and the fresh absorbent and circulating absorbent enter from the top of the tower. The gas-liquid two-phase mass transfer and absorption in the tower absorb and separate the propane and propylene in the product gas. After absorption and separation, the absorption tail gas obtained at the top of the tower enters the multi-stage condensation recovery system, the absorbent taken away in the gas phase at the top of the tower is cooled and recovered, and the remaining tail gas is sent to the expansion system. The rich liquid rich in propane and propylene is obtained at the bottom of the tower and sent to the desorption tower for desorption.

[0030] As a specific embodiment of the present invention, the bottom of the desorption tower is connected to the absorption tower, and the top of the tower is sequentially connected to a multi-stage condensation recovery unit and a light removal tower.

[0031] As a specific embodiment of the present invention, the desorption tower is used to desorb and separate the rich liquid rich in propane and propylene.

[0032] Specifically, the desorption tower uses steam stripping to desorb and separate the rich liquid rich in propane and propylene. The absorbent lean liquid obtained at the bottom of the tower is mixed with fresh absorbent and returned to the absorption tower after cooling; the propane and propylene desorbed gas is obtained at the top of the tower and sent to the light removal tower for separation after a multi-stage condensation recovery system.

[0033] As a specific embodiment of the present invention, the light-removal tower refers to a tower that uses a distillation separation method to separate the crude propane and propylene liquid. The propane and propylene obtained at the bottom of the tower are sent to the product refining unit, and the gas phase at the top of the tower is sent to a recovery tower for deep cold recovery of propane and propylene.

[0034] As a specific embodiment of the present invention, the solvent absorbent includes at least one or a combination of C4 to C9 hydrocarbons, the mass ratio of the solvent absorbent to the product gas is (1 to 8): 1; and the separation temperature of the solvent absorbent is -30 to 10°C.

[0035] Specifically, C4-C9 hydrocarbons are generally divided into C4-C6 light hydrocarbons and C6-C9 heavy hydrocarbons.

[0036] The above raw materials in the present invention can be prepared in-house or commercially available, and the present invention is not particularly limited thereto.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The solvent absorption separation system of the propane dehydrogenation device of the present invention is a novel separation system for separating and recovering propane and propylene in the propane dehydrogenation reaction gas by using shallow cooling + solvent absorption technology. It includes product gas compression and shallow cooling unit, drying bed, absorption tower, desorption tower, light removal tower, expander, and recovery tower. It reduces the deep cooling section of the reaction gas and the deep cooling refrigeration system, and has the advantages of high propane and propylene recovery rate, small absorbent loss, short process flow, and low energy consumption.

[0039] 2. Compared with the deep cold separation technology of the reaction gas of the propane dehydrogenation unit currently in operation, the present invention has the advantages of simple process flow, low requirements for equipment and pipeline materials, low investment in equipment and pipelines, and high energy utilization efficiency. At the same time, the process technology of the present invention can effectively solve the problems of large absorbent consumption, high energy consumption in the absorption and desorption processes, and low propane and propylene recovery rates in conventional absorption and separation technologies, and has the advantages of low process energy consumption and high energy utilization efficiency.

[0040] 3. The product gas compression and shallow cooling unit in the solvent absorption and separation system of the propane dehydrogenation device of the present invention is to perform multi-stage compression and shallow cooling separation on the product gas from the propane dehydrogenation reaction unit, and the cooled product gas is sent to the liquid separator for three-phase separation. Through compression and shallow cooling separation, most of the propane / propylene in the propane dehydrogenation product gas is initially condensed and recovered to reduce the product gas processing volume in the subsequent absorption process, greatly reduce the circulation volume of the absorbent, and thus reduce the energy consumption in the entire absorption and separation process.

[0041] 4. The absorption tower in the solvent absorption and separation system of the propane dehydrogenation device of the present invention uses an absorbent to absorb and separate propane and propylene in the product gas after shallow cold separation. After absorption and separation, a multi-stage low-temperature condensation recovery system is set for the tail gas absorbed at the top of the tower to cool and recover the absorbent taken away in the gas phase at the top of the tower, thereby improving the recovery efficiency of propane and propylene and reducing the loss of the absorbent.

[0042] 5. The desorption tower in the solvent absorption and separation system of the propane dehydrogenation device of the present invention uses steam stripping to desorb and separate the rich liquid rich in propane and propylene. A multi-stage low-temperature condensation and recovery system is used for the propane and propylene desorption gas obtained at the top of the tower to condense and recover the propane and propylene gas, which can reduce the energy consumption of the low-temperature position in the condenser in the light removal tower. At the same time, the condensed material is fed to different tower plates of the light removal tower according to different components, thereby improving the separation efficiency of key components in the light removal tower.

[0043] 6. The expander system in the solvent absorption and separation system of the propane dehydrogenation device of the present invention refers to the expansion of the high-pressure tail gas after multi-stage cooling at the top of the absorption tower to generate electricity, and at the same time, the expanded low-temperature tail gas is used as the cooling source of the intermediate cooling section of the tail gas of the absorption tower and the top condenser of the recovery tower, which greatly improves the energy utilization efficiency of the entire device.

[0044] 7. The recovery tower in the solvent absorption and separation system of the propane dehydrogenation device of the present invention is used to further distill and recover the propane and propylene in the gas phase at the top of the light removal tower, and uses the expanded low-temperature tail gas as a cold source to achieve intermediate cooling recovery and separation of propane and propylene without the need for other deep-cold refrigeration systems, thereby solving the problem of low propane and propylene recovery rate in absorption technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a process flow chart of a solvent absorption and separation system of a propane dehydrogenation device using C4-C6 low-carbon hydrocarbons as absorbents in Example 1 of the present invention;

[0046] Among them, 1-compression system, 2-circulating water cooler, 3-low temperature cooler, 4-liquid separation tank, 5-liquid phase drying bed, 6-gas phase drying bed, 7-absorption tower, 8-desorption tower, 9-light removal tower, 10-recovery tower, 11-absorbent low temperature cooler, 12-absorption tower multi-stage condensation system, 13-desorption tower feed pump, 14-desorption tower reboiler, 15-absorbent circulating water cooler, 16-absorbent circulating pump, 17 -Desorption tower reflux pump, 18-Desorption tower condenser, 19-Desorption tower reflux tank, 20-Desorption tower multi-stage condensation system, 21-Absorption tower condenser, 22-Absorption tower top liquid separation tank, 23-Expander, 24-Recovery tower condenser, 25-Cold box, 26-De-lightness removal tower condenser, 27-De-lightness removal tower reflux pump, 28-De-lightness removal tower reboiler, 29-De-lightness removal tower reflux tank, 30-Recovery tower reflux pump, 31-Absorption tower reflux tank.

[0047] Figure 2 This is a process flow chart of a solvent absorption and separation system of a propane dehydrogenation unit using C6-C9 heavy hydrocarbons as absorbents in Example 2 of the present invention;

[0048] Among them, 1-compression system, 2-circulating water cooler, 3-low-temperature cooler, 4-liquid separation tank, 5-liquid phase drying bed, 6-gas phase drying bed, 7-absorption tower, 8-desorption tower, 9-light removal tower, 10-recovery tower, 11-absorbent low-temperature cooler, 13-desorption tower feed pump, 14-desorption tower reboiler, 15-absorbent circulating water cooler, 16-absorbent circulating pump, 17-desorption tower reflux pump, 18-desorption tower condenser, 19-desorption tower reflux tank, 20-desorption tower multi-stage condensation system, 23-expander, 24-recovery tower condenser, 25-cold box, 26-light removal tower condenser, 27-light removal tower reflux pump, 28-light removal tower reboiler, 29-light removal tower reflux tank, 30-recovery tower reflux pump, 31-absorption tower reflux tank. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with specific embodiments, but they do not constitute any limitation to the present invention.

[0050] Example 1

[0051] This embodiment provides a propane dehydrogenation device solvent absorption separation system using C4-C6 low carbon hydrocarbons as absorbents, combined with Figure 1 , the specific process is as follows:

[0052] The product gas is first compressed by the compression system (1) and then initially cooled and separated by the circulating water cooler (2) and the low-temperature cooler (3). The cooled product gas is separated into three phases in the liquid separator (4), wherein the water phase is used as wastewater to be sent to the wastewater treatment system, the cooled oil phase (mainly containing C3, C4 and C5+ hydrocarbons) is dried by the liquid phase drying bed (5) and then sent to the light removal tower (9) for distillation separation, and the gas phase is dried by the drying bed (6) and then sent to the absorption tower (7) for absorption separation. In the absorption tower, the product gas enters from the bottom of the tower, and the fresh absorbent and the circulating absorbent enter from the top of the tower after being cooled, and the gas and liquid phases are subjected to mass transfer absorption in the tower. A mixed C4 rich liquid rich in propane and propylene is obtained at the bottom of the absorption tower and sent to the regeneration tower (8) for solvent regeneration. In the regeneration tower (8), the absorbent lean liquid obtained at the bottom of the tower after distillation is cooled by the cooler (15) and then returned to the absorption tower for recycling. In order to reduce the condenser load of the light-removing tower (9), the propane and propylene gases obtained at the top of the desorption tower (8) are respectively sent to the light-removing tower after passing through a multi-stage condensation system (20) and are distilled and separated together with the liquid hydrocarbons from the liquid phase drying bed (5). In the light-removing tower (9), propane and propylene liquids are obtained at the bottom of the distillation separation tower and sent to the product refining unit, and in order to control the loss of propane and propylene at the top of the tower, the top gas phase is sent to the recovery tower (10) for deep cold recovery of propane and propylene. The hydrocarbon liquid at the bottom of the recovery tower (10) is returned to the light-removing tower (9), and the ethane-rich tail gas obtained at the top of the tower is used as fuel gas after heat recovery in a cold box. In the gas phase at the top of the absorption tower (7), although the absorbent absorbs the propane and propylene in the product gas, there is a large loss of the absorbent at the top of the tower. Therefore, a three-stage condensation system (12) of the absorption tower is set to condense the gas phase at the top of the absorption tower step by step to achieve the recovery of the absorbent. The remaining tail gas is expanded by the expander (23), and the low-temperature and low-pressure hydrogen-rich tail gas is deep-cold recovered by the absorption tower condenser (21) and the propane recovery tower condenser (24), and after heat exchange in the cold box system (25), it is sent to the hydrogen extraction unit or used as fuel gas.

[0053] Example 1 can separate and recover propane and propylene from the propane dehydrogenation product gas, with the recovery rate of propane and propylene reaching more than 99.95%, and the loss rate of the absorbent reduced to less than 0.1wt%.

[0054] When low-carbon hydrocarbons are used as absorbents in Example 1, low-carbon olefins are easily volatile. In order to reduce the loss rate of low-carbon olefins, it is necessary to add an absorption tower multi-stage condensation system, an absorption tower condenser and an absorption tower top liquid separator.

[0055] Example 2

[0056] This embodiment provides a propane dehydrogenation device solvent absorption separation system using C6-C9 heavy hydrocarbons as absorbents, combined with Figure 2 , the specific process is as follows:

[0057] The product gas is first compressed by the compression system (1) and then initially cooled and separated by the circulating water cooler (2) and the low-temperature cooler (3). The cooled product gas is separated into three phases in the liquid separator (4), wherein the water phase is used as wastewater to be sent to the wastewater treatment system, the cooled oil phase (mainly containing C3, C4 and C5+ hydrocarbons) is dried by the liquid phase drying bed (5) and then sent to the light removal tower (9) for distillation separation, and the gas phase is dried by the drying bed (6) and then sent to the absorption tower (7) for absorption separation. In the absorption tower, the product gas enters from the bottom of the tower, and the fresh absorbent and the circulating absorbent enter from the top of the tower after being cooled, and the gas and liquid phases are subjected to mass transfer absorption in the tower. A mixed C4 rich liquid rich in propane and propylene is obtained at the bottom of the absorption tower and sent to the regeneration tower (8) for solvent regeneration. In the regeneration tower (8), the absorbent lean liquid obtained at the bottom of the tower after distillation is cooled by the cooler (15) and then returned to the absorption tower for recycling. In order to reduce the condenser load of the light-removing tower (9), the propane and propylene gases obtained at the top of the desorption tower (8) are respectively sent to the light-removing tower after passing through a multi-stage condensation system (20) and are distilled and separated together with the liquid hydrocarbons from the liquid phase drying bed (5). In the light-removing tower (9), propane and propylene liquids are obtained at the bottom of the distillation separation tower and sent to the product refining unit, and in order to control the loss of propane and propylene at the top of the tower, the top gas phase is sent to the recovery tower (10) for deep cold recovery of propane and propylene. The hydrocarbon liquid at the bottom of the recovery tower (10) is returned to the light-removing tower (9), and the ethane-rich tail gas obtained at the top of the tower is used as fuel gas after heat recovery in a cold box. After the top gas phase of the absorption tower (7) is expanded by an expander (23), the low-temperature and low-pressure hydrogen-rich tail gas is deep-cold recovered by the recovery tower condenser (24), and after heat exchange in a cold box system (25), it is sent to the hydrogen extraction unit or used as fuel gas.

[0058] Example 2 can separate and recover propane and propylene from the propane dehydrogenation product gas, with the recovery rate of propane and propylene reaching more than 99.95%, and the loss rate of the absorbent reduced to less than 0.1wt%.

[0059] Example 3

[0060] This embodiment takes the product gas of a 600,000 ton / year propane dehydrogenation unit and mixed C4 as an absorbent as an example. The process flow chart is as follows: Figure 1 As shown, the specific implementation details are as follows:

[0061] The product gas (218 t / h, 38°C, -0.07 MPaG) from the reaction unit of the propane dehydrogenation device is first compressed to 3.0 MPaG by the compression system (1), and then initially cooled and separated to 15.0°C by the circulating water cooler (2) and the low-temperature cooler (3). The cooled product gas is separated into three phases in the liquid separator (4), wherein 1.7 t / h of the water phase is used as wastewater to go to the wastewater treatment system, and the cooled 158.4 t / h of the oil phase (mainly containing C3, C4 and C5+ hydrocarbons) is dried by the liquid phase drying bed (5) and then sent to the light removal tower (9) for distillation separation, and 57.9 t / h of the gas phase is dried by the drying bed (6) and then sent to the absorption tower (7) for oil absorption separation. In the absorption tower, the product gas enters from the bottom of the tower, and the fresh mixed C4 and the circulating mixed C4 enter from the top of the tower after being cooled to 0°C. The gas-liquid two-phase mass transfer absorption is carried out in the tower, and the mixed C4 rich liquid rich in propane and propylene is obtained at the bottom of the absorption tower, and is sent to the regeneration tower (8) for solvent regeneration. The gas-liquid ratio of the absorbent to the product gas in the absorption tower is 1.36. The theoretical number of plates of the absorption tower is 30, and the absorption pressure is 2.9MPaG. In the regeneration tower (8), the mixed C4 lean liquid obtained at the bottom of the tower after distillation is cooled to 40°C by the cooler (15) and then returned to the absorption tower for recycling. The theoretical number of plates of the regeneration tower is 45, and the operating pressure is 1.6MPaG. In order to reduce the condenser load of the light removal tower (9), the propane and propylene gases obtained at the top of the desorption tower (8) are sent to the light removal tower respectively after passing through the three-stage condensation recovery system (20), and are distilled and separated together with the liquid hydrocarbons from the liquid phase drying bed (5). The number of theoretical plates of the light-removing tower is 50, and the operating pressure is 0.7 MPaG. In the light-removing tower (9), 201.7 t / h of propane and propylene liquid are obtained at the bottom of the tower after distillation and separation and sent to the product refining unit, and the light component content at the bottom of the tower is controlled within 0.02%wt. In order to control the loss of propane and propylene at the top of the tower, the top gas phase is sent to the recovery tower (10) for deep cold recovery of propane and propylene. The hydrocarbon liquid at the bottom of the recovery tower (10) is returned to the light-removing tower (9), and the ethane-rich tail gas obtained at the top of the tower is used as fuel gas after heat recovery in the cold box. The number of theoretical plates of the recovery tower is 7, and the operating pressure is 0.5 MPaG. In the gas phase at the top of the absorption tower (7), although the mixed C4 absorbs the propane and propylene in the product gas, due to the large loss of the mixed C4 at the top of the tower, the mixed C4 is condensed and recovered step by step through a three-stage condensation recovery system. The remaining tail gas is expanded to 0.6 MPaG by the expander (23), and the low-temperature and low-pressure hydrogen-rich tail gas is deep-cooled and recovered by the absorption tower condenser (21), and after heat exchange in the cold box system, it is sent to the hydrogen extraction unit or used as fuel gas.

[0062] When the propane dehydrogenation product gas separation process system proposed by the present invention is adopted, the recovery rate of propane and propylene reaches more than 99.95%, and the loss rate of the absorbent is reduced to less than 0.1wt%.

[0063] Example 4

[0064] This embodiment takes the product gas of a 600,000 ton / year propane dehydrogenation unit and mixed C7-C9 as absorbent as an example. The process flow chart is as follows: Figure 2 As shown, the specific implementation details are as follows:

[0065] The product gas (218 t / h, 38°C, -0.07 MPaG) from the reaction unit of the propane dehydrogenation device is first compressed to 3.0 MPaG by the compression system (1), and then initially cooled and separated to 15.0°C by the circulating water cooler (2) and the low-temperature cooler (3). The cooled product gas is separated into three phases in the liquid separator (4), wherein 1.7 t / h of the water phase is used as wastewater to go to the wastewater treatment system, and the cooled 158.4 t / h of the oil phase (mainly containing C3, C4 and C5+ hydrocarbons) is dried by the liquid phase drying bed (5) and then sent to the light removal tower (9) for distillation separation, and 57.9 t / h of the gas phase is dried by the drying bed (6) and then sent to the absorption tower (7) for oil absorption separation. In the absorption tower, the product gas enters from the bottom of the tower, and the fresh mixed C7-C9 and the circulating mixed C7-C9 are cooled to 0°C and enter from the top of the tower. The gas-liquid two-phase mass transfer absorption is carried out in the tower, and the mixed C7-C9 rich liquid rich in propane and propylene is obtained at the bottom of the absorption tower, and sent to the regeneration tower (8) for solvent regeneration. The gas-liquid ratio of the absorbent to the product gas in the absorption tower is 2.40. The theoretical number of plates of the absorption tower is 25, and the absorption pressure is 2.9MPaG. In the regeneration tower (8), the mixed C4 lean liquid obtained at the bottom of the tower after distillation is cooled to 40°C by the cooler (15) and then returned to the absorption tower for recycling. The theoretical number of plates of the regeneration tower is 30, and the operating pressure is 0.8MPaG. In order to reduce the condenser load of the light-removing tower (9), the propane and propylene gases obtained at the top of the desorption tower (8) are respectively sent to the light-removing tower after passing through the three-stage condensation recovery system (20), and are distilled and separated together with the liquid hydrocarbons from the liquid phase drying bed (5). The theoretical number of plates of the light-removing tower is 50, and the operating pressure is 0.7MPaG. In the light-removing tower (9), 201.7t / h of propane and propylene liquid are obtained at the bottom of the distillation separation tower and sent to the product refining unit, and the light component content at the bottom of the tower is controlled within 0.02%wt. In order to control the loss of propane and propylene at the top of the tower, the gas phase at the top of the tower is sent to the recovery tower (10) for deep cold recovery of propane and propylene. The hydrocarbon liquid at the bottom of the recovery tower (10) is returned to the light-removing tower (9), and the ethane-rich tail gas obtained at the top of the tower is used as fuel gas after heat recovery in the cold box. The theoretical number of plates of the recovery tower is 7, and the operating pressure is 0.6MPaG. The remaining tail gas is expanded to 0.6 MPaG by the expander (23), and the low-temperature and low-pressure hydrogen-rich tail gas is deep-cooled and recovered by the recovery tower condenser (24), and after heat exchange in the cold box system, it is sent to the hydrogen extraction unit or used as fuel gas.

[0066] When the propane dehydrogenation product gas separation process system proposed by the present invention is adopted, the recovery rate of propane and propylene reaches more than 99.95%, and the loss rate of the absorbent is reduced to less than 0.1wt%.

[0067] In summary, the novel solvent absorption separation system of a propane dehydrogenation device of the present invention proposes a process technology method using shallow cooling + solvent absorption. Through this process technology, the separation and recovery of propane and propylene in the reaction gas of the propane dehydrogenation device can be realized, and the recovery rate of propane and propylene can reach more than 99.95%, and the light component content is controlled within 0.02%wt.

[0068] A novel solvent absorption and separation system for a propane dehydrogenation device of the present invention adopts equipment such as product gas compression and shallow cooling unit, drying bed, oil washing absorption tower, desorption tower, light removal tower, expander, recovery tower, etc., and uses at least one or a combination of C4-C9 hydrocarbons as absorbent to absorb and separate propane and propylene in propane dehydrogenation reaction gas, thereby overcoming the problems of complex separation process, low operating temperature, high equipment and pipeline material requirements, high equipment and pipeline investment in the original propane dehydrogenation reaction gas deep cold separation and recovery process, and realizing the recovery and separation of propane and propylene at shallow cooling temperature.

[0069] In a novel solvent absorption and separation system of a propane dehydrogenation device of the present invention, a multi-stage condensation recovery system is set for a separation process using light olefins as absorption, thereby reducing the consumption of fresh absorbent and the consumption of low-temperature cooling capacity in a light-removal tower condenser, while improving the separation efficiency of key components in the light-removal tower.

[0070] In a novel solvent absorption and separation system for a propane dehydrogenation device of the present invention, an expansion power generation system is provided and a coupling design is used in which the expanded low-temperature tail gas is used as a cold source, thereby solving the problem of low propane and propylene recovery rate in oil washing absorption technology and improving the efficient utilization of high-quality low-temperature energy of the entire process device.

[0071] Any numerical value mentioned in the present invention, if there is only an interval of two units between any minimum value and any maximum value, includes all values ​​from the minimum value to the maximum value each time increasing by one unit. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is declared to be 50-90, in this specification it means that 51-89, 52-88... and 69-71 and 70-71 are specifically listed. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 can be appropriately considered as a unit. These are just some specially specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0072] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A propane dehydrogenation reaction solvent absorption separation method, characterized in that: The method comprises the following steps: S1: compressing the product gas of propane dehydrogenation reaction, and performing three-phase separation by shallow cooling to obtain water phase product, oil phase product and gas phase product; S2: The aqueous phase product is treated as wastewater, the oil phase product is dried and separated by distillation, and the gas phase product is dried and separated by a solvent absorbent.

2. The method according to claim 1, characterized in that In the step S1, the product gas is compressed to 1.0-4.0 MpaG; the shallow cooling temperature is -20-20°C.

3. The method according to claim 1, characterized in that In step S2, the solvent absorbent includes at least one or a combination of C4 to C9 hydrocarbons, and the mass ratio of the solvent absorbent to the product gas is (1 to 8):1; the separation temperature of the solvent absorbent is -30 to 10°C.

4. A propane dehydrogenation reaction solvent absorption and separation system, characterized in that: The system comprises: a compression and shallow cooling unit, a three-phase separation tank, an oil phase rectification and separation unit and a gas phase solvent absorption and separation unit; The compression shallow cooling unit comprises a compression device, a circulating water cooler and a low temperature cooler connected in sequence; The three-phase separation separates the product gas compressed and cooled by the cryocooler into three phases; The oil phase rectification and separation unit comprises a lightness removal tower; The gas phase solvent absorption and separation unit comprises an absorption tower and a desorption tower which are connected in sequence.

5. The system according to claim 4, characterized in that The system also includes an absorption tower multi-stage condensation unit and a desorption tower multi-stage condensation unit, wherein the multi-stage condensation units are independently configured with one or more condensation stages, preferably 2-5 stages, and the condensation temperatures are independently -35 to 25°C; The multi-stage condensation unit of the absorption tower is connected to the top of the absorption tower, and the multi-stage condensation unit of the desorption tower is connected to the top of the desorption tower.

6. The system according to claim 4, characterized in that The system also includes a drying device, which includes a liquid phase drying bed and a gas phase drying bed; the liquid phase drying bed is located at the front end of the lightness removal tower, and the gas phase drying bed is located at the front end of the absorption tower.

7. The system according to claim 4, characterized in that The system also includes a recovery unit, which includes a recovery tower; the recovery tower is connected to the top of the light removal tower, and propane and propylene are deep-cold recovered in the recovery tower.

8. The system according to claim 4, characterized in that The bottom of the light-removal tower obtains propane and propylene products, and the top gas phase is connected to a recovery tower.

9. The system according to claim 4, characterized in that The system also includes an expander, which is connected to the multi-stage condensation unit at the top of the absorption tower to expand the cooled tail gas to generate electricity.

10. The system according to claim 4, characterized in that The absorption tower is provided with a solvent absorbent, and the absorption tower is connected to a low temperature cooler; the top of the tower is connected to a multi-stage condensation recovery system of the absorption tower, and the bottom of the tower is connected to a desorption tower; The desorption tower is connected to the absorption tower at the bottom, and the top is connected to the multi-stage condensation recovery unit and the light removal tower in sequence; The solvent absorbent includes at least one or a combination of C4-C9 hydrocarbons, and the mass ratio of the solvent absorbent to the product gas is (1-8):1; the separation temperature of the solvent absorbent is -30-10°C.

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