A method and apparatus for multistage absorption recovery of light hydrocarbons

Abstract

This invention belongs to the field of oil refining and chemical engineering, and relates to a method and apparatus for multi-stage absorption and recovery of light hydrocarbons. Compared with the prior art, this invention has the following advantages: it eliminates the need for separate absorption stabilization systems in atmospheric and vacuum distillation units and hydrocracking units, reducing the problem of secondary separation of key components; an H2 / C1 coarse separation facility is set up before the absorption tower, which reduces the H2 partial pressure in the feed gas, which is beneficial to reducing the circulation volume, absorption pressure, or absorption temperature of C4 absorbent, while also reducing the size of the absorption tower; the crude hydrocarbons after desulfurization and desulfurization, and the crude hydrocarbons condensed in the outlet cooler of the third feed gas compressor, are all sent to the first absorption section of the multi-stage absorption tower, utilizing the C3 to C5 components contained in the feed gas itself as absorbents, reducing the amount of circulating C4, which helps to reduce energy consumption; the multi-stage absorption tower allows the absorbents to enter different positions in the multi-stage absorption tower according to the different C3 and C4 contents, improving the absorption effect.

Description

Technical Field

[0001] This invention belongs to the field of oil refining and chemical industry, and more specifically, relates to a method and apparatus for multi-stage absorption and recovery of light hydrocarbons. More specifically, it relates to an apparatus and method for the recovery of saturated light hydrocarbons from the entire refinery, including atmospheric and vacuum distillation, hydrocracking, hydrorefining, and aromatic reforming units that produce abundant saturated light hydrocarbons. Background Technology

[0002] Saturated light hydrocarbons in refineries mainly originate from atmospheric and vacuum distillation unit overhead gas and mixed naphtha, rich gas and crude hydrocarbons from the top of hydrogen sulfide stripping towers in various hydrocracking units, and fuel gas from various hydrorefining units. The recovery of light hydrocarbons from these materials primarily involves the recovery of C3 and C4 liquefied petroleum gas components through atmospheric and vacuum distillation unit light hydrocarbon recovery and absorption stabilization systems in various hydrocracking units. The C2 component is used as fuel gas in the dry gas. With the development of integrated refining and chemical production, further recovery of C2 components from dry gas to provide lighter ethylene feedstock for ethylene plants has gained importance. Chemical refineries with ethylene plants typically construct new C2 recovery units to recover C2 components from dry gas and send ethane-rich gas to the ethylene plant's cracking furnace as cracking feedstock, reducing the need for external ethylene feedstock purchases and further improving the refinery's economic efficiency.

[0003] The conventional process setup involves first recovering liquefied petroleum gas (LPG) through absorption stabilization, and then recovering C2 components using a C2 recovery unit employing shallow-cooled oil absorption technology. Since the C2 recovery unit uses C4 as the absorbent, absorbing the C2 components in the absorption tower, but the upstream absorption stabilization system pre-separates the C4 components from the C2 components, the C2 recovery unit needs to supplement with additional C4 as the absorbent to achieve C2 recovery. Therefore, a secondary separation of C2 / C4 components exists. Furthermore, in hydrocracking units, the butane stripping tower / hydrogen sulfide stripping tower separates the C4 components from the naphtha components. In the absorption stabilization system, to achieve the separation of C2 and C3 components, naphtha is used as the absorbent, and the components are mixed again in the absorption tower. To obtain the LPG product, further separation is required in the stabilization tower, resulting in a secondary separation of C4 components from the naphtha components. This secondary separation of key components increases separation energy consumption and the number of equipment required. Since C2, C3, and C4 components can all be used as feedstock for ethylene cracking, and C4 is also required as an absorbent for the recovery of C2 components, the necessity of setting up an absorption stabilization system is greatly reduced for chemical refineries that do not have integrated processing and utilization units for C3 and C4.

[0004] C4 absorbs C2 and higher components in the absorption tower. The higher the partial pressure of the target component in the gaseous feedstock, the more favorable it is for reducing the absorption pressure, which can lower the pressure at the feedstock gas compressor outlet and reduce the amount of circulating absorbent used, and vice versa. In current C2 recovery process designs, the feedstock gas directly enters the absorption tower and comes into countercurrent contact with the C4 absorbent, without considering setting up H2 separation facilities before the absorption tower to reduce the H2 content. This greatly increases the difficulty of recovering C2 from materials with high H2 content.

[0005] Typically, when recovering C2 and higher components, a single absorbent is used in the absorption tower, and a certain recovery rate is achieved by controlling the circulation rate. There is no multi-stage absorption based on different absorbent components to increase the recovery effect.

[0006] To achieve the complete recovery of saturated light hydrocarbons from all units in the plant, provide light ethylene feedstock for the ethylene unit, optimize the component separation sequence, simplify the separation process, and reduce investment and energy consumption, this invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a light hydrocarbon separation device and method with a simple process flow and mild operating conditions. This method can achieve efficient separation and recovery of C2, C3 and C4 components, while the recovered dry gas contains fewer impurities, and hydrogen can be directly recovered by pressure swing adsorption.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for multi-stage absorption and recovery of light hydrocarbons, the recovery method comprising the following steps: (1) Gas phase pressurization I: The sulfur-rich gas from the hydrogenation refining process is compressed and pressurized by the first raw material gas compressor, cooled by the cooler I, and separated by the separator I. The top of the separator yields sulfur-rich gas containing heavy components, and the bottom of the separator yields crude hydrocarbons containing sulfur and heavy components. (2) Stabilization of naphtha throughout the plant: Mixed naphtha, rich gas containing sulfur and heavy components and crude hydrocarbon containing sulfur and heavy components are sent to the stabilization tower for stabilization treatment. Stabilized naphtha is obtained at the bottom of the tower and divided into two parts. One part is used as mixed naphtha product, and the other part is sent to the top of the reabsorption section of the multi-stage absorption tower as a reabsorbent. The top gas phase of the stabilization tower is obtained at the top of the tower. After being condensed by the condenser, it is sent to the stabilization tower reflux tank to obtain rich gas at the top of the stabilization tower reflux tank and liquid phase at the bottom of the stabilization tower reflux tank. (3) Gas phase pressurization II: The rich gas at the top of the stabilizer tower reflux tank is sent to the second raw material gas compressor for compression and pressurization, cooled by cooler II and separated by separator II to obtain the rich gas at the top of separator II and the liquid phase at the bottom of separator II; (4) Rich gas desulfurization: The rich gas at the top of the separator II tank passes through the superheater and is sent to the gas phase desulfurization tower, where it comes into countercurrent contact with the lean amine liquid to remove hydrogen sulfide and obtain sulfur-free rich gas. (5) Crude hydrocarbon desulfurization: The liquid phase at the bottom of the stabilizer reflux tank is pressurized by the stabilizer reflux pump and divided into two parts. One part enters the desulfurization and desulfurization tower, and the liquid phase at the bottom of the separator II is pumped out by the crude hydrocarbon pump II and sent to the desulfurization and desulfurization tower. After removing hydrogen sulfide and mercaptan, sulfur-free crude hydrocarbon is obtained. After being cooled by the shallow cooler II, it is sent to the top of the first absorption section of the multi-stage absorption tower as a first-stage absorbent. (6) H2 / C1 coarse separation: sulfur-free rich gas is subjected to H1 / C1 coarse separation to obtain the H2-rich gas phase after coarse separation and the rich gas after H2 / C1 coarse separation; (7) Gas-liquid balance: After the H2 / C1 coarse separation, the rich gas is cooled by shallow cooler I and then enters the liquid separator IV for liquid separation, resulting in the gas phase at the top of liquid separator IV and the liquid phase at the bottom of liquid separator IV. (8) C3 / C4 separation: The liquid phase at the bottom of the separator IV is sent to the demethanizer. The gas phase at the top of the tower is mixed with the sulfur-rich gas from the hydrorefining process and subjected to step (1) gas phase pressurization I. The liquid phase at the bottom of the tower is sent to the deethaner. The ethane-rich gas product is obtained at the top of the tower. The liquid phase at the bottom of the tower is divided into two parts. One part is sent to the top of the third absorption section of the multi-stage absorption tower as the third-stage absorbent. The other part is sent to the depropanizer. One part of the liquid phase at the top of the tower is sent to the top of the second absorption section of the multi-stage absorption tower as the second-stage absorbent. The remaining part is the liquid propane product. The liquid phase at the bottom of the tower is divided into two parts. One part is used as the mixed C4 product. The other part is sent to the top of the fourth absorption section of the multi-stage absorption tower as the fourth-stage absorbent. (9) Multistage absorption: The gas phase at the top of the separator IV tank is sent to the bottom of the first absorption section of the multistage absorption tower. After passing through the first absorption section, the second absorption section, the third absorption section, the fourth absorption section and the reabsorption section in sequence, multistage absorption is carried out. The top of the multistage absorption tower is obtained as methane hydrogen dry gas. The liquid phase at the bottom of the reabsorption section is sent to the stabilization tower for step (2) naphtha stabilization treatment of the whole plant.

[0009] In this invention, the absorbents in the multi-stage absorption towers, from bottom to top, are crude hydrocarbons after desulfurization, C3 hydrocarbons at the top of the propane removal tower, hydrocarbons at the bottom of the ethane removal tower, C4 hydrocarbons at the bottom of the propane removal tower, and naphtha at the bottom of the stabilization tower. By adjusting the proportion of absorbents in each absorption section, the recovery of C2 and above components is maximized, without the need for additional absorbents from outside the system.

[0010] According to the present invention, preferably, the H2 / Cl coarse fractionation includes one of the following two methods: Method 1: Membrane separation: The sulfur-free rich gas is purified into hydrogen by a membrane separation unit to obtain purified hydrogen and H2 / Cl coarse separation rich gas. The H2 / Cl coarse separation rich gas is sent to gas-liquid equilibrium. The pressure loss of the membrane separation tail gas is 0.2~0.5MPaG. Method 2: Pressure Swing Adsorption (PSA): The sulfur-free rich gas passes through the PSA unit to obtain hydrogen and H2 / Cl coarse separation rich gas. The H2 / Cl coarse separation rich gas is pressurized by the PSA tail gas compressor and then sent to gas-liquid equilibrium. The H2 / Cl coarse separation rich gas is pressurized to 2.5~4.5 MPaG by the PSA tail gas compressor.

[0011] In this invention, the H2 recovery rate is 60%~85%. The purified hydrogen is sent to downstream devices for further hydrogen recovery via a hydrogen compressor, and the hydrogen obtained from the pressure swing adsorption unit is sent to the hydrogen pipeline network.

[0012] According to the present invention, preferably, the operating temperature at the top of the stabilization tower is 40~60℃ and the operating pressure is 0.8~1.2MPaG.

[0013] According to the present invention, preferably, the temperature of the stabilizing tower reflux tank is 30~45°C.

[0014] According to the present invention, preferably, the operating temperature of the gas phase desulfurization tower is 40~45℃ and the operating pressure is 2.5~4.5MPaG.

[0015] According to the present invention, preferably, the operating temperature of the crude hydrocarbon desulfurization and desulfurization tower is 35~45℃ and the operating pressure is 3.0~5.0MPaG.

[0016] According to the present invention, preferably, the outlet pressure of the first raw material gas compressor is 2.5~4.5 MPaG, the sulfur-containing and heavy component crude hydrocarbon is sent to the middle part of the stabilizer, and the sulfur-containing and heavy component rich gas is sent to the upper part of the stabilizer.

[0017] In this invention, the liquid phase at the bottom of the separator I is sent to the middle of the stabilizer tower, and the gas phase at the top is sent to the upper part of the stabilizer tower for stabilization, thereby separating C5 and above components in the raw material, reducing the impact on rich gas desulfurization, and lowering the risk of foaming.

[0018] According to the present invention, preferably, the outlet pressure of the second raw material gas compressor is 2.5~4.5 MPaG.

[0019] According to the present invention, preferably, another portion of the liquid phase at the bottom of the stabilizer reflux tank is sent to the upper part of the stabilizer.

[0020] According to the present invention, preferably, the temperature of the shallow cooler I is 15~20°C and the pressure is 2.0~4.0 MPaG.

[0021] According to the present invention, preferably, the pressure of the multi-stage absorption tower is 2.0~4.0 MPaG.

[0022] According to the present invention, preferably, the top pressure of the demethanizer is 1.0-1.5 MPaG.

[0023] According to the present invention, preferably, the top pressure of the deethaner is 1.5-2.5 MPaG.

[0024] According to the present invention, preferably, the top pressure of the propane removal column is 1.4~2.0 MPaG.

[0025] According to the present invention, preferably, the liquid phase at the bottom of the multi-stage absorption tower is mixed with the rich gas after H2 / Cl coarse separation for step (7) gas-liquid balance treatment.

[0026] In this invention, the bottom liquid phase hydrocarbon gas is balanced with the feed gas at the bottom of the multi-stage absorption tower and cooled together to further absorb C2 and above components in the gas phase before entering the separator.

[0027] According to the present invention, preferably, the ratio of the total amount of absorbent in each section of the multi-stage absorption tower to the amount of gas phase entering the tower is controlled at 2 to 6.

[0028] A second aspect of the present invention provides a multi-stage absorption and recovery device for light hydrocarbons, the device comprising: a mixed naphtha feed pipeline, a hydrorefining sulfur-rich gas feed pipeline, a stabilization tower, a first feed gas compressor, a cooler I, a liquid separator I, a second feed gas compressor, a cooler II, a liquid separator II, a crude hydrocarbon pump II, a superheater, a gas phase desulfurization tower, a desulfurization and desulfurization tower, an H2 / Cl coarse separation unit, a shallow cooler I, a shallow cooler II, a liquid separator IV, a multi-stage absorption tower, a demethanizer tower, a deethanerizer tower, and a depropanizer tower; the multi-stage absorption tower comprises, from bottom to top, a first absorption section, a second absorption section, a third absorption section, a fourth absorption section, and a reabsorption section; The hydrorefining sulfur-rich gas feed pipeline is connected in sequence to the first raw material gas compressor, cooler I and liquid separator I. The liquid separator I is equipped with a top discharge pipeline and a bottom discharge pipeline. The mixed naphtha feed pipeline, the top discharge pipeline of separator I, and the bottom discharge pipeline of separator I are connected to the stabilizer tower. The stabilizer tower is equipped with a top discharge pipeline and a bottom discharge pipeline. The bottom discharge pipeline of the stabilizer tower is divided into two branches, one of which serves as the discharge pipeline for the mixed naphtha product, and the other branch is connected to the reabsorption section of the multi-stage absorption tower. The upper part of the stabilizer tower is also equipped with a condenser and a stabilizer tower reflux tank. The top discharge pipeline of the stabilizer tower is connected to the condenser and the stabilizer tower reflux tank in sequence. The stabilizer tower reflux tank is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the stabilizer tower reflux tank is connected in sequence to the second raw material gas compressor, cooler II and liquid separator II. The liquid separator II is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the liquid separator II is connected in sequence to the superheater and the gas phase desulfurization tower, and the gas phase desulfurization tower is equipped with a gas phase desulfurization tower discharge pipeline. The bottom discharge pipeline of the stabilizer tower reflux tank is connected to the stabilizer tower reflux pump and then splits into two branches. One branch is connected to the desulfurization and desulfurization tower. The bottom discharge pipeline of the separator II is connected to the crude hydrocarbon pump II and the desulfurization and desulfurization tower in sequence. The desulfurization and desulfurization tower is equipped with a desulfurization and desulfurization tower discharge pipeline. The gas phase desulfurization tower discharge pipeline is connected to the H2 / C1 coarse separation unit. The H2 / C1 coarse separation unit is equipped with a hydrogen discharge pipeline and a rich gas discharge pipeline after H2 / C1 coarse separation. The rich gas discharge pipeline after H2 / C1 coarse separation is connected in sequence to the shallow cooler I and the liquid separator IV. The liquid separator IV is equipped with a liquid separator IV top discharge pipeline and a liquid separator IV bottom discharge pipeline. The bottom discharge pipeline of the separator IV is sequentially connected to the demethanizer. The demethanizer is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the demethanizer merges with the feed pipeline of the sulfur-rich gas from the hydrorefining process and then connects to the first feed gas compressor. The bottom discharge pipeline of the demethanizer is connected to the deethaner. The deethaner is equipped with a top discharge pipeline and a bottom discharge pipeline. The bottom discharge pipeline of the deethaner is divided into two branches, one of which connects to the third absorption section of the multi-stage absorption tower, and the other connects to the depropanizer. The depropanizer is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the depropanizer is connected to the second absorption section of the multi-stage absorption tower, and the bottom discharge pipeline of the depropanizer is divided into two branches, one of which serves as the discharge pipeline for the mixed C4 product, and the other connects to the fourth absorption section of the multi-stage absorption tower. The top discharge pipeline of the separator IV is connected to the bottom of the first absorption section of the multi-stage absorption tower. The multi-stage absorption tower is equipped with a top discharge pipeline, a bottom discharge pipeline of the reabsorption section, and a bottom discharge pipeline. The bottom discharge pipeline of the reabsorption section of the multi-stage absorption tower merges with the mixed naphtha feed pipeline.

[0029] In this invention, an intermediate reboiler is installed in the middle of the deethane removal tower, and a bottom reboiler is installed at the bottom of the tower. The intermediate reboiler and the bottom reboiler use the high-temperature liquid hydrocarbon at the bottom of the depropanizer as the heat source, and steam is not required.

[0030] According to the present invention, preferably, the H2 / C1 coarse subdivision unit includes the following two connection methods: Method 1: The gas phase desulfurization tower discharge pipeline is connected to the membrane separation unit. The membrane separation unit is equipped with a membrane separation unit hydrogen discharge pipeline and a membrane separation unit H2 / C1 coarse separation rich gas discharge pipeline. The membrane separation unit H2 / C1 coarse separation rich gas discharge pipeline is connected to shallow cooler I. Method 2: The gas phase desulfurization tower discharge pipeline is connected to the pressure swing adsorption (PSA) unit. The PSA unit is equipped with a PSA unit hydrogen discharge pipeline and a PSA unit H2 / C1 coarse separation rich gas discharge pipeline. The PSA unit H2 / C1 coarse separation rich gas discharge pipeline is connected in sequence to the PSA tail gas compressor and the shallow cooler I.

[0031] According to the present invention, preferably, the top discharge pipeline of the separator I is connected to the upper part of the stabilizer tower, and the bottom discharge pipeline of the separator I is connected to the middle part of the stabilizer tower.

[0032] According to the present invention, preferably, the bottom discharge pipeline of another stabilizer tower reflux tank is connected to the upper part of the stabilizer tower; According to the present invention, preferably, the bottom discharge pipeline of the multi-stage absorption tower is connected to the discharge pipeline of the gas phase desulfurization tower.

[0033] Compared with the prior art, the present invention has the following advantages: (1) In this invention, the atmospheric and vacuum distillation unit, each hydrorefining unit and the naphtha-containing liquid phase after the sulfur-containing gas phase is pressurized and cooled are concentrated and stabilized, reducing the content of heavy components in the sulfur-rich gas and reducing the foaming risk of the gas phase desulfurization tower.

[0034] (2) In this invention, it is no longer required that the atmospheric and vacuum distillation unit and the hydrocracking unit be equipped with separate absorption stabilization systems, which reduces the problem of secondary separation of key components.

[0035] (3) In this invention, an H2 / C1 coarse separation facility is set up in front of the absorption tower, which reduces the H2 partial pressure in the raw gas, which is beneficial to reduce the circulation volume of C4 absorbent, absorption pressure or absorption temperature, and at the same time reduces the size of the absorption tower.

[0036] (4) In this invention, the crude hydrocarbons after desulfurization and desulfurization, and the crude hydrocarbons condensed by the outlet cooler of the third raw material gas compressor are all sent to the first absorption section of the multi-stage absorption tower. The C3 to C5 components contained in the raw material itself are used as absorbents, which reduces the amount of circulating C4 and helps to reduce energy consumption.

[0037] (5) Set up multi-stage absorption towers and enter different positions of the multi-stage absorption towers according to the different contents of C3 and C4 in the absorbent to improve the absorption effect.

[0038] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0039] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0040] Figure 1A process flow diagram of multi-stage absorption and recovery of light hydrocarbons in Embodiment 1 of the present invention is shown.

[0041] Figure 2 A process flow diagram of multi-stage absorption and recovery of light hydrocarbons in Embodiment 2 of the present invention is shown.

[0042] Explanation of reference numerals in the attached figures: 1. Stabilizer; 2. Stabilizer reflux tank; 3. Stabilizer reflux pump; 4. Second feed gas compressor; 5. Cooler II; 6. Separator II; 7. Crude hydrocarbon pump II; 8. Superheater; 9. Gas phase desulfurization tower; 10. First feed gas compressor; 11. Cooler I; 12. Separator I; 17. Shallow cooler I; 18. Shallow cooler II; 19. Desulfurization and desulfurization tower; 20. Membrane separation unit or pressure swing adsorption unit; 22. Pressure swing adsorption tail gas compressor; 23. Separator IV; 24. Multistage absorption tower; 25. Methanogen removal tower; 26. Propane removal tower; 27. Ethane removal tower; S-1, Mixed naphtha; S-2, Rich gas containing sulfur and heavy components; S-3, Crude hydrocarbons containing sulfur and heavy components; S-4, Hydrotreated rich gas containing sulfur; S-6, Rich gas without sulfur; S-7, First-stage absorbent; S-8, Rich gas after H2 / C1 crude separation; S-9, Fourth-stage absorbent; S-10, Mixed C4 products; S-11, Rich ethane gas products; S-12, Methane hydrogen dry gas; S-13, Reabsorbent; S-14, Mixed naphtha products; S-15, Second-stage absorbent; S-16, Third-stage absorbent. Detailed Implementation

[0043] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0044] Example 1

[0045] The multi-stage absorption and recovery unit for light hydrocarbons includes: a mixed naphtha feed pipeline, a hydrorefining sulfur-rich gas feed pipeline, a stabilization tower 1, a first feed gas compressor 10, a cooler I 11, a liquid separator I 12, a second feed gas compressor 4, a cooler II 5, a liquid separator II 6, a crude hydrocarbon pump II 7, a superheater 8, a gas phase desulfurization tower 9, a desulfurization and desulfurization tower 19, a membrane separation unit, a shallow cooler I 17, a shallow cooler II 18, a liquid separator IV 23, a multi-stage absorption tower 24, a demethanizer tower 25, a deethaner tower 27, and a depropanizer tower 26; the multi-stage absorption tower 24 includes, from bottom to top, a first absorption section, a second absorption section, a third absorption section, a fourth absorption section, and a reabsorption section; The hydrorefining sulfur-rich gas feed pipeline is sequentially connected to the first raw material gas compressor 10, cooler I 11, and separator I 12. The separator I is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the separator I is connected to the upper part of the stabilizer tower, and the bottom discharge pipeline of the separator I is connected to the middle part of the stabilizer tower. The mixed naphtha feed pipeline is connected to the lower part of the stabilizer tower. The stabilizer tower is equipped with a top discharge pipeline and a bottom discharge pipeline. The bottom discharge pipeline is divided into two branches, one of which serves as the discharge pipeline for the mixed naphtha product, and the other is connected to the reabsorption section of the multi-stage absorption tower. The upper part of the stabilizer tower is also equipped with a condenser and a stabilizer tower reflux tank. The top discharge pipeline of the stabilizer tower is connected to the condenser and the stabilizer tower reflux tank 2 in sequence. The stabilizer tower reflux tank is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the stabilizer tower reflux tank is connected in sequence to the second raw material gas compressor 4, cooler II 5 and liquid separator II 6. The liquid separator II is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the liquid separator II is connected in sequence to the superheater and the gas phase desulfurization tower, and the gas phase desulfurization tower is equipped with a gas phase desulfurization tower discharge pipeline. The bottom discharge pipeline of the stabilizer tower reflux tank is connected to the stabilizer tower reflux pump and then splits into two branches. One branch is connected to the desulfurization and desulfurization tower. The bottom discharge pipeline of the separator II is connected to the crude hydrocarbon pump II and the desulfurization and desulfurization tower in sequence. The desulfurization and desulfurization tower is equipped with a desulfurization and desulfurization tower discharge pipeline. The gas phase desulfurization tower discharge pipeline is connected to the membrane separation unit. The membrane separation unit is equipped with a hydrogen discharge pipeline and a rich gas discharge pipeline after H2 / Cl coarse separation. The rich gas discharge pipeline after H2 / Cl coarse separation is connected in sequence to the shallow cooler I 17 and the liquid separator IV 23. The liquid separator IV is equipped with a liquid separator IV top discharge pipeline and a liquid separator IV bottom discharge pipeline. The bottom discharge pipeline of the separator IV is sequentially connected to the demethanizer. The demethanizer is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the demethanizer merges with the feed pipeline of the sulfur-rich gas from the hydrorefining process and then connects to the first feed gas compressor. The bottom discharge pipeline of the demethanizer is connected to the deethaner. The deethaner is equipped with a top discharge pipeline and a bottom discharge pipeline. The bottom discharge pipeline of the deethaner is divided into two branches, one of which connects to the third absorption section of the multi-stage absorption tower, and the other connects to the depropanizer. The depropanizer is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the depropanizer is connected to the second absorption section of the multi-stage absorption tower, and the bottom discharge pipeline of the depropanizer is divided into two branches, one of which serves as the discharge pipeline for the mixed C4 product, and the other connects to the fourth absorption section of the multi-stage absorption tower. The top discharge pipeline of the liquid separator IV is connected to the bottom of the first absorption section of the multi-stage absorption tower. The multi-stage absorption tower is equipped with a top discharge pipeline, a bottom discharge pipeline of the reabsorption section, and a bottom discharge pipeline. The bottom discharge pipeline of the reabsorption section of the multi-stage absorption tower merges with the mixed naphtha feed pipeline, and the bottom discharge pipeline of the multi-stage absorption tower merges with the discharge pipeline of the gas phase desulfurization tower.

[0046] The process flow diagram for multi-stage absorption and recovery of light hydrocarbons using the above-mentioned device is as follows: Figure 1 As shown: (1) Gas phase pressurization I: The sulfur-rich gas refined by hydrogenation is compressed and pressurized by the first raw material gas compressor, cooled by the cooler I and separated by the separator I. The top of the separator is rich gas containing sulfur and heavy components, and the bottom of the separator is crude hydrocarbon containing sulfur and heavy components. The outlet pressure of the first raw material gas compressor is 3.0 MPaG.

[0047] (2) Stabilization of naphtha throughout the plant: Mixed naphtha, rich gas containing sulfur and heavy components and crude hydrocarbon containing sulfur and heavy components are sent to the stabilization tower for stabilization treatment. Stabilized naphtha is obtained at the bottom of the tower and divided into two parts. One part is used as mixed naphtha product, and the other part is sent to the top of the reabsorption section of the multi-stage absorption tower as a reabsorbent. The top gas phase of the stabilization tower is obtained at the top of the tower. After being condensed by the condenser, it is sent to the stabilization tower reflux tank to obtain rich gas at the top of the stabilization tower reflux tank and liquid phase at the bottom of the stabilization tower reflux tank. The operating pressure of the stabilization tower is 1.0 MPaG, the top temperature of the tower is 45℃, and the outlet pressure of the stabilization tower reflux pump is 3.5 MPaG.

[0048] (3) Gas phase pressure boosting II: The rich gas at the top of the stabilizer tower reflux tank is sent to the second raw material gas compressor for compression and pressure boosting, the cooler II for cooling, and the separator II for liquid separation, to obtain the rich gas at the top of the separator II and the liquid phase at the bottom of the separator II; the outlet pressure of the first raw material gas compressor is 2.5-4.5 MPaG.

[0049] (4) Rich gas desulfurization: The rich gas at the top of the liquid separator II is sent to the gas phase desulfurization tower after passing through the superheater. It comes into countercurrent contact with the lean amine liquid to remove hydrogen sulfide and obtain sulfur-free rich gas. The superheater 8 controls the superheat at 3-5℃ to avoid condensation and foaming of the gas phase desulfurization tower. The operating pressure of the gas phase desulfurization tower is 2.5~4.5MPaG.

[0050] (5) Crude hydrocarbon desulfurization: The liquid phase at the bottom of the stabilizer reflux tank is pressurized by the stabilizer reflux pump and divided into two parts. One part enters the desulfurization and desulfurization tower, while the liquid phase at the bottom of the separator II is pumped out by the crude hydrocarbon pump II and sent to the desulfurization and desulfurization tower. After removing hydrogen sulfide and mercaptan, sulfur-free crude hydrocarbons are obtained. After being cooled by the shallow cooler II, they are sent to the top of the first absorption section of the multi-stage absorption tower as a first-stage absorbent. The operating temperature of the desulfurization and desulfurization tower is 35~45℃, and the operating pressure is 3.0~5.0MPaG. The crude hydrocarbons are sent to the first absorption section of the multi-stage absorption tower, where the C3-C4 components in the crude hydrocarbon feedstock are used as absorbents to initially absorb the C2 components, which can reduce the amount of circulating absorbent.

[0051] (6) H2 / C1 coarse separation: The sulfur-free rich gas undergoes H1 / C1 coarse separation to obtain a coarsely separated H2-rich gas phase and a rich gas after H2 / C1 coarse separation; the partial pressure of hydrogen in the feed gas after H2 / C1 coarse separation is significantly reduced, while the partial pressure of key components increases, which is beneficial to reducing the amount of absorbent. The H2 recovery rate is 60%~85%, and the pressure loss of the membrane separation tail gas is 0.2~0.5 MPaG.

[0052] (7) Gas-liquid balance: After H2 / C1 coarse separation, the rich gas is cooled by shallow cooler I and then enters the liquid separator IV for liquid separation, resulting in the gas phase at the top of liquid separator IV and the liquid phase at the bottom of liquid separator IV; after mixing and cooling with the raw gas, the hydrocarbon phase at the bottom of the multi-stage absorption tower can further absorb the C2 component in this process, reducing the packing height of the multi-stage absorption tower and the circulating absorption dose. The outlet temperature of shallow cooler I is 15℃.

[0053] (8) C3 / C4 separation: The liquid phase at the bottom of the separator IV is sent to the demethanizer. The gas phase at the top of the tower is mixed with the sulfur-rich gas from the hydrorefining process and subjected to step (1) gas phase pressurization I. The liquid phase at the bottom of the demethanizer is sent to the deethaner, and the ethane-rich gas product is obtained at the top of the tower. The liquid phase at the bottom of the tower is divided into two parts. One part is sent to the top of the third absorption section of the multi-stage absorption tower as the third-stage absorbent, and the other part is sent to the depropanizer. The gas phase at the top of the tower is sent to the top of the second absorption section of the multi-stage absorption tower as the second-stage absorbent. The liquid phase at the bottom of the tower is divided into two parts. One part is used as the mixed C4 product, and the other part is sent to the top of the fourth absorption section of the multi-stage absorption tower as the fourth-stage absorbent. The operating pressure of the demethanizer is 0.5~1.0 MPaG, the deethaner is 1.5-2.5 MPaG, and the depropanizer is 1.5~2.5 MPaG.

[0054] (9) Multistage absorption: The gas phase from the top of the separator IV is sent to the bottom of the first absorption section of the multistage absorption tower. After passing through the first absorption section, the second absorption section, the third absorption section, the fourth absorption section, and the reabsorption section in sequence, multistage absorption is carried out. The top of the multistage absorption tower is obtained as methane hydrogen dry gas, and the liquid phase from the bottom of the reabsorption section is sent to the stabilization tower for step (2) naphtha stabilization treatment of the whole plant. According to the different C3 and C4 contents and compositions of each absorbent, they enter different positions of the multistage absorption tower. Based on the similar compatibility characteristics of the components, the absorption characteristics of each section of absorbent are maximized to achieve the purpose of reducing the absorbent dosage. The operating pressure of the multistage absorption tower is 2.5-4.0 MPaG, and 1-3 intermediate reflux sections can be set. The ratio of the total amount of absorbent in each section of the multistage absorption tower to the amount of gas phase entering the tower is controlled at 2~6.

[0055] The composition and properties of the products obtained by separating dry gas, ethane-rich gas, propane-rich gas, and mixed C4 from light hydrocarbons using the above method are shown in Tables 1-3. The recovery rate of C2 component was 98.5%, and the recovery rates of C3 and C4 components were 99%.

[0056] Table 1 Properties of dry gas

[0057] Table 2 Properties of Ethane-Rich Gas

[0058] Table 3 Properties of mixed C4

[0059] Example 2

[0060] The only difference between the device in this embodiment and that in embodiment 1 is that the H2 / C1 coarse separation unit is a pressure swing adsorption (PSA) unit. The PSA unit is equipped with a PSA unit hydrogen outlet pipeline and a PSA unit H2 / C1 coarse separation rich gas outlet pipeline. The PSA unit H2 / C1 coarse separation rich gas outlet pipeline is connected in sequence to the PSA tail gas compressor 22 and the shallow cooler I 17.

[0061] Adopting such Figure 2 The process flow diagram shown illustrates the desulfurization of oil and gas and the recovery of light hydrocarbons: The only difference between this embodiment and Embodiment 1 is that: (7) H2 / C1 coarse fraction: Pressure Swing Adsorption (PSA): The sulfur-free rich gas passes through the PSA unit to obtain hydrogen and H2 / Cl coarse separation rich gas. The H2 / Cl coarse separation rich gas is pressurized by the PSA tail gas compressor and then sent to gas-liquid equilibrium. The H2 / Cl coarse separation rich gas is pressurized to 2.5~4.5 MPaG by the PSA tail gas compressor.

[0062] The product properties are consistent with those in Tables 1-3 of Example 1.

[0063] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for multi-stage absorption and recovery of light hydrocarbons, characterized in that, The method includes the following steps: (1) Gas phase pressurization I: The sulfur-rich gas from the hydrogenation refining process is compressed and pressurized by the first raw material gas compressor, cooled by the cooler I, and separated by the separator I. The top of the separator yields sulfur-rich gas containing heavy components, and the bottom of the separator yields crude hydrocarbons containing sulfur and heavy components. (2) Stabilization of naphtha throughout the plant: Mixed naphtha, rich gas containing sulfur and heavy components and crude hydrocarbon containing sulfur and heavy components are sent to the stabilization tower for stabilization treatment. Stabilized naphtha is obtained at the bottom of the tower and divided into two parts. One part is used as mixed naphtha product, and the other part is sent to the top of the reabsorption section of the multi-stage absorption tower as a reabsorbent. The top gas phase of the stabilization tower is obtained at the top of the tower. After being condensed by the condenser, it is sent to the stabilization tower reflux tank to obtain rich gas at the top of the stabilization tower reflux tank and liquid phase at the bottom of the stabilization tower reflux tank. (3) Gas phase pressurization II: The rich gas at the top of the stabilizer tower reflux tank is sent to the second raw material gas compressor for compression and pressurization, cooled by cooler II and separated by separator II to obtain the rich gas at the top of separator II and the liquid phase at the bottom of separator II; (4) Rich gas desulfurization: The rich gas at the top of the separator II tank passes through the superheater and is sent to the gas phase desulfurization tower, where it comes into countercurrent contact with the lean amine liquid to remove hydrogen sulfide and obtain sulfur-free rich gas. (5) Crude hydrocarbon desulfurization: The liquid phase at the bottom of the stabilizer reflux tank is pressurized by the stabilizer reflux pump and divided into two parts. One part enters the desulfurization and desulfurization tower, and the liquid phase at the bottom of the separator II is pumped out by the crude hydrocarbon pump II and sent to the desulfurization and desulfurization tower. After removing hydrogen sulfide and mercaptan, sulfur-free crude hydrocarbon is obtained. After being cooled by the shallow cooler II, it is sent to the top of the first absorption section of the multi-stage absorption tower as a first-stage absorbent. (6) H2 / C1 coarse separation: sulfur-free rich gas is subjected to H1 / C1 coarse separation to obtain the H2-rich gas phase after coarse separation and the rich gas after H2 / C1 coarse separation; (7) Gas-liquid balance: After the H2 / C1 coarse separation, the rich gas is cooled by shallow cooler I and then enters the liquid separator IV for liquid separation, resulting in the gas phase at the top of liquid separator IV and the liquid phase at the bottom of liquid separator IV. (8) C3 / C4 separation: The liquid phase at the bottom of the separator IV is sent to the demethanizer. The gas phase at the top of the tower is mixed with the sulfur-rich gas from the hydrorefining process and subjected to step (1) gas phase pressurization I. The liquid phase at the bottom of the tower is sent to the deethaner. The ethane-rich gas product is obtained at the top of the tower. The liquid phase at the bottom of the tower is divided into two parts. One part is sent to the top of the third absorption section of the multi-stage absorption tower as the third-stage absorbent. The other part is sent to the depropanizer. One part of the liquid phase at the top of the tower is sent to the top of the second absorption section of the multi-stage absorption tower as the second-stage absorbent. The remaining part is used as the liquid propane product. The liquid phase at the bottom of the tower is divided into two parts. One part is used as the mixed C4 product. The other part is sent to the top of the fourth absorption section of the multi-stage absorption tower as the fourth-stage absorbent. (9) Multistage absorption: The gas phase at the top of the separator IV tank is sent to the bottom of the first absorption section of the multistage absorption tower. After passing through the first absorption section, the second absorption section, the third absorption section, the fourth absorption section and the reabsorption section in sequence, multistage absorption is carried out. The top of the multistage absorption tower is obtained as methane hydrogen dry gas. The liquid phase at the bottom of the reabsorption section is sent to the stabilization tower for step (2) naphtha stabilization treatment of the whole plant.

2. The method for multi-stage absorption and recovery of light hydrocarbons according to claim 1, wherein, The H2 / C1 coarse division includes one of the following two methods: Method 1: Membrane separation: The sulfur-free rich gas is purified into hydrogen by a membrane separation unit to obtain purified hydrogen and H2 / Cl coarse separation rich gas. The H2 / Cl coarse separation rich gas is sent to gas-liquid equilibrium. The pressure loss of the membrane separation tail gas is 0.2~0.5MPaG. Method 2: Pressure Swing Adsorption (PSA): The sulfur-free rich gas passes through the PSA unit to obtain hydrogen and H2 / Cl coarse separation rich gas. The H2 / Cl coarse separation rich gas is pressurized by the PSA tail gas compressor and then sent to gas-liquid equilibrium. The H2 / Cl coarse separation rich gas is pressurized to 2.5~4.5 MPaG by the PSA tail gas compressor.

3. The method for multi-stage absorption and recovery of light hydrocarbons according to claim 1, wherein, The operating temperature at the top of the stabilizer tower is 40~60℃, and the operating pressure is 0.8~1.2MPaG; The temperature of the stabilizer tower reflux tank is 30~45℃; The operating temperature of the gas phase desulfurization tower is 40~45℃, and the operating pressure is 2.5~4.5MPaG; The operating temperature of the desulfurization and desulfurization tower is 35~45℃, and the operating pressure is 3.0~5.0MPaG.

4. The method for multi-stage absorption and recovery of light hydrocarbons according to claim 1, wherein, The outlet pressure of the first raw material gas compressor is 2.5~4.5 MPaG. The sulfur-containing and heavy component crude hydrocarbon is sent to the middle part of the stabilizer tower, and the sulfur-containing and heavy component rich gas is sent to the upper part of the stabilizer tower. The outlet pressure of the second raw material gas compressor is 2.5~4.5 MPaG; Another portion of the liquid phase from the bottom of the stabilizer reflux tank is sent to the upper part of the stabilizer.

5. The method for multi-stage absorption and recovery of light hydrocarbons according to claim 1, wherein, The temperature of the shallow cooler I is 15~20℃, and the pressure is 2.0~4.0MPaG; The pressure of the multi-stage absorption tower is 2.0~4.0 MPaG.

6. The method for multi-stage absorption and recovery of light hydrocarbons according to claim 1, wherein, The top pressure of the demethanizer is 1.0-1.5 MPaG; The top pressure of the deethanizer is 1.5-2.5 MPaG; The top pressure of the propane removal column is 1.4~2.0 MPaG.

7. The method for multi-stage absorption and recovery of light hydrocarbons according to claim 1, wherein, The bottom liquid phase of the multi-stage absorption tower is mixed with the rich gas after H2 / Cl coarse separation and then subjected to step (7) gas-liquid balance treatment. The ratio of the total amount of absorbent in each stage of the multi-stage absorption tower to the amount of gas entering the tower is controlled between 2 and 6.

8. A multi-stage absorption and recovery device for light hydrocarbons, characterized in that, The device includes: a mixed naphtha feed line, a hydrorefining sulfur-rich gas feed line, a stabilizer tower, a first feed gas compressor, a cooler I, a separator I, a second feed gas compressor, a cooler II, a separator II, a crude hydrocarbon pump II, a superheater, a gas phase desulfurization tower, a desulfurization and desulfurization tower, an H2 / Cl coarse separation unit, a shallow cooler I, a shallow cooler II, a separator IV, a multi-stage absorption tower, a demethanizer tower, a deethanerizer tower, and a depropanizer tower; the multi-stage absorption tower, from bottom to top, includes a first absorption section, a second absorption section, a third absorption section, a fourth absorption section, and a reabsorption section; The hydrorefining sulfur-rich gas feed pipeline is connected in sequence to the first raw material gas compressor, cooler I and liquid separator I. The liquid separator I is equipped with a top discharge pipeline and a bottom discharge pipeline. The mixed naphtha feed pipeline, the top discharge pipeline of separator I, and the bottom discharge pipeline of separator I are connected to the stabilizer tower. The stabilizer tower is equipped with a top discharge pipeline and a bottom discharge pipeline. The bottom discharge pipeline of the stabilizer tower is divided into two branches, one of which serves as the discharge pipeline for the mixed naphtha product, and the other branch is connected to the reabsorption section of the multi-stage absorption tower. The upper part of the stabilizer tower is also equipped with a condenser and a stabilizer tower reflux tank. The top discharge pipeline of the stabilizer tower is connected to the condenser and the stabilizer tower reflux tank in sequence. The stabilizer tower reflux tank is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the stabilizer tower reflux tank is connected in sequence to the second raw material gas compressor, cooler II and liquid separator II. The liquid separator II is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the liquid separator II is connected in sequence to the superheater and the gas phase desulfurization tower, and the gas phase desulfurization tower is equipped with a gas phase desulfurization tower discharge pipeline. The bottom discharge pipeline of the stabilizer tower reflux tank is connected to the stabilizer tower reflux pump and then splits into two branches. One branch is connected to the desulfurization and desulfurization tower. The bottom discharge pipeline of the separator II is connected to the crude hydrocarbon pump II and the desulfurization and desulfurization tower in sequence. The desulfurization and desulfurization tower is equipped with a desulfurization and desulfurization tower discharge pipeline. The gas phase desulfurization tower discharge pipeline is connected to the H2 / C1 coarse separation unit. The H2 / C1 coarse separation unit is equipped with a hydrogen discharge pipeline and a rich gas discharge pipeline after H2 / C1 coarse separation. The rich gas discharge pipeline after H2 / C1 coarse separation is connected in sequence to the shallow cooler I and the liquid separator IV. The liquid separator IV is equipped with a liquid separator IV top discharge pipeline and a liquid separator IV bottom discharge pipeline. The bottom discharge pipeline of the separator IV is sequentially connected to the demethanizer. The demethanizer is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the demethanizer merges with the feed pipeline of the sulfur-rich gas from the hydrorefining process and then connects to the first feed gas compressor. The bottom discharge pipeline of the demethanizer is connected to the deethaner. The deethaner is equipped with a top discharge pipeline and a bottom discharge pipeline. The bottom discharge pipeline of the deethaner is divided into two branches, one of which connects to the third absorption section of the multi-stage absorption tower, and the other connects to the depropanizer. The depropanizer is equipped with a top discharge pipeline and a bottom discharge pipeline. The top discharge pipeline of the depropanizer is connected to the second absorption section of the multi-stage absorption tower, and the bottom discharge pipeline of the depropanizer is divided into two branches, one of which serves as the discharge pipeline for the mixed C4 product, and the other connects to the fourth absorption section of the multi-stage absorption tower. The top discharge pipeline of the separator IV is connected to the bottom of the first absorption section of the multi-stage absorption tower. The multi-stage absorption tower is equipped with a top discharge pipeline, a bottom discharge pipeline of the reabsorption section, and a bottom discharge pipeline. The bottom discharge pipeline of the reabsorption section of the multi-stage absorption tower merges with the mixed naphtha feed pipeline.

9. The multi-stage absorption and recovery device for light hydrocarbons according to claim 8, wherein, The H2 / C1 coarse subdivision unit includes the following two connection methods: Method 1: The gas phase desulfurization tower discharge pipeline is connected to the membrane separation unit. The membrane separation unit is equipped with a membrane separation unit hydrogen discharge pipeline and a membrane separation unit H2 / C1 coarse separation rich gas discharge pipeline. The membrane separation unit H2 / C1 coarse separation rich gas discharge pipeline is connected to shallow cooler I. Method 2: The gas phase desulfurization tower discharge pipeline is connected to the pressure swing adsorption (PSA) unit. The PSA unit is equipped with a PSA unit hydrogen discharge pipeline and a PSA unit H2 / C1 coarse separation rich gas discharge pipeline. The PSA unit H2 / C1 coarse separation rich gas discharge pipeline is connected in sequence to the PSA tail gas compressor and the shallow cooler I.

10. The multi-stage absorption and recovery device for light hydrocarbons according to claim 8, wherein, The top discharge pipeline of the separator I is connected to the upper part of the stabilizer tower, and the bottom discharge pipeline of the separator I is connected to the middle of the stabilizer tower. The bottom discharge pipeline of the other stabilizer tower reflux tank is connected to the upper part of the stabilizer tower; The discharge pipeline at the bottom of the multi-stage absorption tower merges with the discharge pipeline of the gas phase desulfurization tower.

Images