Process for recovering ethylene and ethane

Abstract

This invention relates to the field of chemical engineering and discloses a method for recovering ethylene and ethane. The method includes: (1) sequentially subjecting refinery dry gas to alkaline washing and deoxygenation to obtain pretreated gas, and then performing gas-liquid separation on the pretreated gas to obtain a first gas phase and a first liquid phase; (2) sequentially subjecting the first gas phase to pre-absorption drying and pre-absorption cooling to obtain a pre-absorption gas phase; and subjecting the first liquid phase to pre-absorption drying to obtain a pre-absorption liquid phase; (3) feeding the pre-absorption gas phase and pre-absorption liquid phase into a cryogenic absorption tower for cryogenic absorption to obtain a cryogenic tower top gas phase and a cryogenic tower bottom liquid phase. This method can separate and recover components from refinery dry gas, while also achieving a high recovery rate and low energy consumption.

Description

Technical Field

[0001] This invention relates to the field of gas processing, and more specifically to a method for recovering ethylene and ethane. Background Technology

[0002] Refinery dry gas mainly comes from the secondary processing of crude oil, such as catalytic cracking, thermal cracking, delayed coking, and hydrocracking. However, currently, most refineries still burn refinery dry gas as fuel gas, which has low utilization value and causes great waste of resources and environmental pollution.

[0003] Refinery dry gas is generally classified into saturated and unsaturated dry gas. Saturated dry gas contains higher levels of ethane and propane, while its ethylene and propylene content is very low. Unsaturated dry gas contains more ethylene. Of the ethylene and ethane in refinery dry gas, ethane is an ideal feedstock for cracking, and ethylene is also an important basic raw material for organic chemicals. If the components in refinery dry gas can be separated to recover certain target gases, especially ethylene and ethane, it can generate considerable economic benefits. However, current separation processes still suffer from problems such as high energy consumption and low recovery rates. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a method for recovering ethylene and ethane. This method can separate and recover the components of refinery dry gas to obtain ethylene and ethane, while having a high recovery rate and low energy consumption.

[0005] To achieve the above objectives, the present invention provides a method for recovering ethylene and ethane, the method comprising:

[0006] (1) The dry gas from the refinery is subjected to alkali washing and deoxygenation treatment in sequence to obtain pretreated gas, and the pretreated gas is subjected to gas-liquid separation to obtain the first gas phase and the first liquid phase;

[0007] (2) The first gas phase is dried and cooled before absorption in sequence to obtain the gas phase before absorption; the first liquid phase is dried before absorption to obtain the liquid phase before absorption.

[0008] (3) The gas phase and liquid phase before absorption are fed into the cryogenic absorption tower for cryogenic absorption to obtain the gas phase at the top of the cryogenic tower and the liquid phase at the bottom of the cryogenic tower.

[0009] Through the above technical solution, the present invention can fully separate and recover the target gas in refinery dry gas to obtain ethylene and ethane, with a high recovery rate and low energy consumption. Attached Figure Description

[0010] Figure 1 This is a process flow diagram for recovering ethylene and ethane according to a preferred embodiment of the present invention.

[0011] Explanation of reference numerals in the attached figures

[0012] 1-Compressor; 2-Amine washing tower; 3-Inorganic alkali washing tower; 4-Deoxygenation reactor; 5-Cooler; 6-Gas-liquid separator; 7-Liquid phase dryer; 8-Gas phase dryer; 9-Cold box; 10-Cryogenic absorption tower; 11-Refinery dry gas; 12-Cryogenic absorbent; 13-Cryogenic tower bottom liquid phase; 14-Cryogenic tower top gas phase. Detailed Implementation

[0013] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0014] This invention provides a method for recovering ethylene and ethane, the method comprising:

[0015] (1) The dry gas from the refinery is subjected to alkali washing and deoxygenation treatment in sequence to obtain pretreated gas, and the pretreated gas is subjected to gas-liquid separation to obtain the first gas phase and the first liquid phase;

[0016] (2) The first gas phase is dried and cooled before absorption in sequence to obtain the gas phase before absorption; the first liquid phase is dried before absorption to obtain the liquid phase before absorption.

[0017] (3) The gas phase and liquid phase before absorption are fed into the cryogenic absorption tower for cryogenic absorption to obtain the gas phase at the top of the cryogenic tower and the liquid phase at the bottom of the cryogenic tower.

[0018] Refinery dry gas typically contains hydrogen, nitrogen, carbon monoxide, carbon dioxide, and water. Saturated refinery dry gas also contains C1-C4 alkanes, with a slightly lower olefin content; unsaturated refinery dry gas contains both C1-C4 alkanes and C2-C4 olefins. To recover hydrocarbons from refinery dry gas, alkaline washing is required to remove acidic gases and oxygen. Using the method described in this invention, the lower temperature in the cryogenic absorption tower allows for more complete separation of methane, hydrogen, and other components. The majority of the C2 components (ethylene and ethane) enter the cryogenic tower bottom liquid phase, resulting in a high C2 component recovery rate. Downstream industries can then perform further separation as needed. It is understood that the chemical industry commonly uses "standard oil" to measure energy consumption; one kilogram of standard oil is approximately 10,000 kilocalories.

[0019] According to the present invention, preferably, the refinery dry gas used for alkali washing meets the following requirements: pressure from 0.8 MPa to 3.2 MPa, and temperature from 20°C to 50°C. The pressure of the refinery dry gas can be increased to the above range by a compressor before alkali washing, and a cooler can be installed at the compressor outlet to adjust the temperature to the above range.

[0020] According to the present invention, preferably, the alkaline washing method includes: sequentially subjecting refinery dry gas to organic amine washing and inorganic alkaline washing.

[0021] According to the present invention, preferably, the conditions for the organic amine washing include: the eluent is an organic amine solution, and the mass concentration of the organic amine in the organic amine solution is 15-25 wt%. The amine washing can be carried out in an amine washing tower.

[0022] According to the present invention, preferably, the organic amine is methyldiethanolamine.

[0023] According to the present invention, the preferred conditions for inorganic alkaline washing include: the eluent is an alkali metal hydroxide solution, and the mass concentration of the alkali metal hydroxide in the alkali metal hydroxide solution is 5-10 wt%.

[0024] According to the present invention, preferably, the alkali metal hydroxide is sodium hydroxide. Inorganic alkaline washing can be carried out in an inorganic alkaline washing tower.

[0025] It is understandable that the gas can be pressurized before deoxygenation, based on the pressure required for cryogenic absorption.

[0026] According to the present invention, preferably, the conditions for the deoxidation treatment include: a temperature of 50-380℃ (for example, 50℃, 60℃, 80℃, 100℃, 130℃, 150℃, 170℃, 200℃, 220℃, 250℃, 270℃, 300℃, 320℃, 340℃, 360℃, 380℃, and values ​​within any two of the above values), and a pressure of 1-6.5MPa (for example, 1.2MPa, 1.3MPa, 1.4MPa, 1.5MPa, 1.7MPa, 2MPa, 2.3MPa, 2.5MPa, 2.7MPa, 3MPa, 3.3MPa, 3.5MPa, 3.7MPa, 4MPa, 4.3MPa, 4.5MPa, 5MPa, 6MPa, 6.5MPa, and values ​​within any two of the above values). The gas temperature can be heated to the above range using a heater.

[0027] According to the present invention, preferably, the material temperature for gas-liquid separation is 5 to 38°C (for example, it can be 5°C, 7°C, 10°C, 12°C, 15°C, 17°C, 20°C, 23°C, 25°C, 28°C, 30°C, 32°C, 34°C, 36°C, 38°C, and any two of the above values). The pre-treated gas can be pre-cooled in a cooler before gas-liquid separation.

[0028] According to the present invention, preferably, the first gas phase is cooled to a temperature of -70°C to -110°C before absorption. The cooling of the first gas phase before absorption can be carried out in a cold box.

[0029] According to the present invention, preferably, the conditions for pre-absorption drying are such that the water content in the dried material is ≤1.5 ppm by volume. The aforementioned pre-absorption drying refers to pre-absorption drying of the first gas phase and pre-absorption drying of the first liquid phase.

[0030] The first liquid phase is dried and sent directly into the cryogenic absorption tower, without needing to pass through the cold box, thus reducing the load on the cold box.

[0031] It is understandable that water needs to be removed from the material as much as possible to prevent it from freezing in the cryogenic absorption tower.

[0032] According to the present invention, a preferred method for cryogenic absorption includes: carrying out the process in the presence of a cryogenic absorbent; feeding the pre-absorption gas phase into the upper middle part of the cryogenic absorption tower and feeding the pre-absorption liquid phase into the lower part of the cryogenic absorption tower. According to the present invention, preferably, the gas phase at the top of the cryogenic tower is used as the first gas phase for at least a portion of the refrigerant used for pre-absorption cooling. This also reduces the amount of additional refrigerant introduced into the cold box and allows for sufficient recovery of the cold energy in the gas phase at the top of the cryogenic tower. The cryogenic absorbent can be a light hydrocarbon with C3 to C5 as its main components, offering high selectivity, easy availability, and low cost.

[0033] According to the present invention, preferably, no condenser is installed in the cryogenic absorption tower, and the cryogenic absorbent is fed into the cryogenic absorption tower from the top. The presence of the cryogenic absorbent allows for the further and more complete absorption of components other than methane hydrogen present in the upper part of the tower without the need for a condenser, reducing the consumption of cooling capacity. Specifically, relative to the total mass of the pre-absorption gas phase and pre-absorption liquid phase introduced into the cryogenic absorption tower per unit time, the mass consumption of the cryogenic absorbent per unit time can be maintained at 0.03-0.4 times the total mass. The cooling capacity required for the cryogenic absorption tower can be utilized from the ethylene or propylene refrigeration compressor of the ethylene plant, eliminating the need for an expander, resulting in lower investment and simpler operation. The cryogenic absorbent introduced from the outside can be cooled to -60°C to -120°C in a cold box before the first gas phase is absorbed before being introduced into the cryogenic absorption tower.

[0034] According to the present invention, the preferred operating conditions in the cryogenic absorption tower include: a theoretical plate number preferably of 30 to 80 (for example, it can be 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or any two of the above values), and an operating pressure of 0.5 to 5.5 MPa (for example, it can be 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa, or any two of the above values). The temperature at the top of the column is -60℃ to -110℃ (for example, it can be -60℃, -65℃, -70℃, -75℃, -80℃, -85℃, -90℃, -95℃, -100℃, -105℃, -110℃, or any two of the above values), and the temperature at the bottom of the column is -30℃ to 60℃ (for example, it can be -30℃, -20℃, -10℃, 0℃, 10℃, 20℃, 30℃, 40℃, 50℃, 55℃, 60℃, or any two of the above values). In a cryogenic absorption tower, the lower temperature, combined with the cryogenic absorbent, causes the relative volatility of the gas components to differ. Methane and hydrogen move towards the top of the column in gaseous form, while other hydrocarbons are condensed or absorbed by the absorbent and move towards the bottom of the column.

[0035] The present invention will be described in detail below through examples. The methods for recovering ethylene and ethane in Examples 1-3, such as... Figure 1 The process is carried out in the equipment shown.

[0036] Figure 1 In the diagram, 1 is the compressor; 2 is the amine washing tower; 3 is the inorganic alkali washing tower; 4 is the deoxygenation reactor; 5 is the cooler; 6 is the gas-liquid separator; 7 is the liquid phase dryer; 8 is the gas phase dryer; 9 is the cold box; 10 is the cryogenic absorption tower; 11 is the refinery dry gas; 12 is the cryogenic absorbent; 13 is the cryogenic tower bottom liquid phase; and 14 is the cryogenic tower top gas phase.

[0037] According to the material flow, amine washing tower 2, inorganic alkaline washing tower 3, deoxygenation reactor 4, and cooler 5 are connected sequentially by pipelines. Compressors 1 are installed before amine washing tower 2 and after inorganic alkaline washing tower 3 (the compressor outlet before amine washing tower 2 also has a cooler, and the compressor outlet after inorganic alkaline washing tower 3 has a heater, not shown in the diagram). Compressors 1 can be selectively activated to achieve the target pressure. Gas-liquid separator 6 is connected to liquid dryer 7 and gas dryer 8, respectively, so that the gas phase separated by gas-liquid separator 6 can enter gas dryer 8, and the liquid phase can enter liquid dryer 7. Liquid dryer 7 is connected to cryogenic absorption tower 10 by pipelines, so that the material from liquid dryer 7 enters cryogenic absorption tower 10 through the lower part of cryogenic absorption tower 10. The gas phase dryer 8, cold box 9, and cryogenic absorption tower 10 are connected in sequence, so that the material from the gas phase dryer 8 is cooled by the cold box 9 and then enters the cryogenic absorption tower 10 from the upper middle part. The top of the cryogenic absorption tower 10 is connected to the cold box 9 via a pipe, allowing the gas phase at the top of the cryogenic absorption tower 10 to flow back into the cold box 9 as a refrigerant before being drawn out from the cold box 9. Furthermore, the piping arrangement ensures that the cryogenic absorbent 12 introduced from the outside first passes through the cold box 9 before being introduced into the cryogenic absorption tower.

[0038] Example 1

[0039] The composition and mass flow rate of the saturated refinery dry gas 11 used in this embodiment, as well as the composition and mass flow rate of the introduced cryogenic absorbent 12, are shown in Table 1.

[0040] Table 1

[0041]

[0042]

[0043] The specific method for recovering refinery dry gas using the oil separation absorption method is as follows:

[0044] (1) Refinery dry gas 11 (pressure 0.5 MPa) is introduced into compressor 1 to increase the pressure to 2 MPa, and then cooled to 40°C by the cooler at the outlet of compressor 1. It is then sent to amine washing tower 2 (the eluent is an aqueous solution of methyl diethanolamine with a concentration of 18% by mass) for organic amine washing. The material after organic amine washing is then sent to inorganic alkali washing tower 3 (the eluent is an aqueous solution of sodium hydroxide with a concentration of 10% by mass) for inorganic alkali washing.

[0045] The material after inorganic alkaline washing is increased to 4.0 MPa by compressor 1 and heated to 150°C by heater. It is then introduced into deoxygenation reactor 4 to remove oxygen and obtain pretreated gas.

[0046] (2) The pretreated gas is introduced into the cooler 5 and pre-cooled to 15°C. Then it is sent to the gas-liquid separator 6 for gas-liquid separation to obtain the first gas phase and the first liquid phase.

[0047] (3) The first liquid phase is introduced into the liquid phase dryer 7 for liquid phase drying until the water content is ≤1.5 ppm by volume, and then sent to the lower part of the cryogenic absorption tower 10.

[0048] The first gas phase is introduced into the gas phase dryer 8 and dried until the water content is ≤1.5 ppm by volume. After gas phase drying, it is sent to the cold box 9 and cooled to -97°C before being introduced into the upper middle part of the cryogenic absorption tower 10.

[0049] The cryogenic absorption tower 10 does not have a condenser, has a theoretical plate count of 52, and operates at a pressure of 3.1 MPa. The cryogenic absorbent 12 is cooled to -100°C by the cold box 9 before being fed to the top of the tower. The top temperature is -84°C, and the bottom temperature is 44°C. The vapor phase 14 from the top of the cryogenic tower is discharged from the unit after the cold box recovers its refrigeration. The cryogenic bottom liquid phase 13 is obtained in the bottom of the cryogenic tower.

[0050] The discharge flow rates and compositions of the cryogenic tower top gas phase 14 and cryogenic tower bottom liquid phase 13 are shown in Table 2.

[0051] Table 2

[0052] Cryogenic tower kettle liquid phase 13 Cryogenic Tower Top Gas Phase 14 Mass flow rate (kg / hr) 91409 48126 Molar composition (%) hydrogen 0 55.93 Nitrogen 0 6.13 oxygen 0 0 carbon monoxide 0 0.43 carbon dioxide 0 0 methane 0 36.89 Ethane 57.50 0.24 propane 25.25 0.35 Isobutane 8.71 0.02 n-Butane 4.31 0.01 pentane 3.14 0 hexane 1.09 0 water 0 0

[0053] In the cryogenic tower bottom liquid phase 13, the C2 recovery rate is greater than 99.0%. The energy consumption is 61 kg standard oil / t feed (feed refers to the refinery dry gas entering the unit).

[0054] Example 2

[0055] The composition of the unsaturated refinery dry gas 11 used in this embodiment and the mass flow rate of the introduction device, as well as the composition of the introduced cryogenic absorbent 12 and the mass flow rate of the introduction device, are shown in Table 3.

[0056] Table 3

[0057]

[0058]

[0059] The specific method for recovering refinery dry gas using the oil separation absorption method is as follows:

[0060] (1) Refinery dry gas B (pressure 0.6 MPa) is introduced into compressor 1 to increase the pressure to 2.2 MPa, and then cooled to 45°C by the cooler at the outlet of compressor 1. It is then sent to amine washing tower 2 (the eluent is an aqueous solution of methyl diethanolamine with a concentration of 22% by mass) for organic amine washing. The material after organic amine washing is then sent to inorganic alkali washing tower 3 (the eluent is an aqueous solution of sodium hydroxide with a concentration of 8.5% by mass) for inorganic alkali washing.

[0061] After the inorganic alkaline washing material is heated to 130°C by a heater, it is introduced into deoxygenation reactor 4 to remove oxygen and obtain pretreated gas.

[0062] (2) The pretreated gas is introduced into the cooler 5 and pre-cooled to 20°C. Then it is sent to the gas-liquid separator 6 for gas-liquid separation to obtain the first gas phase and the first liquid phase.

[0063] (3) The first liquid phase is introduced into the liquid phase dryer 7 for liquid phase drying until the water content is ≤1.5 ppm by volume, and then sent to the lower part of the cryogenic absorption tower 10.

[0064] The first gas phase is introduced into the gas phase dryer 8 and dried until the water content is ≤1.5 ppm by volume. After gas phase drying, it is sent to the cold box 9 and cooled to -99°C before being introduced into the upper middle part of the cryogenic absorption tower 10.

[0065] The cryogenic absorption tower 10 does not have a condenser, has a theoretical plate count of 54, and operates at a pressure of 1.4 MPa. The cryogenic absorbent 12 is cooled to -115°C by the cold box 9 before being fed to the top of the tower, where the top temperature is -72°C and the bottom temperature is 24°C. The vapor phase 14 from the top of the cryogenic tower is discharged from the unit after the cold box recovers its cooling capacity. The cryogenic bottom liquid phase 13 is obtained in the bottom of the cryogenic tower.

[0066] The discharge flow rates and compositions of the cryogenic tower top gas phase 14 and cryogenic tower bottom liquid phase 13 are shown in Table 4.

[0067] Table 4

[0068] Cryogenic tower kettle liquid phase 13 Cryogenic Tower Top Gas Phase 14 Mass flow rate (kg / hr) 117930 50194 Molar composition (%) hydrogen 0 51.64 Nitrogen 0 7.85 oxygen 0 0 carbon monoxide 0 0.44 carbon dioxide 0 0 methane 0 37.84 ethylene 24.16 0.42 Ethane 22.51 0.04 propylene 14.64 0.76 propane 27.68 1.01 Isobutane 5.36 0 n-Butane 2.57 0 pentane 2.28 0 hexane 0.80 0 water 0 0

[0069] In the cryogenic tower bottom liquid phase 13, the C2 recovery rate is greater than 98.5%. The energy consumption is 64 kg standard oil / t feed.

[0070] Example 3

[0071] The composition of the saturated refinery dry gas 11 used in this embodiment and the mass flow rate of the introduction device, as well as the composition of the introduced cryogenic absorbent 12 and the mass flow rate of the introduction device, are shown in Table 5.

[0072] Table 5

[0073] Refinery dry gas 11 Cryogenic Absorbent 12 Mass flow rate (kg / hr) 100000 50000 Molar composition (%) hydrogen 35.66 0 Nitrogen 5.16 0 oxygen 0.87 0 carbon monoxide 0.29 0 carbon dioxide 2.54 0 methane 24.87 0 ethylene 10.21 0 Ethane 9.24 0.27 propylene 2.15 4.99 propane 4.06 3.99 Isobutane 2.13 59.84 n-Butane 1.05 30.91 pentane 0.94 0 hexane 0.33 0 water 0.50 0

[0074] The specific method for recovering refinery dry gas using the oil separation absorption method is as follows:

[0075] (1) Refinery dry gas 11 (pressure 0.7 MPa) is introduced into compressor 1 to increase the pressure to 1.2 MPa, and then cooled to 45°C by the cooler at the outlet of compressor 1. It is then sent to amine washing tower 2 (eluent is an aqueous solution of methyl diethanolamine with a concentration of 25% by mass) for organic amine washing. The material after organic amine washing is then sent to inorganic alkali washing tower 3 (eluent is an aqueous solution of sodium hydroxide with a concentration of 7.5% by mass) for inorganic alkali washing.

[0076] After the inorganic alkaline washing material is heated to 140°C by a heater, it is introduced into deoxygenation reactor 4 to remove oxygen and obtain pretreated gas.

[0077] (2) The pretreated gas is introduced into the cooler 5 and pre-cooled to 17°C. Then it is sent to the gas-liquid separator 6 for gas-liquid separation to obtain the first gas phase and the first liquid phase.

[0078] (3) The first liquid phase is introduced into the liquid phase dryer 7 for liquid phase drying until the water content is ≤1.5 ppm by volume, and then sent to the lower part of the cryogenic absorption tower 10.

[0079] The first gas phase is introduced into the gas phase dryer 8 and dried until the water content is ≤1.5 ppm by volume. After gas phase drying, it is sent to the cold box 9 and cooled to -95°C before being introduced into the upper middle part of the cryogenic absorption tower 10.

[0080] The cryogenic absorption tower 10 does not have a condenser, has a theoretical plate count of 57, and operates at a pressure of 0.6 MPa. The cryogenic absorbent 12 is cooled to -70°C by the cold box 9 before being fed to the top of the tower. The top temperature is -82°C, and the bottom temperature is -25°C. The vapor phase 14 from the top of the cryogenic tower is discharged from the unit after the cold box recovers its cooling capacity. The bottom liquid phase 13 of the cryogenic tower is obtained at the bottom of the tower.

[0081] The discharge flow rates and compositions of the cryogenic tower top gas phase 14 and cryogenic tower bottom liquid phase 13 are shown in Table 6.

[0082] Table 6

[0083] Cryogenic tower kettle liquid phase 13 Cryogenic Tower Top Gas Phase 14 Mass flow rate (kg / hr) 105926 35891 Molar composition (%) hydrogen 0 51.54 Nitrogen 0 7.84 oxygen 0 0 carbon monoxide 0 0.43 carbon dioxide 0 0 methane 0 37.77 ethylene 20.36 1.53 Ethane 20.43 0.09 propylene 6.31 0.19 propane 10.29 0.12 Isobutane 26.23 0.39 n-Butane 13.59 0.10 pentane 2.07 0 hexane 0.72 0 water 0 0

[0084] In the cryogenic tower bottom liquid phase 13, the C2 recovery rate is greater than 94.8%. The energy consumption is 88 kg standard oil / t feed.

[0085] Comparative Example 1

[0086] The refinery dry gas and method of Example 1 are separated, except that cryogenic absorbent 12 is not introduced into the cryogenic absorption tower.

[0087] The discharge flow rates and compositions of the cryogenic tower top gas phase 14 and cryogenic tower bottom liquid phase 13 are shown in Table 7.

[0088] Table 7

[0089] Cryogenic tower kettle liquid phase 13 Cryogenic Tower Top Gas Phase 14 Mass flow rate (kg / hr) 80070 51465 Molar composition (%) hydrogen 0 54.67 Nitrogen 0 5.99 oxygen 0 0 carbon monoxide 0 0.42 carbon dioxide 0 0 methane 0 36.06 Ethane 58.61 2.85 propane 24.41 0.01 Isobutane 8.14 0 n-Butane 4.02 0 pentane 3.57 0 hexane 1.25 0 water 0 0

[0090] In the cryogenic tower bottom liquid phase 13, the C2 recovery rate is approximately 88.0%.

[0091] As can be seen from the above, the technical solutions of this invention achieve high C2 recovery rates, with energy consumption generally below 100 kg of standard oil / t of feedstock, indicating low energy consumption. In contrast, the technical solution of Comparative Example 1, which does not use a cryogenic absorbent, results in a significantly lower recovery rate.

[0092] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for recovering ethylene and ethane, characterized in that, The method includes: (1) The dry gas from the refinery is subjected to alkali washing and deoxygenation treatment in sequence to obtain pretreated gas, and the pretreated gas is subjected to gas-liquid separation to obtain the first gas phase and the first liquid phase; (2) The first gas phase is dried and cooled before absorption to obtain the gas phase before absorption; the first liquid phase is dried before absorption to obtain the liquid phase before absorption; the first liquid phase is directly sent into the cryogenic absorption tower after drying, without passing through the cold box. (3) The gas phase and liquid phase before absorption are fed into the cryogenic absorption tower for cryogenic absorption to obtain the gas phase at the top of the cryogenic tower and the liquid phase at the bottom of the cryogenic tower. The methods for cryogenic absorption include: carrying out the process in the presence of a cryogenic absorbent; sending the pre-absorption gas phase into the upper middle part of the cryogenic absorption tower and sending the pre-absorption liquid phase into the lower part of the cryogenic absorption tower. In this type of cryogenic absorption tower, no condenser is installed, and the cryogenic absorbent is fed into the cryogenic absorption tower from the top.

2. The method according to claim 1, wherein, The refinery dry gas used for alkali washing must meet the following requirements: pressure from 0.8 MPa to 3.2 MPa and temperature from 20°C to 50°C.

3. The method according to claim 1, wherein, Alkali washing methods include sequentially washing refinery dry gas with organic amines and then with inorganic alkalis.

4. The method according to claim 3, wherein, The conditions for the organic amine washing include: the eluent is an organic amine solution, and the mass concentration of organic amine in the organic amine solution is 15-25 wt%.

5. The method according to claim 3, wherein, The organic amine is methyldiethanolamine.

6. The method according to claim 3, wherein, The conditions for inorganic alkaline washing include: the eluent is an alkali metal hydroxide solution, and the mass concentration of the alkali metal hydroxide in the alkali metal hydroxide solution is 5-10 wt%.

7. The method according to claim 6, wherein, The alkali metal hydroxide is sodium hydroxide.

8. The method according to claim 1 or 6, wherein, The conditions for the deoxygenation treatment include: a temperature of 50-380℃ and a pressure of 1-6.5MPa.

9. The method according to claim 1, wherein, The material temperature for gas-liquid separation is 5 to 38°C.

10. The method according to claim 1 or 9, wherein, The first gas phase is cooled to a temperature of -70°C to -110°C before absorption.

11. The method according to claim 10, wherein, The drying conditions before absorption ensure that the water content in the dried material is ≤1.5 ppm by volume.

12. The method according to claim 1, wherein, The top gas phase of the cryogenic tower is used as at least part of the refrigerant for cooling before absorption, serving as the first gas phase.

13. The method according to claim 1, wherein, The operating conditions in the cryogenic absorption tower include: a theoretical plate number of 30 to 80, an operating pressure of 0.5 to 5.5 MPa, a top temperature of -60°C to -110°C, and a bottom temperature of -30°C to 60°C.

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