Ethane recovery system and recovery method suitable for high carbon dioxide rich gas

Abstract

The invention relates to the technical field of ethane recovery systems, and in particular to an ethane recovery system and a recovery method thereof suitable for high-carbon dioxide-rich gas, comprising a first precooling cold box, a second precooling cold box, a supercooling cold box, a low-temperature separator, an absorption tower, a tower top separator and a demethanizer; the precooling input end of the first precooling cold box and the precooling input end of the second precooling cold box are both connected to external raw gas, when in use, the absorption tower and the demethanizer tower top separator replace the low-temperature distillation section of the demethanizer, so that the CO2 content in the gas phase entering the low-temperature zone is reduced, and most of the CO2 is diverted to the demethanizer stripping section, which effectively solves the freezing and blocking problem of the traditional demethanizer when the CO2 content is ≥2mol%; at the same time, the operating pressure of the demethanizer is ≥300KPa higher than that of the absorption tower, which greatly reduces the power consumption of the external transmission compressor, and the ethane recovery device is more energy-efficient, and is suitable for medium-pressure and high-carbon dioxide-rich gas ethane recovery devices.

Description

Technical Field

[0001] The present invention relates to the technical field of ethane recovery systems, and in particular to an ethane recovery system and a recovery method thereof suitable for high-carbon dioxide-containing rich gas. Background Art

[0002] With the continuous advancement of quality improvement and efficiency enhancement projects in major domestic oil fields, oil and gas fields with high carbon dioxide content are continuously developed, and the economic potential brought by natural gas ethane and above heavy hydrocarbon products is continuously explored. Therefore, the development and research of high carbon dioxide rich gas ethane recovery technology is extremely important.

[0003] like Figure 2 As shown, the ethane recovery process of the existing typical partial dry gas recycling process is characterized in that part of the external dry gas is supercooled into a liquid phase and then used as the top feed of the demethanizer, and the ethane recovery rate is improved by increasing the reflux rate and liquefaction rate of the external dry gas. When the CO2 content in the feed gas is high, the CO2 freezing problem is solved by increasing the amount of low-temperature separator liquid phase mixed in the second feed of the demethanizer or increasing the pressure of the demethanizer, but a large amount of propane and heavier hydrocarbons above will be mixed into the external dry gas, resulting in the loss of heavy hydrocarbons. At the same time, increasing the pressure of the demethanizer will reduce the expansion refrigeration capacity, increase the demand for external refrigeration, and greatly increase the compression work of the external refrigeration device, resulting in a significant increase in system energy consumption and a reduction in the economic benefits of the ethane recovery device. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in order to solve the problems that the CO2 content of the raw gas is ≥2 mol% in the existing partial dry gas recycling process, the total compression power consumption of the device is large, there is no available pressure difference when the raw gas pressure is almost equal to the external transmission pressure, and the medium and high pressure rich gas is processed on a large scale, an ethane recovery system and a recovery method suitable for high carbon dioxide rich gas are provided.

[0005] The technical solution adopted by the present invention to solve the technical problem is: an ethane recovery system suitable for high-carbon dioxide-rich gas, comprising a first precooling cold box, a second precooling cold box, a supercooling cold box, a low-temperature separator, an absorption tower, a tower top separator and a demethanizer;

[0006] The precooling input end of the first precooling box and the precooling input end of the second precooling box are both connected to the external raw gas, the precooling output end of the first precooling box is connected to the precooling input end of the subcooling box, the precooling output end of the subcooling box is connected to the top of the absorption tower, the precooling output end of the second precooling box is connected to the low-temperature separator, the gas phase end of the low-temperature separator is connected to the middle of the absorption tower through the expansion end of the first turbine expander, and the liquid phase end of the low-temperature separator is respectively connected to the bottom of the absorption tower and the precooling output end of the first precooling box;

[0007] The gas phase end at the top of the absorption tower is connected to the heat exchange input end of the supercooling box, the heat exchange output end of the supercooling box is respectively connected to the heat exchange input end of the first precooling box and the heat exchange input end of the second precooling box, the heat exchange output end of the first precooling box and the heat exchange output end of the second precooling box are both connected to the input end of the external transmission compressor through the boosting end of the second turbine expander, the output end of the external transmission compressor is connected to the output end of the air cooler, the output end of the air cooler is respectively connected to the outside and the precooling input end of the first precooling box, the precooling output end of the first precooling box is connected to the precooling input end of the second precooling box, the precooling output end of the second precooling box is connected to the top of the absorption tower, the bottom of the absorption tower is connected to the upper part of the demethanizer through the first liquid phase pump, the gas phase end at the top of the demethanizer is connected to the heat exchange input end of the supercooling box, and the heat exchange output end of the supercooling box is connected to the tower top separator;

[0008] The gas phase end of the tower top separator is connected to the heat exchange input end of the supercooling box, the heat exchange output end of the supercooling box is connected to the heat exchange input end of the first precooling box, the heat exchange input end of the first precooling box is connected to the input end of the external transmission compressor, the liquid phase end of the tower top separator is connected to the upper part of the demethanizer through the second liquid phase pump, and the bottom of the demethanizer is provided with a condensate product discharge end. Compared with the prior art, this scheme also replaces the low-temperature distillation section of the demethanizer with the absorption tower and the demethanizer top separator, reduces the CO2 content in the gas phase entering the low-temperature zone, and diverts most of the CO2 to the demethanizer stripping section, effectively solving the freezing and blocking problem of the traditional demethanizer when the CO2 content is ≥2mol%; at the same time, the operating pressure of the demethanizer is ≥300KPa higher than that of the absorption tower, which greatly reduces the power consumption of the external transmission compressor, and the ethane recovery device is more energy-efficient, which is suitable for medium-pressure, high-carbon dioxide-rich ethane recovery devices.

[0009] In some preferred embodiments, the first liquid phase pump passes through the second pre-cooling cold box through an external pipeline and is connected to the bottom of the demethanizer.

[0010] In some preferred embodiments, the bottom of the demethanizer passes through a second pre-cooling cold box through an external pipeline and is connected to the bottom of the demethanizer.

[0011] A recovery method using the above-mentioned ethane recovery system suitable for high carbon dioxide-rich gas, the specific operation steps are as follows: the raw gas is divided into two paths, the first path of raw gas is pre-cooled by the first pre-cooling box and then mixed with part of the low-temperature separator liquid, and then enters the supercooling box for supercooling and throttling to enter the upper part of the absorption tower;

[0012] The second feed gas is precooled by the second precooling box and then enters the low-temperature separator. The gas phase separated by the low-temperature separator enters the expansion end of the first turbine expander for pressure reduction and temperature reduction, and then enters the middle of the absorption tower. The liquid phase separated by the low-temperature separator enters the bottom of the absorption tower.

[0013] Part of the externally transmitted dry gas is throttled and cooled after heat exchange and cooling in the first pre-cooling cold box and the super-cooling cold box, and then enters the top of the absorption tower;

[0014] The liquid phase at the bottom of the absorption tower is pressurized by the first liquid phase pump and then divided into two paths. The first path of liquid phase is throttled and cooled before entering the upper part of the demethanizer. The second path of liquid phase is throttled and cooled before entering the second pre-cooling box for heat exchange and temperature increase, and then enters the middle part of the demethanizer.

[0015] The gas phase at the top of the demethanizer tower is heated by heat exchange in a cold box and then enters the separator at the top of the demethanizer tower. The gas phase separated by the separator at the top of the demethanizer tower is heated by heat exchange in a cold box and a first pre-cooling box in turn, then pressurized by an external compressor, and finally cooled by an air cooler before being externally transmitted. The second liquid phase separated by the separator at the top of the demethanizer tower is pressurized by a pump and enters the top of the demethanizer tower.

[0016] The gas phase at the top of the absorption tower is divided into two paths after heat exchange and temperature increase in the cold box, and then enters the first pre-cooling cold box and the second pre-cooling cold box respectively, and then merges, and after being pressurized at the booster end of the second turbine expander, it merges with the gas phase at the top of the demethanizer and enters the external transmission compressor for pressurization; the condensate product at the bottom of the demethanizer enters the subsequent deethanizer and other distillation processing units for treatment.

[0017] The beneficial effects of the present invention are as follows: the present invention is applicable to an ethane recovery system for high-carbon dioxide-rich gas and its recovery method. When in use, the absorption tower and the demethanizer top separator replace the low-temperature distillation section of the demethanizer, reducing the CO2 content in the gas phase entering the low-temperature zone, and diverting most of the CO2 to the demethanizer stripping section, effectively solving the freezing and blocking problem of the traditional demethanizer when the CO2 content is ≥2 mol%; at the same time, the operating pressure of the demethanizer is ≥300 KPa higher than that of the absorption tower, which greatly reduces the power consumption of the external transmission compressor, and the ethane recovery device is more energy-efficient, and is suitable for medium- and high-pressure ethane recovery devices with high carbon dioxide-rich gas. The present invention develops a method for recovering ethane from medium- and high-pressure rich gas with high carbon dioxide content. The ethane recovery rate is as high as 95% under high CO2 content, and the total compression power consumption of the device is reduced, thereby improving the economic and social benefits of the ethane recovery device, and avoiding the problems of raw gas CO2 content ≥2 mol%, large total compression power consumption of the device, no available pressure difference, and large-scale medium- and high-pressure rich gas in the existing partial dry gas recycling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0019] Figure 1 It is a schematic diagram of the structure of the present invention;

[0020] Figure 2 It is a structural schematic diagram of the prior art.

[0021] In the figure: E1, the first pre-cooling cold box, V1, the low-temperature separator, E2, the second pre-cooling cold box, V2, the tower top separator, K1, the expansion end of the first turbine expander, E3, the subcooling cold box, T1, the absorption tower, T2, the demethanizer, A1, the air cooler, K2, the boosting end of the second turbine expander, K3, the external transmission compressor, P1, the first liquid phase pump, P2, the second liquid phase pump. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with embodiments:

[0023] The present invention is not limited to the following specific embodiments. A person skilled in the art can implement the present invention in various other specific embodiments according to the contents disclosed in the present invention, or any simple changes or modifications made to the design structure and ideas of the present invention fall within the protection scope of the present invention. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0024] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0025] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0026] Example 1

[0027] like Figure 1As shown, an ethane recovery system suitable for high carbon dioxide-rich gas includes a first precooling cold box E1, a second precooling cold box E2, a subcooling cold box E3, a low-temperature separator V1, an absorption tower T1, a tower top separator V2 and a demethanizer T2;

[0028] The precooling input end of the first precooling cold box E1 and the precooling input end of the second precooling cold box E2 are both connected to the external raw gas, the precooling output end of the first precooling cold box E1 is connected to the precooling input end of the subcooling cold box E3, the precooling output end of the subcooling cold box E3 is connected to the top of the absorption tower T1, the precooling output end of the second precooling cold box E2 is connected to the low-temperature separator V1, the gas phase end of the low-temperature separator V1 is connected to the middle of the absorption tower T1 through the expansion end K1 of the first turbine expander, and the liquid phase end of the low-temperature separator V1 is respectively connected to the bottom of the absorption tower T1 and the precooling output end of the first precooling cold box E1;

[0029] The gas phase end at the top of the absorption tower T1 is connected to the heat exchange input end of the supercooling cold box E3, and the heat exchange output end of the supercooling cold box E3 is respectively connected to the heat exchange input end of the first precooling cold box E1 and the heat exchange input end of the second precooling cold box E2. The heat exchange output end of the first precooling cold box E1 and the heat exchange output end of the second precooling cold box E2 are both connected to the input end of the external transmission compressor K3 through the second turbine expander booster end K2, and the output end of the external transmission compressor K3 is connected to the output end of the air cooler A1. The air cooler A1 The output end is respectively connected to the outside and the precooling input end of the first precooling cold box E1, the precooling output end of the first precooling cold box E1 is connected to the precooling input end of the second precooling cold box E2, the precooling output end of the second precooling cold box E2 is connected to the top of the absorption tower T1, the bottom of the absorption tower T1 is connected to the upper part of the demethanizer T2 through the first liquid phase pump P1, the gas phase end of the top of the demethanizer T2 is connected to the heat exchange input end of the supercooling cold box E3, and the heat exchange output end of the supercooling cold box E3 is connected to the tower top separator V2;

[0030] The gas phase end of the tower top separator V2 is connected to the heat exchange input end of the supercooling cold box E3, the heat exchange output end of the supercooling cold box E3 is connected to the heat exchange input end of the first precooling cold box E1, the heat exchange output end of the first precooling cold box E1 is connected to the input end of the external transmission compressor K3, the liquid phase end of the tower top separator V2 is connected to the upper part of the demethanizer T2 through the second liquid phase pump P2, and a condensate product discharge end is provided at the bottom of the demethanizer T2.

[0031] The first liquid phase pump P1 passes through the second pre-cooling cold box E2 through an external pipeline and is connected to the bottom of the demethanizer T2.

[0032] The bottom of the demethanizer T2 passes through the second precooling cold box E2 through an external pipeline and is connected to the bottom of the demethanizer T2.

[0033] The external gas is divided into two routes: the first route of gas, which accounts for 10% to 15% of the total gas, enters after being cooled and throttled by the first pre-cooling cold box E1 and the supercooling cold box E3, and the second route of gas is exported as qualified product natural gas.

[0034] The raw gas is divided into two paths: the first path of gas phase, accounting for 20% to 25% of the total gas phase, enters the upper part of the absorption tower T1 after being cooled and throttled by the first precooling cold box E1 and the supercooling cold box E3; the second path of gas phase enters the low-temperature separator V1 after being precooled by the second precooling cold box E2.

[0035] The liquid phase at the bottom of the low-temperature separator V1 is divided into two paths: the first liquid phase, which accounts for 75% to 95% of the total liquid phase, is mixed with the first raw gas, and the mixed phase enters the upper part of the absorption tower T1 after being cooled and throttled by the cold box E3; the second liquid phase enters the bottom of the absorption tower T1 after throttling and cooling.

[0036] The liquid phase at the bottom of the absorption tower T1 is divided into two paths: the first liquid phase, which accounts for 40% to 60% of the total liquid phase, enters the upper part of the demethanizer T2 after throttling and cooling; the second liquid phase enters the upper part of the absorption tower T1 after throttling and cooling; the second liquid phase enters the first pre-cooling cold box E1 after throttling and cooling, and enters the lower part of the absorption tower T1 after heat exchange and temperature rise.

[0037] The first precooling cold box E1, the second precooling cold box E2, and the supercooling cold box E3 all adopt multiple plate-fin heat exchangers, and two hot flows and two cold flows, one hot flow and multiple cold flows, and two hot flows and multiple cold flows are respectively integrated in the first precooling cold box E1, the second precooling cold box E2, and the supercooling cold box E3.

[0038] The two hot streams in the first pre-cooling cold box E1 are: one is the raw gas, and one is the external dry gas; the two cold streams are: one is the gas phase of the absorption tower T1 after heat exchange and temperature increase in the cold box E3, and one is the gas phase of the top separator V2 of the demethanizer T2 after heat exchange and temperature increase in the cold box E3. The hot stream of the second pre-cooling cold box E2 is the raw gas; the multiple cold streams are: one is the gas phase of the absorption tower T1 after heat exchange and temperature increase in the cold box E3, one is the bottom liquid phase of the absorption tower T1 after throttling and temperature reduction, two side lines of the demethanizer T2, one is -12℃~-16℃ with propane refrigerant, and one is -24℃~-32℃ with propane refrigerant. The two hot flows in the supercooling cold box E3 are: one is a mixed phase of the raw gas and part of the liquid phase after heat exchange and temperature increase in the first precooling cold box E1, and one is the external dry gas after heat exchange and temperature increase in the first precooling cold box E1; the multiple cold flows are: one is the gas phase of the top separator V2 of the demethanizer T2, one is the gas phase, and one is the gas phase at the top of the demethanizer T2.

[0039] Example 2

[0040] Example 2 is an application of Example 1, specifically: a recovery method using the above-mentioned ethane recovery system suitable for high carbon dioxide-rich gas, the specific operation steps are as follows: the raw gas is divided into two paths, the first path of raw gas is pre-cooled by the first pre-cooling cold box E1 and then mixed with part of the low-temperature separator V1 liquid, and then enters the supercooling cold box E3 for supercooling and throttling and cooling before entering the upper part of the absorption tower T1;

[0041] The second feed gas is precooled by the second precooling box E2 and then enters the low-temperature separator V1. The gas phase separated by the low-temperature separator V1 enters the expansion end K1 of the first turbine expander for decompression and temperature reduction, and then enters the middle of the absorption tower T1. A part of the liquid phase separated by the low-temperature separator V1 enters the bottom of the absorption tower T1.

[0042] Part of the external dry gas is throttled and cooled after heat exchange in the first pre-cooling cold box E1 and the sub-cooling cold box E3 and then enters the top of the absorption tower T1;

[0043] The first liquid phase pump P1 at the bottom of the absorption tower T1 is pressurized and then divided into two paths. The first liquid phase enters the upper part of the demethanizer T2 after throttling and cooling, and the second liquid phase enters the second pre-cooling cold box E2 for heat exchange and temperature increase, and then enters the middle part of the demethanizer T2;

[0044] The gas phase at the top of the demethanizer T2 is heated by heat exchange in the cold box E3, and then enters the top separator V2 of the demethanizer T2. The gas phase separated by the top separator V2 of the demethanizer T2 is successively heated by the cold box E3 and the first pre-cooling cold box E1, and then pressurized by the external transmission compressor K3, and finally cooled by the air cooler A1 before being transmitted to the outside; the second liquid phase separated by the top separator V2 of the demethanizer T2 is pressurized by the pump P2 and enters the top of the demethanizer T2;

[0045] The gas phase at the top of the absorption tower T1 is divided into two paths after heat exchange and temperature increase in the cold box E3, and then enters the first pre-cooling cold box E1 and the second pre-cooling cold box E2 respectively, and then merges, and after being pressurized by the second turbine expander booster end K2, it merges with the gas phase at the top of the demethanizer T2 and enters the external output compressor K3 for pressurization; the condensate product at the bottom of the demethanizer T2 enters the subsequent deethanizer and other distillation processing units for treatment.

[0046] When the above ethane recovery system and recovery method applicable to high carbon dioxide-rich gas are used, the raw gas quality components and working conditions are as follows:

[0047] Raw gas processing scale: 1000×104m 3 / d, raw gas pressure: 5.4MPa, raw gas temperature: 36℃, dry gas output pressure: 5.4MPa.

[0048] The composition of the raw gas is shown in Table 1 below

[0049] Table 1

[0050] composition <![CDATA[N2]]> <![CDATA[CO2]]> <![CDATA[C1]]> <![CDATA[C2]]> <![CDATA[C3]]> <![CDATA[iC4]]> <![CDATA[nC4]]> <![CDATA[iC5]]> <![CDATA[nC5]]> <![CDATA[C6]]> <![CDATA[C7]]> <![CDATA[C 8+ ]]> mol% 0.56 2.5 84.4 8.39 2.25 0.63 0.57 0.27 0.12 0.13 0.12 0.06

[0051] Raw gas temperature: 36°C, dry gas output pressure: 5.4MPa, raw gas is divided into two routes, the first route raw gas accounts for 21.5% of the total raw gas volume, the first route raw gas is precooled to a temperature of -54.5°C and a pressure of 5.36MPa in the first precooling cold box E1, and then mixed with part of the low-temperature separator V1 liquid, the mixed part of the liquid accounts for 48% of the liquid phase flow at the bottom of the low-temperature separator V1, and then enters the supercooling cold box E3 for supercooling and throttling to -92.6°C, the pressure is 2.75MPa, and then enters the upper part of the absorption tower T1.

[0052] The second feed gas accounts for 81.5% of the total feed gas volume and is precooled to -54.5℃ and 5.36MPa by the second precooling box E2, and then enters the low-temperature separator V1. The gas phase separated by the low-temperature separator V1 all enters the expansion end K1 of the first turbine expander to reduce the pressure and temperature to -76.7℃ and 2.75MPa, and then enters the middle of the absorption tower T1. A part of the liquid phase separated by the low-temperature separator V1 accounts for 52% of the liquid phase flow at the bottom of the low-temperature separator V1, and enters the bottom of the absorption tower T1; part of the external dry gas accounts for the total flow of the external dry gas. The amount of dry gas is 10.5%, and part of the external transmission dry gas is throttled and cooled to -98.8℃ after heat exchange and cooling in the first pre-cooling cold box E1 and the super-cooling cold box E3, and the pressure is 2.75MPa, and then enters the top of the absorption tower T1; the first liquid phase pump P1 at the bottom of the absorption tower T1 is pressurized and divided into two paths, the first liquid phase accounts for 49% of the liquid phase flow at the bottom of the absorption tower T1, and the first liquid phase enters the upper part of the demethanizer T2 after throttling and cooling, and the second liquid phase accounts for 51% of the liquid phase flow at the bottom of the absorption tower T1. After throttling and cooling, the second liquid phase enters the second pre-cooling cold box E2 for heat exchange and temperature rise to -74.3℃, and the pressure is 2.75MPa. The gas phase separated by the top separator V2 at the top of the demethanizer T2 passes through the cold box E3 and the first pre-cooling cold box E1 for heat exchange and temperature increase, and then passes through the external transmission compressor K3 to increase the pressure to 5.45MPa and the temperature to 82.5℃, and finally passes through the air cooler A1 to cool to 4 0℃, pressure is 5.4MPa and then it is transmitted externally; the second liquid phase separated by the top separator V2 at the top of the demethanizer T2 is pumped into the top of the demethanizer T2 after being pressurized by the second liquid pump P2; the gas phase at the top of the absorption tower T1 is heated to -68.6℃ by the cold box E3 and the pressure is 2.68MPa, then it is divided into two paths and enters the first pre-cooling cold box E1 and the second pre-cooling cold box E2 for heat exchange and temperature rise, and then merges, and is pressurized to 3.13MPa by the second turbine expander booster end K2, and the temperature is 39.6℃, and then merges with the gas phase at the top of the demethanizer T2 and enters the external transmission compressor K3 for pressurization.

[0053] Two low-temperature liquid phases are extracted from the middle and lower part of the demethanizer T2, one of which has a temperature of -56.8°C and the other has a temperature of -70.5°C. The two low-temperature liquid phases are respectively heated with the second precooling cold box E2 and the subcooling cold box E3 and then flow into the demethanizer T2 as the heat source for the side reboiler; a liquid phase with a low temperature of -1.9°C is extracted from the bottom and heated with the second precooling cold box E2 to provide a heat source for the reboiler. The propane refrigeration system provides two temperatures of -37.28°C and -14.12°C for the second precooling cold box E2, and the shaft power of the propane refrigeration system is 6312kW.

[0054] The condensate product at the bottom of the demethanizer T2 enters the subsequent deethanizer and other distillation processing units for processing. The product is ethane with a recovery rate of 94%, a pressure of 3.2 MPa, and a temperature of 29.6°C.

[0055] The simulation results of this example show that: under the same operating conditions, compared with the existing partial dry gas recycling ethane recovery process, the ethane recovery rate of the present invention is increased by 4.6%, the CO2 minimum freezing and blocking margin of the upper plate of the absorption tower T1 is increased from 5°C to 7°C, the ethane product volume is increased by 25.36t / d, and the system compression power is reduced by 236kW. The system compression power is the sum of the compression work of the external compressor K3 and the propane refrigeration compression work. The CO2 freezing resistance and ethane recovery rate of the ethane recovery device are improved, and its economic benefits are significantly improved.

[0056] The above-mentioned ideal embodiments of the present invention are for inspiration. Through the above-mentioned description, relevant staff can make various changes and modifications without departing from the technical idea of ​​the present invention. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. An ethane recovery system suitable for high carbon dioxide rich gas, characterized by: It includes a first precooling box (E1), a second precooling box (E2), a supercooling box (E3), a low-temperature separator (V1), an absorption tower (T1), a tower top separator (V2) and a demethanizer (T2); The precooling input end of the first precooling cold box (E1) and the precooling input end of the second precooling cold box (E2) are both connected to the external raw gas, the precooling output end of the first precooling cold box (E1) is connected to the precooling input end of the subcooling cold box (E3), the precooling output end of the subcooling cold box (E3) is connected to the top of the absorption tower (T1), the precooling output end of the second precooling cold box (E2) is connected to the low-temperature separator (V1), the gas phase end of the low-temperature separator (V1) is connected to the middle of the absorption tower (T1) through the expansion end (K1) of the first turbine expander, and the liquid phase end of the low-temperature separator (V1) is respectively connected to the bottom of the absorption tower (T1) and the precooling output end of the first precooling cold box (E1); The gas phase end at the top of the absorption tower (T1) is connected to the heat exchange input end of the subcooling box (E3), and the heat exchange output end of the subcooling box (E3) is respectively connected to the heat exchange input end of the first precooling box (E1) and the heat exchange input end of the second precooling box (E2). The heat exchange output end of the first precooling box (E1) and the heat exchange output end of the second precooling box (E2) are both connected to the input end of the external transmission compressor (K3) through the booster end (K2) of the second turbine expander, and the output end of the external transmission compressor (K3) is connected to the input end of the air cooler (A1). The output end of the first precooling box (E1) is respectively connected to the outside and the precooling input end of the first precooling box (E1), the precooling output end of the first precooling box (E1) is connected to the precooling input end of the subcooling box (E3), the precooling output end of the subcooling box (E3) is connected to the top of the absorption tower (T1), the bottom of the absorption tower (T1) is connected to the upper part of the demethanizer (T2) through the first liquid phase pump (P1), the gas phase end of the top of the demethanizer (T2) is connected to the heat exchange input end of the subcooling box (E3), and the heat exchange output end of the subcooling box (E3) is connected to the tower top separator (V2); The gas phase end of the tower top separator (V2) is connected to the heat exchange input end of the subcooling cold box (E3), the heat exchange output end of the subcooling cold box (E3) is connected to the heat exchange input end of the first precooling cold box (E1), the heat exchange output end of the first precooling cold box (E1) is connected to the input end of the external transmission compressor (K3), the liquid phase end of the tower top separator (V2) is connected to the upper part of the demethanizer (T2) through the second liquid phase pump (P2), and the bottom of the demethanizer (T2) is provided with a condensate product discharge end.

2. The ethane recovery system suitable for high carbon dioxide rich gas according to claim 1, characterized in that: The first liquid phase pump (P1) passes through the second pre-cooling box (E2) through an external pipeline and is connected to the bottom of the demethanizer (T2).

3. The ethane recovery system suitable for high carbon dioxide rich gas according to claim 1, characterized in that: The bottom of the demethanizer (T2) passes through the second pre-cooling cold box (E2) through an external pipeline and is connected to the bottom of the demethanizer (T2).

4. A recovery method using the ethane recovery system applicable to high carbon dioxide-rich gas as described in any one of claims 1 to 3, characterized in that: The specific operation steps are as follows: the raw gas is divided into two paths, the first path of raw gas is pre-cooled in the first pre-cooling box (E1) and then mixed with part of the low-temperature separator (V1) liquid, and then enters the sub-cooling box (E3) for sub-cooling and throttling and cooling before entering the upper part of the absorption tower (T1); The second feed gas is pre-cooled by the second pre-cooling box (E2) and then enters the low-temperature separator (V1). The gas phase separated by the low-temperature separator (V1) enters the expansion end (K1) of the first turbine expander for pressure reduction and temperature reduction and then enters the middle of the absorption tower (T1). A portion of the liquid phase separated by the low-temperature separator (V1) enters the bottom of the absorption tower (T1). Part of the externally transmitted dry gas is throttled and cooled after heat exchange in the first pre-cooling box (E1) and the sub-cooling box (E3) before entering the top of the absorption tower (T1); The first liquid phase pump (P1) at the bottom of the absorption tower (T1) is pressurized and then divided into two paths. The first path of liquid phase is throttled and cooled before entering the upper part of the demethanizer (T2). The second path of liquid phase is throttled and cooled before entering the second pre-cooling box (E2) for heat exchange and temperature increase, and then enters the middle part of the demethanizer (T2). The gas phase at the top of the demethanizer (T2) is heated by heat exchange in the cold box (E3) and then enters the top separator (V2) of the demethanizer (T2). The gas phase separated by the top separator (V2) of the demethanizer (T2) is successively heated by heat exchange in the cold box (E3) and the first pre-cooling cold box (E1), and then pressurized by the external transmission compressor (K3). Finally, it is cooled by the air cooler (A1) and then transmitted to the outside. The liquid phase separated by the top separator (V2) of the demethanizer (T2) is pressurized by the second liquid phase pump (P2) and then enters the top of the demethanizer (T2). The gas phase at the top of the absorption tower (T1) is heated by heat exchange in the cold box (E3) and then divided into two paths, entering the first pre-cooling cold box (E1) and the second pre-cooling cold box (E2) for heat exchange and temperature increase, and then merged. After being pressurized by the booster end (K2) of the second turbine expander, it merges with the gas phase at the top of the demethanizer (T2) and enters the external transmission compressor (K3) for pressurization; the condensate product at the bottom of the demethanizer (T2) enters the subsequent deethanizer for treatment.

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