阅读说明：本技术 一种高压天然气的乙烷回收方法 (Ethane recovery method of high-pressure natural gas ) 是由 蒋洪 王金波 黄靖珊 李浩玉 杨铜林 于 2020-12-18 设计创作，主要内容包括：本发明公开了一种高压天然气的乙烷回收方法,涉及天然气加工工艺技术领域,该方法将传统的脱甲烷塔分别设置为高压吸收塔和脱甲烷塔,高压吸收塔和脱甲烷塔压力可独立设置,两塔由脱甲烷塔塔顶压缩机进行联系；高压吸收塔提高了高压吸收塔塔顶气相出料压力,有利于降低外输气压缩功；脱甲烷塔塔顶温度升高,有利于提高二氧化碳冻堵裕量,脱甲烷塔在较低的压力下运行,有利于原料气与脱甲烷塔塔底重沸器热集成。乙烷回收装置的节能效果显著,适合于原料气压力高于6MPa的乙烷回收装置。(The invention discloses an ethane recovery method of high-pressure natural gas, which relates to the technical field of natural gas processing technology.A traditional demethanizer is respectively arranged as a high-pressure absorption tower and a demethanizer, the pressures of the high-pressure absorption tower and the demethanizer can be independently arranged, and the two towers are connected by a compressor at the top of the demethanizer; the high-pressure absorption tower improves the gas-phase discharge pressure at the top of the high-pressure absorption tower, and is beneficial to reducing the compression work of external gas transmission; the temperature of the top of the demethanizer is increased, which is beneficial to improving the freezing and blocking allowance of carbon dioxide, the demethanizer operates under lower pressure, and the thermal integration of the feed gas and the reboiler at the bottom of the demethanizer is facilitated. The ethane recovery device has obvious energy-saving effect and is suitable for the ethane recovery device with the raw material gas pressure higher than 6 MPa.)

1. A process for ethane recovery of high pressure natural gas, characterized by: the method comprises the steps that a raw material gas is cooled through a main cooling box (E11) and enters a low-temperature separator (V11) for gas-liquid separation, a part or all of a liquid phase separated by the low-temperature separator (V11) is subjected to pressure regulation and then enters the middle lower part of a demethanizer (T12), a gas phase separated by the low-temperature separator (V11) is divided into two parts, one part of the gas phase is cooled through an expansion end (K12) of an expansion unit and then enters the bottom of a high-pressure absorption tower (T11), the other part of the gas phase is subjected to heat exchange and temperature reduction through a supercooling cooling box (E12) and then is subjected to pressure regulation and enters the middle upper part of demethanizer (T12), the other part of the gas phase is subjected to pressure regulation and temperature reduction through a supercooling cooling box (E382) and then enters the top of the demethanizer (T11), the gas phase at the top of the high-pressure absorption tower (T11) is used as an external gas transmission and sequentially subjected to heat exchange with the supercooling cooling box (E82, The output compressor (K14) is pressurized and then outputs; the partial external gas is subjected to heat exchange, temperature reduction and supercooling through a main cooling box (E11) and a supercooling cooling box (E12) in sequence, pressure regulation is carried out, the partial external gas enters the top of a high-pressure absorption tower (T11), the gas phase at the top of a demethanizer (T12) is pressurized through a tower top compressor (K11), the gas phase at the bottom of the supercooling cooling box (E12) is subjected to temperature reduction, pressure regulation is carried out, the gas phase at the top of the demethanizer (T11) enters the middle upper part of the high-pressure absorption tower (T11), the liquid phase at the bottom of the demethanizer (T12) enters a subsequent fractionation unit, the pressure of the high-pressure absorption tower (T11) and the pressure of the demethanizer (T12).

2. The process for ethane recovery of high pressure natural gas according to claim 1, wherein: the external gas reflux amount accounts for 10-20% of the total external gas transmission amount, and the external gas reflux amount is subjected to heat exchange and supercooling through a main cold box (E11) and a supercooling cold box (E12) and then pressure regulation to enter the top of a high-pressure absorption tower (T11).

3. The process for ethane recovery of high pressure natural gas according to claim 1, wherein: when the freezing and blocking allowance of carbon dioxide is small, a liquid phase separated by the low-temperature separator (V11) is divided into two parts, wherein a part of the liquid phase (30% -50%) is mixed with a strand of gas phase at the top of the low-temperature separator (V11), enters a supercooling cold box (E12) for heat exchange and supercooling, then is subjected to pressure regulation, enters the middle part of a high-pressure absorption tower (T11), and the rest of the liquid phase is subjected to pressure regulation, enters the lower part of the high-pressure absorption tower (T11).

4. The process for ethane recovery of high pressure natural gas according to claim 1, wherein: and the top gas phase of the demethanizer (T12) is pressurized to 4-4.5 MPa by a tower top compressor (K11), subjected to heat exchange and supercooling by a supercooling cold box (E12), and subjected to pressure regulation to enter the middle upper part of the high-pressure absorption tower (T11).

5. The process for ethane recovery of high pressure natural gas according to claim 1, wherein: 10-20% of the gas phase at the top of the low-temperature separator (V11) is subjected to heat exchange and supercooling through a supercooling cold box (E12) and then pressure regulation and enters the middle upper part of the high-pressure absorption tower, and 80-90% of the gas phase at the top of the low-temperature separator (V11) is subjected to pressure reduction and temperature reduction through an expansion end (K12) of an expansion unit and then enters the middle lower part of the high-pressure absorption tower (T11).

6. The process for ethane recovery of high pressure natural gas according to claim 1, wherein: the main cold box (E11) and the supercooling cold box (E12) both adopt a multi-strand plate-fin heat exchanger, and two hot flows and five cold flows as well as three hot flows and two cold flows are respectively integrated in the main cold box (E11) and the supercooling cold box (E12).

7. The process for ethane recovery of high pressure natural gas according to claim 1, wherein: the refrigeration process combines propane refrigerant refrigeration and expander refrigeration, and the propane refrigeration process provides refrigeration for the main cold box (E11) and the subsequent fractionation units.

Technical Field

The invention relates to the technical field of natural gas processing technology, in particular to an ethane recovery method of high-pressure natural gas.

Background

The ethane recovery process scheme is closely related to the pressure of the raw material gas. The condensed gas field natural gas treatment plant developed in gas fields of Xinjiang, Tarim and the like in China has high pressure (up to 12MPa) when entering the plant, the ethane content is more than 5 percent, and ethane recovery is necessary, so that the resource utilization rate can be improved, and more economic values are effectively created. The ethane recovery process is a low temperature production system with high energy consumption, and the energy consumption directly influences the economic benefit of ethane recovery. At present, the natural gas ethane recovery process is developed in the direction of high yield, low energy consumption and simplified process. The types of ethane recovery process flows at home and abroad are more, and the current relatively representative high-efficiency ethane recovery process is the RSV (respiratory syncytial Virus) process of the United states Ortloff company. The RSV process is based on GSP process, after partial high pressure dry gas at the outlet of the gas compressor of the external gas transmission and the top gas of the demethanizer are condensed by heat exchange, the pressure regulating flash evaporation enters the top of the demethanizer to provide reflux. The reflux of the outgoing dry gas (almost pure CH4) rectifies the overhead vapor phase, minimizing the loss of ethane and heavier components at the top of the column. The process has high ethane recovery rate and low investment.

In the prior patent CN105037069A, a method for recovering ethane from high-pressure natural gas (greater than 7MPa) is proposed, as shown in fig. 1, the process adopts a two-tower arrangement, the raw gas enters a low-temperature separator (V11) after being pre-cooled by a cold box (E11), the liquid phase of the separator enters the middle lower part of a demethanizer (T12), part of the gas phase of the separator enters the lower part of a high-pressure absorber (T11) after being depressurized and cooled by an expansion end (K11) of an expander, the rest of the gas phase of the separator is divided into two streams, one stream enters the middle upper part of the high-pressure absorber after being regulated in pressure, the other stream enters the middle upper part of the demethanizer after being regulated in pressure, the external gas is divided into two streams after being cooled by the cold box, one stream enters the top of the high-pressure absorber after being regulated in pressure, the other stream enters the upper part of the demethanizer after being regulated in pressure, the demethanizer and the top gas phase of the high-pressure absorber pass through the, The external transportation compressor (K13) is pressurized and then is transported externally, the liquid phase at the bottom of the absorption tower enters the middle part of the demethanizer after pressure regulation, and the liquid phase at the bottom of the demethanizer is ethane and liquid hydrocarbon with components above the ethane. The reflux of the gas transmission outside the process is relatively large (15%), and compared with the RSV ethane recovery process, the energy-saving effect is not obvious enough under the same ethane recovery rate; and the other part of the gas is transported to the demethanizer, so that the temperature at the top of the demethanizer is low, and the carbon dioxide is easily frozen and blocked.

Patent CN210458012 proposes an ethane recovery plant for high-pressure natural gas, as shown in fig. 2, the process adopts a double-tower process, wherein a feed gas enters a low-temperature separator (2) after being cooled by a main cold box (1), a separator liquid phase enters a demethanizer (7) after being subjected to pressure regulation, most of a separator gas phase enters the bottom of a high-pressure absorption tower (4) after being cooled by an expansion end (3) of an expander, the rest of the low-temperature separator gas phase enters the middle of the high-pressure absorption tower after being subjected to heat exchange and supercooling by a supercooling cold box (5), a demethanizer top gas phase enters the top of the high-pressure absorption tower after being subjected to pressure boost by a tower top compressor (8) and heat exchange and supercooling by the supercooling cold box, the high-pressure absorption tower top gas phase is subjected to heat exchange and temperature rise by the supercooling cold box, an expansion unit compression end (3) and an external gas compressor (9) are. The process lacks external gas transmission reflux, and the top gas quality of the demethanizer is richer, so that the top temperature of the high-pressure absorption tower is higher, and the ethane recovery rate is lower (90%). If the ethane recovery rate of the system is improved, the supercooling temperature of the feeding material at the top of the high-pressure absorption tower needs to be reduced, so that the gas phase discharging material at the top of the demethanizer is increased, and compared with the RSV process, the system has an insignificant energy-saving effect under the same ethane recovery rate.

During the adaptive simulation of the RSV process, the external gas transmission compression work is obviously increased along with the increase of the pressure of the raw material gas (more than 7MPa) and the increase of the external gas transmission pressure (more than 6.0 MPa). The design goal of a high-efficiency ethane recovery device is to reduce the energy consumption of the system to the maximum extent on the premise of ensuring higher ethane recovery rate. The conventional RSV ethane recovery process suffers from the following problems: (1) when ethane in natural gas is recovered, the demethanizer pressure is limited by the thermal integration of the feed gas and the demethanizer reboiler, and the demethanizer pressure is not too high (3.5 MPa). For the recovery of high-pressure natural gas (more than 6MPa) ethane, when the system adopts an expander and propane refrigeration combined refrigeration, the outlet pressure of the expander is lower, and the output compression work is increased. (2) The mode of reducing the output compression work by increasing the pressure of the demethanizer can lead to the increase of the temperature and the heat load of a reboiler at the bottom of the demethanizer, the difficulty of heat integration of the reboiler of the demethanizer and raw material gas, and the need of an external heat source, and the increase of the energy consumption and the investment of public works. (3) Excessive demethanizer column pressures (greater than 3.5MPa) will result in reduced tray separation efficiency.

Disclosure of Invention

The invention aims to solve the problem of High energy consumption of the existing ethane recovery method of High-Pressure natural gas, provides an ethane recovery method of natural gas, and develops a High-Pressure natural gas ethane recovery process MRHPA (multiple Reflux High Pressure absorber), wherein the process is to set the traditional demethanizer as a High-Pressure absorption tower and a demethanizer respectively, the Pressure of the High-Pressure absorption tower and the demethanizer can be independently set, the tower Pressure of the High-Pressure absorption tower is 0.6 MPa-1 MPa higher than that of the demethanizer, the High-Pressure absorption tower adopts multi-strand feeding and High-Pressure operation modes, the output Reflux quantity and the output gas compression work are reduced, and the carbon dioxide freezing and blocking allowance is increased. The demethanizer operates at a lower pressure, which facilitates thermal integration of the feed gas with the demethanizer bottoms reboiler. The process reduces the compression work of the ethane recovery system, improves the heat integration level of the system, and has obvious energy-saving effect of the ethane recovery device.

The invention provides an ethane recovery method of natural gas, aiming at the problems in the traditional RSV process, the main solution is as follows:

(1) in the MRHPA process, a traditional demethanizer is respectively arranged as a high-pressure absorption tower (T11) and a demethanizer (T12), the pressures of the high-pressure absorption tower and the demethanizer are independently arranged, the top gas of the demethanizer is connected with the high-pressure absorption tower through a tower top compressor (K11), and the pressure of the high-pressure absorption tower is 0.6 MPa-1 MPa higher than that of the demethanizer.

(2) The high pressure absorber (T11) used multiple feeds: the external gas part returns to the main cold box (E11) and the supercooling cold box (E12) for heat exchange and supercooling and then enters the high-pressure absorption tower (T11) under the pressure regulation; the demethanizer overhead gas is pressurized to 4-4.5 MPa by an overhead compressor (K11), and is subjected to heat exchange and supercooling by a cold box (E12) and pressure regulation to enter a high-pressure absorption tower; part of gas phase (10-20%) of the low-temperature separator is subjected to heat exchange and supercooling through a supercooling cold box and then pressure-regulated to enter a high-pressure absorption tower; and the residual gas phase of the low-temperature separator is subjected to pressure reduction and temperature reduction through an expansion end (K13) of an expansion unit and then enters a high-pressure absorption tower.

(3) The liquid phase at the bottom of the high-pressure absorption tower is divided into two streams, and one stream (40-60%) of liquid phase enters a supercooling cold box for heat exchange and supercooling and then is subjected to pressure regulation to enter the middle upper part of demethanization; the other liquid phase enters the top of the demethanizer after pressure regulation; the gas phase at the top of the high-pressure absorption tower is used as an external gas to be sequentially subjected to heat exchange with the supercooling cold box (E12) and the main cold box (E11), and then is pressurized by the pressurization end of the expansion machine and the external compressor and then is output.

(4) The condenser at the top of the deethanizer of the subsequent liquid hydrocarbon fractionation unit needs low-temperature level cold energy, and a propane refrigeration system is arranged in the process, so that the energy conservation is facilitated.

(5) When the pressure of the raw material gas is lower than 7MPa and the molar content of carbon dioxide is more than 2.0 percent, the liquid phase separated by the low-temperature separator is divided into two parts, and partial liquid phase (10 percent to 50 percent) is mixed with partial gas phase of the low-temperature separator, enters a supercooling cold box (E12) for heat exchange and supercooling, then is subjected to pressure regulation and enters the middle part of the high-pressure absorption tower. The rest liquid phase enters the lower part of the demethanizer after pressure regulation.

(6) The main cold box (E11) and the sub-cold box (E12) both adopt a multi-strand plate-fin heat exchanger, and two heat flows and five cold flows as well as three heat flows and two cold flows are respectively integrated in the main cold box and the sub-cold box. The heat flow of the main cold box is raw material gas and output reflux, and five cold flows respectively output gas, demethanizer side line extraction and low-temperature propane. The three hot flows of the supercooling cold box are a part of gas phase of the low-temperature separator, a part of gas transmission reflux and the top gas phase of the demethanizer. The two cold flows are respectively a gas phase at the top of the high-pressure absorption tower and a liquid phase at the bottom of the high-pressure absorption tower.

Compared with the prior art, the invention has the advantages that:

(1) the rectification section and the stripping section of the demethanizer in the traditional RSV process are respectively set into a high-pressure absorption tower and a low-pressure demethanizer, and the pressures of the two towers are mutually independent.

(2) On the premise of meeting the refrigeration requirement, the pressure of the high-pressure absorption tower can be increased as much as possible, and the compression work required by pressurization of the external gas transmission is reduced.

(3) The demethanizer operates at a lower pressure, and can utilize the feed gas as a heat source of the reboiler, thereby improving the heat integration of the system and reducing the heat demand on public works.

(4) The high-pressure absorption tower adopts a plurality of strands of feeding materials, and has a plurality of strands of feeding materials such as external gas transmission reflux, demethanizer top gas phase reflux, low-temperature separator gas phase and the like, and the adjustability and adaptability of the process are enhanced. The high-pressure absorption tower has high pressure, the demethanizer has high tower top temperature, and the adaptability to carbon dioxide is enhanced.

(5) The method reduces the compression work of the ethane recovery system, improves the heat integration level of the system, effectively improves the economic benefit of the operation of the ethane recovery device, and is suitable for the ethane recovery device with the raw material gas pressure higher than 6 MPa.

Advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Drawings

The invention is described in further detail in the following with reference to the figures and the detailed description of the invention

FIG. 1 is a process flow chart proposed in patent CN105037069A

FIG. 2 is a process flow diagram of patent CN210458012

Fig. 3 is a flow diagram of a conventional RSV process.

FIG. 4 is a flow chart of the MRHPA process of examples 1 and 2.

FIG. 5 is a flow diagram of the MRHPA process of example 3.

FIG. 6 is an attached figure of the abstract of the MRHPA process flow

The main equipment numbers in fig. 3: e21-main cold box; e22-supercooling cold box; v21-cryogenic separator; t21-demethanizer; k21-expansion end of expansion machine set; k22-the booster end of the expander set; k23-external gas compressor; a21-air cooler; W22-Water cooler. I, transporting natural gas out; II, raw material gas natural gas; III-low temperature propane refrigerant; IV-liquid hydrocarbons containing ethane and heavier components above ethane.

Main device numbers in fig. 4 and 5: e11-main cold box; e12-supercooling cold box; v11-cryogenic separator; t11-high pressure absorber column; t12-demethanizer; k11-overhead compressor; k12-expansion end of expansion machine set; k13-the booster end of the expander set; k14-export compressor; a11-air cooler; W11-Water cooler. I, transporting natural gas out; II, raw material gas natural gas; III-low temperature propane refrigerant; IV-liquid hydrocarbons containing ethane and heavier components above ethane.

Detailed Description

The present invention will now be described with reference to the following examples, which are provided for illustration and explanation and are not intended to limit the scope of the invention.

Example 1

The gas composition and working conditions of the dehydrated raw material gas are as follows:

scale of raw material gas treatment: 1000X 10⁴m³/d

Raw material gas pressure: 7.0MPa

Temperature of raw material gas: 33 deg.C

The natural gas output pressure: not less than 6.0MPa

The feed gas composition is shown in table 1.

TABLE 1 composition of dehydrated feed gas

Natural gas component	N2	CO2	C1	C2	C3	iC4	nC4
								The composition of natural gas is mol%	0.61	3.00	89.09	4.70	1.40	0.27	0.30
Natural gas component	iC5	nC5	C6	C7	C8	C9	C10
								The composition of natural gas is mol%	0.13	0.09	0.13	0.10	0.09	0.06	0.04

The process flow diagram of the natural gas ethane recovery method of the invention in example 1 is shown in fig. 3, and the flow diagram is briefly described as follows:

(1) the dehydrated feed gas (7.0MPa, 34 ℃) is cooled to-43 ℃ by a main cold box (E11) and then enters a low-temperature separator (V11).

(2) The gas phase (6.92MPa and 35 ℃) of the low-temperature separator is divided into two parts, most of the gas phase (84%) enters the middle lower part of a high-pressure absorption tower (T11) after being cooled and depressurized (3.7MPa and 70 ℃) through an expansion end K12 of an expansion unit, and the rest of the gas phase (16%) enters the middle part of the high-pressure absorption tower after being subjected to heat exchange in a supercooling cold box (E12) to-85 ℃ for supercooling and then being regulated to 3.35 MPa. The liquid phase at the bottom of the low-temperature separator is adjusted to 3.7MPa and then enters the middle-lower part of the demethanizer.

(3) After the gas phase at the top of the high-pressure absorption tower is used as external gas to exchange heat with a supercooling cold box (E12) and a main cold box (E11), the gas phase is pressurized by a pressurizing end (K13) of an expansion unit, pressurized by an external compressor (K14) and cooled by an air cooler A11 and then is output; wherein 18% of the external gas is subjected to heat exchange through a water cooler (W11), a main cold box (E11) and a supercooling cold box (E12) in sequence to-85 ℃, is subjected to supercooling, is subjected to pressure regulation to 3.65MPa, and then enters the top of a high-pressure absorption tower (T11). The liquid phase at the bottom of the high-pressure absorption tower is divided into two parts, 50% of the liquid phase exchanges heat with the supercooling cold box and then is regulated to 2.85MPa to be used as the second feed of the demethanizer, and the rest liquid phase is regulated to 2.85MPa to be used as the first feed of the demethanizer and then enters the demethanizer.

(4) The gas phase at the top of the demethanizer (T12) enters a supercooling cold box (E12) for heat exchange after being pressurized (5.6MPa) by a top compressor (K11) to-85 ℃ for supercooling, then pressure is regulated to enter the upper part of a high-pressure absorption tower, and the low liquid phase of the demethanizer enters a subsequent fractionation unit. The refrigeration process combines propane refrigerant refrigeration and expander refrigeration.

(5) The liquid phase at the bottom of the demethanizer enters a deethanizer (T13) for fractionation. The gas phase discharged from the top of the deethanizer is divided into two parts, wherein part of the gas phase (40-50%) exchanges heat with a high-temperature (40 ℃) refrigerant and then enters a downstream flow for treatment, and the rest of the gas phase enters a propane refrigerant cooler and then enters a reflux tank for complete condensation, is pressurized by a pump and then serves as deethanizer for reflux. The bottom discharge of the deethanizer is propane and liquid hydrocarbon above propane, and enters downstream flow processing.

The main parameters of the RSV and MRHPA flow are compared in Table 2, and it can be seen that the simulation results show that: when the molar content of carbon dioxide in natural gas is 3%, the minimum freezing and plugging allowance of carbon dioxide is increased and the system compression function consumption is reduced by 8.8% compared with the RSV process under the condition that the ethane recovery rate is 94%.

TABLE 2 comparison of major parameters for RSV and MRHPA procedures

Example 2

The gas composition and working conditions of the dehydrated raw material gas are as follows:

scale of raw material gas treatment: 1000X 10⁴m³/d

Raw material gas pressure: 8.0MPa

Temperature of raw material gas: 37 deg.C

The natural gas output pressure: not less than 6.0MPa

The feed gas composition is shown in table 3.

TABLE 3 composition of dehydrated feed gas

Natural gas component	N2	CO2	C1	C2	C3	iC4	nC4
								The composition of natural gas is mol%	1.02	0.1	88.54	7.41	1.50	0.3	0.31
Natural gas component	iC5	nC5	C6	C7	C8	C9	C10
								The composition of natural gas is mol%	0.13	0.09	0.15	0.20	0.18	0.05	0.02

The process flow diagram of the natural gas ethane recovery method of the invention in example 2 is shown in fig. 4, and the flow diagram is briefly described as follows:

(1) the dehydrated feed gas (8.0MPa, 37 ℃) is cooled to-43 ℃ by a main cold box (E11) and then enters a low-temperature separator (V11).

(2) The gas phase (7.92 MPa-33 ℃) of the low-temperature separator is divided into two parts, and most of the gas phase (82%) enters the middle-lower part of a high-pressure absorption tower T11 after being cooled and depressurized (3.8 MPa-68 ℃) by an expansion end K12 of an expander set; the residual gas phase (18%) is cooled to-85 ℃ by a supercooling cold box E12, and then pressure is regulated to 3.75MPa to enter the middle part of the high-pressure absorption tower; the liquid phase of the cryogenic separator was pressure adjusted to 3.8MPa and fed to the bottom of a high pressure absorber (T11).

(3) The liquid phase at the bottom of the high-pressure absorption tower is divided into two streams, one stream of liquid phase (50%) enters a supercooling cold box (E12) to be cooled and regulated to 3.25MPa, and then enters the middle upper part of the demethanizer to be used as the second stream of feed of the demethanizer; the other liquid phase (the remaining 50%) was depressurized and pressure-regulated to 3.25MPa and fed to the top of the demethanizer as the first feed to the demethanizer. The gas phase at the top of the high-pressure absorption tower is used as external gas to be sequentially subjected to heat exchange with the supercooling cold box (E12) and the main cold box (E11), then is subjected to pressurization through a pressurization end (K13) of an expansion unit, pressurization through an external compressor (K13), and external transportation after being cooled by an air cooler (A11); wherein, after heat exchange and temperature reduction of 17% of the external gas are carried out by a water cooler (W11), a main cooling box (E11) and a supercooling cooling box (E12) in sequence to-85 ℃, pressure regulation and pressure reduction are carried out to 3.75MPa, and then the gas enters the top of a high-pressure absorption tower (T11).

(4) The gas phase at the top of the demethanizer (T12) enters a supercooling cold box (E12) to be cooled to-85 ℃ and regulated to 3.35MPa after being pressurized by a top compressor (K11) (5.8MPa), and then enters the upper part of the high-pressure absorption tower. The lower liquid phase of the demethanizer enters a subsequent fractionation unit. The refrigeration process adopts propane refrigeration, and provides two temperature levels of refrigeration capacity for the ethane recovery process. Table 2 compares RSV with the major parameters of the inventive mrapa flowsheet.

(5) The liquid phase at the bottom of the demethanizer (T12) enters a deethanizer (T13) for fractionation. The gas phase discharged from the top of the deethanizer is divided into two parts, wherein part of the gas phase (40-50%) exchanges heat with high-temperature (40 ℃) liquid propane in a cold box (E13) and then enters a downstream flow for treatment, and the rest of the gas phase enters a propane refrigerant cooler (E14) and then enters a reflux tank (V12) for complete condensation, is pressurized by a pump (P11) and then is used as the reflux of the deethanizer. The bottom discharge of the deethanizer is propane and liquid hydrocarbon above propane, and enters downstream flow processing.

As can be seen from table 4, the simulation results show that: under the condition that the natural gas pressure and the external gas transmission pressure are both high, the system compression function consumption is reduced by 12.2 percent compared with the RSV process under the condition that the ethane recovery rate is 94 percent.

TABLE 4 comparison of major parameters for RSV and MRHPA flowsheets

Example 3

The gas composition and working conditions of the dehydrated raw material gas are as follows:

scale of raw material gas treatment: 1000X 104m3/d

Raw material gas pressure: 6.0MPa

Temperature of raw material gas: 37 deg.C

The natural gas output pressure: not less than 6.0MPa

The feed gas composition is shown in table 5.

TABLE 5 composition of dehydrated feed gas

Natural gas component	N2	CO2	C1	C2	C3	nC4
							The composition of natural gas is mol%	0.61	2	90.09	4.7	1.40	0.4
Natural gas component	iC5	nC5	C6	C7	C8	C10
							The composition of natural gas is mol%	0.13	0.09	0.13	0.10	0.09	0.04

The process flow diagram of the natural gas ethane recovery method of the invention in example 3 is shown in fig. 5, and the flow diagram is briefly described as follows:

the dehydrated raw material gas (6.0MPa and 37 ℃) is cooled to-43 ℃ through a main cooling box (E11) and then enters a low-temperature separator (V11), the gas phase (5.92MPa and-42 ℃) of the low-temperature separator is divided into two paths, most of the gas phase (84%) is cooled and depressurized (3.4MPa and-69 ℃) through an expansion end (K12) of an expansion unit and then enters the middle lower part of a high-pressure absorption tower (T12), the rest gas phase (16%) is mixed with part of the liquid phase (30%) of the low-temperature separator, then is subjected to heat exchange and supercooling to-85 ℃ through a supercooling cooling box (E12), then is regulated to 3.75MPa and enters the middle part of the high-pressure absorption tower, most of the liquid phase (70%) of the low-temperature separator is regulated to 3.4MPa and then enters the bottom of the high-pressure absorption tower, the gas phase at the top of the demethanizer is pressurized (K11) through a tower top compressor (5.8MPa) and then enters a supercooling cooling, The main cold box (E11) and the supercooling cold box (E12) exchange heat and supercool to-85 ℃, and enter the top of the high-pressure absorption tower after the pressure is regulated to 3.4 MPa. The gas phase at the top of the high-pressure absorption tower is used as external gas to exchange heat with a supercooling cold box (E12) and a main cold box (E11), and then is pressurized by an expander set pressurization end (K13) and an external compressor (K14) and then is output, the liquid phase at the bottom of the high-pressure absorption tower is divided into two parts, 50% of the liquid phase exchanges heat with the cold box and then is regulated to 3.3MPa to be used as the second strand of feeding material of the demethanizer, and the rest of the liquid phase is regulated to 2.8MPa to be used as the first strand of feeding material of the demethanizer and then enters the. The demethanizer overhead gas phase is used as a second feed of the high-pressure absorption tower, is subjected to pressure boosting (5.7MPa) by an overhead compressor (K11) and heat exchange and supercooling by a supercooling cold box (E12), is subjected to pressure regulation, and enters the high-pressure absorption tower, and the demethanizer low-liquid phase enters a subsequent fractionation unit. The refrigeration process adopts propane refrigeration, and provides two temperature levels of refrigeration capacity for the ethane recovery process. Table 6 compares the major parameters of the RSV and mrapa flowsheets.

As can be seen from table 6, the simulation results show that: under the condition that the pressure of the raw material gas and the external gas transmission pressure are both high, and under the condition that the ethane recovery rate is 94%, compared with the RSV process, the system has the advantages that the compression function consumption is reduced by 6.6%, and the freezing and blocking allowance of carbon dioxide is increased by 3 ℃.

TABLE 6 comparison of main parameters of RSV and MRHPA flow

In conclusion, the method adopts a double-tower flow combining the high-pressure absorption tower and the demethanizer, has a plurality of strands of feeding materials such as external gas transmission reflux, demethanizer top gas phase reflux, a low-temperature separator gas phase and the like, and has higher pre-separation temperature. The ethane recovery rate can be flexibly adjusted by arranging a plurality of strands of feeding materials of the high-pressure absorption tower, and the operation is convenient. The ethane recovery device has the characteristics of high recovery rate, low system energy consumption, strong freezing and blocking adaptability to carbon dioxide, high thermal integration degree and the like for the ethane recovery device with higher feed gas pressure and high external gas transmission pressure.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.