CO2 trapping and liquefying device and CO2 trapping method for exhaust gas of natural gas purification plant

Abstract

The invention discloses a CO2 trapping and liquefying device for exhaust gas of a natural gas purification plant, which comprises a carbon dioxide trapping module, the carbon dioxide trapping module is connected with a refrigeration purification liquefying module, the carbon dioxide trapping module comprises an absorption tower, the absorption tower is connected with a rich and lean liquid heat exchanger, the rich and lean liquid heat exchanger is connected with a desorption tower, and the desorption tower is connected with a liquid storage tank. The refrigeration, purification and liquefaction module comprises a carbon dioxide cold box, the carbon dioxide cold box is connected with a propane refrigeration unit, the carbon dioxide cold box is further connected with a carbon dioxide purification tower, an MDEA-PZ mixed amine liquid trapping and propane refrigeration and liquefaction combined technology is adopted, the CO2 trapping rate can be guaranteed, energy consumption can be reduced, and the CO2 trapping cost can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of natural gas separation and processing methods, and relates to a CO2 capture and liquefaction process of exhaust gas from a natural gas purification plant. Background Art

[0002] Carbon dioxide (CO2) capture, utilization and storage (CCUS) is an emerging technology with the potential for large-scale emission reduction. As one of the CCUS technologies, CO2 injection to displace low permeability oil and gas reservoirs (CO2-Enhanced Oil Recovery, CO2-EOR) is considered to be a low-permeability oilfield recovery technology with good development prospects. By injecting CO2 into low-permeability, pressure-depleted and other oil-bearing formations, it can not only improve crude oil recovery, but also achieve underground storage of CO2, thereby reducing greenhouse gas CO2 emissions. During the operation of CO2-EOR in oil and gas fields, the CO2 gas contained in the exhaust gas of the natural gas purification plant is of high concentration and large emission. Capturing and utilizing the CO2 in the exhaust gas of the natural gas purification plant is an important means to help achieve carbon emission reduction goals and ensure the stable supply of high-concentration carbon sources in CCUS projects.

[0003] At present, there are three main methods for capturing medium-concentration CO2: alcohol amine liquid absorption-regeneration method (abbreviated as "alcohol amine method"), which is suitable for the situation where the CO2 content in the mixed gas is low, has high removal efficiency, simple operation, strong economic adaptability, and is widely used in the fields of petroleum and petrochemicals at home and abroad, but its regeneration heat load is high; pressure swing adsorption method is a new cost-effective separation method, which is widely used in flue gas capture, but the energy consumption required for the regeneration of its adsorption medium is large; low-temperature separation is to achieve gas separation by relying on the principle that various gases have different condensation phase characteristics, but its energy consumption is large and the cost is high, and it is not widely used in the industry. It is the first time that CO2 is captured in the exhaust gas of a natural gas purification plant in China. For this reason, a CO2 capture liquefaction process is designed to adapt to the gas quality conditions of the exhaust gas of the natural gas purification plant.

[0004] For the exhaust gas from the purification plant, in order to obtain higher CO2 capture concentration and lower energy consumption, the CO2 separation and liquefaction process is optimized to efficiently capture CO2 in the exhaust gas from the liquefaction purification plant. Summary of the invention

[0005] The purpose of the present invention is to provide a CO2 capture and liquefaction device for exhaust gas from a natural gas purification plant, which solves the problem of deep removal of CO2 from exhaust gas in the prior art. Another purpose of the present invention is to provide a CO2 capture method for exhaust gas from a natural gas purification plant, which has the characteristics of high CO2 capture rate. The above expression can also be replaced by the following form:

[0006] The technical solution adopted by the present invention is that the CO2 capture and liquefaction device of the exhaust gas of the natural gas purification plant includes a carbon dioxide capture module, the carbon dioxide capture module is connected to a refrigeration purification liquefaction module, the carbon dioxide capture module includes an absorption tower, the absorption tower is connected to a lean-rich liquid heat exchanger, the lean-rich liquid heat exchanger is connected to a desorption tower, the refrigeration purification liquefaction module includes a carbon dioxide cold box, the carbon dioxide cold box is connected to a propane refrigeration unit, and the carbon dioxide cold box is also connected to a carbon dioxide purification tower.

[0007] The present invention is also characterized in that: the carbon dioxide capture module includes an absorption tower, the bottom inlet of the absorption tower is connected to an exhaust gas compressor, the bottom outlet of the absorption tower is sequentially connected to a buffer tank, a filter, and a rich liquid pump through a pipeline, the rich liquid pump is connected to a lean and rich liquid heat exchanger, the top outlet of the absorption tower is sequentially connected to a lean liquid cooler, a purified gas separator, and an activator pump through a pipeline, the purified gas separator is provided with a gas outlet and a liquid outlet, the liquid outlet is connected to the activator pump through a pipeline, the activator pump is connected to an inlet on one side of the top of the absorption tower through a pipeline, the lean and rich liquid heat exchanger is connected to an inlet on one side of the upper part of the desorption tower, the lean and rich liquid heat exchanger is connected to the absorption tower through a pipeline, a lean liquid pump is arranged on the pipeline between the lean and rich liquid heat exchanger and the absorption tower, the top outlet of the desorption tower is connected to a refrigeration purification liquefaction module through a pipeline, the desorption tower is also connected to an inlet of a reboiler, and a loop is formed between the reboiler and the desorption tower;

[0008] The refrigeration purification liquefaction module includes a carbon dioxide cooler, which is connected to the desorption tower through a pipeline. The carbon dioxide cooler is connected to a wet gas compressor, a molecular sieve dehydration skid carbon dioxide cold box in sequence through the pipeline. The carbon dioxide cold box is connected to the carbon dioxide purification tower, and the carbon dioxide cold box is also connected to a propane refrigeration unit.

[0009] Another technical solution of the present invention is a method for capturing CO2 from exhaust gas from a natural gas purification plant. The method uses a CO2 capture and liquefaction device for exhaust gas from a natural gas purification plant. The specific steps are as follows:

[0010] Step 1: The exhaust gas from the natural gas purification plant is sent to the carbon dioxide capture module, which is pressurized by the exhaust gas compressor in the carbon dioxide capture module and sent to the absorption tower for decarbonization reaction to obtain a rich liquid that absorbs carbon dioxide. The rich liquid that absorbs carbon dioxide is sent to the desorption tower for flash evaporation to obtain carbon dioxide capture gas, and the lean liquid obtained after flash evaporation is sent back to the absorption tower for reabsorption;

[0011] Step 2: The captured carbon dioxide gas is sent to the refrigeration, purification and liquefaction module, and after cooling, secondary pressurization and dehydration, it is liquefied through a carbon dioxide cold box to obtain liquid carbon dioxide;

[0012] Step 3: The liquid carbon dioxide is purified and cooled through a purification tower and then transported to a storage tank. At the same time, the non-condensable gas is discharged after heat exchange through a propane refrigeration unit.

[0013] The present invention is also characterized in that: Step 1 is specifically: the exhaust gas from the natural gas purification plant is sent to the carbon dioxide capture module and pressurized to 0.5MPa-0.7MPa by the exhaust gas compressor to obtain the pressurized exhaust gas, and the pressurized exhaust gas is introduced into the bottom inlet of the absorption tower. The pressurized exhaust gas moves from bottom to top in the absorption tower, and the bottom outlet of the absorption tower passes through the lean liquid cooler, the purified gas separator, and the activator pump in sequence. N-methyldiethanolamine-piperazine solvent is sent into the lean liquid through the activator pump to generate a lean liquid absorbent, and the lean liquid absorbent enters through the inlet on one side of the top of the absorption tower and is sprayed from top to bottom, and the lean liquid absorbent is countercurrently contacted with the pressurized exhaust gas to perform a decarbonization reaction. The rich liquid that absorbs carbon dioxide gas is discharged from the outlet at the bottom of the absorption tower, and the rich liquid that absorbs carbon dioxide gas passes through a buffer tank, a filter and a rich liquid pump in sequence and then enters a lean-rich liquid heat exchanger. The rich liquid that absorbs carbon dioxide gas is heated by the hot lean liquid and then enters the upper part of the desorption tower operated under low pressure, so that most of the acidic components are flashed from the rich liquid that absorbs carbon dioxide gas on the top plate of the desorption tower to obtain carbon dioxide capture gas. The lean liquid generated after desorption is discharged from the outlet at the bottom of the desorption tower to the reboiler. The lean liquid generated after desorption is heated in the reboiler, and then transported through a pipeline and passes through the desorption tower, the lean-rich liquid heat exchanger and the lean liquid pump in sequence and enters the absorption tower to restart the absorption process.

[0014] The mass fraction of N-methyldiethanolamine solution in the N-methyldiethanolamine-piperazine solvent transported by the activator pump is 18%-22%, the heat load of the reboiler is 14500kW-15500kW, and the pressure of the reboiler is 0.15MPa-0.25MPa.

[0015] Step 2 is specifically as follows: the carbon dioxide captured gas coming out of the top of the desorption tower passes through a carbon dioxide cooler, is then secondary pressurized to 2.4MPa-2.6MPa by a wet gas compressor, is then dehydrated by a molecular sieve dehydration skid, and is liquefied by a carbon dioxide cold box to obtain liquid carbon dioxide.

[0016] Step 3 is specifically as follows: liquid carbon dioxide is sent to a purification tower, the purification tower heats the liquid carbon dioxide, the non-condensable gas generated after heating is discharged after heat exchange through a propane refrigeration unit, and the remaining liquid carbon dioxide is supercooled by the propane refrigeration unit and then sent to a storage tank.

[0017] The beneficial effects of the present invention are as follows: (1) the use of MDEA-PZ mixed amine liquid capture combined with propane refrigeration liquefaction process can not only ensure the CO2 capture rate, but also reduce energy consumption and reduce the CO2 capture cost;

[0018] (2) PZ is used as the activator of MDEA absorption solution, which can be used for the deep removal of CO2 in the exhaust gas and coordinately adjust the optimal process parameters of the CO2 capture project to ensure that the CO2 capture concentration reaches more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the CO2 capture and liquefaction device of the exhaust gas of the natural gas purification plant of the present invention;

[0020] Figure 2 It is a process flow chart of the CO2 capture and liquefaction process of the exhaust gas of the natural gas purification plant of the present invention.

[0021] In the figure, 1. carbon dioxide capture module, 2. refrigeration purification liquefaction module, 101. exhaust gas compressor, 102. absorption tower, 103. buffer tank, 104. filter, 105. rich liquid pump, 106. lean and rich liquid heat exchanger, 107. lean liquid pump, 108. purified gas separator, 109. lean liquid cooler, 110. desorption tower, 111. reboiler, 112. activator pump, 201. carbon dioxide cooler, 202. wet gas compressor, 203. molecular sieve dehydration skid, 204. carbon dioxide cold box, 205. propane refrigeration unit, 206. carbon dioxide purification tower. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] The CO2 capture and liquefaction device of the exhaust gas of the natural gas purification plant of the present invention is as follows: Figure 1As shown, it includes a carbon dioxide capture module 1, which is connected to a refrigeration purification liquefaction module 2. The carbon dioxide capture module 1 includes an absorption tower 102, the bottom inlet of the absorption tower 102 is connected to an exhaust gas compressor 101, the bottom outlet of the absorption tower 102 is sequentially connected to a filter 104 and a rich liquid pump 105 through a pipeline, the rich liquid pump 105 is connected to a lean and rich liquid heat exchanger 106, the top outlet of the absorption tower 102 is sequentially connected to a lean liquid cooler 109 and a purified gas separator 108 through a pipeline, the purified gas separator 108 is provided with a gas outlet and a liquid outlet, the liquid outlet is connected to an inlet on one side of the top of the absorption tower 102 through a pipeline, the lean and rich liquid heat exchanger 106 is connected to an inlet on one side of the upper part of the desorption tower 110, and the lean and rich liquid heat exchanger 106 is connected to the absorption tower 102. The towers 102 are connected by pipelines, a lean liquid pump 107 is provided on the pipeline between the lean-rich liquid heat exchanger 106 and the absorption tower 102, the top outlet of the desorption tower 110 is connected to the refrigeration purification liquefaction module 2 through a pipeline, the desorption tower 110 is also connected to the inlet of the reboiler 111, and a loop is formed between the reboiler 111 and the desorption tower 110, the refrigeration purification liquefaction module 2 includes a carbon dioxide cooler 201, and the carbon dioxide cooler 201 is sequentially connected to a wet gas compressor 202, a molecular sieve dehydration skid 203, and a carbon dioxide cold box 204 through pipelines, the carbon dioxide cold box 204 is connected to a carbon dioxide purification tower 206, the carbon dioxide cold box 204 is also connected to a propane refrigeration unit 205, and the carbon dioxide cooler 201 is also connected to the desorption tower 110 through a pipeline.

[0024] The method for capturing CO2 from exhaust gas from a natural gas purification plant of the present invention is as follows: Figure 2 As shown in the figure, the specific steps of the CO2 capture and liquefaction process of the exhaust gas of the natural gas purification plant are as follows:

[0025] Step 1: The exhaust gas from the natural gas purification plant is sent to the carbon dioxide capture module 1 and pressurized to 0.55MPa-0.65MPa by the exhaust gas compressor 101 to obtain the pressurized exhaust gas, and the pressurized exhaust gas is passed into the bottom inlet of the absorption tower 102. The pressurized exhaust gas passes through the bottom outlet from bottom to top and passes through the lean liquid cooler 109 and the purified gas separator 108 in turn to generate a lean liquid absorbent, which enters the inlet on one side of the top of the absorption tower 102 and is sprayed from top to bottom. The lean liquid absorbent is countercurrently contacted with the pressurized exhaust gas to perform a decarbonization reaction, so that the rich liquid that absorbs the carbon dioxide gas is discharged from the outlet 204 at the bottom of the absorption tower 102, and the rich liquid that absorbs the carbon dioxide gas is discharged from the outlet 204 at the bottom of the absorption tower 102. The liquid passes through the buffer tank 103, the filter 104 and the rich liquid pump 105 in sequence and then enters the lean-rich liquid heat exchanger 106. The hot lean liquid is used to heat the rich liquid that absorbs the carbon dioxide gas and then enters the upper part of the desorption tower 110 operated under low pressure, so that most of the acidic components are flashed from the rich liquid that absorbs the carbon dioxide gas on the top plate of the desorption tower 110 to obtain carbon dioxide capture gas. The lean liquid generated after desorption is discharged from the bottom outlet of the desorption tower 110 to the reboiler 111. The lean liquid generated after desorption is heated by the reboiler 111 and then transported through the desorption tower 110, the lean-rich liquid heat exchanger 106 and the lean liquid pump 107 in sequence through a pipeline to enter the absorption tower 102 to restart the absorption process;

[0026] Step 2: The captured carbon dioxide gas is sent to the refrigeration, purification and liquefaction module 2. The captured carbon dioxide gas coming out of the top of the desorption tower 110 passes through the carbon dioxide cooler 201, and then passes through the wet gas compressor 202 for secondary pressurization to 2.5 MPa, and then passes through the molecular sieve dehydration skid 203 and liquefied through the carbon dioxide cold box 204 to obtain liquid carbon dioxide;

[0027] Step 3: The liquid carbon dioxide is sent to the purification tower 206, and the purification tower 206 heats the liquid carbon dioxide. The non-condensable gas generated after heating is discharged after heat exchange through the propane refrigeration unit 205, and the remaining liquid carbon dioxide is supercooled by the propane refrigeration unit 205 and then sent to the storage tank.

[0028] The functions of the main components of the CO2 capture and liquefaction device of the exhaust gas of the natural gas purification plant of the present invention are as follows:

[0029] Absorption tower: The absorption tower provides sufficient contact area and contact time for the carbon dioxide in the tower and the lean liquid absorbent;

[0030] Lean-rich liquid heat exchanger: transfers heat from the lean liquid to the rich liquid, forming a more concentrated solution in the rich liquid, thereby reducing the temperature of the lean liquid and making the concentration in the lean liquid more dilute;

[0031] Desorber: releases carbon dioxide from the rich liquid by flash evaporation.

[0032] Example 1

[0033] like Figure 1 As shown, the CO2 capture and liquefaction device of the exhaust gas of the natural gas purification plant in this embodiment includes a carbon dioxide capture module 1, the carbon dioxide capture module 1 is connected to a refrigeration purification liquefaction module 2, the carbon dioxide capture module 1 includes an absorption tower 102, the absorption tower 102 is connected to a lean-rich liquid heat exchanger 106, the lean-rich liquid heat exchanger 106 is connected to a desorption tower 110, the refrigeration purification liquefaction module 2 includes a carbon dioxide cold box 204, the carbon dioxide cold box 204 is connected to a propane refrigeration unit 205, and the carbon dioxide cold box 204 is also connected to a carbon dioxide purification tower 206.

[0034] Example 2

[0035] like Figure 1 As shown, the CO2 capture and liquefaction device of the exhaust gas of the natural gas purification plant in this embodiment includes a carbon dioxide capture module 1, the carbon dioxide capture module 1 is connected to a refrigeration purification liquefaction module 2, the carbon dioxide capture module 1 includes an absorption tower 102, the absorption tower 102 is connected to a lean-rich liquid heat exchanger 106, the lean-rich liquid heat exchanger 106 is connected to a desorption tower 110, the refrigeration purification liquefaction module 2 includes a carbon dioxide cold box 204, the carbon dioxide cold box 204 is connected to a propane refrigeration unit 205, and the carbon dioxide cold box 204 is also connected to a carbon dioxide purification tower 206.

[0036] The carbon dioxide capture module 1 includes an absorption tower 102, the bottom inlet of the absorption tower 102 is connected to the exhaust gas compressor 101, the bottom outlet of the absorption tower 102 is connected to the filter 104 and the rich liquid pump 105 in sequence through pipelines, the rich liquid pump 105 is connected to the lean and rich liquid heat exchanger 106, the top outlet of the absorption tower 102 is connected to the lean liquid cooler 109, the purified gas separator 108 and the activator pump 112 in sequence through pipelines, the purified gas separator 108 is provided with a gas outlet and a liquid outlet, the liquid outlet is connected to the activator pump 112 through a pipeline, The activator pump 112 is connected to the inlet on the top side of the absorption tower 102 through a pipeline, the lean-rich liquid heat exchanger 106 is connected to the inlet on the upper side of the desorption tower 110, the lean-rich liquid heat exchanger 106 and the absorption tower 102 are connected by a pipeline, a lean liquid pump 107 is arranged on the pipeline between the lean-rich liquid heat exchanger 106 and the absorption tower 102, the top outlet of the desorption tower 110 is connected to the refrigeration purification liquefaction module 2 through a pipeline, the desorption tower 110 is also connected to the inlet of the reboiler 111, and a loop is formed between the reboiler 111 and the desorption tower 110.

[0037] Example 3

[0038] like Figure 1As shown, the CO2 capture and liquefaction device of the exhaust gas of the natural gas purification plant in this embodiment includes a carbon dioxide capture module 1, the carbon dioxide capture module 1 is connected to a refrigeration purification liquefaction module 2, the carbon dioxide capture module 1 includes an absorption tower 102, the absorption tower 102 is connected to a lean-rich liquid heat exchanger 106, the lean-rich liquid heat exchanger 106 is connected to a desorption tower 110, the refrigeration purification liquefaction module 2 includes a carbon dioxide cold box 204, the carbon dioxide cold box 204 is connected to a propane refrigeration unit 205, and the carbon dioxide cold box 204 is also connected to a carbon dioxide purification tower 206.

[0039] The carbon dioxide capture module 1 includes an absorption tower 102, the bottom inlet of the absorption tower 102 is connected to the exhaust gas compressor 101, the bottom outlet of the absorption tower 102 is connected to the filter 104 and the rich liquid pump 105 in sequence through pipelines, the rich liquid pump 105 is connected to the lean and rich liquid heat exchanger 106, the top outlet of the absorption tower 102 is connected to the lean liquid cooler 109, the purified gas separator 108 and the activator pump 112 in sequence through pipelines, the purified gas separator 108 is provided with a gas outlet and a liquid outlet, the liquid outlet is connected to the activator pump 112 through a pipeline, The activator pump 112 is connected to the inlet on the top side of the absorption tower 102 through a pipeline, the lean-rich liquid heat exchanger 106 is connected to the inlet on the upper side of the desorption tower 110, the lean-rich liquid heat exchanger 106 and the absorption tower 102 are connected by a pipeline, a lean liquid pump 107 is arranged on the pipeline between the lean-rich liquid heat exchanger 106 and the absorption tower 102, the top outlet of the desorption tower 110 is connected to the refrigeration purification liquefaction module 2 through a pipeline, the desorption tower 110 is also connected to the inlet of the reboiler 111, and a loop is formed between the reboiler 111 and the desorption tower 110.

[0040] The refrigeration purification liquefaction module 2 includes a carbon dioxide cooler 201, which is connected to the desorption tower 110 through a pipeline. The carbon dioxide cooler 201 is connected to a wet gas compressor 202, a molecular sieve dehydration skid 203, and a carbon dioxide cold box 204 in sequence through pipelines. The carbon dioxide cold box 204 is connected to a carbon dioxide purification tower 206, and the carbon dioxide cold box 204 is also connected to a propane refrigeration unit 205.

[0041] Example 4

[0042] like Figure 2As shown, the method for capturing CO2 from the exhaust gas of a natural gas purification plant of the present invention comprises the following steps: step 1: sending the exhaust gas of the natural gas purification plant into a carbon dioxide capture module 1 and pressurizing it to 0.7 MPa through an exhaust gas compressor 101 to obtain pressurized exhaust gas, and passing the pressurized exhaust gas into a bottom inlet of an absorption tower 102. The pressurized exhaust gas moves from bottom to top in the absorption tower 102. The bottom outlet of the absorption tower 102 passes through a lean liquid cooler 109, a purified gas separator 108, and an activator pump 112 in sequence. N-methyldiethanolamine-piperazine solvent is sent into the lean liquid through the activator pump 112 to form a lean liquid absorbent. The mass fraction of N-methyldiethanolamine solution in the N-methyldiethanolamine-piperazine solvent is 20%. The lean liquid absorbent enters through an inlet on one side of the top of the absorption tower 102 and is sprayed from top to bottom. The lean liquid absorbent is in countercurrent contact with the pressurized exhaust gas to perform a decarbonization reaction, so that the absorbent The rich liquid of carbon dioxide gas is discharged from the outlet 204 at the bottom of the absorption tower 102. The rich liquid absorbing carbon dioxide gas enters the lean-rich liquid heat exchanger 106 after passing through the buffer tank 103, the filter 104 and the rich liquid pump 105 in sequence. The rich liquid absorbing carbon dioxide gas is heated by the hot lean liquid and enters the upper part of the desorption tower 110 operated under low pressure, so that most of the acidic components are flashed from the rich liquid absorbing carbon dioxide gas on the top plate of the desorption tower 110 to obtain carbon dioxide capture gas. The lean liquid generated after desorption is discharged from the bottom outlet of the desorption tower 110 to the reboiler 111. The lean liquid generated after desorption is heated by the reboiler 111 and then transported through the desorption tower 110, the lean-rich liquid heat exchanger 106 and the lean liquid pump 107 in sequence to enter the absorption tower 102 to restart the absorption process. The heat load of the reboiler is 15000kW and the pressure of the reboiler is 0.20MPa. ;

[0043] Step 2: The carbon dioxide captured gas from the top of the desorption tower 110 passes through the carbon dioxide cooler 201, and then passes through the wet gas compressor 202 for secondary pressurization to 2.5 MPa, and then passes through the molecular sieve dehydration skid 203 and liquefies through the carbon dioxide cold box 204 to obtain liquid carbon dioxide;

[0044] Step 3: The liquid carbon dioxide is sent to the purification tower 206, and the purification tower 206 heats the liquid carbon dioxide. The non-condensable gas generated after heating is discharged after heat exchange through the propane refrigeration unit 205, and the remaining liquid carbon dioxide is supercooled by the propane refrigeration unit 205 and then sent to the storage tank.

[0045] The CO2 capture and liquefaction device of the exhaust gas of the natural gas purification plant and the CO2 capture method thereof of the present invention have the advantages of: using MDEA-PZ mixed amine liquid capture combined with propane refrigeration liquefaction process, which can not only ensure the CO2 capture rate but also reduce energy consumption, and reduce the CO2 capture cost by using a lean-rich liquid heat exchanger in conjunction with a desorption tower and an absorption tower.

Claims

1. A CO2 capture and liquefaction device for exhaust gas from a natural gas purification plant, characterized in that: The invention comprises a carbon dioxide capture module (1), wherein the carbon dioxide capture module (1) is connected to a refrigeration, purification and liquefaction module (2), wherein the carbon dioxide capture module (1) comprises an absorption tower (102), wherein the absorption tower (102) is connected to a lean-rich liquid heat exchanger (106), wherein the lean-rich liquid heat exchanger (106) is connected to a desorption tower (110), wherein the refrigeration, purification and liquefaction module (2) comprises a carbon dioxide cold box (204), wherein the carbon dioxide cold box (204) is connected to a propane refrigeration unit (205), and wherein the carbon dioxide cold box (204) is further connected to a carbon dioxide purification tower (206).

2. The CO2 capture and liquefaction device for exhaust gas from a natural gas purification plant according to claim 1, characterized in that: The carbon dioxide capture module (1) comprises an absorption tower (102), wherein the bottom inlet of the absorption tower (102) is connected to an exhaust gas compressor (101), the bottom outlet of the absorption tower (102) is connected to a filter (104) and a rich liquid pump (105) in sequence through a pipeline, the rich liquid pump (105) is connected to a lean liquid cooler (109), a purified gas separator (108) and an activator pump (112) in sequence through a pipeline, the purified gas separator (108) is provided with a gas outlet and a liquid outlet, the liquid outlet is connected to the activator pump (112) through a pipeline, The activator pump (112) is connected to the inlet on one side of the top of the absorption tower (102) through a pipeline, the lean-rich liquid heat exchanger (106) is connected to the inlet on one side of the upper part of the desorption tower (110), the lean-rich liquid heat exchanger (106) and the absorption tower (102) are connected through a pipeline, a lean liquid pump (107) is arranged on the pipeline between the lean-rich liquid heat exchanger (106) and the absorption tower (102), the top outlet of the desorption tower (110) is connected to the refrigeration purification liquefaction module (2) through a pipeline, the desorption tower (110) is also connected to the inlet of the reboiler (111), and a loop is formed between the reboiler (111) and the desorption tower (110).

3. The CO2 capture and liquefaction device for exhaust gas from a natural gas purification plant according to claim 1, characterized in that: The refrigeration purification liquefaction module (2) comprises a carbon dioxide cooler (201), the carbon dioxide cooler (201) is connected to the desorption tower (110) via a pipeline, the carbon dioxide cooler (201) is sequentially connected to a wet gas compressor (202), a molecular sieve dehydration skid (203) and a carbon dioxide cold box (204) via pipelines, the carbon dioxide cold box (204) is connected to a carbon dioxide purification tower (206), and the carbon dioxide cold box (204) is also connected to a propane refrigeration unit (205).

4. A method for capturing CO2 from exhaust gas from a natural gas purification plant, characterized in that: The method uses the device as claimed in claim 3, and the specific steps are as follows: Step 1: sending the exhaust gas of the natural gas purification plant into the carbon dioxide capture module (1), using the exhaust gas compressor (101) in the carbon dioxide capture module (1) to pressurize and send it to the absorption tower (102) for decarbonization reaction to obtain a rich liquid that absorbs carbon dioxide, sending the rich liquid that absorbs carbon dioxide to the desorption tower (110) for flash evaporation to obtain carbon dioxide captured gas, and at the same time sending the lean liquid obtained after flash evaporation back to the absorption tower (102) to start re-absorption; Step 2: The captured carbon dioxide gas is sent to the refrigeration, purification and liquefaction module (2), and after cooling, secondary pressurization and dehydration, it is liquefied through the carbon dioxide cold box (204) to obtain liquid carbon dioxide; Step 3: The liquid carbon dioxide is purified and cooled by a purification tower (206) and then transported to a storage tank, while the non-condensable gas is discharged after heat exchange by a propane refrigeration unit (205).

5. The method for capturing CO2 from exhaust gas from a natural gas purification plant according to claim 4, characterized in that: The step 1 specifically comprises: sending the exhaust gas from the natural gas purification plant into the carbon dioxide capture module (1) and pressurizing it to 0.5MPa-0.7MPa through the exhaust gas compressor (101) to obtain pressurized exhaust gas, and passing the pressurized exhaust gas into the bottom inlet of the absorption tower (102). The pressurized exhaust gas moves from bottom to top in the absorption tower (102). The bottom outlet of the absorption tower (102) passes through the lean liquid cooler (109), the purified gas separator (108), and the activator pump (112) in sequence. N-methyldiethanolamine-piperazine solvent is sent into the lean liquid through the activator pump (112) to generate a lean liquid absorbent. The lean liquid absorbent enters through the inlet on one side of the top of the absorption tower (102) and is sprayed from top to bottom. The lean liquid absorbent contacts with the pressurized exhaust gas in countercurrent to perform a decarbonization reaction, so that the rich liquid that absorbs the carbon dioxide gas is discharged from the absorption tower. The rich liquid that absorbs carbon dioxide gas is discharged from the outlet (204) at the bottom of the desorption tower (102), and the rich liquid that absorbs carbon dioxide gas passes through the buffer tank (103), the filter (104) and the rich liquid pump (105) in sequence and then enters the lean-rich liquid heat exchanger (106). The rich liquid that absorbs carbon dioxide gas is heated by the hot lean liquid and then enters the upper part of the desorption tower (110) operated at low pressure, so that most of the acidic components are flashed from the rich liquid that absorbs carbon dioxide gas on the top plate of the desorption tower (110) to obtain carbon dioxide capture gas. The lean liquid generated after desorption is discharged from the bottom outlet of the desorption tower (110) to the reboiler (111). The lean liquid generated after desorption is heated in the reboiler (111) and then transported through a pipeline through the desorption tower (110), the lean-rich liquid heat exchanger (106) and the lean liquid pump (107) in sequence to enter the absorption tower (102) to restart the absorption process.

6. The method for capturing CO2 from exhaust gas from a natural gas purification plant according to claim 5, characterized in that: The mass fraction of N-methyldiethanolamine solution in the N-methyldiethanolamine-piperazine solvent transported by the activator pump (112) is 18%-22%, the heat load of the reboiler is 14500kW-15500kW, and the pressure of the reboiler is 0.15MPa-0.25MPa.

7. The method for capturing CO2 from exhaust gas from a natural gas purification plant according to claim 4, characterized in that: The step 2 specifically comprises: the carbon dioxide captured gas coming out of the top of the desorption tower (110) passes through a carbon dioxide cooler (201), and then passes through a wet gas compressor (202) for secondary pressurization to 2.4 MPa-2.6 MPa, and then passes through a molecular sieve dehydration skid (203) and is liquefied through a carbon dioxide cold box (204) to obtain liquid carbon dioxide.

8. The method for capturing CO2 from exhaust gas from a natural gas purification plant according to claim 4, characterized in that: The step 3 specifically comprises: sending the liquid carbon dioxide into a purification tower (206), wherein the purification tower (206) heats the liquid carbon dioxide, and the non-condensable gas generated after heating is discharged after heat exchange through a propane refrigeration unit (205), and the remaining liquid carbon dioxide is supercooled by the propane refrigeration unit (205) and then sent to a storage tank.

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