A continuous method for removing carbon dioxide from methane or natural gas

Abstract

The application discloses a continuous impurity removal method for carbon dioxide in methane or natural gas. The method adopts an impurity removal device, and the impurity removal device comprises two impurity removal units. Heat exchange pipe assemblies are arranged in the housings of the two impurity removal units. Each of the two impurity removal units can perform condensation and sublimation operations for removing carbon dioxide. The two impurity removal units alternately perform the condensation and sublimation operations for removing carbon dioxide, so that the carbon dioxide in the methane or natural gas is continuously removed. The application has the advantages that the superheating exchange condenses the carbon dioxide in the methane or natural gas into crystal form and separates the carbon dioxide from the methane or natural gas, which effectively reduces the energy consumption for removing the carbon dioxide and reduces the equipment cost. The two impurity removal units alternately perform the condensation and sublimation operations for removing the carbon dioxide, so that the carbon dioxide in the methane or natural gas is continuously removed.

Description

Technical Field

[0001] This invention relates to the field of clean energy technology, specifically to a process for producing methane or natural gas liquefaction. Background Technology

[0002] Liquefied methane or liquefied natural gas, as clean energy sources, have advantages such as high calorific value, high storage and transportation density, strong safety, and stable raw material supply, and are widely used in various scenarios such as ship power, industrial fuel, and city gas.

[0003] In methane or natural gas liquefaction processes, methane or natural gas contains small amounts of impurities such as carbon dioxide, which have high sublimation temperatures. These impurities can cause "ice blockage" damage to equipment and pipelines during further cooling. Current technologies typically use the MDEA method to remove CO2 impurities; however, the MDEA method is energy-intensive, has high equipment investment and maintenance costs, and is unsuitable for small-scale liquefaction processes. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for continuous removal of carbon dioxide from methane or natural gas, which can achieve continuous removal of carbon dioxide from methane or natural gas and is suitable for small-scale production of liquefied methane or liquefied natural gas.

[0005] To solve the above problems, the technical solution adopted by the present invention is: a continuous method for removing carbon dioxide from methane or natural gas, using a removal device, the removal device comprising: two removal units, each removal unit comprising a shell, the upper and lower ends of the shell being respectively provided with a process gas inlet and a process gas outlet, a heat exchange tube assembly being provided inside the shell between the process gas inlet and the process gas outlet, the heat exchange tube assembly including a heat exchange medium inlet and a heat exchange medium outlet; Each impurity removal unit can perform sublimation to remove carbon dioxide and sublimation to remove carbon dioxide. The steps of the carbon dioxide removal operation by sublimation include: introducing a refrigerant into the heat exchange tube assembly of the impurity removal unit, and inputting the methane or natural gas to be removed from the process gas inlet of the impurity removal unit. During the process of the methane or natural gas to be removed moving towards the process gas outlet, it exchanges heat with the heat exchange tube assembly. The impurity carbon dioxide in the methane or natural gas to be removed is directly sublimated into crystals, thereby separating it from the methane or natural gas. The carbon dioxide that has been sublimated into crystals remains in the shell of the impurity removal unit, and the removed methane or natural gas is output from the process gas outlet of the impurity removal unit. When too much carbon dioxide crystals remain in the shell of a purification unit, another purification unit will perform a sublimation carbon dioxide removal operation. The purification unit with carbon dioxide crystals remaining will then perform a sublimation carbon dioxide removal operation. The steps of the sublimation carbon dioxide removal operation include: introducing a heat medium into the heat exchange tube assembly of the purification unit, directly sublimating and removing the impurity carbon dioxide crystals remaining in the shell until they are completely removed. The purification unit that has removed all carbon dioxide is ready for the next sublimation carbon dioxide removal operation. Two impurity removal units alternately perform condensation to remove carbon dioxide and sublimation to remove carbon dioxide, thereby continuously removing carbon dioxide from methane or natural gas.

[0006] Furthermore, in the aforementioned method for continuous removal of carbon dioxide from methane or natural gas, the heat exchange tube assembly comprises several U-shaped heat exchange tube structures, all of which are arranged at intervals above and below.

[0007] Furthermore, in the aforementioned method for continuous removal of carbon dioxide from methane or natural gas, each U-shaped heat exchanger tube assembly includes: a heat exchanger tube cylinder fixedly and sealed to one side of the shell; a tube sheet detachably and fixedly installed at the outer end of the heat exchanger tube cylinder; a tube box fixedly and sealed outside the tube sheet; a partition plate inside the tube box dividing the tube box into an inlet chamber and an outlet chamber; a tube box inlet on the tube box in the inlet chamber; and a tube box outlet on the tube box in the outlet chamber. The body of the U-shaped heat exchanger tube is located inside the shell, and both the inlet and outlet ends of the U-shaped heat exchanger tube pass through the heat exchanger tube cylinder. The U-shaped heat exchange tubes, which pass through the tube sheet, have inlets that connect to the inlet chamber and outlets that connect to the outlet chamber. All U-shaped heat exchange tube structures are connected in series from bottom to top. Specifically, in each pair of adjacent U-shaped heat exchange tube structures, the outlet of the tube box of the lower U-shaped heat exchange tube structure connects to the inlet of the tube box of the upper U-shaped heat exchange tube structure. The inlet of the tube box of the lowermost U-shaped heat exchange tube structure is the heat exchange medium inlet of the purification unit, and the outlet of the tube box of the uppermost U-shaped heat exchange tube structure is the heat exchange medium outlet of the purification unit.

[0008] Furthermore, in the aforementioned method for continuous removal of carbon dioxide from methane or natural gas, the heat exchange tube cylinders of each of two adjacent U-shaped heat exchange tube mechanisms are located on both sides of the shell.

[0009] Furthermore, in the aforementioned method for continuous removal of carbon dioxide from methane or natural gas, the bottom of the shell is inclined, and a backup outlet is provided on the lowest position of the shell. During the sublimation and discharge of carbon dioxide, a vacuum mechanism is connected to the backup outlet, and the carbon dioxide gas formed by sublimation is continuously discharged from the backup outlet under the action of the vacuum mechanism.

[0010] Furthermore, in the aforementioned method for continuous removal of carbon dioxide from methane or natural gas, each removal unit has a cold-insulating heat exchange tube installed on its outer wall. The two ends of the cold-insulating heat exchange tube are connected to a cold-insulating medium inlet pipe with a control valve and a cold-insulating medium outlet pipe with a control valve. A thermal insulation layer is installed outside the cold-insulating heat exchange tube. When a removal unit is started, refrigerant is introduced into the heat exchange tube assembly of the removal unit, and simultaneously, the refrigerant is introduced into the cold-insulating heat exchange tube through the cold-insulating medium inlet pipe. The cold-insulating heat exchange tube and the heat exchange tube assembly work together to rapidly cool the interior of the shell.

[0011] Furthermore, in the aforementioned method for continuous removal of carbon dioxide from methane or natural gas, the process gas inlets on the shells of both removal units are connected to the process gas input main; the heat exchange medium inlets of both removal units are connected to the heat exchange medium input main; and the heat exchange medium outlets of both removal units are connected to the heat exchange medium output main; the heat exchange medium input main is connected to a cold source heat exchange medium input pipe for conveying a refrigerant for sublimating carbon dioxide gas and a heat source heat exchange medium input pipe for sublimating crystalline carbon dioxide.

[0012] Furthermore, in the aforementioned method for continuous removal of carbon dioxide from methane or natural gas, the process gas inlets on the shells of two removal units are connected to the process gas input main pipe via process gas input three-way valves; each removal unit's heat exchange medium inlet is equipped with a removal unit heat exchange medium input pipe, both removal unit heat exchange medium input pipes are connected to the heat exchange medium input main pipe, and each cold insulation medium input pipe is connected to the corresponding removal unit heat exchange medium input pipe; each removal unit's heat exchange medium outlet is equipped with a removal unit heat exchange medium outlet pipe, both removal unit heat exchange medium outlet pipes are connected to the heat exchange medium outlet main pipe, and each cold insulation medium outlet pipe is connected to the corresponding removal unit heat exchange medium outlet pipe.

[0013] Furthermore, in the aforementioned method for continuous removal of carbon dioxide from methane or natural gas, each removal unit is equipped with a pressure monitoring device at both the process gas outlet and the process gas inlet, and a gas composition monitoring device is also installed at the process gas outlet. When the pressure difference between the process gas outlet and the process gas inlet of the removal unit is greater than a pressure difference set value and / or the carbon dioxide content in the gas discharged from the process gas outlet is greater than or equal to a carbon dioxide content set value, it is determined that too much carbon dioxide crystals are retained in the shell of the removal unit, and at this time, the process is switched to another removal unit for sublimation removal of carbon dioxide.

[0014] The advantages of this invention are: This application provides a continuous method for removing carbon dioxide from methane or natural gas. The process steps are simple. Carbon dioxide in methane or natural gas is directly condensed into crystals and separated from methane or natural gas through heat exchange. This effectively reduces the energy consumption for carbon dioxide removal and reduces equipment costs.

[0015] This application achieves continuous removal of carbon dioxide from methane or natural gas by setting up two impurity removal units, which alternately perform sublimation to remove carbon dioxide and sublimation to remove carbon dioxide.

[0016] The continuous carbon dioxide removal method for methane or natural gas described in this application is applicable to small-scale liquefied methane or liquefied natural gas production processes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the impurity removal unit in the impurity removal device used in the continuous impurity removal method for carbon dioxide in methane or natural gas according to the present invention.

[0018] Figure 2 This is a schematic diagram of the principle structure of the impurity removal device used in the continuous impurity removal method for methane or natural gas described in this invention. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and preferred embodiments.

[0020] Example 1: As Figure 1 , Figure 2 As shown, a continuous method for removing carbon dioxide from methane or natural gas employs a purification device, which includes two purification units: a first purification unit 10 and a second purification unit 20. Each purification unit includes a housing 1, with a process gas inlet 11 and a process gas outlet 12 respectively located at its upper and lower ends. A heat exchange tube assembly 40 is disposed within the housing 1 between the process gas inlet 11 and the process gas outlet 12. The heat exchange tube assembly 40 includes a heat exchange medium inlet and a heat exchange medium outlet.

[0021] Each impurity removal unit can perform sublimation to remove carbon dioxide and sublimation to remove carbon dioxide.

[0022] The steps of the carbon dioxide removal operation by sublimation include: introducing a refrigerant into the heat exchange tube assembly 40 of the impurity removal unit, and inputting the methane or natural gas to be removed from the process gas inlet 11 of the impurity removal unit. During its movement within the shell towards the process gas outlet 12, the methane or natural gas exchanges heat with the heat exchange tube assembly 40, causing the impurity carbon dioxide in the methane or natural gas to be directly sublimated into crystals, thus separating it from the methane or natural gas. The sublimated carbon dioxide crystals remain within the shell of the impurity removal unit, and the removed methane or natural gas is output from the process gas outlet 11 of the impurity removal unit. The refrigerant can be liquid nitrogen or methane.

[0023] When too much carbon dioxide crystal remains in the shell 1 of the impurity removal unit, another impurity removal unit performs a sublimation carbon dioxide removal operation. The impurity removal unit with remaining carbon dioxide crystals then performs a sublimation carbon dioxide removal operation. The sublimation carbon dioxide removal operation includes: introducing a heat medium into the heat exchange tube assembly 40 of the impurity removal unit to directly sublimate and remove the impurity carbon dioxide crystals remaining in the shell 1 until they are completely removed. The impurity removal unit that has removed all carbon dioxide is ready for the next sublimation carbon dioxide removal operation. The heat medium can be a reheated refrigerant.

[0024] The first impurity removal unit 10 and the second impurity removal unit 20 alternately perform sublimation to remove carbon dioxide and sublimation to remove carbon dioxide, thereby continuously removing carbon dioxide from methane or natural gas.

[0025] Example 2: Compared to Example 1, this example includes pressure monitoring mechanisms at both the process gas outlet 12 and the process gas inlet 11. These mechanisms can be pressure sensors. A gas composition monitoring mechanism, such as an online chromatograph or an online infrared analyzer, is also provided at the process gas outlet 12. When the pressure difference between the process gas outlet 12 and the process gas inlet 11 of the impurity removal unit exceeds a set pressure difference value and / or the carbon dioxide content in the gas discharged from the process gas outlet exceeds a set carbon dioxide content value, it is determined that excessive carbon dioxide crystals are retained within the housing 1 of the impurity removal unit. In this case, another impurity removal unit will perform sublimation to remove the carbon dioxide.

[0026] The carbon dioxide removal status within the purification unit is monitored by changes in pressure differential and / or the carbon dioxide content in the gas discharged from the process gas outlet. Excessive carbon dioxide crystals within the purification unit will affect the removal efficiency; therefore, another purification unit needs to alternately perform sublimation carbon dioxide removal operations. By monitoring the pressure differential and / or the carbon dioxide content in the gas discharged from the process gas outlet, it is possible to promptly determine whether the two purification units should alternately perform sublimation carbon dioxide removal operations, thereby ensuring that carbon dioxide in methane or natural gas is always effectively removed.

[0027] Example 3: As Figure 1 As shown, in this embodiment, compared to Embodiment 1 or Embodiment 2, a cold-insulating heat exchange tube 3 is provided on the outer wall of the shell 1 of each impurity removal unit, and a heat insulation layer is provided outside the cold-insulating heat exchange tube 3. To illustrate the cold-insulating heat exchange tube 3, Figure 1 The thermal insulation layer is omitted. The two ends of the cold-insulating heat exchange tube 3 are a cold-insulating medium inlet 31 and a cold-insulating medium outlet 32, respectively. The cold-insulating medium inlet 31 and outlet 32 ​​are connected to a cold-insulating medium inlet pipe 311 with a control valve and a cold-insulating medium outlet pipe 321 with a control valve, respectively. The refrigerant in the cold-insulating heat exchange tube 3 can be the same as that in the heat exchange tube assembly 40.

[0028] When a purification unit is started, refrigerant is introduced into the heat exchange tube assembly of the purification unit. At the same time, the refrigerant is introduced into the heat exchange tube 3 through the heat insulation medium inlet pipe 311. The heat exchange tube 3 and the heat exchange tube assembly 40 work together to rapidly cool the shell 1 to the temperature required for the sublimation of impurity carbon dioxide, which greatly improves the working efficiency of the equipment.

[0029] Example 4: Compared to Example 3, the heat exchange tube assembly 40 in this example includes several U-shaped heat exchange tube mechanisms, all of which are arranged at intervals. Each U-shaped heat exchange tube mechanism includes: a heat exchange tube cylinder 4 fixedly and sealed to one side of the shell 1; a tube sheet 41 is detachably and fixedly sealed at the outer end of the heat exchange tube cylinder 4; a tube box 42 is fixedly and sealed outside the tube sheet 41; a partition 43 is provided inside the tube box 42; the partition 43 divides the tube box 42 into an inlet chamber 421 and an outlet chamber 422; a tube box inlet 4211 is provided on the tube box 42 in the inlet chamber 421; and a tube box outlet 4221 is provided on the tube box 42 in the outlet chamber 422. The body of the U-shaped heat exchange tube 44 is located inside the shell 1. The inlet and outlet ends of the U-shaped heat exchange tube 44 are both inserted through the tube holes of the tube sheet 41 via the heat exchange tube cylinder 4. The inlets of the U-shaped heat exchange tubes are all connected to the inlet chamber 421, and the outlets of the U-shaped heat exchange tubes are all connected to the outlet chamber 422. All U-shaped heat exchange tube structures are connected in series from bottom to top. That is, in every two adjacent U-shaped heat exchange tube structures, the tube box outlet 4221 of the tube box 42 of the lower U-shaped heat exchange tube structure is connected to the tube box inlet 4211 of the tube box 42 of the upper U-shaped heat exchange tube structure through a pipeline. The tube box inlet of the tube box 42 of the lowermost U-shaped heat exchange tube structure is the heat exchange medium inlet of the impurity removal unit, and the tube box outlet of the tube box of the uppermost U-shaped heat exchange tube structure is the heat exchange medium outlet of the impurity removal unit. For ease of installation, the heat exchange tube cylinders 4 of each of the two adjacent U-shaped heat exchange tube mechanisms are located on both sides of the shell 1.

[0030] In this embodiment, the process gas inlets 11 on the shells 1 of the two impurity removal units are connected to the process gas input main pipe 5 via process gas input three-way valves 51. Each impurity removal unit has a heat exchange medium inlet 611, and both heat exchange medium inlets 611 are connected to the heat exchange medium input main pipe 6. Each cold insulation medium inlet 311 is connected to the corresponding impurity removal unit heat exchange medium inlet 611. Each impurity removal unit has a heat exchange medium outlet 711, and both heat exchange medium outlets 711 are connected to the heat exchange medium outlet main pipe 7. Each cold insulation medium outlet 321 is connected to the corresponding impurity removal unit heat exchange medium outlet 711. The heat exchange medium input main pipe 6 is connected to the cold source heat exchange medium inlet 61 for conveying the refrigerant used to condense carbon dioxide gas and the heat source heat exchange medium inlet 62 for sublimating crystalline carbon dioxide.

[0031] When a purification unit needs to perform sublimation and carbon dioxide removal, the refrigerant used to provide cooling capacity enters the purification unit's heat exchange medium inlet pipe 611 from the cold source heat exchange medium inlet pipe 61 via the heat exchange medium inlet main pipe 6. During equipment startup, to accelerate cooling, the refrigerant in the purification unit's heat exchange medium inlet pipe 611 is divided into two parts. One part enters from the purification unit's heat exchange medium inlet into the inlet chamber 421 of a U-shaped heat exchange tube mechanism located at the bottom of the shell 1. The refrigerant in the inlet chamber 421 enters the U-shaped heat exchange tubes. The refrigerant that has completed heat exchange in the U-shaped heat exchange tubes enters the outlet chamber 422, and then enters the next U-shaped heat exchange tube mechanism via pipelines. From bottom to top, it passes through the U-shaped heat exchange tube bundles in each U-shaped heat exchange tube mechanism, and then exits from the heat exchange medium outlet of the U-shaped heat exchange tube mechanism located at the top of the shell via the purification unit's heat exchange medium outlet pipe 711. Another portion of the refrigerant, after being superheated, enters the cold-insulating heat exchange tube 3 through the cold-insulating medium inlet pipe 311. After exchange, the refrigerant in the cold-insulating heat exchange tube 3 is sequentially discharged through the cold-insulating medium outlet pipe 321 and the impurity removal unit heat exchange medium outlet pipe 711. The U-shaped heat exchange tube mechanism and the cold-insulating heat exchange tube 3 work together to rapidly cool the interior of the shell. Afterward, the valve on the cold-insulating medium inlet pipe 311 closes, and all the refrigerant enters the U-shaped heat exchange tube mechanism.

[0032] In this embodiment, the bottom of the housing 1 is inclined, and a spare outlet 13 is provided on the lowest position of the housing 1. The spare outlet 13 can be used for draining liquid, sewage, or impurity gas carbon dioxide. During the sublimation and discharge of carbon dioxide, a vacuum mechanism is connected to the spare outlet 13, and the carbon dioxide gas formed by sublimation is continuously discharged from the spare outlet 13 under the action of the vacuum mechanism.

[0033] This embodiment illustrates the specific structure of the heat exchanger tube assembly 40. It includes several U-shaped heat exchanger tube mechanisms, which have a simple structure. The U-shaped heat exchanger tube bundles in each U-shaped heat exchanger tube mechanism are installed independently, and the U-shaped heat exchanger tube inlet and outlet are located at the same end. In this way, if the U-shaped heat exchanger tube bundle fails, it can be repaired simply by pulling the U-shaped heat exchanger tube bundle in the corresponding U-shaped heat exchanger tube mechanism out of the heat exchanger tube cylinder 4, which greatly improves the convenience of equipment maintenance.

[0034] The following is a detailed explanation using the first impurity removal unit 10 as an example of performing sublimation to remove carbon dioxide.

[0035] The methane or natural gas requiring purification enters the shell 1 through the continuous process gas input main 5 and the process gas inlet 11 of the first impurity removal unit 10. As the methane or natural gas moves from top to bottom within the shell 1, it sequentially exchanges heat with the U-shaped heat exchange tube bundles in each U-shaped heat exchange tube mechanism. The impurity carbon dioxide in the methane or natural gas is sublimated into solid crystals and remains on the outer wall of the U-shaped heat exchange tube 44. This sublimation process separates carbon dioxide from the methane or natural gas. The purified methane or natural gas is continuously discharged from the process gas outlet 12 of the first impurity removal unit 10.

[0036] After the first impurity removal unit 10 has been performing sublimation carbon dioxide removal for a period of time, if the pressure difference between the process gas outlet 12 and the process gas inlet 11 exceeds the pressure difference set value and / or the carbon dioxide content in the gas discharged from the process gas outlet exceeds the carbon dioxide content set value, it indicates that there are too many carbon dioxide crystals on the outer wall of the U-shaped heat pipe bundle inside the shell of the first impurity removal unit 10, and the impurity removal effect of the first impurity removal unit 10 is reduced. At this time, the process is switched to the second impurity removal unit 20 to perform sublimation carbon dioxide removal. The sublimation carbon dioxide removal operation of the second impurity removal unit 20 is the same as the sublimation carbon dioxide removal operation process of the first impurity removal unit 10 described above.

[0037] The first impurity removal unit 10 performs sublimation to remove carbon dioxide. The heat medium providing heat enters the impurity removal unit's heat medium inlet pipe 611 from the heat source heat exchange medium inlet pipe 62 via the heat exchange medium inlet main pipe 6. The heat medium in the impurity removal unit's heat exchange medium inlet pipe 611 enters the inlet chamber 421 of a U-shaped heat exchange tube mechanism located at the bottom of the shell 1 from the heat exchange medium inlet of the first impurity removal unit. The heat medium in the inlet chamber 421 enters the U-shaped heat exchange tube, and the heat medium that completes heat exchange in the U-shaped heat exchange tube enters the outlet chamber 422. Then, it enters the next U-shaped heat exchange tube mechanism through a pipeline, passing sequentially from bottom to top through the U-shaped heat exchange tube bundles in each U-shaped heat exchange tube mechanism, and finally exits from the heat exchange medium outlet of the first impurity removal unit in the U-shaped heat exchange tube mechanism located at the top of the shell through the impurity removal unit's heat exchange medium outlet pipe 711. During this process, the heat medium heats the crystalline carbon dioxide on the outer wall of the U-shaped heat exchange tube, causing it to sublimate directly into gas. The spare outlet 13 of the housing 1 is connected to a vacuum mechanism. Under the action of the vacuum mechanism, the carbon dioxide gas formed by sublimation is continuously discharged from the spare outlet 13 until it is completely discharged. The first impurity removal unit 10, after the carbon dioxide is discharged, is ready for the next sublimation carbon dioxide removal operation.

[0038] The first impurity removal unit 10 and the second impurity removal unit 20 alternately perform sublimation to remove carbon dioxide and sublimation to remove carbon dioxide, thereby achieving continuous removal of carbon dioxide from methane or natural gas.

[0039] This application provides a continuous method for removing carbon dioxide from methane or natural gas. The method is simple, using heat exchange to directly condense carbon dioxide from methane or natural gas into crystals, thus separating it from the methane or natural gas. This effectively reduces energy consumption and equipment costs for carbon dioxide removal. This application utilizes two removal units that alternately perform sublimation and carbon dioxide removal operations, thereby achieving continuous removal of carbon dioxide from methane or natural gas. The continuous carbon dioxide removal method for methane or natural gas described in this application is suitable for small-scale production of liquefied methane or liquefied natural gas.

Claims

1. A continuous method for removing carbon dioxide from methane or natural gas, characterized in that: The impurity removal device includes two impurity removal units, each of which includes a shell. The upper and lower ends of the shell are respectively provided with a process gas inlet and a process gas outlet. A heat exchange tube assembly is provided inside the shell between the process gas inlet and the process gas outlet. The heat exchange tube assembly includes a heat exchange medium inlet and a heat exchange medium outlet. Each impurity removal unit can perform sublimation to remove carbon dioxide and sublimation to remove carbon dioxide. The steps of the carbon dioxide removal operation by sublimation include: introducing a refrigerant into the heat exchange tube assembly of the impurity removal unit, and inputting the methane or natural gas to be removed from the process gas inlet of the impurity removal unit. During the process of the methane or natural gas to be removed moving towards the process gas outlet, it exchanges heat with the heat exchange tube assembly. The impurity carbon dioxide in the methane or natural gas to be removed is directly sublimated into crystals, thereby separating it from the methane or natural gas. The carbon dioxide that has been sublimated into crystals remains in the shell of the impurity removal unit, and the removed methane or natural gas is output from the process gas outlet of the impurity removal unit. When too much carbon dioxide crystals remain in the shell of a purification unit, another purification unit will perform a sublimation carbon dioxide removal operation. The purification unit with carbon dioxide crystals remaining will then perform a sublimation carbon dioxide removal operation. The steps of the sublimation carbon dioxide removal operation include: introducing a heat medium into the heat exchange tube assembly of the purification unit, directly sublimating and removing the impurity carbon dioxide crystals remaining in the shell until they are completely removed. The purification unit that has removed all carbon dioxide is ready for the next sublimation carbon dioxide removal operation. Two impurity removal units alternately perform condensation to remove carbon dioxide and sublimation to remove carbon dioxide, thereby continuously removing carbon dioxide from methane or natural gas.

2. The method for continuous removal of carbon dioxide from methane or natural gas according to claim 1, characterized in that: The heat exchanger tube assembly comprises several U-shaped heat exchanger tube structures, all of which are spaced apart at the top and bottom.

3. The method for continuous removal of carbon dioxide from methane or natural gas according to claim 2, characterized in that: Each U-shaped heat exchanger tube assembly includes: a heat exchanger tube body fixedly and sealed to one side of the shell; a tube sheet detachably and fixedly installed at the outer end of the heat exchanger tube body; a tube box fixedly and sealed outside the tube sheet; a partition plate inside the tube box dividing the tube box into an inlet chamber and an outlet chamber; a tube box inlet on the tube box in the inlet chamber; and a tube box outlet on the tube box in the outlet chamber. The body of the U-shaped heat exchanger tube is located inside the shell, and both the inlet and outlet ends of the U-shaped heat exchanger tube pass through the tube body through the tube holes in the tube sheet. All are connected to the inlet chamber, and all U-shaped heat exchange tube outlets are connected to the outlet chamber; all U-shaped heat exchange tube structures are connected in series from bottom to top, that is: in every two adjacent U-shaped heat exchange tube structures, the tube box outlet of the lower U-shaped heat exchange tube structure is connected to the tube box inlet of the upper U-shaped heat exchange tube structure, the tube box inlet of the lowermost U-shaped heat exchange tube structure is the heat exchange medium inlet of the impurity removal unit, and the tube box outlet of the uppermost U-shaped heat exchange tube structure is the heat exchange medium outlet of the impurity removal unit.

4. The method for continuous removal of carbon dioxide from methane or natural gas according to claim 3, characterized in that: The heat exchange tube cylinders of each pair of adjacent U-shaped heat exchange tube mechanisms are located on both sides of the shell.

5. The method for continuous removal of carbon dioxide from methane or natural gas according to claim 3, characterized in that: The bottom of the shell is inclined, and a spare outlet is provided on the lowest part of the shell. During the sublimation and discharge of carbon dioxide, a vacuum mechanism is connected to the spare outlet. Under the action of the vacuum mechanism, the carbon dioxide gas formed by sublimation is continuously discharged from the spare outlet.

6. A method for continuous removal of carbon dioxide from methane or natural gas according to any one of claims 1 to 5, characterized in that: Each impurity removal unit has a cold insulation heat exchange tube installed on its outer shell. The two ends of the cold insulation heat exchange tube are connected to a cold insulation medium inlet pipe with a control valve and a cold insulation medium outlet pipe with a control valve. The cold insulation heat exchange tube is covered with a heat insulation layer. When an impurity removal unit is started, refrigerant is introduced into the heat exchange tube assembly of the impurity removal unit. At the same time, the refrigerant is introduced into the cold insulation heat exchange tube through the cold insulation medium inlet pipe. The cold insulation heat exchange tube and the heat exchange tube assembly work together to rapidly cool the inside of the shell.

7. A method for continuous removal of carbon dioxide from methane or natural gas according to any one of claims 1 to 5, characterized in that: The process gas inlets on the shells of both impurity removal units are connected to the process gas input main pipe; the heat exchange medium inlets of both impurity removal units are connected to the heat exchange medium input main pipe; and the heat exchange medium outlets of both impurity removal units are connected to the heat exchange medium output main pipe. The heat exchange medium input main pipe is connected to the cold source heat exchange medium input pipe for conveying the refrigerant used to condense carbon dioxide gas and the heat source heat exchange medium input pipe for the heat medium used to sublimate crystalline carbon dioxide.

8. The method for continuous removal of carbon dioxide from methane or natural gas according to claim 6, characterized in that: The process gas inlets on the shells of the two impurity removal units are connected to the process gas input main pipe via process gas input three-way valves; each impurity removal unit's heat exchange medium inlet is equipped with an impurity removal unit heat exchange medium input pipe, and both impurity removal unit heat exchange medium input pipes are connected to the heat exchange medium input main pipe, and each cold insulation medium input pipe is connected to the corresponding impurity removal unit heat exchange medium input pipe; each impurity removal unit's heat exchange medium outlet is equipped with an impurity removal unit heat exchange medium outlet pipe, and both impurity removal unit heat exchange medium outlet pipes are connected to the heat exchange medium outlet main pipe, and each cold insulation medium outlet pipe is connected to the corresponding impurity removal unit heat exchange medium outlet pipe.

9. A method for continuous removal of carbon dioxide from methane or natural gas according to any one of claims 1 to 5, characterized in that: Each impurity removal unit is equipped with a pressure monitoring device at both the process gas outlet and the process gas inlet, and a gas composition monitoring device is also installed at the process gas outlet. When the pressure difference between the process gas outlet and the process gas inlet of the impurity removal unit is greater than the pressure difference set value and / or the carbon dioxide content in the gas discharged from the process gas outlet is greater than or equal to the carbon dioxide content set value, it is determined that too much carbon dioxide crystals are retained in the shell of the impurity removal unit. At this time, the unit is switched to another impurity removal unit for sublimation carbon dioxide removal operation.

10. A method for continuous removal of carbon dioxide from methane or natural gas according to claim 6, characterized in that: Each impurity removal unit is equipped with a pressure monitoring device at both the process gas outlet and the process gas inlet, and a gas composition monitoring device is also installed at the process gas outlet. When the pressure difference between the process gas outlet and the process gas inlet of the impurity removal unit is greater than the pressure difference set value and / or the carbon dioxide content in the gas discharged from the process gas outlet is greater than or equal to the carbon dioxide content set value, it is determined that too much carbon dioxide crystals are retained in the shell of the impurity removal unit. At this time, the unit is switched to another impurity removal unit for sublimation carbon dioxide removal operation.

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