Liquefied natural gas light hydrocarbon separation device and method

Abstract

The invention relates to the technical field of light hydrocarbon separation of liquefied natural gas, and discloses a light hydrocarbon separation device and method of liquefied natural gas, the light hydrocarbon separation device of liquefied natural gas comprises a preprocessor, a step-by-step cooling device, a rectifying tower and a liquid inlet header pipe, the preprocessor guides the treated liquefied natural gas into the step-by-step cooling device, the step-by-step cooling device guides the cooled liquefied natural gas into the rectifying tower for separation, and four groups of filters are adopted for split-flow filtering, so that the filtering effect is improved, the flow velocity of the liquefied natural gas can be slowed down through split-flow filtering, and the quality of the liquefied natural gas is improved. The preheating assembly can better preheat the liquefied natural gas, the preheating assembly and the filter are integrated in the same preprocessor, the occupied space of the whole equipment can be reduced, and the cooling capacity loss of the liquefied natural gas caused by long-distance conveying is reduced.

Description

Technical Field

[0001] This invention relates to the field of light hydrocarbon separation technology for liquefied natural gas, specifically to a light hydrocarbon separation device and method for liquefied natural gas. Background Technology

[0002] With the rapid development of the energy industry, people are paying more and more attention to the use of clean energy, and energy conservation, environmental protection, and high efficiency have become major themes in the energy sector today. According to statistics from the International Gas Union (IGU), global LNG trade volume reached 406 million tons in 2023 and is expected to exceed 600 million tons by 2030. In the LNG industry chain, light hydrocarbon separation is a key link in achieving refined resource utilization and increasing added value. Light hydrocarbons such as ethane, propane, and butane are not only important chemical raw materials but can also be used as fuels in multiple fields. Common light hydrocarbon separation methods for liquefied natural gas include cryogenic distillation, expansion refrigeration separation, adsorption separation, and membrane separation. Regardless of the separation method, liquefied natural gas requires pretreatment. Common pretreatment methods include filtration and preheating, which often involve different equipment, are time-consuming, and require a large space. Summary of the Invention

[0003] The purpose of this invention is to provide a light hydrocarbon separation device and method for liquefied natural gas to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a light hydrocarbon separation device for liquefied natural gas, comprising a pre-processor, a step-by-step cooling device, a distillation column, and a liquid inlet manifold, wherein the liquid inlet manifold introduces liquefied natural gas into the pre-processor, the pre-processor introduces the processed liquefied natural gas into the step-by-step cooling device, and the step-by-step cooling device introduces the cooled liquefied natural gas into the distillation column for separation; The pre-processor is equipped with four sets of filters. A preheating component is installed on the outside of each filter, and a backwashing component is installed inside each filter. The input pipe of each filter is connected to the main inlet pipe through an inlet branch pipe. The output pipe of each filter is connected to an outlet manifold through a three-way valve. The bottom end of the outlet manifold is connected to the main outlet pipe, and the main outlet pipe is connected to the input end of the step-by-step cooling device.

[0005] Furthermore, the filter is equipped with a composite filter screen, and a drain pipe is provided at the bottom of the filter. The pre-processor is equipped with a collection chamber, and the bottom of the drain pipe is connected to the collection chamber. The composite filter screen is made of stainless steel wire mesh and nanofiber filter membrane, and the composite filter screen separates the output pipe from the drain pipe.

[0006] Furthermore, the backwashing assembly includes a diversion chamber and an air inlet component. The diversion chamber is fixedly installed inside the filter, and an air blowing head is fixedly installed at the top of the diversion chamber. The air blowing head extends into the inner side of the composite filter screen. The air blowing head is a frustum-shaped structure that is thinner at the top and thicker at the bottom. Air blowing holes are opened on the outer surface of the air blowing head. The interior of the air blowing head is connected to the interior of the diversion chamber. A rotating hollow rod is connected to the top of the diversion chamber through a rotary joint. An arc-shaped air nozzle is fixedly installed on the outer wall of the rotating hollow rod. Multiple arc-shaped air nozzles are provided and are spirally arranged on the rotating hollow rod. The rotating hollow rod is located outside the composite filter screen. The air outlet of the air inlet component is connected to the air inlet of the diversion chamber, and the air inlet of the air inlet component is connected to the liquid nitrogen delivery pipeline.

[0007] Furthermore, the air intake component includes an air intake manifold, one end of which is connected to a liquid nitrogen delivery pipeline, and the other end of which is connected to a gas channel. A gas distribution pipe is connected to the gas channel, and four gas distribution pipes are arranged in a circumferential array on the gas channel. The gas distribution pipes are connected to the air intake end of the distribution chamber, and a pulse gas valve is provided at the connection between the gas distribution pipes and the distribution chamber.

[0008] Furthermore, the preheating assembly includes a heat exchanger body and a heat exchange hood, the heat exchange hood covering the filter, the top and bottom of the heat exchange hood being connected to heat exchange tubes, the heat exchange tubes being coiled on the input pipe and the drain pipe, the heat exchange medium circulation port of the heat exchanger body being connected to a circulation pipe, and the circulation pipe being connected to the heat exchange tubes.

[0009] Furthermore, a high-pressure gas chamber is fixedly installed inside the pre-processor. The inlet end of the high-pressure gas chamber is connected to the liquid nitrogen delivery pipeline, and the outlet end of the high-pressure gas chamber is connected to an inlet secondary pipe. The bottom end of the inlet secondary pipe is connected to the output pipe through a three-way valve.

[0010] Furthermore, the step-by-step cooling device is equipped with a first-stage refrigeration cycle, a second-stage refrigeration cycle, and a third-stage refrigeration cycle. The first-stage refrigeration cycle, the second-stage refrigeration cycle, and the third-stage refrigeration cycle all use a mixed refrigerant of nitrogen, methane, and ethylene, and the proportions of each mixed refrigerant are different in the first-stage refrigeration cycle, the second-stage refrigeration cycle, and the third-stage refrigeration cycle.

[0011] Furthermore, the feed pipe on the distillation column is connected to the output end of the third-stage refrigeration cycle, and the distillation column is provided with a top discharge pipe, a middle discharge pipe, and a bottom discharge pipe from top to bottom.

[0012] A method for separating light hydrocarbons from liquefied natural gas includes the following steps: S1, liquefied natural gas is transported into the inlet manifold, and the liquefied natural gas in the inlet manifold enters the filter and is filtered out of impurities; S2. The preheating component heats the filter, thereby heating the liquefied natural gas passing through the filter, achieving the purpose of preheating the liquefied natural gas. S3. The heated liquefied natural gas is transported to the staged cooling device. After being cooled by the first-stage refrigeration cycle, the second-stage refrigeration cycle, and the third-stage refrigeration cycle, the liquefied natural gas is then fed into the distillation tower. S4. The liquefied natural gas enters the distillation tower and is separated by distillation. The middle discharge pipe is used to collect propane, the top discharge pipe is used to collect ethane, and the bottom discharge pipe is used to collect butane and heavier components.

[0013] Furthermore, in step S1, when filtering liquefied natural gas, only one or two valves on the inlet diversion pipe need to be opened. The opened inlet diversion pipes are replaced periodically. When the inlet diversion pipe corresponding to the filter is closed, the valve on the drain pipe can be opened, and the connection port of the three-way valve can be switched to connect the inlet secondary pipe and the output pipe. The pulse gas valve is opened to allow liquid nitrogen to enter the inlet secondary pipe and then enter the filter for backwashing. The pulse gas valve introduces liquid nitrogen into the diversion chamber in a pulse manner. Part of the liquid nitrogen flows into the blowing head and then sprays out from the blowing hole to wash the inside of the composite filter screen. The other part enters the rotating hollow rod and then sprays out from the arc-shaped jet nozzle on the rotating hollow rod to wash the outside of the composite filter screen.

[0014] Compared with the prior art, the beneficial effects of the present invention are: Four sets of filters are used for diversion filtration, which improves the filtration effect. Diversion filtration can also slow down the flow rate of liquefied natural gas, so that the preheating component can better preheat the liquefied natural gas. By concentrating the preheating component and the filter in the same pre-processor, the overall space occupied by the equipment can be reduced, as well as the loss of cold energy of liquefied natural gas caused by long-distance transportation. Liquid nitrogen is introduced into the distribution chamber through the air intake component. Part of the liquid nitrogen flows into the air blowing head and is then sprayed out from the air blowing hole to rinse the inside of the composite filter screen. The other part enters the rotating hollow rod and is then sprayed out from the arc-shaped air nozzle on the rotating hollow rod to rinse the outside of the composite filter screen. The specially designed arc-shaped air nozzle can generate a torsional force under the propulsion of the liquid nitrogen, which in turn drives the rotating hollow rod to rotate. The rotation of the rotating hollow rod drives the arc-shaped air nozzle to rotate, so as to achieve the purpose of rotating spraying and uniformly rinsing the outside of the composite filter screen. Liquid nitrogen is introduced into the distribution chamber in a pulsed flow through a pulsed gas valve, allowing the liquid nitrogen to be introduced into the distribution chamber periodically. Then, the composite filter screen is periodically rinsed, and the impurities washed away are allowed to fall into the drain pipe and be discharged during the rinsing intervals. Attached Figure Description

[0015] Figure 1This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the step-by-step cooling device of the present invention; Figure 3 This is a schematic diagram of the distillation column of the present invention; Figure 4 This is a schematic diagram of the front cross-section of the pre-processor of the present invention; Figure 5 This is a schematic diagram of the internal structure of the pre-processor of the present invention; Figure 6 This is a schematic diagram of the preheating component and filter of the present invention; Figure 7 This is a structural schematic diagram of the heat exchange hood and filter of the present invention in a front sectional view; Figure 8 This is a schematic diagram of the structure of the heat exchange shroud and heat exchange tube of the present invention; Figure 9 This is a schematic diagram of the backwashing assembly and filter of the present invention; Figure 10 This is a schematic diagram of the backwashing assembly of the present invention.

[0016] In the diagram: 1. Pre-processor; 2. Staged cooling device; 201. First-stage refrigeration cycle; 202. Second-stage refrigeration cycle; 203. Third-stage refrigeration cycle; 3. Distillation column; 301. Feed pipe; 302. Middle discharge pipe; 303. Top discharge pipe; 304. Bottom discharge pipe; 4. Main inlet pipe; 5. Diverter pipe; 6. Filter; 601. Input pipe; 602. Output pipe; 603. Composite filter screen; 604. Drain pipe; 7. Backwash assembly; 701. Diversion chamber; 702. Air blowing head; 703. Air inlet; 704. Rotary joint; 705. Rotary hollow rod; 706. Arc-shaped jet nozzle; 707. Air intake component; 7071. Main air intake pipe; 7072. Gas passage; 7073. Gas diversion pipe; 7074. Pulse gas valve; 8. Three-way valve; 9. Collection chamber; 10. Liquid outlet manifold; 11. Main liquid outlet pipe; 12. Preheating assembly; 1201. Heat exchanger body; 1202. Circulation pipe; 1203. Heat exchange hood; 1204. Heat exchange tube; 13. Secondary air intake pipe; 14. High-pressure gas chamber. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0018] Example 1: Please refer to Figures 1-10The present invention provides a technical solution: a light hydrocarbon separation device for liquefied natural gas, comprising a pre-processor 1, a step-by-step cooling device 2, a distillation column 3, and a liquid inlet manifold 4. The liquid inlet manifold 4 introduces liquefied natural gas into the pre-processor 1, the pre-processor 1 introduces the processed liquefied natural gas into the step-by-step cooling device 2, and the step-by-step cooling device 2 introduces the cooled liquefied natural gas into the distillation column 3 for separation. The pre-processor 1 is equipped with four sets of filters 6. A preheating component 12 is installed outside the filters 6, and a backwashing component 7 is installed inside the filters 6. The inlet pipe 601 of the filters 6 is connected to the inlet main pipe 4 through the inlet diversion pipe 5. The outlet pipe 602 of the filters 6 is connected to the outlet manifold 10 through the three-way valve 8. The bottom end of the outlet manifold 10 is connected to the outlet main pipe 11. The outlet main pipe 11 is connected to the input end of the step-by-step cooling device 2. The use of four sets of filters 6 for diversion filtration improves the filtration effect. Diversion filtration can also slow down the flow rate of liquefied natural gas, so that the preheating component 12 can better preheat the liquefied natural gas. By concentrating the preheating component 12 and the filters 6 in the same pre-processor 1, the space occupied by the overall equipment can be reduced, as well as the loss of cold energy of liquefied natural gas caused by long-distance transportation can be reduced. The filter 6 is equipped with a composite filter screen 603, and a drain pipe 604 is provided at the bottom of the filter 6. The pre-processor 1 is equipped with a collection chamber 9, and the bottom of the drain pipe 604 is connected to the collection chamber 9. The composite filter screen 603 is made of stainless steel wire mesh and nanofiber filter membrane. The composite filter screen 603 separates the output pipe 602 from the drain pipe 604. The drain pipe 604 is used to discharge sewage during backwashing. The composite filter screen 603 can effectively intercept solid impurities with a particle size greater than 0.1μm in liquefied natural gas, such as mud, rust, and pipe debris. The backwash assembly 7 includes a diversion chamber 701 and an air inlet component 707. The diversion chamber 701 is fixedly installed inside the filter 6. An air blowing head 702 is fixedly installed at the top of the diversion chamber 701, extending into the inner side of the composite filter screen 603. The air blowing head 702 is a frustum-shaped structure, tapering at the top and widening at the bottom. Air blowing holes 703 are formed on the outer surface of the air blowing head 702. The interior of the air blowing head 702 communicates with the interior of the diversion chamber 701. The top of the diversion chamber 701 is connected to a rotating hollow rod 705 via a rotary joint 704. Multiple arc-shaped air nozzles 706 are fixedly installed on the outer wall of the rotating hollow rod 705, which is spirally mounted on the rotating hollow rod 705. The rotating hollow rod 705 is located on the outer side of the composite filter screen 603. The air outlet end of the air inlet component 707 is connected to the diversion chamber 701. The air inlet of the flow chamber 701 is connected to the air inlet of the air inlet component 707, which is connected to the liquid nitrogen delivery pipeline. Liquid nitrogen is introduced into the flow chamber 701 through the air inlet component 707. Part of the liquid nitrogen flows into the air blowing head 702 and is then sprayed out from the air blowing hole 703 to rinse the inside of the composite filter screen 603. The other part enters the rotating hollow rod 705 and is then sprayed out from the arc-shaped air nozzle 706 on the rotating hollow rod 705 to rinse the outside of the composite filter screen 603. The specially designed arc-shaped air nozzle 706 can generate a torsional force under the pushing action of liquid nitrogen, thereby driving the rotating hollow rod 705 to rotate. The rotation of the rotating hollow rod 705 drives the arc-shaped air nozzle 706 to rotate, so that the purpose of rotational spraying is to achieve the purpose of uniform rinsing of the outside of the composite filter screen 603. The air intake component 707 includes an air intake manifold 7071. One end of the air intake manifold 7071 is connected to a liquid nitrogen delivery pipeline, and the other end of the air intake manifold 7071 is connected to a gas channel 7072. A gas distribution pipe 7073 is connected to the gas channel 7072. Four gas distribution pipes 7073 are arranged in a circumferential array on the gas channel 7072. The gas distribution pipes 7073 are connected to the air intake end of the distribution chamber 701. A pulse gas valve 7074 is provided at the connection between the gas distribution pipes 7073 and the distribution chamber 701. The pulse gas valve 7074 is used to introduce liquid nitrogen into the distribution chamber 701 in a pulse flow manner, so that the liquid nitrogen is periodically introduced into the distribution chamber 701 and then periodically flushes the composite filter screen 603. During the flushing interval, the impurities washed away fall into the drain pipe 604 and are then discharged. The preheating assembly 12 includes a heat exchanger body 1201 and a heat exchange hood 1203. The heat exchange hood 1203 covers the filter 6. The top and bottom ends of the heat exchange hood 1203 are connected to heat exchange tubes 1204. The heat exchange tubes 1204 are coiled on the inlet pipe 601 and the drain pipe 604. The heat exchange medium circulation port of the heat exchanger body 1201 is connected to a circulation pipe 1202. The circulation pipe 1202 is connected to the heat exchange tubes 1204. The medium-temperature heat transfer oil (temperature controlled at 80-120℃) heated by the heat exchanger body 1201 heats the liquefied natural gas flowing in the filter 6. The LNG is preheated to -140℃ to -130℃ through countercurrent heat exchange. A high-pressure gas chamber 14 is fixedly installed inside the pre-processor 1. The inlet end of the high-pressure gas chamber 14 is connected to the liquid nitrogen delivery pipeline, and the outlet end of the high-pressure gas chamber 14 is connected to the inlet secondary pipe 13. The bottom end of the inlet secondary pipe 13 is connected to the output pipe 602 through a three-way valve 8. This is used to introduce liquid nitrogen from the high-pressure gas chamber 14 into the inlet secondary pipe 13, and then into the output pipe 602 through the three-way valve 8. This is used to backflush away the liquefied natural gas remaining in the output pipe 602 and to flush the inside of the output pipe 602. The staged cooling device 2 is equipped with a first-stage refrigeration cycle 201, a second-stage refrigeration cycle 202, and a third-stage refrigeration cycle 203. All three stages use a mixed refrigerant of nitrogen, methane, and ethylene. The proportions of the mixed refrigerants in the first-stage refrigeration cycle 201, the second-stage refrigeration cycle 202, and the third-stage refrigeration cycle 203 are different. By utilizing the optimal operating range of the mixed refrigerant, efficient staged cooling of liquefied natural gas can be achieved. The mixed refrigerant composition in the first-stage refrigeration cycle 201 is (30% nitrogen, 40% methane, and 30% ethylene), the mixed refrigerant composition in the second-stage refrigeration cycle 202 is (20% nitrogen, 30% methane, and 50% ethylene), and the mixed refrigerant composition in the third-stage refrigeration cycle 203 is (ethylene and a small amount of nitrogen and methane). The feed pipe 301 on the distillation column 3 is connected to the output end of the third-stage refrigeration cycle 203. The distillation column 3 is provided with a top discharge pipe 303, a middle discharge pipe 302, and a bottom discharge pipe 304 from top to bottom. The middle discharge pipe 302 is used to collect propane, the top discharge pipe 303 is used to collect ethane, and the bottom discharge pipe 304 is used to collect butane and heavier components.

[0019] Working principle: In use, first open the valves on the two inlet manifolds 5 to allow liquefied natural gas (LNG) to enter the main inlet manifold 4. The LNG then flows from the main inlet manifold 4 into the inlet manifolds 5, then into the input pipe 601, and then into the filter 6. After being filtered by the composite filter screen 603, the LNG enters the three-way valve 8 through the output pipe 602, then into the outlet manifold 10, and then into the outlet manifold 11. From the outlet manifold 11, the LNG enters the staged cooling device 2, where it is cooled sequentially by the first-stage refrigeration cycle 201, the second-stage refrigeration cycle 202, and the third-stage refrigeration cycle 203 before being fed into the distillation column 3. The distillation column 3 separates the LNG. The middle outlet pipe 302 is used to collect propane, the top outlet pipe 303 is used to collect ethane, and the lower outlet pipe 304 is used to collect butane and other heavier components.

[0020] Example 2: Please refer to Figures 1-10 This invention provides a technical solution: a method for separating light hydrocarbons from liquefied natural gas, comprising the following steps: S1, liquefied natural gas is transported into the inlet main pipe 4, and the liquefied natural gas in the inlet main pipe 4 enters the filter 6 and is filtered out of impurities by the filter 6. When filtering liquefied natural gas, only one or two valves on the inlet branch pipes 5 need to be opened. The opened inlet branch pipes 5 are replaced periodically. When the inlet branch pipe 5 corresponding to the filter 6 is closed, the valve on the drain pipe 604 can be opened, and the connection port of the three-way valve 8 can be switched to allow gas to enter. The secondary pipe 13 is connected to the output pipe 602. The pulse gas valve 7074 is opened to allow liquid nitrogen to enter the intake secondary pipe 13 and then enter the filter 6 for backwashing. The pulse gas valve 7074 introduces liquid nitrogen into the diversion chamber 701 in a pulse manner. Part of the liquid nitrogen flows into the blowing head 702 and then sprays out from the blowing hole 703 to wash the inside of the composite filter screen 603. The other part enters the rotating hollow rod 705 and then sprays out from the arc-shaped jet nozzle 706 on the rotating hollow rod 705 to wash the outside of the composite filter screen 603. S2. The preheating component 12 heats the filter 6, thereby heating the liquefied natural gas passing through the filter 6, achieving the purpose of preheating the liquefied natural gas. S3. The heated liquefied natural gas is transported to the staged cooling device 2. The liquefied natural gas is cooled by passing through the first-stage refrigeration cycle 201, the second-stage refrigeration cycle 202, and the third-stage refrigeration cycle 203 before being fed into the distillation column 3. S4. The liquefied natural gas enters the distillation column 3 and is separated by distillation. The middle discharge pipe 302 is used to collect propane, the top discharge pipe 303 is used to collect ethane, and the lower discharge pipe 304 is used to collect butane and heavier components.

[0021] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A light hydrocarbon separation device for liquefied natural gas, comprising a pre-processor (1), a staged cooling device (2), a distillation column (3), and a main inlet pipe (4), characterized in that: The main inlet pipe (4) introduces liquefied natural gas into the pre-processor (1), the pre-processor (1) introduces the processed liquefied natural gas into the step-by-step cooling device (2), and the step-by-step cooling device (2) introduces the cooled liquefied natural gas into the distillation column (3) for separation. The pre-processor (1) is equipped with four sets of filters (6). A preheating component (12) is provided on the outside of the filter (6). A backwashing component (7) is provided inside the filter (6). The input pipe (601) of the filter (6) is connected to the main inlet pipe (4) through the inlet branch pipe (5). The output pipe (602) of the filter (6) is connected to the outlet manifold (10) through the three-way valve (8). The bottom end of the outlet manifold (10) is connected to the outlet main pipe (11). The outlet main pipe (11) is connected to the input end of the step-by-step cooling device (2).

2. The light hydrocarbon separation device for liquefied natural gas according to claim 1, characterized in that: The filter (6) is provided with a composite filter screen (603), and the bottom end of the filter (6) is provided with a drain pipe (604). The pre-processor (1) is provided with a collection chamber (9). The bottom end of the drain pipe (604) is connected to the collection chamber (9). The composite filter screen (603) is made of stainless steel wire mesh and nanofiber filter membrane. The composite filter screen (603) separates the output pipe (602) from the drain pipe (604).

3. The light hydrocarbon separation device for liquefied natural gas according to claim 1, characterized in that: The backwashing assembly (7) includes a diversion chamber (701) and an air inlet component (707). The diversion chamber (701) is fixedly installed inside the filter (6). An air blowing head (702) is fixedly installed at the top of the diversion chamber (701). The air blowing head (702) extends into the inner side of the composite filter screen (603). The air blowing head (702) is a frustum-shaped structure that is thinner at the top and thicker at the bottom. An air blowing hole (703) is opened on the outer surface of the air blowing head (702). The interior of the air blowing head (702) is connected to the interior of the diversion chamber (701). The top of (701) is connected to a rotating hollow rod (705) via a rotary joint (704). An arc-shaped jet nozzle (706) is fixedly installed on the outer wall of the rotating hollow rod (705). Multiple arc-shaped jet nozzles (706) are provided and are spirally arranged on the rotating hollow rod (705). The rotating hollow rod (705) is located outside the composite filter (603). The outlet end of the air inlet component (707) is connected to the air inlet end of the diversion chamber (701). The air inlet end of the air inlet component (707) is connected to the liquid nitrogen delivery pipeline.

4. A light hydrocarbon separation device for liquefied natural gas according to claim 3, characterized in that: The air intake component (707) includes an air intake manifold (7071), one end of which is connected to a liquid nitrogen delivery pipeline, and the other end of which is connected to a gas channel (7072). A gas distribution pipe (7073) is connected to the gas channel (7072). Four gas distribution pipes (7073) are provided and are arranged in a circular array on the gas channel (7072). The gas distribution pipes (7073) are connected to the air intake end of the distribution chamber (701), and a pulse gas valve (7074) is provided at the connection between the gas distribution pipes (7073) and the distribution chamber (701).

5. A light hydrocarbon separation device for liquefied natural gas according to claim 1, characterized in that: The preheating assembly (12) includes a heat exchanger body (1201) and a heat exchange hood (1203). The heat exchange hood (1203) covers the filter (6). The top and bottom of the heat exchange hood (1203) are connected to heat exchange tubes (1204). The heat exchange tubes (1204) are coiled on the inlet pipe (601) and the drain pipe (604). The heat exchange medium circulation port of the heat exchanger body (1201) is connected to a circulation pipe (1202). The circulation pipe (1202) is connected to the heat exchange tubes (1204).

6. A light hydrocarbon separation device for liquefied natural gas according to claim 1, characterized in that: The pre-processor (1) is fixedly installed with a high-pressure gas chamber (14). The inlet end of the high-pressure gas chamber (14) is connected to the liquid nitrogen delivery pipeline. The outlet end of the high-pressure gas chamber (14) is connected to an inlet sub-pipe (13). The bottom end of the inlet sub-pipe (13) is connected to the output pipe (602) through a three-way valve (8).

7. A light hydrocarbon separation device for liquefied natural gas according to claim 1, characterized in that: The step-by-step cooling device (2) is equipped with a first-stage refrigeration cycle (201), a second-stage refrigeration cycle (202), and a third-stage refrigeration cycle (203). The first-stage refrigeration cycle (201), the second-stage refrigeration cycle (202), and the third-stage refrigeration cycle (203) all use a mixed refrigerant of nitrogen, methane, and ethylene, and the proportions of each mixed refrigerant in the first-stage refrigeration cycle (201), the second-stage refrigeration cycle (202), and the third-stage refrigeration cycle (203) are different.

8. A light hydrocarbon separation device for liquefied natural gas according to claim 1, characterized in that: The feed pipe (301) on the distillation column (3) is connected to the output end of the third-stage refrigeration cycle (203). The distillation column (3) is provided with a top discharge pipe (303), a middle discharge pipe (302), and a bottom discharge pipe (304) from top to bottom.

9. A method for separating light hydrocarbons from liquefied natural gas, characterized in that, Includes the following steps: S1. Liquefied natural gas is transported into the inlet manifold (4). The liquefied natural gas in the inlet manifold (4) enters the filter (6) and is filtered out of impurities by the filter (6). S2. The preheating component (12) heats the filter (6) and then heats the liquefied natural gas passing through the filter (6) to achieve the purpose of preheating the liquefied natural gas. S3. The heated liquefied natural gas is transported to the staged cooling device (2). The liquefied natural gas is cooled by passing through the first stage refrigeration cycle (201), the second stage refrigeration cycle (202), and the third stage refrigeration cycle (203) in sequence before being fed into the distillation column (3). S4. The liquefied natural gas enters the distillation tower (3) and is separated by distillation. The middle discharge pipe (302) is used to collect propane, the top discharge pipe (303) is used to collect ethane, and the lower discharge pipe (304) is used to collect butane and heavier components.

10. A method for separating light hydrocarbons from liquefied natural gas according to claim 9, characterized in that: In step S1, when filtering liquefied natural gas, only one or two valves on the inlet diversion pipe (5) need to be opened. The opened inlet diversion pipe (5) is replaced periodically. When the inlet diversion pipe (5) corresponding to the filter (6) is closed, the valve on the drain pipe (604) can be opened, and the connection port of the three-way valve (8) can be switched to connect the inlet sub-pipe (13) with the output pipe (602). The pulse gas valve (7074) is opened to allow liquid nitrogen to enter the inlet sub-pipe (13). Then it enters the filter (6) and is backwashed sequentially. The pulse valve (7074) introduces liquid nitrogen into the diversion chamber (701) in a pulse manner. Part of the liquid nitrogen flows into the blowing head (702) and is then sprayed out from the blowing hole (703) to rinse the inside of the composite filter screen (603). The other part enters the rotating hollow rod (705) and is then sprayed out from the arc-shaped jet nozzle (706) on the rotating hollow rod (705) to rinse the outside of the composite filter screen (603).

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