An lpg wash heavy hydrocarbon removal system and method

Abstract

The application relates to an LPG washing heavy hydrocarbon removal system and method, relates to the heavy hydrocarbon removal field of natural gas LNG production, and adds LPG to replenish heavy hydrocarbons to raw gas or a purification gas system, after filtering, drying and other treatments on the raw gas, the generated purified gas is sent into a refrigerator unit for cooling and temperature reduction, the purified gas after the cooling and temperature reduction is sent into a heavy hydrocarbon removal tower for heavy hydrocarbon removal, then the purified gas is cooled again and sent into a low-temperature separator to separate liquid heavy hydrocarbons, and the separated liquid heavy hydrocarbons are sent into the heavy hydrocarbon removal tower for spraying, so that the heavy hydrocarbon content of the purified gas in the heavy hydrocarbon removal tower is increased, and the efficiency and the heavy hydrocarbon removal effect of the heavy hydrocarbon removal work are effectively improved. According to the embodiments provided by the application, the heavy hydrocarbon removal effect can be effectively improved, the cold box freezing and blocking situation can be avoided, the operation cost is greatly reduced, the existing natural gas LNG device is adapted, and good industrial practicability is achieved.

Description

Technical Field

[0001] This application relates to the field of liquefied natural gas technology, and in particular to an LPG washing and heavy hydrocarbon removal system and method. Background Technology

[0002] LPG, or liquefied petroleum gas, is a gaseous mixture of hydrocarbons that exists at room temperature and pressure. It is primarily composed of propane, butane, or a mixture containing both propane and butane. The mixture mainly consists of propane, n-butane, isobutane, and small amounts of ethane, organic compounds with more than five carbon atoms, and unsaturated hydrocarbons. In the field of liquefied natural gas, hydrocarbons with more than five carbon atoms are considered heavy hydrocarbons. Since the boiling point of hydrocarbons is directly proportional to their molecular weight, heavy hydrocarbons generally condense first during the liquefaction process. If heavy hydrocarbons are not separated from the natural gas beforehand, there is a risk of them freezing and clogging equipment during the deep-cooling process. To ensure the normal operation of the natural gas liquefaction system, especially the cold box, measures must be taken to remove heavy hydrocarbons from the natural gas before it enters the cold box or the deep-cooling section. Existing technologies include methods for removing heavy hydrocarbons from natural gas: 1) Adsorption method: This method utilizes the principle of solid adsorption to remove heavy hydrocarbons from natural gas. The overall structure of the device used in this method is simple, the heavy hydrocarbon removal efficiency is high, and moisture in the natural gas can be removed simultaneously. However, this method is limited by the saturated adsorption capacity of the solid adsorbent, and its treatment effect is poor for natural gas with a high content of heavy hydrocarbons.

[0003] 2) Absorption method: This method utilizes the principle of "like dissolves like" to absorb heavy hydrocarbons from natural gas using organic solvents. This method is effective at removing heavy hydrocarbons, reducing the molar concentration of heavy hydrocarbons after purification to below 10 ppm, and the equipment has low energy consumption. However, this method has a relatively complex overall process, and energy is also required for absorbent regeneration.

[0004] 3) After precooling the natural gas to -30 to -60°C, it is separated into one or more stages by a heavy hydrocarbon separator. For feed gas with low heavy hydrocarbon content and containing neopentane, sufficient washing liquid cannot be formed, and heavy hydrocarbons are not completely removed. Summary of the Invention

[0005] This application provides an LPG washing and heavy hydrocarbon removal system and method to solve the problem in the prior art where the low-temperature separator cannot separate enough heavy hydrocarbons to form a washing liquid when the feed gas contains neopentane and has a low hydrocarbon content, resulting in incomplete removal of heavy hydrocarbons and freezing blockage of the cold box. At the same time, it replaces isopentane as a supplementary medium, which greatly reduces operating costs.

[0006] In a first aspect, this application provides an LPG washing and heavy hydrocarbon removal system, comprising: a pretreatment unit, a refrigeration unit, a cryogenic separator, a heavy hydrocarbon removal tower, and an LPG supply unit connected sequentially via pipelines, wherein: The pretreatment unit is connected to the refrigeration unit and the heavy hydrocarbon removal tower. The refrigeration unit is connected to the pretreatment unit, the heavy hydrocarbon removal tower, and the cryogenic separator, and is also connected to the outside of the system. The heavy hydrocarbon removal tower is connected to the refrigeration unit at the top and lower middle sections, respectively, and to the pretreatment unit and the outside of the system at the bottom. The top is connected to the low-temperature separator. The cryogenic separator is connected to the LPG supply unit, the refrigeration unit, and the heavy hydrocarbon removal tower; the cryogenic separator is connected to the heavy hydrocarbon removal tower via a heavy hydrocarbon reflux pump. The LPG supply unit is connected to the pretreatment unit and the refrigeration unit.

[0007] Furthermore, the pretreatment unit includes a raw gas treatment group and a purified gas treatment group connected in sequence by pipelines. After passing through the raw gas treatment group, the raw gas is mixed with LPG through pipelines and enters the purified gas treatment group.

[0008] Furthermore, the raw gas treatment group includes a raw gas filter, the front end of which is supplied with raw gas through a pipeline, and the raw gas filtered by the raw gas filter is mixed with LPG supplied by the LPG supply unit through a pipeline before entering the purified gas treatment group.

[0009] Furthermore, the purified gas treatment group includes: a purified gas heat exchanger, an absorption tower, a purified gas separator, a coalescing filter, several drying towers, a mercury removal tower, and a dust filter. A pipe connecting the lower middle input end of the absorption tower and a pipe connecting the top output end of the absorption tower pass through the purified gas heat exchanger. A pipe connecting the top output end of the absorption tower passes through the purified gas heat exchanger and connects to the purified gas separator. The top output end of the purified gas separator is connected to the output end of the coalescing filter via a pipe. The output end of the coalescing filter is connected to the input end of each drying tower via a branch pipe. The output end of the drying tower is connected to the input end of the mercury removal tower via a pipe. The pipe connecting the output end of the mercury removal tower is connected to the dust filter and then connected to the heavy hydrocarbon removal tower and the refrigeration unit.

[0010] Furthermore, the purified gas treatment group is connected to a regenerated gas treatment group, which includes a regenerated gas cooler, a regenerated gas separator, a regenerated gas heat exchanger, and a regenerated gas heater. A first branch is provided on the branch pipeline connecting the coalescing filter and each drying tower, connecting to the regenerated gas cooler. A second branch is provided on the pipeline connecting the drying tower and the mercury removal tower, connecting to the regenerated gas heater. The first branch and the second branch pass through the regenerated gas heat exchanger. The first branch passes through the regenerated gas cooler and then connects to the regenerated gas separator. The output end of the regenerated gas separator is connected to the branch pipeline between the coalescing filter and the drying tower through a pipeline. The output end of the regenerated gas heater is connected to the pipeline between the drying tower and the mercury removal tower through a pipeline.

[0011] Furthermore, the refrigeration unit includes a cold box and a refrigerant compressor unit. The refrigerant compressor unit is connected to the cold box through a pipeline to circulate the refrigerant in the cold box. The cold box is provided with a first cooling section, a second cooling section and a third cooling section. The first cooling section is connected to the pretreatment unit and the heavy hydrocarbon removal tower. The second cooling section is connected to the heavy hydrocarbon removal tower and the low-temperature separator. The third cooling section is connected to the low-temperature separator and external equipment.

[0012] Furthermore, the LPG supply unit includes: an LPG storage tank, an LPG dryer, and an LPG booster pump. The output end of the LPG storage tank is connected to the LPG booster pump and the LPG dryer, respectively. The output end of the LPG dryer is connected to the input end of the LPG booster pump, and the output end of the LPG booster pump is connected to a cryogenic separator and a pretreatment unit via pipelines.

[0013] Secondly, this application provides an LPG washing method for removing heavy hydrocarbons, employing the LPG washing system for removing heavy hydrocarbons as described above, comprising the following steps: In the pretreatment unit, the raw gas and LPG are mixed and then subjected to deacidification, cooling separation, filtration, dehydration, mercury removal and dust removal in sequence to obtain purified gas; The purified gas is divided into two parts. One part is sent into the cold box of the refrigeration unit. After being cooled in the cold box, it is passed into the heavy hydrocarbon removal tower. Liquid heavy hydrocarbons sprayed from the top of the tower exchange heat with the purified gas to remove the heavy hydrocarbon components from the purified gas. The purified gas after heavy hydrocarbon removal enters a cold box for secondary cooling and is then sent to a cryogenic separator to obtain liquid heavy hydrocarbons. The liquid heavy hydrocarbons are then sent back to the heavy hydrocarbon removal tower via a heavy hydrocarbon reflux pump. The purified gas obtained after separating heavy hydrocarbons is returned to the cold box for three-stage cooling and then sent to external equipment for use or storage.

[0014] Furthermore, another portion of the purified gas from the pretreatment unit enters from the bottom of the heavy hydrocarbon removal tower, passes through the heavy hydrocarbon removal tower from bottom to top, stabilizes and reheats the low-temperature heavy hydrocarbons in the heavy hydrocarbon removal tower, and discharges the reheated liquid heavy hydrocarbons from the bottom of the heavy hydrocarbon removal tower.

[0015] Furthermore, the liquid heavy hydrocarbons produced by the cryogenic separator are mixed with pressurized LPG and then sent back to the heavy hydrocarbon removal tower via a heavy hydrocarbon reflux pump for spray washing.

[0016] The technical solutions provided in this application have the following advantages compared with the prior art: 1. Solving the problem of incomplete removal of heavy hydrocarbons: By adding LPG to the system to supplement the heavy hydrocarbon content, sufficient washing liquid is formed in the low-temperature separator, which effectively solves the problem of insufficient washing liquid when the feed gas contains neopentane and has low hydrocarbon content, achieving efficient removal of heavy hydrocarbons and completely avoiding the risk of blockage in the cold box due to freezing of heavy hydrocarbons. 2. Significantly reduced operating costs: Using inexpensive LPG instead of expensive isopentane as the washing liquid replenishment medium, and with high LPG utilization and no large-scale loss, significantly reduces the operating costs of industrial production; 3. Flexible filling method: The filling point and filling pressure can be flexibly selected according to the quality of LPG. If the LPG contains impurities, it is injected into the raw material gas system and the impurities are removed through subsequent deacidification and dehydration processes. If the LPG is pure, it is directly injected into the purified gas system or the low temperature separator, which not only ensures the process effect, but also avoids impurities from entering the cold box and causing secondary freezing blockage. 4. Strong process compatibility: This process integrates mature processes such as absorption and deacidification, dehydration and drying, mercury removal and dust removal, cold box refrigeration, heavy hydrocarbon removal tower washing, and low temperature separation. The process flow is smooth and can be directly adapted to existing industrial plants for natural gas to LNG, with low modification costs. 5. High refrigeration efficiency: It adopts a closed-loop mixed refrigerant refrigeration system, which can achieve refrigeration at multiple temperature levels from -15℃ to -162℃ through a single refrigerant system. It has high refrigeration efficiency and no refrigerant loss due to the closed-loop circulation, further reducing operating costs. 6. Heavy hydrocarbon recovery: The removed heavy hydrocarbons are stabilized and reheated before being collected and stored as heavy hydrocarbon products, realizing resource recovery and utilization and improving the economic benefits of the process. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0020] Figure 1 This is a connection diagram of an LPG washing and heavy hydrocarbon removal system provided in an embodiment of this application.

[0021] Figure 2 Connection diagram of the pretreatment unit Figure 1 .

[0022] Figure 3 Connection diagram of the pretreatment unit Figure 2 .

[0023] Figure 4 This is a connection diagram of the refrigeration unit, cryogenic separator, heavy hydrocarbon removal tower, and LPG supply unit.

[0024] Explanation of reference numerals in the attached figures: 1. Raw material gas filter; 2. Purified gas heat exchanger; 3. Absorption tower; 4. Purified gas separator; 5. Coalescing filter; 6. Drying tower; 7. Regenerated gas cooler; 8. Regenerated gas separator; 9. Regenerated gas heat exchanger; 10. Regenerated gas heater; 11. Mercury removal tower; 12. Dust filter; 13. Heavy hydrocarbon removal tower; 14. Cryogenic separator; 15. Heavy hydrocarbon reflux pump; 16. Refrigerant compressor unit; 17. Cold box; 18. LPG storage tank; 19. LPG dryer; 20. LPG booster pump. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] The following disclosure provides numerous different embodiments or examples for implementing various structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0027] For ease of description, spatial relative terms may be used in the text to describe the relative position or movement of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "front," "back," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure undergoes a positional flip, orientation change, or change of motion, these directional indications will change accordingly. For instance, an element described as "below other elements or features" or "below other elements or features" will subsequently be oriented "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions), and the spatial relative descriptors used in the text will be interpreted accordingly.

[0028] To address the problem in existing technologies where cryogenic separators cannot separate enough heavy hydrocarbons to form a washing liquid when the feed gas contains neopentane and has a low hydrocarbon content, leading to incomplete heavy hydrocarbon removal and cold box freezing, this application provides an LPG washing and heavy hydrocarbon removal system and method that can effectively improve the heavy hydrocarbon removal effect, avoid cold box freezing, significantly reduce operating costs, and is compatible with existing natural gas to LNG plants, demonstrating good industrial applicability.

[0029] Firstly, please refer to Figures 1 to 4 This application provides an LPG washing and heavy hydrocarbon removal system, comprising: a pretreatment unit, a refrigeration unit, a cryogenic separator 14, a heavy hydrocarbon removal tower 13, and an LPG supply unit connected sequentially via pipelines, wherein: The pretreatment unit is connected to the refrigeration unit, the heavy hydrocarbon removal tower 13 and the LPG supply unit through pipelines. It is used to fully mix, gasify and purify the raw gas sent from the outside with the LPG injected by the LPG supply unit, and send the purified gas to the refrigeration unit and the heavy hydrocarbon removal tower 13 respectively. The refrigeration unit is connected to the pretreatment unit, the cryogenic separator 14 and the heavy hydrocarbon removal tower 13 via pipelines. It is used to cool the purified gas generated by the pretreatment unit and send it to the heavy hydrocarbon removal tower 13 to form cooled purified gas; to cool the gas phase sent from the top of the heavy hydrocarbon removal tower 13 and send it to the cryogenic separator 14; and to deeply cool the gas phase sent from the cryogenic separator 14 and then transport it to the outside of the system. The cooling and purified gas after being cooled by the refrigeration unit is injected into the lower middle part of the heavy hydrocarbon removal tower 13, and the purified gas after being purified by the pretreatment unit is injected into the bottom of the heavy hydrocarbon removal tower 13. The liquid heavy hydrocarbons separated by the low-temperature separator 14 are injected into the top of the heavy hydrocarbon removal tower 13. The gas phase formed after heavy hydrocarbon removal in the heavy hydrocarbon removal tower 13 is sent out from the top of the heavy hydrocarbon removal tower 13 and sent into the refrigeration unit. The liquid heavy hydrocarbons formed after heavy hydrocarbon removal in the heavy hydrocarbon removal tower 13 are sent out from the bottom of the heavy hydrocarbon removal tower 13 to the outside of the system. The cryogenic separator 14 is connected to the refrigeration unit, the heavy hydrocarbon removal tower 13 and the LPG supply unit through pipelines. It is used to separate the LPG fed into the LPG supply unit from the cooling gas phase fed into the refrigeration unit, and send the separated LNG to the refrigeration unit for deep cooling. At the same time, the separated liquefied heavy hydrocarbons are sent to the top of the heavy hydrocarbon removal tower 13. The LPG supply unit is connected to the cryogenic separator 14 and the pretreatment unit through pipelines. The LPG is supplied to the pretreatment unit and mixed with the feed gas. The LPG is sent to the cryogenic separator 14 and separated from the cooling gas phase sent by the refrigeration unit.

[0030] During operation, the feed gas is filtered and dried by the pretreatment unit. Simultaneously, LPG gas is injected into the pretreatment unit through the LPG supply unit, ensuring thorough mixing between the LPG and feed gas. In the pretreatment unit, the LPG gas and feed gas undergo simultaneous drying and acid removal, resulting in a dry and purified gas. After pretreatment, a portion of the dried and purified gas is cooled by a refrigeration unit and then fed into the lower part of the heavy hydrocarbon removal tower 13. The remaining portion is directly fed into the lower part of the heavy hydrocarbon removal tower 13. In the heavy hydrocarbon removal tower 13, liquid heavy hydrocarbons sprayed downwards from the top of the tower come into full contact with the dried and purified gas, thereby washing and removing the heavy hydrocarbon components from the purified gas. After the purified gas, having undergone heavy hydrocarbon removal, is sent to a refrigeration unit for further cooling, it is then sent to a cryogenic separator 14 to contact with LPG gas, thereby removing heavy hydrocarbons from the LPG and forming LNG natural gas and liquid heavy hydrocarbons. The LNG is then sent to the refrigeration unit for deep cooling, while the liquid heavy hydrocarbons are sent to the top of the heavy hydrocarbon removal tower 13 for spraying from the top interior of the tower, meeting the requirements for heavy hydrocarbon removal from subsequent purified gas. Purified gas, without cooling, is sent directly to the lower part of the heavy hydrocarbon removal tower 13, flowing upwards through the tower to stabilize and reheat the cryogenic heavy hydrocarbons. The reheated liquid heavy hydrocarbons flow out from the bottom of the tower 13 and are then sent to an external heavy hydrocarbon storage tank for storage.

[0031] In practice, the injection point can be changed according to the quality of the LPG. If the LPG contains a high amount of saturated water, carbon dioxide, organic sulfur, and inorganic sulfur, it should be injected before the deacidification process in the pretreatment unit to allow for simultaneous gas purification with the feed gas, resulting in a clean gas mixture. If the LPG contains only trace amounts of carbon dioxide and sulfides, or if the dew point after drying meets the gas cleanliness requirements, it can be injected at the rear end of the pretreatment unit.

[0032] In some optional embodiments, the pretreatment unit includes a raw gas treatment group and a purified gas treatment group connected in sequence by pipelines. After passing through the raw gas treatment group, the raw gas is mixed with LPG through pipelines and enters the purified gas treatment group.

[0033] In some optional embodiments, the raw gas treatment group includes: a raw gas filter 1, the front end of which is supplied with raw gas through a pipeline, and the raw gas filtered by the raw gas filter 1 is mixed with LPG supplied by the LPG supply unit through a pipeline and then enters the purified gas treatment group. The purified gas treatment group includes: a purified gas heat exchanger 2, an absorption tower 3, a purified gas separator 4, a coalescing filter 5, several drying towers 6, a mercury removal tower 11, and a dust filter 12. The pipe connecting the lower middle part of the absorption tower 3 to the input end and the pipe connecting the top of the absorption tower 3 to the output end respectively pass through the purified gas heat exchanger 2. The pipe connecting the top of the absorption tower 3 to the output end passes through the purified gas heat exchanger 2 and then connects to the purified gas separator 4. The top output end of the purified gas separator 4 is connected to the output end of the coalescing filter 5 through a pipe. The output end of the coalescing filter 5 is connected to the input end of each drying tower 6 through a branch pipe. The output end of the drying tower 6 is connected to the input end of the mercury removal tower 11 through a pipe. The pipe connecting the output end of the mercury removal tower 11 is connected to the dust filter 12 and then connected to the heavy hydrocarbon removal tower 13 and the refrigeration unit.

[0034] Mechanical impurities and droplets in the raw gas are filtered out by the raw gas filter 1 in the raw gas processing unit. The temperature of the mixture of raw gas and LPG is regulated by the purified gas heat exchanger 2. The mixture is then sent to the absorption tower 3 to remove carbon dioxide and hydrogen sulfide, achieving the deacidification step. After deacidification, droplets in the mixture are separated by the purified gas separator 4, and finally filtered out by the coalescing filter 5 to obtain clean purified gas. The dehydrated purified gas is then passed through the mercury removal tower 11 for mercury removal, and then through the dust filter 12 to remove dust, thus obtaining dry and clean purified natural gas, preparing for subsequent liquefaction and heavy hydrocarbon removal processes.

[0035] In some optional embodiments, the purified gas treatment group is connected to a regenerated gas treatment group, which includes a regenerated gas cooler 7, a regenerated gas separator 8, a regenerated gas heat exchanger 9, and a regenerated gas heater 10. A first branch is provided on the branch pipeline connecting the coalescing filter 5 and each drying tower 6 to the regenerated gas cooler 7. A second branch is provided on the pipeline connecting the drying tower 6 and the mercury removal tower 11 to the regenerated gas heater 10. The first branch and the second branch pass through the regenerated gas heat exchanger 9 respectively. The first branch passes through the regenerated gas cooler 7 and is connected to the regenerated gas separator 8. The output end of the regenerated gas separator 8 is connected to the branch pipeline between the coalescing filter 5 and the drying tower 6 through a pipeline. The output end of the regenerated gas heater 10 is connected to the pipeline between the drying tower 6 and the mercury removal tower 11 through a pipeline. By configuring multiple drying towers 6, the adsorption and regeneration cycles of multiple drying towers 6 are alternately carried out to ensure the continuous and stable operation of the dehydration process. At the same time, the regeneration gas in the regeneration process is treated and recovered in compliance with regulations, which avoids energy waste and process disorder. It ensures that the drying tower 6 continuously provides purified gas with a water dew point ≤-70℃ to the process, and prevents water from entering the cold box 17, heavy hydrocarbon removal tower 13 and other low-temperature equipment caused by raw material gas, which may cause freezing and blockage. It is a prerequisite guarantee for the stable operation of the low-temperature section of the entire process.

[0036] In some optional embodiments, the refrigeration unit includes a cold box 17 and a refrigerant compressor unit 16. The refrigerant compressor unit 16 is connected to the cold box 17 via pipelines to circulate the refrigerant in the cold box 17. The cold box 17 is provided with a first cooling section, a second cooling section and a third cooling section. The first cooling section is connected to the pretreatment unit and the heavy hydrocarbon removal tower 13. The second cooling section is connected to the heavy hydrocarbon removal tower 13 and the cryogenic separator 14. The third cooling section is connected to the cryogenic separator 14 and external equipment.

[0037] The refrigeration unit adopts a closed-loop cycle, forming an independent closed system. In the embodiments provided in this application, methane, ethylene, propane, nitrogen, and isopentane are used as a mixed refrigerant. After two-stage pressurization by the refrigerant compressor unit 16, the refrigerant delivery pressure is increased to 4.3 MPaG to meet the requirements of the mixed refrigerant circulation in the cold box 17. The first cooling section connects the pretreatment unit and the heavy hydrocarbon removal tower 13, thereby pre-cooling the purified gas generated after processing by the pretreatment unit to -15°C. The second cooling section performs secondary cooling on the purified gas output from the heavy hydrocarbon removal tower 13, cooling the purified gas that has undergone heavy hydrocarbon removal to -60 to -80°C, and then sends the purified gas to the cryogenic separator 14, so that liquid heavy hydrocarbons are generated in the cryogenic separator 14, and the low-temperature liquid heavy hydrocarbons are allowed to fully contact with the purified gas in the heavy hydrocarbon removal tower 13, thereby achieving the removal of heavy hydrocarbons from the purified gas in the heavy hydrocarbon removal tower 13. The third cooling section deeply cools the LNG gas phase after liquid heavy hydrocarbon separation to -162°C, so that the LNG gas phase forms liquid natural gas, which is then sent to an external LNG storage tank for storage.

[0038] In some optional embodiments, the liquid heavy hydrocarbon output end of the cryogenic separator 14 is connected to a heavy hydrocarbon reflux pump 15, which sends the liquid heavy hydrocarbons into the heavy hydrocarbon removal tower 13. The heavy hydrocarbon reflux pump 15 provides the conveying power for the liquid heavy hydrocarbons separated in the cryogenic separator 14, thereby pumping the liquid heavy hydrocarbons to the top of the heavy hydrocarbon removal tower 13, and achieving a spraying effect inside the heavy hydrocarbon removal tower 13 to ensure sufficient contact between the heavy hydrocarbons and the purified gas inside the heavy hydrocarbon removal tower 13, ensuring that the heavy hydrocarbons in the purified gas are washed and removed.

[0039] In some optional embodiments, the LPG supply unit includes an LPG storage tank 18, an LPG dryer 19, and an LPG booster pump 20. The output of the LPG storage tank 18 is connected to both the LPG booster pump 20 and the LPG dryer 19. The output of the LPG dryer 19 is connected to the input of the LPG booster pump 20. The output of the LPG booster pump 20 is connected via pipelines to both a cryogenic separator 14 and a pretreatment unit. The injection point can be changed according to the quality of the LPG. If the LPG contains a high amount of saturated water, carbon dioxide, organic sulfur, and inorganic sulfur, it is injected before the deacidification process in the pretreatment unit to allow for simultaneous gas purification of the LPG and the feed gas, resulting in a clean mixed gas. If the LPG contains only trace amounts of carbon dioxide and sulfides, or if the dew point after drying meets the gas cleanliness requirements, the LPG can be added to the rear end of the pretreatment unit.

[0040] Secondly, this application provides an LPG washing method for removing heavy hydrocarbons, employing the LPG washing system for removing heavy hydrocarbons as described above, comprising the following steps: In the pretreatment unit, acid removal, cooling separation, filtration, dehydration, mercury removal, and dust removal are carried out in sequence to obtain dry and purified gas; The purified gas is divided into two parts. One part is sent into the cold box 17 of the refrigeration unit. After being cooled in the cold box 17, it is introduced into the heavy hydrocarbon removal tower 13. The liquid heavy hydrocarbons sprayed from the top of the heavy hydrocarbon removal tower 13 exchange heat with the purified gas to remove the heavy hydrocarbon components from the purified gas. The purified gas after heavy hydrocarbon removal enters the cold box 17 for secondary cooling and is sent to the low-temperature separator 14 to obtain liquid heavy hydrocarbons. The liquid heavy hydrocarbons are sent back to the heavy hydrocarbon removal tower 13 via the heavy hydrocarbon reflux pump 15. The purified gas obtained after separating heavy hydrocarbons is returned to the cold box 17 for three-stage cooling and then sent to external equipment for use or storage.

[0041] In some optional embodiments, another portion of the dried purified gas from the pretreatment unit enters from the bottom of the heavy hydrocarbon removal tower 13, passes through the heavy hydrocarbon removal tower 13 from bottom to top, stabilizes and reheats the low-temperature heavy hydrocarbons in the heavy hydrocarbon removal tower 13, and discharges the reheated liquid heavy hydrocarbons from the bottom of the heavy hydrocarbon removal tower 13.

[0042] In some optional embodiments, the liquid heavy hydrocarbons produced by the cryogenic separator 14 are mixed with pressurized LPG and then sent back to the heavy hydrocarbon removal tower 13 via the heavy hydrocarbon reflux pump 15 for spray washing.

[0043] In some optional embodiments, the temperature of the primary cooling stage in the cold box 17 is -10 to -15°C, the temperature of the secondary cooling stage is -60 to -80°C, and the temperature of the tertiary cooling stage is -145 to -162°C.

[0044] The specific implementation of this solution will be described in detail. The scope of protection of this application is not limited to the following embodiments. All equivalent transformations made based on the embodiments of this specification shall fall within the scope of protection of this invention.

[0045] Example 1: Heavy hydrocarbon removal process of LPG containing trace amounts of water added to cryogenic separator 14 This embodiment targets low-hydrogen-content natural gas feedstock with 0.5% pentane and 0.3% C5 or higher heavy hydrocarbons. Industrial-grade LPG (propane:butane = 7:3) containing trace amounts of moisture (water dew point -20℃) and free of CO2 and sulfides is selected. The LPG is added to the cryogenic separator 14 to implement the heavy hydrocarbon removal process of this invention. Specific steps are as follows: Raw material gas pretreatment: 6.0 MPaG, 25℃ external raw material gas is filtered by raw material gas filter 1 to remove mechanical impurities and droplets, and then mixed with subsequently added LPG for gasification. After being heated to 40℃ by purified gas heat exchanger 2, it enters absorption tower 3, where CO2 and hydrogen sulfide are removed using MDEA solution. After acid removal, the purified gas is cooled to 30℃ by purified gas cooler and enters purified gas separator 4 to remove entrained MDEA solution. Then, it passes through coalescing filter 5 to filter residual droplets and enters drying tower 6 for dehydration using molecular sieves to a water dew point ≤ -70℃. Subsequently, it passes through mercury removal tower 11 to remove mercury content ≤ 0.01 μg / m³ and dust filter 12 to remove dust content ≤ 1 mg / m³, resulting in dry purified gas. LPG filling: The LPG in LPG storage tank 18 is dehydrated by molecular sieve to a water dew point of ≤-70℃ by LPG dryer 19, and then pressurized to 5.2MPaG by LPG booster pump 20 before being directly added to cryogenic separator 14; Heavy hydrocarbon removal scrubbing: 70% of the dried and purified gas enters the pre-cooling section of the cold box 17, and after shallow cooling and heat exchange with mixed refrigerant to -15℃, it is drawn out and enters from the lower part of the heavy hydrocarbon removal tower 13; the liquid heavy hydrocarbons separated by the low-temperature separator 14 are mixed with the injected LPG, and after being pressurized to 4.9MPaG by the heavy hydrocarbon reflux pump 15, they are sprayed from the top of the heavy hydrocarbon removal tower 13. The operating parameters of the heavy hydrocarbon removal tower 13 are: operating pressure 4.9MPaG, bottom temperature 5℃, top temperature -48℃, and the gas phase and liquid phase are in countercurrent contact to complete the removal of heavy hydrocarbons; LNG preparation and heavy hydrocarbon recovery: The purified gas from the top of the heavy hydrocarbon removal tower 13 is returned to the cold box 17, pre-cooled to -70°C in two stages, and then enters the cryogenic separator 14 to separate liquid heavy hydrocarbons; the separated gas phase is returned to the cryogenic section of the cold box 17, where it is heated to -162°C, and then its pressure is reduced to 0.5 MPaG by the regulating valve before being sent to the LNG storage tank; 30% of the gas phase is drawn from the dried purified gas before entering the cold box 17 and enters the tower from the bottom of the heavy hydrocarbon removal tower 13 to stabilize and reheat the low-temperature heavy hydrocarbons in the tower. The reheated liquid heavy hydrocarbon product is drawn from the bottom of the tower and sent to the external heavy hydrocarbon storage tank for storage; Refrigeration system operation: The refrigerant mixture of methane:ethylene:propane:nitrogen:isopentane = 25:30:20:5:20 is used. After being pressurized to 4.3MPaG in two stages by the refrigerant compressor unit 16, it is cooled and separated, and enters the cold box 17 to complete three-stage refrigeration: first stage pre-cooling to -15℃, second stage pre-cooling to -70℃, and deep cooling to -162℃. After each stage of refrigerant is throttled and depressurized, it returns to 17-cold box 17 for reheating, realizing a closed-loop refrigerant cycle.

[0046] In this embodiment, after the feed gas is processed, the new pentane removal rate reaches 99.95%, the molar content of heavy hydrocarbons above C5 is reduced to 3ppm, the LNG preparation system has been running continuously for 3 months without the freezing blockage of cold box 17, and the heavy hydrocarbon recovery efficiency reaches 96%. Compared with the isopentane refueling process, the operating cost per ton of LNG is reduced by 65%.

[0047] Example 2: Heavy hydrocarbon removal process for high-purity LPG injected into the feed gas system This embodiment targets a low-hydrocarbon feedstock gas with 0.8% pentane and 0.2% C5 or higher heavy hydrocarbons. High-purity LPG (propane:butane = 6:4, water dew point ≤ -80℃, free of CO2, sulfides, and other impurities) is selected. The LPG is added to the feedstock gas system at the outlet of feedstock gas filter 1 to implement the heavy hydrocarbon removal process of this invention. Specific steps are as follows: Raw material gas pretreatment: 6.0 MPaG, 25℃ external raw material gas is filtered by raw material gas filter 1 to remove mechanical impurities and droplets, and then fully mixed and vaporized with injected high-purity LPG. After being heated to 40℃ by purified gas heat exchanger 2, it enters absorption tower 3, where CO2 and hydrogen sulfide are removed using MDEA solution. After deacidification, the purified gas is cooled to 30℃ by purified gas cooler and enters purified gas separator 4 to remove entrained MDEA solution. Then, it passes through coalescing filter 5 to filter residual droplets and enters drying tower 6 to be dehydrated by molecular sieve to a water dew point ≤ -70℃. Subsequently, it passes through mercury removal tower 11 to remove mercury content ≤ 0.01 μg / m³ and dust filter 12 to remove dust content ≤ 1 mg / m³, resulting in dry purified gas. LPG refueling: The high-purity LPG in LPG storage tank 18 passes through LPG dryer 19, is pressurized to 6.2 MPaG by LPG booster pump 20, and then added to the feed gas system at the outlet of feed gas filter 1, where it is mixed and vaporized with 6.0 MPaG feed gas at 25°C. Heavy hydrocarbon removal scrubbing: 65% of the dried and purified gas enters the pre-cooling section of the cold box 17, and after shallow cooling and heat exchange with mixed refrigerant to -15℃, it is drawn out and enters from the lower part of the heavy hydrocarbon removal tower 13; the liquid heavy hydrocarbon and LPG mixture separated by the low temperature separator 14 is pressurized to 4.8MPaG by the heavy hydrocarbon reflux pump 15 and then sprayed from the top of the heavy hydrocarbon removal tower 13. The operating parameters of the heavy hydrocarbon removal tower 13 are: operating pressure 4.8MPaG, bottom temperature 0℃, top temperature -45℃, and the gas phase and liquid phase are in countercurrent contact to complete the removal of heavy hydrocarbons; LNG preparation and heavy hydrocarbon recovery: The purified gas from the top of the heavy hydrocarbon removal tower 13 is returned to the cold box 17, pre-cooled to -65°C in two stages, and then enters the cryogenic separator 14 to separate liquid heavy hydrocarbons; the separated gas phase is returned to the cryogenic section of the cold box 17, heat-exchanged to -162°C, and then throttled and depressurized to 0.5 MPaG by the regulating valve before being sent to the LNG storage tank; 35% of the gas phase is drawn from the dried purified gas before entering the cold box 17 and enters the tower from the bottom of the heavy hydrocarbon removal tower 13 to stabilize and reheat the low-temperature heavy hydrocarbons in the tower. The reheated liquid heavy hydrocarbon product is drawn from the bottom of the tower and sent to the external heavy hydrocarbon storage tank for storage; Refrigeration system operation: The refrigerant mixture of methane: ethylene: propane: nitrogen: isopentane = 20:35:20:5:20 is used as the refrigerant. After being pressurized to 4.3 MPaG in two stages by the refrigerant compressor unit 16, it is cooled and separated, and enters the cold box 17 to complete three-stage refrigeration, namely, the first stage pre-cooling to -15℃, the second stage pre-cooling to -65℃, and the deep cooling to -162℃. After each stage of refrigerant is throttled and depressurized, it returns to the cold box 17 for reheating, realizing a closed-loop refrigerant cycle.

[0048] In this embodiment, after the feed gas is processed, the removal rate of new pentane reaches 99.92%, the molar content of heavy hydrocarbons above C5 is reduced to 4ppm, the LNG preparation system has been running continuously for 4 months without the freezing blockage of cold box 17, the heavy hydrocarbon recovery efficiency reaches 95.5%, and the operating cost per ton of LNG is reduced by 8% compared with Example 1 and by 70% compared with the isopentane refueling process due to the elimination of the LPG drying process.

[0049] Example 3: Heavy hydrocarbon removal process by injecting LPG into the inlet of heavy hydrocarbon removal tower 13 This embodiment targets a low-hydrocarbon feedstock gas with 0.6% neopentane and 0.4% C5 or higher heavy hydrocarbons. Industrial-grade LPG (propane:butane = 8:2) containing trace amounts of sulfides (H2S content 5 mg / m³) and a water dew point of -15°C is selected. The LPG is added to the purified gas pipeline at the inlet of heavy hydrocarbon removal tower 13 to implement the heavy hydrocarbon removal process of this invention. Specific steps are as follows: Raw material gas pretreatment: 6.0 MPaG, 25℃ external raw material gas is filtered by raw material gas filter 1 to remove mechanical impurities and droplets, then mixed and gasified with subsequently added LPG. After being heated to 40℃ by purified gas heat exchanger 2, it enters absorption tower 3, where CO2 and hydrogen sulfide are removed using MDEA solution until the H2S content in the deacidified raw material gas is ≤2mg / m³. The deacidified purified gas is cooled to 30℃ by purified gas cooler and enters purified gas separator 4 to remove entrained MDEA solution. Then, it passes through coalescing filter 5 to filter residual droplets and enters drying tower 6 for dehydration using molecular sieves until the water dew point is ≤-70℃. Subsequently, it passes through mercury removal tower 11 to remove mercury content to ≤0.01μg / m³ and dust filter 12 to remove dust content to ≤1mg / m³, resulting in dry purified gas. LPG refueling: The LPG in LPG storage tank 18 is dehydrated by molecular sieve to a water dew point of ≤-70℃ by LPG dryer 19, and then pressurized to 5.2MPaG by LPG booster pump 20 before being added to the purified gas pipeline at the inlet of heavy hydrocarbon removal tower 13 and mixed with purified gas precooled to -15℃ by cold box 17. Heavy hydrocarbon removal washing: The mixed gas phase enters from the lower part of the heavy hydrocarbon removal tower 13. The liquid heavy hydrocarbons and LPG mixture separated by the low temperature separator 14 are pressurized to 5.0 MPaG by the heavy hydrocarbon reflux pump 15 and then sprayed from the top of the heavy hydrocarbon removal tower 13. The operating parameters of the heavy hydrocarbon removal tower 13 are: operating pressure 5.0 MPaG, bottom temperature 10℃, top temperature -55℃. The gas phase and liquid phase are in countercurrent contact to complete the removal of heavy hydrocarbons. LNG preparation and heavy hydrocarbon recovery: The purified gas from the top of the heavy hydrocarbon removal tower 13 is returned to the cold box 17, pre-cooled to -77°C in two stages, and then enters the cryogenic separator 14 to separate liquid heavy hydrocarbons; the separated gas phase is returned to the cryogenic section of the cold box 17, where it is heated to -162°C, and then its pressure is reduced to 0.5 MPaG by the regulating valve before being sent to the LNG storage tank; 25% of the gas phase is drawn from the dried purified gas before entering the cold box 17 and enters the tower from the bottom of the heavy hydrocarbon removal tower 13 to stabilize and reheat the low-temperature heavy hydrocarbons in the tower. The reheated liquid heavy hydrocarbon product is drawn from the bottom of the tower and sent to the external heavy hydrocarbon storage tank for storage; Refrigeration system operation: The refrigerant mixture of methane: ethylene: propane: nitrogen: isopentane = 30:25:20:5:20 is used. After being pressurized to 4.3 MPaG in two stages by the refrigerant compressor unit 16, it is cooled and separated, and enters the cold box 17 to complete three-stage refrigeration, namely, first-stage pre-cooling to -15℃, second-stage pre-cooling to -77℃, and deep cooling to -162℃. After each stage of refrigerant is throttled and depressurized, it returns to the cold box 17 for reheating, realizing a closed-loop refrigerant cycle.

[0050] In this embodiment, after the feed gas is processed, the new pentane removal rate reaches 99.96%, the molar content of heavy hydrocarbons above C5 is reduced to 2ppm, the LNG preparation system has been running continuously for 5 months without the cold box 17 freezing blockage, and the heavy hydrocarbon recovery efficiency reaches 96.5%. Compared with the isopentane filling process, the operating cost per ton of LNG is reduced by 68%.

[0051] In the embodiments provided in this application, heavy hydrocarbons are supplemented by adding LPG to the feed gas or purified gas system. After the feed gas is filtered and dried, the resulting purified gas is passed into a refrigeration unit for cooling. The cooled purified gas is then sent to the heavy hydrocarbon removal tower 13 for heavy hydrocarbon removal. After further cooling, the purified gas is sent to a cryogenic separator 14 to separate liquid heavy hydrocarbons. The separated liquid heavy hydrocarbons are then sent back to the heavy hydrocarbon removal tower 13 for spraying to increase the heavy hydrocarbon content of the purified gas in the heavy hydrocarbon removal tower 13, thereby effectively improving the efficiency and effect of heavy hydrocarbon removal. Using the embodiments provided in this application can effectively improve the heavy hydrocarbon removal effect, avoid freezing blockage of the cold box 17, significantly reduce operating costs, and is compatible with existing natural gas to LNG plants, demonstrating good industrial applicability.

[0052] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0053] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0054] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0055] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0056] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0058] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Since these modifications and variations fall within the scope of the claims and their equivalents, this application also intends to include these modifications and variations.

[0059] The above description describes specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An LPG wash de-hydrocarbon system characterized by, include: The pretreatment unit, refrigeration unit, cryogenic separator, heavy hydrocarbon removal tower, and LPG supply unit are connected sequentially via pipelines, wherein: The pretreatment unit is connected to the refrigeration unit and the heavy hydrocarbon removal tower. The refrigeration unit is connected to the pretreatment unit, the heavy hydrocarbon removal tower, and the cryogenic separator, and is also connected to the outside of the system. The heavy hydrocarbon removal tower is connected to the refrigeration unit at the top and lower middle sections, respectively, and to the pretreatment unit and the outside of the system at the bottom. The top is connected to the low-temperature separator. The cryogenic separator is connected to the LPG supply unit, the refrigeration unit, and the heavy hydrocarbon removal tower; the cryogenic separator is connected to the heavy hydrocarbon removal tower via a heavy hydrocarbon reflux pump. The LPG supply unit is connected to the pretreatment unit and the refrigeration unit.

2. The LPG washing and heavy hydrocarbon removal system according to claim 1, characterized in that, The pretreatment unit includes a raw gas treatment group and a purified gas treatment group connected in sequence by pipelines. After passing through the raw gas treatment group, the raw gas is mixed with LPG through pipelines and enters the purified gas treatment group.

3. The LPG washing and heavy hydrocarbon removal system according to claim 2, characterized in that, The raw gas treatment group includes a raw gas filter. Raw gas is introduced into the front end of the raw gas filter through a pipeline. The raw gas filtered by the raw gas filter is mixed with LPG supplied by the LPG supply unit through a pipeline and then enters the purified gas treatment group.

4. The LPG washing and heavy hydrocarbon removal system according to claim 2, characterized in that, The purified gas treatment unit includes: a purified gas heat exchanger, an absorption tower, a purified gas separator, a coalescing filter, several drying towers, a mercury removal tower, and a dust filter. Pipes connecting the lower middle part of the absorption tower to its input end and pipes connecting the top of the absorption tower to its output end pass through the purified gas heat exchanger. Pipes connecting the top of the absorption tower to its output end pass through the purified gas heat exchanger and then connect to the purified gas separator. The top output end of the purified gas separator is connected to the output end of the coalescing filter via a pipe. The output end of the coalescing filter is connected to the input end of each drying tower via branch pipes. The output end of each drying tower is connected to the input end of the mercury removal tower via a pipe. The pipe connecting the output end of the mercury removal tower is connected to the dust filter and then to the heavy hydrocarbon removal tower and refrigeration unit.

5. The LPG washing and heavy hydrocarbon removal system according to claim 4, characterized in that, The purified gas treatment group is connected to a regenerated gas treatment group, which includes a regenerated gas cooler, a regenerated gas separator, a regenerated gas heat exchanger, and a regenerated gas heater. A first branch is provided on the branch pipeline connecting the coalescing filter and each drying tower, connecting to the regenerated gas cooler. A second branch is provided on the pipeline connecting the drying tower and the mercury removal tower, connecting to the regenerated gas heater. The first branch and the second branch pass through the regenerated gas heat exchanger. After passing through the regenerated gas cooler, the first branch is connected to the regenerated gas separator. The output end of the regenerated gas separator is connected to the branch pipeline between the coalescing filter and the drying tower through a pipeline. The output end of the regenerated gas heater is connected to the pipeline between the drying tower and the mercury removal tower through a pipeline.

6. The LPG washing and heavy hydrocarbon removal system according to claim 1, characterized in that, The refrigeration unit includes a cold box and a refrigerant compressor unit. The refrigerant compressor unit is connected to the cold box through a pipeline to circulate the refrigerant in the cold box. The cold box is provided with a first cooling section, a second cooling section and a third cooling section. The first cooling section is connected to the pretreatment unit and the heavy hydrocarbon removal tower. The second cooling section is connected to the heavy hydrocarbon removal tower and the low-temperature separator. The third cooling section is connected to the low-temperature separator and external equipment.

7. The LPG washing and heavy hydrocarbon removal system according to claim 1, characterized in that, The LPG supply unit includes an LPG storage tank, an LPG dryer, and an LPG booster pump. The output end of the LPG storage tank is connected to the LPG booster pump and the LPG dryer, respectively. The output end of the LPG dryer is connected to the input end of the LPG booster pump, and the output end of the LPG booster pump is connected to a cryogenic separator and a pretreatment unit via pipelines.

8. A method for removing heavy hydrocarbons by washing LPG, characterized in that, Includes the following steps: In the pretreatment unit, the raw gas and LPG are mixed and then subjected to deacidification, cooling separation, filtration, dehydration, mercury removal and dust removal in sequence to obtain purified gas; The purified gas is divided into two parts. One part is sent into the cold box of the refrigeration unit. After being cooled in the cold box, it is passed into the heavy hydrocarbon removal tower. Liquid heavy hydrocarbons sprayed from the top of the tower exchange heat with the purified gas to remove the heavy hydrocarbon components from the purified gas. The purified gas after heavy hydrocarbon removal enters a cold box for secondary cooling and is then sent to a cryogenic separator to obtain liquid heavy hydrocarbons. The liquid heavy hydrocarbons are then sent back to the heavy hydrocarbon removal tower via a heavy hydrocarbon reflux pump. The purified gas obtained after separating heavy hydrocarbons is returned to the cold box for three-stage cooling and then sent to external equipment for use or storage.

9. The LPG washing and heavy hydrocarbon removal method according to claim 8, characterized in that, Another portion of the purified gas from the pretreatment unit enters from the bottom of the heavy hydrocarbon removal tower, passes through the tower from bottom to top, stabilizes and reheats the low-temperature heavy hydrocarbons in the tower, and discharges the reheated liquid heavy hydrocarbons from the bottom of the tower.

10. The LPG washing and heavy hydrocarbon removal method according to claim 8, characterized in that, The liquid heavy hydrocarbons produced by the cryogenic separator are mixed with pressurized LPG and then sent back to the heavy hydrocarbon removal tower via a heavy hydrocarbon reflux pump for spray washing.

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