A dehydration and desulfurization treatment system and method for liquefied natural gas

Abstract

The present invention relates to the technical field of natural gas purification, and particularly relates to a dehydration and desulfurization treatment system and method for liquefied natural gas. The dehydration and desulfurization treatment system for liquefied natural gas includes a desulfurization device, a dehydration device, and an automatic salt discharging device. The automatic salt discharging device is communicated with the desulfurization device. The automatic salt discharging device includes a first cyclone and a second cyclone that work in a time-sequential alternating manner. The dehydration device includes a molecular sieve regeneration device, and the molecular sieve regeneration device includes a regeneration gas heat exchanger, a first-stage heater, and a second-stage heater that are connected in series step by step. The dehydration and desulfurization treatment method for liquefied natural gas is applied to the above treatment system, which can discharge the by-products generated in the desulfurization tower on the premise of ensuring the stable operation of the desulfurization tower without manual shutdown for salt discharging. By heating the regeneration gas in stages, the step-by-step temperature rise of the molecular sieve is realized, the service life of the molecular sieve is prolonged, and the maintenance cost of the treatment system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas purification, and particularly relates to a dehydration and desulfurization treatment system and method for liquefied natural gas. Background Art

[0002] During the liquefaction process of natural gas, the moisture in natural gas may freeze in the working parts of the liquefaction device in the form of ice or frost, resulting in blockages of pipelines, nozzles, and separation equipment; while the sulfides in natural gas will corrode the pipelines and equipment inside the liquefaction device after entering the liquefaction device, seriously affecting the liquefaction process of natural gas. Compared with the dehydration and desulfurization treatment system for natural gas that does not require liquefaction, the natural gas liquefaction device is in a low-temperature and high-pressure state, and is more sensitive to the residual water and residual sulfur content in natural gas. Therefore, a more strict and higher-standard dehydration and desulfurization treatment system for natural gas is required.

[0003] In order to obtain deeply purified natural gas, some dehydration and desulfurization systems for liquefied natural gas choose to adopt a combined process of wet desulfurization and molecular sieve dehydration. Wet desulfurization can efficiently remove hydrogen sulfide and sulfur components, and the molecular sieve can deeply dehydrate and remove the residual sulfur components. This combined process can meet the strict requirements of natural gas liquefaction for high purity, low sulfur content, and ultra-low dew point of natural gas.

[0004] During the wet desulfurization process, by-products such as sulfates and thiosulfates generated by side reactions in the desulfurization tower are likely to accumulate in the desulfurization tower, resulting in a decrease in desulfurization efficiency, equipment blockage, and an increase in pressure difference, which will further exacerbate the instability of the treatment system. For this reason, the existing treatment system will select a dedicated time period to shut down all devices and valves and stop the machine for salt discharge treatment of the desulfurization tower. The shutdown interrupts the continuity of the production process, consumes additional time, labor, and material costs, and reduces the economic benefits of the treatment system; after using molecular sieve dehydration, the molecular sieve needs to be regenerated through a regeneration process. In industry, the regeneration of molecular sieves mostly adopts the method of introducing heated regeneration gas to raise the temperature of the molecular sieve, but the sharp increase in temperature is likely to cause thermal stress damage to the molecular sieve, accelerate the deterioration process of the molecular sieve, reduce the service life of the molecular sieve, and require frequent replacement of the molecular sieve to ensure the good operation of the system, increasing the equipment maintenance cost and time cost.

[0005] Therefore, a dehydration and desulfurization treatment system and method for natural gas are needed to enable the dehydration and desulfurization process of liquefied natural gas to proceed continuously, effectively, and stably for a long time, reducing the waste of time, labor, and material costs. Summary of the Invention

[0006] The purpose of the present invention is to provide a dehydration and desulfurization treatment system and method for liquefied natural gas to solve the technical problems proposed in the above background art.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A dehydration and desulfurization treatment system for liquefied natural gas, comprising a desulfurization device, a dehydration device and an automatic salt discharging device. The desulfurization device is communicated with the dehydration device, and the automatic salt discharging device is communicated with the desulfurization device. The automatic salt discharging device includes a first cyclone and a second cyclone that work alternately in sequence. The dehydration device includes a molecular sieve regeneration device, and the molecular sieve regeneration device includes a regeneration gas heat exchanger, a first-stage heater and a second-stage heater. The regeneration gas heat exchanger, the first-stage heater and the second-stage heater are connected in series step by step.

[0009] Further, the desulfurization device includes a desulfurization tower. The desulfurization tower includes a tower body and a filter membrane. The filter membrane is arranged at the bottom of the tower body. The filter membrane divides the bottom of the tower body into a high-salt amine liquid area and a low-salt amine liquid area. The first cyclone and the second cyclone are respectively arranged on both sides outside the tower body. The inlets of the first cyclone and the second cyclone are both communicated with the high-salt amine liquid area above the filter membrane. The overflow ports at the upper parts of the first cyclone and the second cyclone are both communicated with the low-salt amine liquid area below the filter membrane. An amine liquid inlet is arranged on the side of the desulfurization tower in the low-salt amine liquid area.

[0010] Further, the automatic salt discharging device further includes a first reactor, a second reactor and a feed liquid flowmeter. The inlets of the first reactor and the second reactor are respectively communicated with the outlets at the bottoms of the first cyclone and the second cyclone. A liquid outlet flowmeter one is arranged on the connecting pipe between the first cyclone and the first reactor. A liquid outlet flowmeter two is arranged on the connecting pipe between the second cyclone and the second reactor. The outlets of the first reactor and the second reactor are respectively communicated with a first feed liquid pump and a second feed liquid pump. The outlets of the first feed liquid pump and the second feed liquid pump are both communicated with the amine liquid inlet. The feed liquid flowmeter is arranged on

[0011] the connecting pipe of the amine liquid inlet.

[0012] Further, the automatic salt discharging device further includes an amine liquid supplement tank and a replenishing and returning liquid valve. The amine liquid supplement tank is respectively communicated with a replenishing liquid pump and a returning liquid pump. The replenishing and returning liquid valve includes a replenishing liquid port, a returning liquid port, a first inlet and a second inlet. The replenishing liquid port is communicated with the outlet of the replenishing liquid pump. The returning liquid port is communicated with the inlet of the returning liquid pump. The first inlet is communicated with the first feed liquid pump. The second inlet is communicated with the second feed liquid pump.

[0013] Further, the desulfurization tower further includes a lean liquid distributor, a swirl plate, a scraper and a stirrer. The stirrer is arranged in the high-salt amine liquid area and is rotatably connected to the bottom of the tower body. The lean liquid distributor is installed in the tower body and is provided with multiple layers from bottom to top. The swirl plate is installed below each layer of the lean liquid distributor. The scrapers are symmetrically installed on the upper and lower sides of the swirl plate. A plurality of scrapers are evenly arranged along the circumferential direction of the tower body on each side. The scrapers are rotatably connected to the middle of the swirl plate through connecting rods and are in contact with the inner wall of the tower body.

[0014] Furthermore, the molecular sieve regeneration device further includes a first switching valve and a second switching valve. The first switching valve includes a first air inlet, a first air outlet, and a second air outlet. The first air inlet is communicated with the heating side outlet end of the regeneration gas heat exchanger. The second air outlet is communicated with the inlet of the first heater. The second switching valve includes a second air inlet, a third air outlet, and a fourth air outlet. The second air inlet is communicated with the outlet of the first heater. The fourth air outlet is communicated with the inlet of the second heater.

[0015] Furthermore, the dehydration device further includes a first dehydration tower and a second dehydration tower. The bottom inlets of the first dehydration tower and the second dehydration tower are respectively communicated with the first air outlet, the third air outlet, and the outlet of the second heater. The top outlets of the first dehydration tower and the second dehydration tower are communicated with the cooling side inlet end of the regeneration gas heat exchanger. A compressor is communicated with the heating side inlet end of the regeneration gas heat exchanger. A cooler is communicated with the cooling side outlet end of the regeneration gas heat exchanger. The outlet end of the cooler is communicated with a water separator. The outlet of the water separator is communicated with the inlet end of the compressor.

[0016] Furthermore, the desulfurization device further includes an amine liquid regeneration device. The amine liquid regeneration device includes a flash evaporation device, a rich and lean liquid heat exchanger, and a regeneration tower. The bottom outlet of the desulfurization tower is communicated with the inlet of the flash evaporation device. The bottom outlet of the flash evaporation device is communicated with the inlet end of the rich and lean liquid heat exchanger. The outlet end of the rich and lean liquid heat exchanger is communicated with the upper inlet of the regeneration tower. The bottom outlet of the regeneration tower is communicated with the rich and lean liquid heat exchanger. The outlet end of the rich and lean liquid heat exchanger is communicated with a regeneration pump. The outlet end of the regeneration pump is communicated with the upper part of the desulfurization tower.

[0017] Furthermore, the top inlets of the first dehydration tower and the second dehydration tower are both communicated with the top outlet of the desulfurization tower. The bottom outlets of the first dehydration tower and the second dehydration tower are communicated with a gas storage tank. The outlet of the gas storage tank is communicated with a liquefaction device.

[0018] The present invention also provides a dehydration and desulfurization treatment method for liquefied natural gas, which is applied to the dehydration and desulfurization treatment system for liquefied natural gas, and includes the following steps:

[0019] S1: The raw material gas enters the desulfurization tower and contacts the lean amine liquid sprayed from top to bottom in the tower in a countercurrent manner to remove sulfur components, and the desulfurized gas is obtained. The lean amine liquid adsorbed with sulfur components is converted into rich amine liquid. During the desulfurization process, S2 and S5 are alternately executed;

[0020] S2: Close Hydrocyclone 2, start Hydrocyclone 1. The high-salt amine solution flows out from the bottom of Hydrocyclone 1 and enters Reactor 1 for desalination reaction. Start Feed Pump 2, and the amine solution in Buffer Tank 2 returns to the bottom of the desulfurization tower. Effluent Flowmeter 1 and Inlet Flowmeter respectively monitor the outlet flow of Hydrocyclone 1 and the inlet flow of the amine solution inlet. If the outlet flow of Hydrocyclone 1 is greater than the inlet flow of the amine solution inlet, execute S3; if the outlet flow of Hydrocyclone 1 is less than or equal to the inlet flow of the amine solution inlet, execute S4;

[0021] S3: Adjust the make-up return valve to connect the make-up pump with Feed Pump 1. Start the make-up pump and close the return pump. The amine solution replenishment tank replenishes the amine solution to the amine solution inlet.

[0022] S4: Adjust the make-up return valve to connect the return pump with Feed Pump 1. Close the make-up pump and start the return pump. The excess amine solution in front of the amine solution inlet returns to the amine solution replenishment tank.

[0023] S5: Close Hydrocyclone 1, start Hydrocyclone 2. The high-salt amine solution flows out from the bottom of Hydrocyclone 2 and enters Reactor 2 for desalination reaction. Start Feed Pump 1, and the amine solution in Buffer Tank 1 returns to the bottom of the desulfurization tower. Effluent Flowmeter 2 and Inlet Flowmeter respectively monitor the outlet flow of Hydrocyclone 2 and the inlet flow of the amine solution inlet. If the outlet flow of Hydrocyclone 2 is greater than the inlet flow of the amine solution inlet, execute S6; if the outlet flow of Hydrocyclone 2 is less than or equal to the inlet flow of the amine solution inlet, execute S7;

[0024] S6: Adjust the make-up return valve to connect the make-up pump with Feed Pump 2. Start the make-up pump and close the return pump. The amine solution replenishment tank replenishes the amine solution to the amine solution inlet.

[0025] S7: Adjust the make-up return valve to connect the return pump with Feed Pump 2. Close the make-up pump and start the return pump. The excess amine solution in front of the amine solution inlet returns to the amine solution replenishment tank.

[0026] S8: The rich amine solution flows into the amine solution regeneration device from the bottom of the desulfurization tower for regeneration and then returns to the desulfurization tower. The desulfurized gas enters the dehydration device for dehydration, and Dehydration Tower 1 and Dehydration Tower 2 in the dehydration device alternate for dehydration and regeneration processes;

[0027] S9: The cold regenerated gas is pressurized by the compressor and then enters the regenerated gas heat exchanger for heat exchange and temperature rise. Adjust the first-stage reversing valve and the second-stage reversing valve to gradually heat up the molecular sieve. The heating process passes through the low-temperature stage, medium-temperature stage, and high-temperature stage respectively;

[0028] S10: After the regenerated gas exchanged heat with the molecular sieve enters the regenerated gas heat exchanger for heat exchange and temperature reduction, it is further cooled by the cooler and then enters the water separator to obtain the cold regenerated gas, and the cold regenerated gas returns to the inlet end of the compressor again;

[0029] S11: The desulfurized gas is dehydrated to obtain dry natural gas. The dry natural gas enters the gas storage tank and then enters the liquefaction unit for natural gas liquefaction treatment, and finally liquefied natural gas is obtained.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. A dehydration and desulfurization treatment system for liquefied natural gas provided by the present invention, by alternately executing the first cyclone and the second cyclone of the automatic salt discharging device, enables the desulfurization tower to continuously carry out the salt slurry discharging, desalting reaction and amine liquid feeding processes, and can discharge the by-products generated in the desulfurization tower in real time on the premise of ensuring the stable operation of the desulfurization tower, without manual shutdown for salt discharging, saving time and labor costs and expanding the economic benefits of the treatment system.

[0032] 2. A dehydration and desulfurization treatment system for liquefied natural gas provided by the present invention is provided with a scraper and a stirrer in the desulfurization tower, and the rotation of the scraper and the stirring of the stirrer ensure that the by-products will not deposit on the tower body.

[0033] 3. A dehydration and desulfurization treatment system for liquefied natural gas provided by the present invention, by adjusting the number of heaters participating in the regeneration gas heating, performs stepped heating on the molecular sieve in three different temperature rising stages, reduces the thermal stress damage during the regeneration of the molecular sieve, prolongs the service life of the molecular sieve, and reduces the equipment maintenance cost and time cost of the treatment system.

[0034] 4. A dehydration and desulfurization treatment method for liquefied natural gas provided by the present invention has the same beneficial effects as a dehydration and desulfurization treatment system for liquefied natural gas, which will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic diagram of the dehydration and desulfurization treatment system for liquefied natural gas according to an embodiment of the present invention;

[0036] Figure 2 is a schematic diagram of the automatic salt discharging device according to an embodiment of the present invention;

[0037] Figure 3 is a schematic diagram of the internal structure of the desulfurization tower according to an embodiment of the present invention;

[0038] Figure 4 is a schematic diagram of the molecular sieve regeneration device according to an embodiment of the present invention.

[0039] In the figure: 1, desulfurization tower; 11, tower body; 111, lean liquid distributor; 112, cyclone plate; 113, scraper; 114, stirrer; 115, pressure sensor; 116, filter membrane; 117, amine liquid inlet; 12, flash evaporation device; 13, rich and lean liquid heat exchanger; 14, amine absorber; 2, regeneration tower; 21, reboiler; 22, acid gas treatment device; 23, sulfur storage tank; 24, regeneration pump; 3, first dehydration tower; 31, second dehydration tower; 4, amine liquid supplementary tank; 41, first cyclone; 411, second cyclone; 412, first valve; 413, second valve; 42, first liquid outlet flowmeter; 421, second liquid outlet flowmeter; 43, first reactor; 431, second reactor; 44, first buffer tank; 441, second buffer tank; 45, first liquid inlet pump; 451, second liquid inlet pump; 46, make-up and return liquid valve; 47, make-up liquid pump; 471, return liquid pump; 48, liquid inlet flowmeter; 49, first regulating valve; 491, second regulating valve; 5, compressor; 51, regeneration gas heat exchanger; 52, first heater; 53, second heater; 54, first reversing valve; 55, second reversing valve; 56, cooler; 57, water separator; 6, sulfur recovery device; 7, gas storage tank; 8, liquefaction device. Detailed implementation mode

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0041] In the following description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation. The term "connection" only indicates the connection between devices and has no special meaning.

[0042] In addition, the technical fields and installation methods involved in the embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] For the specific embodiments, please refer to Figures 1-4 , a dehydration and desulfurization treatment system for liquefied natural gas, including a desulfurization device, a dehydration device and an automatic salt discharging device. The desulfurization device is communicated with the dehydration device, and the automatic salt discharging device is communicated with the desulfurization device. The raw material gas first undergoes desulfurization treatment through the desulfurization device and then enters the dehydration device for dehydration and deep desulfurization.

[0044] Furthermore, the desulfurization device adopts a wet desulfurization process. In this example, an organic solvent, methyldiethanolamine (abbreviated as MDEA), is selected as the desulfurization agent. The desulfurization device includes a desulfurization tower 1 and an amine solution regeneration device. The amine solution regeneration device includes a flash evaporation device 12, a rich and lean liquid heat exchanger 13, a regeneration tower 2, and an acid gas treatment device 22. The bottom outlet of the desulfurization tower 1 is connected to the inlet of the flash evaporation device 12. The top outlet of the desulfurization tower 1 is connected to an amine absorber 14, and the outlet of the amine absorber 14 is connected to a dehydration device. The rich and lean liquid heat exchanger 13 includes a rich liquid heating channel and a lean liquid cooling channel. The bottom outlet of the flash evaporation device 12 is connected to the inlet end of the rich liquid heating channel, and the upper outlet of the flash evaporation device 12 is connected to a gas storage tank 7. Inside the regeneration tower 2, from top to bottom, there are a gas-liquid separation zone, an absorption zone, and a sedimentation zone. The outlet end of the rich liquid heating channel is connected to the upper inlet of the absorption zone of the regeneration tower 2. The bottom outlet of the regeneration tower 2 is connected to the inlet end of the lean liquid cooling channel. The outlet end of the lean liquid cooling channel is connected to a regeneration pump 24, and the outlet end of the regeneration pump 24 is connected to the upper part of the desulfurization tower 1. A reboiler 21 is arranged outside the regeneration tower 2. The inlet of the reboiler 21 is connected to the bottom sedimentation zone of the regeneration tower 2, and the outlet of the reboiler 21 is connected to the absorption zone of the regeneration tower 2. The bottom outlet of the acid gas treatment device 22 is connected to the absorption zone of the regeneration tower 2. The upper inlet of the acid gas treatment device 22 is connected to the top of the regeneration tower 2. Another outlet of the acid gas treatment device 22 is connected to a sulfur storage tank 23, and the outlet of the sulfur storage tank 23 is connected to a sulfur recovery device 6.

[0045] The raw material gas enters from the lower part of the desulfurization tower 1 and contacts countercurrently with the lean amine solution flowing downward. The sulfur-containing components in the raw material gas are adsorbed by the lean amine solution, and the desulfurized gas flows out from the top of the desulfurization tower 1. After the desulfurized gas enters the amine absorber 14 to remove the small amount of amine solution carried, it enters the dehydration device; the lean amine solution becomes rich amine solution after absorbing the sulfur-containing components in the raw material gas. The rich amine solution flows out from the bottom of the desulfurization tower 1 and enters the flash evaporation device 12. The rich amine solution flashes out the dissolved hydrocarbon gas in the flash evaporation device 12, and the hydrocarbon gas enters the gas storage tank 7 for storage. The rich amine solution after removing the hydrocarbon gas enters the rich liquid heating channel of the rich and lean liquid heat exchanger 13 to be heated. The heated rich amine solution enters the upper part of the absorption zone of the regeneration tower 2. The rich amine solution flowing from top to bottom contacts countercurrently with the steam flowing from bottom to top, and the sulfur-containing components are desorbed. The steam is generated by the reboiler 21 heating the regeneration solution flowing out from the sedimentation zone. The regenerated rich amine solution becomes lean amine solution and flows out from the bottom of the sedimentation zone of the regeneration tower 2 and enters the lean liquid cooling channel of the rich and lean liquid heat exchanger 13 to be cooled. The cooled lean amine solution returns to the upper part of the desulfurization tower 1 under the driving action of the regeneration pump 24; the acidic steam absorbing the sulfur-containing components flows out from the top of the regeneration tower 2, and after being treated by the acid gas treatment device 22, the free acid water and the regeneration solution are separated. The regeneration solution flows out from the bottom of the acid gas treatment device 22 and returns to the absorption zone of the regeneration tower 2, and the free acid water flows into the sulfur storage tank 23. The sulfur components in the sulfur storage tank 23 enter the sulfur recovery device 6 for recovery treatment.

[0046] Further, the desulfurization tower 1 includes a tower body 11, a lean liquid distributor 111, a swirl plate 112, a scraper 113, a stirrer 114 and a filter membrane 116. The lean liquid distributor 111 is installed in the tower body 11. The lean liquid distributor 111 is provided with multiple layers from top to bottom. Each layer of the lean liquid distributor 111 is communicated with the outlet of the regeneration pump 24 through a pipeline. A plurality of nozzles are installed on the lean liquid distributor 111 for uniformly distributing and spraying the lean amine solution introduced into the tower body 11. The swirl plate 112 is installed below each layer of the lean liquid distributor 111. When the raw material gas entering from the lower part of the tower body 11 passes upward through the swirl plate 112, the air flow rotates due to the guiding action of the blades of the swirl plate 112, and the rotated air flow can contact more fully with the lean amine solution sprayed above countercurrently. The lean liquid distributor 111 and the swirl plate 112 are prior arts and will not be elaborated here; pressure sensors 115 are arranged above and below the inner wall of the tower body 11 for monitoring the pressure difference between the upper and lower parts of the tower body 11.

[0047] The scraper 113 is symmetrically installed on the upper and lower sides of the cyclone plate 112. A plurality of scrapers 113 are evenly arranged along the circumferential direction of the tower body 11 on each side. The scraper 113 is rotatably connected to the middle of the cyclone plate 112 through a connecting rod. The scraper 113 abuts against the inner wall of the tower body 11. The scraper 113 rotates driven by the rotating airflow passing through the cyclone plate 112, so that the inner wall of the tower body 11 can be cleaned during the countercurrent contact process of the raw material gas and the lean amine solution, preventing by-products from depositing on the inner wall of the tower body 11. The filter membrane 116 is arranged at the bottom of the tower body 11. The filter membrane 116 divides the bottom of the tower body 11 into a high-salt amine solution area and a low-salt amine solution area. The high-salt amine solution area is above the filter membrane 116, and the low-salt amine solution area is below the filter membrane 116. The rich amine solution and by-products generated by the upper desulfurization reaction of the desulfurization tower 1 accumulate in the high-salt amine solution area above the filter membrane 116 to form a high-salt amine solution. A stirrer 114 is arranged in the high-salt amine solution area. The stirrer 114 is rotatably connected to the bottom of the tower body 11. A driving motor is installed at the bottom of the tower body 11 to drive the stirrer 114 to rotate. The stirrer 114 ensures that the by-products are in a solution state instead of depositing at the bottom of the tower body 11. The automatic salt discharging device includes a first cyclone 41 and a second cyclone 411. The first cyclone 41 and the second cyclone 411 are respectively arranged on the two outer sides of the tower body 11. The inlets of the first cyclone 41 and the second cyclone 411 are both communicated with the high-salt amine solution area above the filter membrane 116. Valves 412 and 413 are respectively arranged on the connecting pipes of the first cyclone 41 and the second cyclone 411 communicating with the high-salt amine solution area. The overflow ports at the upper parts of the first cyclone 41 and the second cyclone 411 are both communicated with the low-salt amine solution area below the filter membrane 116. After the high-salt amine solution enters the first cyclone 41 or the second cyclone 411, it is separated into a low-salt amine solution and a concentrated salt slurry through cyclone action. The low-salt amine solution overflows into the low-salt amine solution area and flows out from the bottom outlet of the tower body 11. The concentrated salt slurry flows out from the bottom outlet of the first cyclone 41 or the second cyclone 411. An amine solution inlet 117 is provided on the side of the desulfurization tower 1 in the low-salt amine solution area. When the pressure difference inside the desulfurization tower 1 monitored by the pressure sensor 115 is too large, the opening degrees of the valve 412 or the valve 413 are adjusted to be smaller to reduce the inlet flow rate of the first cyclone 41 or the second cyclone 411, so as to ensure the pressure balance inside the desulfurization tower 1.

[0048] Further, the automatic desalting device further includes an amine liquid replenishment tank 4, a first reactor 43, a second reactor 431, a replenishment and return liquid valve 46, and a liquid inlet flowmeter 48. The inlets of the first reactor 43 and the second reactor 431 are respectively connected to the outlets at the bottoms of the first hydrocyclone 41 and the second hydrocyclone 411, and are respectively used for performing desalting reactions on the concentrated salt slurry flowing out from the outlets at the bottoms of the first hydrocyclone 41 and the second hydrocyclone 411. The first liquid outlet flowmeter 42 is installed on the connecting pipeline between the first hydrocyclone 41 and the first reactor 43, and the second liquid outlet flowmeter 421 is installed on the connecting pipeline between the second hydrocyclone 411 and the second reactor 431. The outlets of the first reactor 43 and the second reactor 431 are respectively connected to a first buffer tank 44 and a second buffer tank 441. The other outlets of the first reactor 43 and the second reactor 431 are both connected to the sulfur storage tank 23. The outlets of the first buffer tank 44 and the second buffer tank 441 are connected to a first liquid inlet pump 45 and a second liquid inlet pump 451. The outlets of the first liquid inlet pump 45 and the second liquid inlet pump 451 are both connected to the amine liquid inlet 117. The liquid inlet flowmeter 48 is arranged on the connecting pipeline of the amine liquid inlet 117. The amine liquid replenishment tank 4 is respectively connected to a replenishment liquid pump 47 and a return liquid pump 471. The replenishment and return liquid valve 46 is a four-way four-position electromagnetic valve. The replenishment and return liquid valve 46 includes a replenishment liquid port, a return liquid port, a first liquid inlet, and a second liquid inlet. The replenishment liquid port is connected to the outlet of the replenishment liquid pump 47, the return liquid port is connected to the inlet of the return liquid pump 471, the first liquid inlet is connected to the first liquid inlet pump 45, a first regulating valve 49 is arranged on the connecting pipeline between the first liquid inlet and the first liquid inlet pump 45, the second liquid inlet is connected to the second liquid inlet pump 451, a second regulating valve 491 is arranged on the connecting pipeline between the second liquid inlet and the second liquid inlet pump 451. The opening degrees of the first regulating valve 49 and the second regulating valve 491 are adjustable. The replenishment and return liquid valve 46 is respectively located in four positions from left to right, denoted as the first position, the second position, the third position, and the fourth position. When the replenishment and return liquid valve 46 is in the first position, the replenishment liquid port is connected to the first liquid inlet, and the replenishment liquid pump 47 is connected to the first liquid inlet pump 45. When the replenishment and return liquid valve 46 is in the second position, the first liquid inlet is connected to the return liquid port, and the return liquid pump 471 is connected to the first liquid inlet pump 45. When the replenishment and return liquid valve 46 is in the third position, the replenishment liquid port is connected to the second liquid inlet, and the replenishment liquid pump 47 is connected to the second liquid inlet pump 451. When the replenishment and return liquid valve 46 is in the fourth position, the second liquid inlet is connected to the return liquid port, and the return liquid pump 471 is connected to the second liquid inlet pump 451.

[0049] The hydrocyclone 41 and the hydrocyclone 411 work in a sequential alternating manner. When the hydrocyclone 41 is working, the hydrocyclone 411 is closed. The high-salt amine liquid in the high-salt amine liquid area at the bottom of the desulfurization tower 1 enters the hydrocyclone 41 for separation to produce concentrated salt slurry. The concentrated salt slurry flows out from the bottom of the hydrocyclone 41 and enters the reactor 43 for desalting reaction. At this time, the desalting reaction in the reactor 431 has been completed. After desalting, the concentrated salt slurry is transformed into low-salt amine liquid and enters the buffer tank 441. The liquid inlet pump 451 is started to pump the amine liquid in the buffer tank 441 back to the bottom of the desulfurization tower 1. The outlet flowmeter 42 and the inlet flowmeter 48 respectively monitor the flow rate of the concentrated salt slurry flowing out from the bottom of the hydrocyclone 41 and the flow rate of the amine liquid flowing back into the desulfurization tower 1. When the flow rate of the concentrated salt slurry is greater than the flow rate of the reflux amine liquid, the valve core of the make-up and return liquid valve 46 moves to the first position, and the make-up liquid pump 47 is started. The amine liquid supply tank 4 supplies amine liquid to the amine liquid inlet 117. When the flow rate of the concentrated salt slurry is less than the flow rate of the reflux amine liquid, the valve core of the make-up and return liquid valve 46 moves to the second position, and the return liquid pump 471 is started. The excess amine liquid in front of the amine liquid inlet 117 returns to the amine liquid supply tank 4. Similarly, when the hydrocyclone 41 is closed, the hydrocyclone 411 works, and the reactor 431 conducts desalting reaction. The liquid inlet pump 45 is started to pump the amine liquid in the buffer tank 44 back to the bottom of the desulfurization tower 1. The outlet flowmeter 421 monitors the flow rate of the concentrated salt slurry flowing out from the bottom of the hydrocyclone 411. When the flow rate of the concentrated salt slurry is greater than the flow rate of the reflux amine liquid, the valve core of the make-up and return liquid valve 46 moves to the third position, and the make-up liquid pump 47 is started. The amine liquid supply tank 4 supplies amine liquid to the amine liquid inlet 117. When the flow rate of the concentrated salt slurry is less than the flow rate of the reflux amine liquid, the valve core of the make-up and return liquid valve 46 moves to the fourth position, and the return liquid pump 471 is started. The excess amine liquid in front of the amine liquid inlet 117 returns to the amine liquid supply tank 4. The opening degree of the regulating valve 49 or the regulating valve 491 is adjusted according to the flow rate difference between the concentrated salt slurry flow rate and the reflux amine liquid flow rate. Through the alternating work of the hydrocyclone 41 and the hydrocyclone 411, sufficient reaction time is given to the desalting reaction, ensuring that the desulfurization tower 1 can obtain stable reflux amine liquid, realizing automatic salt discharge of the desulfurization tower 1 during the working state. By using the amine liquid supply tank 4 to supplement or recover amine liquid for the amine liquid inlet 117, the inlet and outlet flow balance at the bottom of the desulfurization tower 1 is ensured.

[0050] Further, the dehydration device adopts a molecular sieve dehydration process. The molecular sieve dehydration tower in the molecular sieve dehydration process can be selected as a two-tower molecular sieve or a multi-tower molecular sieve. In this example, a two-tower molecular sieve is adopted. The dehydration device includes a first dehydration tower 3, a second dehydration tower 31 and a molecular sieve regeneration device. The top inlets of the first dehydration tower 3 and the second dehydration tower 31 are both communicated with the outlet of the amine absorber 14, and the bottom outlets of the first dehydration tower 3 and the second dehydration tower 31 are both communicated with the inlet of the gas storage tank 7. The outlet of the gas storage tank 7 is communicated with a liquefaction device 8. The desulfurized gas after desulfurization treatment enters the first dehydration tower 3 for dehydration treatment. At this time, the second dehydration tower 31 is regenerated through the molecular sieve regeneration device. Similarly, after the regeneration treatment of the second dehydration tower 31 is completed, the desulfurized gas enters the second dehydration tower 31 for dehydration treatment, and the first dehydration tower 3 is regenerated. The desulfurized gas is dehydrated to obtain dry natural gas, and the dry natural gas enters the gas storage tank 7 and enters the liquefaction device 8 together with the hydrocarbon gas flashed out by the flash evaporation device 12 for natural gas liquefaction treatment to finally obtain liquefied natural gas.

[0051] Further, the molecular sieve regeneration device includes a compressor 5, a regeneration gas heat exchanger 51, a primary heater 52, a secondary heater 53, a primary reversing valve 54 and a secondary reversing valve 55. A regeneration gas heating channel is provided on the heating side of the regeneration gas heat exchanger 51, and a regeneration gas cooling channel is provided on the cooling side of the regeneration gas heat exchanger 51. The inlet end of the regeneration gas heating channel is communicated with the outlet end of the compressor 5. The primary reversing valve 54 is a two-position three-way solenoid valve, and the primary reversing valve 54 includes a primary air inlet, a first air outlet and a second air outlet. The primary air inlet is communicated with the outlet end of the regeneration gas heating channel, the first air outlet is communicated with the bottom inlets of the first dehydration tower 3 and the second dehydration tower 31, and the second air outlet is communicated with the inlet of the primary heater 52. When the valve core of the primary reversing valve 54 is in the left position, the primary air inlet is communicated with the first air outlet. When the valve core of the primary reversing valve 54 is in the right position, the primary air inlet is communicated with the second air outlet. The secondary reversing valve 55 is a two-position three-way solenoid valve, and the secondary reversing valve 55 includes a secondary air inlet, a third air outlet and a fourth air outlet. The secondary air inlet is communicated with the outlet of the primary heater 52, the third air outlet is communicated with the bottom inlets of the first dehydration tower 3 and the second dehydration tower 31, and the fourth air outlet is communicated with the inlet of the secondary heater 53. When the valve core of the secondary reversing valve 55 is in the left position, the secondary air inlet is communicated with the third air outlet. When the valve core of the secondary reversing valve 55 is in the right position, the secondary air inlet is communicated with the fourth air outlet. The outlet of the secondary heater 53 is communicated with the bottom inlets of the first dehydration tower 3 and the second dehydration tower 31. The inlet end of the regeneration gas cooling channel is respectively communicated with the top outlets of the first dehydration tower 3 and the second dehydration tower 31. The outlet end of the regeneration gas cooling channel is communicated with a cooler 56. The outlet end of the cooler 56 is communicated with a water separator 57. The outlet of the water separator 57 is communicated with the inlet of the compressor 5, and another outlet of the water separator 57 is communicated with the inlet of the compressor 5 and the sulfur recovery device 6.

[0052] The molecular sieve regeneration device has three working states, namely low-temperature regeneration, medium-temperature regeneration, and high-temperature regeneration working states. In the low-temperature regeneration working state, the valve core of the first-stage reversing valve 54 is located at the left position, the valve core of the second-stage reversing valve 55 is located at the left position, and the outlet end of the regeneration gas heating channel of the regeneration gas heat exchanger 51 is communicated with the bottom inlets of the first dehydration tower 3 and the second dehydration tower 31. In the medium-temperature regeneration working state, the valve core of the first-stage reversing valve 54 is located at the right position, the valve core of the second-stage reversing valve 55 is located at the left position, the outlet end of the regeneration gas heating channel of the regeneration gas heat exchanger 51 is communicated with the inlet end of the first-stage heater 52, the outlet end of the first-stage heater 52 is communicated with the bottom inlets of the first dehydration tower 3 and the second dehydration tower 31, and the regeneration gas heating channel is connected in series with the first-stage heater 52. In the high-temperature regeneration state, the valve core of the first-stage reversing valve 54 is located at the right position, the valve core of the second-stage reversing valve 55 is located at the right position, the outlet end of the regeneration gas heating channel of the regeneration gas heat exchanger 51 is communicated with the inlet end of the first-stage heater 52, the outlet end of the first-stage heater 52 is communicated with the inlet end of the second-stage heater 53, the outlet end of the second-stage heater 53 is communicated with the bottom inlets of the first dehydration tower 3 and the second dehydration tower 31, and the regeneration gas heating channel is connected in series with the first-stage heater 52 and the second-stage heater 53 step by step.

[0053] The cold regeneration gas is pressurized by the compressor 5 and then enters the regeneration gas heat exchanger 51 to be heated and raised in temperature to obtain the low-temperature regeneration gas. When the molecular sieve starts to be regenerated through the molecular sieve regeneration device, it needs to be heated in a stepped manner in three stages, namely the low-temperature stage, the medium-temperature stage, and the high-temperature stage. In the low-temperature stage, the molecular sieve regeneration device is in the low-temperature regeneration working state. The low-temperature regeneration gas heated and raised in temperature by the regeneration gas heat exchanger 51 directly enters the first dehydration tower 3 or the second dehydration tower 31, so that the temperature of the molecular sieve in the tower rises until the free moisture on the surface and in the macropores of the molecular sieve is desorbed. In the medium-temperature stage, the molecular sieve regeneration device is in the medium-temperature regeneration working state. The low-temperature regeneration gas heated and raised in temperature by the regeneration gas heat exchanger 51 enters the first heater 52 to be further heated to obtain the medium-temperature regeneration gas. The medium-temperature regeneration gas enters the first dehydration tower 3 or the second dehydration tower 31, so that the temperature of the molecular sieve in the tower rises further until the bound moisture in the micropores of the molecular sieve is desorbed. In the high-temperature stage, the molecular sieve regeneration device is in the high-temperature regeneration working state. The low-temperature regeneration gas heated and raised in temperature by the regeneration gas heat exchanger 51 successively enters the first heater 52 and the second heater 53 to be further heated to obtain the high-temperature regeneration gas. The high-temperature regeneration gas enters the first dehydration tower 3 or the second dehydration tower 31, so that the temperature of the molecular sieve in the tower rises further until the residual moisture in the molecular sieve is fully desorbed. At the same time, the residual sulfur components not removed by the desulfurization device in the molecular sieve are desorbed together. By heating the molecular sieve in a stepped manner in three different temperature-raising stages, the thermal stress damage during the thermal regeneration of the molecular sieve can be reduced, the service life of the molecular sieve can be extended, and the energy consumption during the heating process of the regeneration gas can also be reduced. The regeneration gas leaving the first dehydration tower 3 or the second dehydration tower 31 enters the regeneration gas heat exchanger 51 to be cooled by heat exchange, then enters the cooler 56 to be further cooled, and then enters the water separator 57. The water separator 57 separates the moisture and the desorbed sulfur carried in the regeneration gas to obtain the cold regeneration gas. The cold regeneration gas returns to the inlet end of the compressor 5 again. The desorbed sulfur and the sulfur components in the sulfur storage tank 23 enter the sulfur recovery device 6 together for recovery treatment.

[0054] The present invention also provides a dehydration and desulfurization treatment method for liquefied natural gas using the above method, which is applied to the above dehydration and desulfurization treatment system for liquefied natural gas, and includes the following steps:

[0055] S1: The raw material gas enters the desulfurization tower 1 and contacts the lean amine solution sprayed from top to bottom in the tower in a countercurrent manner to carry out a desulfurization reaction to remove sulfur components, and then the desulfurized gas is obtained. The lean amine solution adsorbing sulfur components is converted into rich amine solution. The by-products generated by the desulfurization reaction and the rich amine solution accumulate in the high-salt amine liquid area to form high-salt amine liquid. During the desulfurization process, S2 and S5 are alternately executed;

[0056] S2: Close the second cyclone 411, start the first cyclone 41. The high-salt amine liquid flows out from the bottom of the first cyclone 41 and enters the first reactor 43 for desalting reaction. Start the second feed pump 451, and the amine liquid in the second buffer tank 441 returns to the bottom of the desulfurization tower 1. The first effluent flowmeter 42 and the feed flowmeter 48 respectively monitor the outlet flow of the first cyclone 41 and the inlet flow of the amine liquid at the inlet 117 of the amine liquid. If the outlet flow of the first cyclone 41 is greater than the inlet flow of the amine liquid at the inlet 117, execute S3; if the outlet flow of the first cyclone 41 is less than or equal to the inlet flow of the amine liquid at the inlet 117, execute S4;

[0057] Among them, when the pressure difference inside the desulfurization tower 1 is too large, the liquid blocking phenomenon will occur, affecting the stable operation of the desulfurization tower 1. When the pressure difference inside the tower is too small, the desulfurization efficiency will be affected. Therefore, it is very important to ensure the stability of the pressure difference inside the desulfurization tower 1. In this embodiment, the pressure difference inside the tower is adjusted by adjusting the salt slurry flow rate flowing out of the desulfurization tower 1 to ensure that the pressure difference inside the desulfurization tower 1 can be kept stable during the automatic salt discharge process.

[0058] S3: Adjust the replenishing and returning liquid valve 46 to connect the replenishing pump 47 with the first feed pump 45. Start the replenishing pump 47, close the returning liquid pump 471, and the amine liquid supplement tank 4 supplements amine liquid to the amine liquid inlet 117;

[0059] S4: Adjust the replenishing and returning liquid valve 46 to connect the returning liquid pump 471 with the first feed pump 45. Close the replenishing pump 47, start the returning liquid pump 471, and the excess amine liquid in front of the amine liquid inlet 117 returns to the amine liquid supplement tank 4;

[0060] S5: Close the first cyclone 41, start the second cyclone 411. The high-salt amine liquid flows out from the bottom of the second cyclone 411 and enters the second reactor 431 for desalting reaction. Start the first feed pump 45, and the amine liquid in the first buffer tank 44 returns to the bottom of the desulfurization tower 1. The second effluent flowmeter 421 and the feed flowmeter 48 respectively monitor the outlet flow of the second cyclone 411 and the inlet flow of the amine liquid at the inlet 117 of the amine liquid. If the outlet flow of the second cyclone 411 is greater than the inlet flow of the amine liquid at the inlet 117, execute S6; if the outlet flow of the second cyclone 411 is less than or equal to the inlet flow of the amine liquid at the inlet 117, execute S7;

[0061] S6: Adjust the replenishing and returning liquid valve 46 to connect the replenishing pump 47 with the second feed pump 451. Start the replenishing pump 47, close the returning liquid pump 471, and the amine liquid supplement tank 4 supplements amine liquid to the amine liquid inlet 117;

[0062] S7: Adjust the replenishing and returning liquid valve 46 to connect the returning liquid pump 471 with the second feed pump 451. Close the replenishing pump 47, start the returning liquid pump 471, and the excess amine liquid in front of the amine liquid inlet 117 returns to the amine liquid supplement tank 4;

[0063] Among them, in order to ensure that the desulfurization reaction in the desulfurization tower 1 can still operate normally during the automatic salt discharge process, it is required that the inlet and outlet flows at the bottom of the desulfurization tower 1 are approximately the same. By alternately executing S2 and S5, the desulfurization tower 1 can continuously carry out the salt slurry discharge, desalination reaction, and amine liquid inlet process. At the same time, the amine liquid supplement tank 4 is used to supplement or recover amine liquid for the amine liquid inlet 117, ensuring the balance of the inlet and outlet flows at the bottom of the desulfurization tower 1.

[0064] S8: The rich amine liquid flows into the amine liquid regeneration device from the bottom of the desulfurization tower 1 and returns to the desulfurization tower 1 after regeneration. The hydrocarbon gas flashed during the process of treating the amine liquid by the amine liquid regeneration device enters the gas storage tank 7. The desulfurized gas enters the amine absorber 14 from the top of the desulfurization tower 1 to remove the small amount of amine liquid carried, and then enters the dehydration device for dehydration treatment. The dehydration tower 1 and the dehydration tower 2 31 in the dehydration device alternately carry out the dehydration and regeneration processes. When the desulfurized gas enters the dehydration tower 1 for dehydration treatment, the dehydration tower 2 31 is regenerated through the molecular sieve regeneration device; after the regeneration treatment of the dehydration tower 2 31 is completed, the desulfurized gas enters the dehydration tower 2 31 for dehydration treatment, and the dehydration tower 1 is regenerated.

[0065] S9: The cold regenerated gas is pressurized by the compressor 5 and then enters the regenerated gas heat exchanger 51 for heat exchange and temperature rise. The first-stage reversing valve 54 and the second-stage reversing valve 55 are adjusted to gradually heat up the molecular sieve. The heating process passes through the low-temperature stage, medium-temperature stage, and high-temperature stage respectively;

[0066] In the low-temperature stage, the valve core of the first-stage reversing valve 54 is adjusted to the left position, the first-stage air inlet is communicated with the first air outlet, the valve core of the second-stage reversing valve 55 is adjusted to the left position, the second-stage air inlet is communicated with the third air outlet, and the low-temperature regenerated gas heated by the regenerated gas heat exchanger 51 enters the dehydration tower 1 or the dehydration tower 2 31, and the temperature of the molecular sieve in the tower rises to desorb the free water on the surface and in the macropores of the molecular sieve;

[0067] In the medium-temperature stage, the valve core of the first-stage reversing valve 54 is adjusted to the right position, the first-stage air inlet is communicated with the second air outlet, the low-temperature regenerated gas heated by the regenerated gas heat exchanger 51 enters the first-stage heater 52 for further heating to obtain medium-temperature regenerated gas, and the medium-temperature regenerated gas enters the dehydration tower 1 or the dehydration tower 2 31, so that the temperature of the molecular sieve in the tower further rises until the bound water in the micropores of the molecular sieve is desorbed;

[0068] In the high-temperature stage, the spool of the secondary reversing valve 55 is adjusted to the right position, and the secondary air inlet is communicated with the fourth air outlet. The low-temperature regenerated gas that has been heated through heat exchange in the regenerated gas heat exchanger 51 enters the primary heater 52 and the secondary heater 53 in sequence to be further heated to obtain high-temperature regenerated gas. The high-temperature regenerated gas enters the first dehydration tower 3 or the second dehydration tower 31, so that the temperature of the molecular sieve in the tower is further increased until the residual moisture in the molecular sieve is fully desorbed. At the same time, the residual sulfur components that have not been removed by the desulfurization device in the molecular sieve are desorbed together;

[0069] Among them, by adjusting the primary reversing valve 54 and the secondary reversing valve 55, the number of heaters participating in the heating of the regenerated gas is adjusted, and the molecular sieve is subjected to stepped heating in three different temperature-rising stages, which can reduce the thermal stress damage during the thermal regeneration of the molecular sieve, extend the service life of the molecular sieve, and also reduce the energy consumption when heating the regenerated gas.

[0070] S10: The regenerated gas after heat exchange with the molecular sieve enters the regenerated gas heat exchanger 51 for heat exchange and cooling, and then enters the water separator 57 after further cooling by the cooler 56. The water separator 57 separates the moisture and the desorbed sulfur carried in the regenerated gas to obtain cold regenerated gas. The cold regenerated gas returns to the inlet end of the compressor 5 again, and the desorbed sulfur and the sulfur-containing components in the sulfur storage tank 23 enter the sulfur recovery device 6 for recovery treatment together;

[0071] S11: The desulfurized gas undergoes dehydration treatment to obtain dry natural gas. The dry natural gas enters the gas storage tank 7 and enters the liquefaction device 8 together with the hydrocarbon gas flashed out in the amine liquid regeneration device for natural gas liquefaction treatment, and finally obtains liquefied natural gas.

[0072] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A dehydration and desulfurization treatment system for liquefied natural gas, characterized in that: It comprises a desulfurization device, a dehydration device and an automatic salt discharge device, wherein the desulfurization device is connected to the dehydration device, the automatic salt discharge device is connected to the desulfurization device, the automatic salt discharge device comprises a cyclone 1 (41) and a cyclone 2 (411) which work in a time sequence alternating manner, the dehydration device comprises a molecular sieve regeneration device, the molecular sieve regeneration device comprises a regeneration gas heat exchanger (51), a primary heater (52) and a secondary heater (53), and the regeneration gas heat exchanger (51), the primary heater (52) and the secondary heater (53) are connected in series step by step; The desulfurization device comprises a desulfurization tower (1), wherein the desulfurization tower (1) comprises a tower body (11) and a filter membrane (116), wherein the filter membrane (116) is arranged at the bottom of the tower body (11), and the filter membrane (116) divides the bottom of the tower body (11) into a high-salt amine liquid area and a low-salt amine liquid area, wherein a cyclone 1 (41) and a cyclone 2 (411) are respectively arranged on two sides outside the tower body (11), wherein the inlets of the cyclone 1 (41) and the cyclone 2 (411) are both connected to the high-salt amine liquid area above the filter membrane (116), and the upper overflow ports of the cyclone 1 (41) and the cyclone 2 (411) are both connected to the low-salt amine liquid area below the filter membrane (116), and the desulfurization tower (1) is provided with an amine liquid inlet (117) on the side of the low-salt amine liquid area; The automatic salt discharge device further comprises a reactor 1 (43), a reactor 2 (431) and a liquid inlet flowmeter (48); the inlets of the reactor 1 (43) and the reactor 2 (431) are respectively connected to the bottom outlets of the cyclone 1 (41) and the cyclone 2 (411); a liquid outlet flowmeter 1 (42) is arranged on the connecting pipe between the cyclone 1 (41) and the reactor 1 (43); a liquid outlet flowmeter 2 (421) is arranged on the connecting pipe between the cyclone 2 (411) and the reactor 2 (431); the outlets of the reactor 1 (43) and the reactor 2 (431) are respectively connected to a liquid inlet pump 1 (45) and a liquid inlet pump 2 (451); the outlets of the liquid inlet pump 1 (45) and the liquid inlet pump 2 (451) are both connected to the amine liquid inlet (117); and the liquid inlet flowmeter (48) is arranged on the connecting pipe of the amine liquid inlet (117); The automatic salt discharge device also includes an amine liquid replenishing tank (4) and a replenishing and returning liquid valve (46), wherein the amine liquid replenishing tank (4) is respectively connected to a replenishing pump (47) and a returning liquid pump (471), and the replenishing and returning liquid valve (46) includes a replenishing port, a returning liquid port, a first liquid inlet, and a second liquid inlet, wherein the replenishing port is connected to the outlet of the replenishing pump (47), the returning liquid port is connected to the inlet of the returning liquid pump (471), the first liquid inlet is connected to the first liquid inlet pump (45), and the second liquid inlet is connected to the second liquid inlet pump (451); The molecular sieve regeneration device further comprises a primary reversing valve (54) and a secondary reversing valve (55), wherein the primary reversing valve (54) comprises a primary air inlet, a first air outlet and a second air outlet, wherein the primary air inlet is in communication with the outlet end of the heating side of the regeneration gas heat exchanger (51), and the second air outlet is in communication with the inlet of the primary heater (52), and the secondary reversing valve (55) comprises a secondary air inlet, a third air outlet and a fourth air outlet, wherein the secondary air inlet is in communication with the outlet of the primary heater (52), and the fourth air outlet is in communication with the inlet of the secondary heater (53); The outlets of reactor 1 (43) and reactor 2 (431) are connected to buffer tank 1 (44) and buffer tank 2 (441) respectively, and the outlets of buffer tank 1 (44) and buffer tank 2 (441) are connected to liquid inlet pump 1 (45) and liquid inlet pump 2 (451).

2. A liquefied natural gas dehydration and desulfurization treatment system according to claim 1, characterized in that: The desulfurization tower (1) further comprises a lean liquid distributor (111), a swirl plate (112), a scraper (113) and an agitator (114). The agitator (114) is arranged in a high-salt amine liquid area. The agitator (114) is rotatably connected to the bottom of the tower body (11). The lean liquid distributor (111) is installed in the tower body (11). The lean liquid distributor (111) is provided with multiple layers from bottom to top. The swirl plate (112) is installed below each layer of the lean liquid distributor (111). The scraper (113) is symmetrically installed on the upper and lower sides of the swirl plate (112). Multiple scrapers (113) are evenly arranged on each side along the circumference of the tower body (11). The scraper (113) is rotatably connected to the middle of the swirl plate (112) through a connecting rod. The scraper (113) abuts against the inner wall of the tower body (11).

3. A liquefied natural gas dehydration and desulfurization treatment system according to claim 2, characterized in that: The dehydration device further comprises a dehydration tower 1 (3) and a dehydration tower 2 (31); the bottom inlets of the dehydration tower 1 (3) and the dehydration tower 2 (31) are respectively connected to the first air outlet, the third air outlet and the outlet of the secondary heater (53); the top outlets of the dehydration tower 1 (3) and the dehydration tower 2 (31) are connected to the cooling side inlet of the regeneration gas heat exchanger (51); the heating side inlet of the regeneration gas heat exchanger (51) is connected to the compressor (5); the cooling side outlet of the regeneration gas heat exchanger (51) is connected to the cooler (56); the outlet of the cooler (56) is connected to the water separator (57); the outlet of the water separator (57) is connected to the inlet of the compressor (5).

4. A liquefied natural gas dehydration and desulfurization treatment system according to claim 3, characterized in that: The desulfurization device further comprises an amine liquid regeneration device, the amine liquid regeneration device comprising a flash device (12), a lean-rich liquid heat exchanger (13) and a regeneration tower (2), the bottom outlet of the desulfurization tower (1) being connected to the inlet of the flash device (12), the bottom outlet of the flash device (12) being connected to the inlet end of the lean-rich liquid heat exchanger (13), the outlet end of the lean-rich liquid heat exchanger (13) being connected to the upper inlet of the regeneration tower (2), the bottom outlet of the regeneration tower (2) being connected to the lean-rich liquid heat exchanger (13), the outlet end of the lean-rich liquid heat exchanger (13) being connected to a regeneration pump (24), and the outlet end of the regeneration pump (24) being connected to the upper part of the desulfurization tower (1).

5. A liquefied natural gas dehydration and desulfurization treatment system according to claim 4, characterized in that: The top inlets of the dehydration tower 1 (3) and the dehydration tower 2 (31) are both connected to the top outlet of the desulfurization tower (1), the bottom outlets of the dehydration tower 1 (3) and the dehydration tower 2 (31) are connected to a gas storage tank (7), and the outlet of the gas storage tank (7) is connected to a liquefaction device (8).

6. A method for dehydration and desulfurization of liquefied natural gas, applied to the dehydration and desulfurization system for liquefied natural gas according to claim 5, characterized in that: The steps include: S1: The raw gas enters the desulfurization tower (1) and contacts with the lean amine liquid sprayed from top to bottom in the tower in countercurrent to undergo a desulfurization reaction to remove the sulfur components to obtain desulfurized gas. The lean amine liquid that adsorbs the sulfur components is converted into rich amine liquid. The secondary salts produced by the desulfurization reaction and the rich amine liquid gather in the high-salt amine liquid area to form a high-salt amine liquid. During the desulfurization process, S2 and S5 are performed alternately; S2: Close cyclone 2 (411), start cyclone 1 (41), high-salt amine liquid passes through cyclone 1 (41) and enters reactor 1 (43) for desalination reaction, start inlet pump 2 (451), low-salt amine liquid in buffer tank 2 (441) returns to the bottom of desulfurization tower (1), outlet flow meter 1 (42) and inlet flow meter (48) monitor the outlet flow of cyclone 1 (41) and the inlet flow of amine liquid inlet (117) respectively. If the outlet flow of cyclone 1 (41) is greater than the inlet flow of amine liquid inlet (117), execute S3; if the outlet flow of cyclone 1 (41) is less than or equal to the inlet flow of amine liquid inlet (117), execute S4; S3: the liquid replenishment valve (46) is adjusted to connect the liquid replenishment pump (47) to the liquid inlet pump 1 (45), the liquid replenishment pump (47) is started, the liquid return pump (471) is closed, and the amine liquid replenishment tank (4) replenishes amine liquid to the amine liquid inlet (117); S4: the liquid return valve (46) is adjusted to connect the liquid return pump (471) with the liquid inlet pump 1 (45), the liquid replenishment pump (47) is closed, the liquid return pump (471) is started, and the excess amine liquid in front of the amine liquid inlet (117) is returned to the amine liquid replenishment tank (4); S5: close the cyclone 1 (41), start the cyclone 2 (411), the high-salt amine liquid passes through the cyclone 2 (411) and enters the reactor 2 (431) for desalination reaction, start the liquid inlet pump 1 (45), and the amine liquid in the buffer tank 1 (44) returns to the bottom of the desulfurization tower (1), and the outlet flow meter 2 (421) and the inlet flow meter (48) respectively monitor the outlet flow of the cyclone 2 (411) and the inlet flow of the amine liquid inlet (117). If the outlet flow of the cyclone 2 (411) is greater than the inlet flow of the amine liquid inlet (117), execute S6; if the outlet flow of the cyclone 2 (411) is less than or equal to the inlet flow of the amine liquid inlet (117), execute S7; S6: the liquid replenishment valve (46) is adjusted to connect the liquid replenishment pump (47) with the second liquid inlet pump (451), the liquid replenishment pump (47) is started, the liquid return pump (471) is closed, and the amine liquid replenishment tank (4) replenishes amine liquid to the amine liquid inlet (117); S7: the liquid replenishment valve (46) is adjusted to connect the liquid return pump (471) with the second liquid inlet pump (451), the liquid replenishment pump (47) is closed, the liquid return pump (471) is started, and the excess amine liquid in front of the amine liquid inlet (117) is returned to the amine liquid replenishment tank (4); S8: The rich amine liquid flows from the bottom of the desulfurization tower (1) into the amine liquid regeneration device for regeneration and then returns to the desulfurization tower (1). The desulfurized gas enters the dehydration device for dehydration. The dehydration tower 1 (3) and the dehydration tower 2 (31) in the dehydration device perform dehydration and regeneration processes alternately. S9: After being pressurized by the compressor (5), the cold regeneration gas enters the regeneration gas heat exchanger (51) for heat exchange and temperature increase to obtain low-temperature regeneration gas. The primary reversing valve (54) and the secondary reversing valve (55) are adjusted to gradually increase the temperature of the molecular sieve. The temperature increase process goes through a low-temperature stage, a medium-temperature stage and a high-temperature stage respectively. S10: the regeneration gas after heat exchange with the molecular sieve enters the regeneration gas heat exchanger (51) for heat exchange and cooling, and then enters the water separator (57) for further cooling to obtain cold regeneration gas. The cold regeneration gas returns to the inlet end of the compressor (5) again; S11: After dehydration, the desulfurized gas is dehydrated to obtain dry natural gas, which enters the gas storage tank (7) and then enters the liquefaction device (8) for natural gas liquefaction treatment to finally obtain liquefied natural gas.

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