A recirculating clean natural gas processing system

Abstract

The application discloses a kind of recyclable purification natural gas processing system, belong to natural gas processing technical field, including natural gas purification system and natural gas liquefaction system, in natural gas purification system, MDEA removes acid unit to raw material natural gas and removes acid gas, molecular sieve dehydration unit is equipped with two dry towers, molecular sieve bed is equipped in tower and the predehydration unit of bottom, predehydration unit realizes preliminary dehydration, residual acid gas can also be removed, circulating gas compressor can be returned MDEA removes acid unit recycling purification after the natural gas of not meeting standard or the natural gas of load when needing to adjust is pressurized, in natural gas liquefaction system, liquefied cold box is liquefied to the natural gas after purification, refrigerant compression unit provides cold source for liquefaction and can form circulation with molecular sieve dehydration unit to assist driving replacement, system realizes automatic control by process control valve and DCS system, guarantee continuous operation, improve energy utilization efficiency, purification effect and working condition adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas processing, and more particularly to a recyclable purification natural gas processing system. BACKGROUND

[0002] In the face of the continuous growth of energy demand, natural gas, as a clean and efficient energy, its purification and liquefaction technology in the process of processing and utilization is concerned. Natural gas raw materials usually contain acid gases (such as hydrogen sulfide, carbon dioxide, etc.) and moisture. If these impurities are not effectively removed, they will cause corrosion to the subsequent processing equipment, reduce the service life of the equipment, and also affect the liquefaction efficiency of natural gas and product quality, so the natural gas purification system is a key link in the natural gas processing process.

[0003] At present, the deacidification technology commonly used in the industry is mainly based on the alcohol amine method, among which MDEA (N-methyl diethanolamine) is widely used in MDEA deacidification unit due to its high selectivity and low energy consumption. However, in the existing MDEA deacidification unit, the temperature of the gas at the top of the absorption tower is still high after being cooled by the air cooler, which leads to a larger humidity of the gas to be treated in the subsequent dehydration unit, not only increasing the dehydration load of the dehydration unit, but also making the dehydration tower size larger, and the heat load of the dehydration regeneration gas also increases accordingly, causing energy waste and being not conducive to the improvement of the overall energy efficiency of the system.

[0004] In the dehydration link, the molecular sieve dehydration unit is the mainstream choice, which has the advantages of high dehydration efficiency and can reduce the water dew point of natural gas to a low level, meeting the strict requirements of natural gas liquefaction on water content. However, the existing molecular sieve dehydration unit has many problems in actual operation. On the one hand, a small amount of acid gases may still remain in the natural gas after being treated by the MDEA deacidification unit, which will react with the molecular sieve, affecting the dehydration performance and service life of the molecular sieve, and increasing the difficulty of molecular sieve regeneration; on the other hand, the humidity of the deacidified natural gas is usually high, and a large amount of water directly enters the molecular sieve drying tower, which greatly increases the dehydration burden of the molecular sieve, leading to an increase in the regeneration frequency of the molecular sieve, an increase in the energy consumption in the regeneration process, and a decrease in the overall purification efficiency of the system.

[0005] In addition, the lack of synergy between the natural gas liquefaction system and the purification system is also a pain point faced by the current industry. During the liquefaction process, the LNG loading unit will produce BOG (boil-off gas). If these BOGs are not reasonably utilized, direct emission will not only cause energy waste, but also have a certain impact on the environment. At the same time, during the displacement process before the start of the refrigerant compression unit, a large amount of displacement gas (such as nitrogen, natural gas, etc.) needs to be consumed, the displacement time is relatively long, which affects the production efficiency of the equipment, and the control of the refrigerant circulation amount lacks linkage with the purification system, making it difficult to dynamically adjust according to the change of the natural gas flow at the outlet of the purification system, resulting in high overall energy consumption of the system and poor adaptability to working condition fluctuations. SUMMARY

[0006] The purpose of the present application is to provide a recyclable purified natural gas processing system to solve the above problems.

[0007] In order to achieve the above-mentioned purpose, the technical scheme provided by an embodiment of the present application is as follows:

[0008] A recyclable purified natural gas processing system, comprising a natural gas purification system and a natural gas liquefaction system, the natural gas purification system comprising a tower top cooler, an MDEA acid removal unit, a molecular sieve dehydration unit and a circulating gas compressor;

[0009] The molecular sieve dehydration unit comprises two drying towers, a molecular sieve bed is installed in the middle of the drying tower, a cooling water jacket is arranged at the bottom of the side of the drying tower, a pre-dehydration unit is installed at the bottom of the drying tower, and the pre-dehydration unit is located below the molecular sieve bed;

[0010] The pre-dehydration unit comprises a shunt column fixedly installed at the bottom of the drying tower, an electromagnet module is integrated at the center of the shunt column, a plurality of groups of condensing columns arranged in a ring array are fixedly connected between the shunt column and the molecular sieve bed, and a matching composite scraping ring is slidably installed on the condensing column.

[0011] As a further improvement of the present application, the MDEA acid removal unit inlet is connected with the raw natural gas, the MDEA acid removal unit outlet is connected with the molecular sieve dehydration unit inlet, the molecular sieve dehydration unit outlet is connected with the circulating gas compressor inlet, and the circulating gas compressor outlet is connected with the MDEA acid removal unit inlet, to complete the circulation of the natural gas purification system.

[0012] As a further improvement of the present application, the shell side inlet of the tower top cooler is connected with the outlet of the overhead air cooler in the MDEA acid removal unit, and the shell side outlet of the tower top cooler is connected with the inlet of the overhead separator in the MDEA acid removal unit.

[0013] As a further improvement of the present application, the condensing column comprises an outer condensing layer, an inner cooling water pipe is inlaidly installed inside the outer condensing layer, and the inner cooling water pipe is connected with the cooling water jacket and extends to the inside of the cooling water jacket, and a plurality of annularly arrayed condensing fins are fixedly connected to the outer surface of the outer condensing layer.

[0014] As a further improvement of the present application, the composite scraping ring comprises a moving ring, an annular scraping strip matched with the condensing column is fixedly installed inside the moving ring, and an inner reinforcing rib is inlaidly installed inside the annular scraping strip.

[0015] As a further improvement of the present application, annular magnetic sheets are fixedly connected to the front and rear ends of the moving ring, and protective patches are covered on the outer surfaces of the annular magnetic sheets.

[0016] As a further improvement of the present application, the moving ring is of a ring-shaped hollow structure, and is filled with a solid amine adsorbent, and a plurality of uniformly distributed air-permeable micropores are formed in the outer surface of the moving ring.

[0017] As a further improvement of the present application, the molecular sieve dehydration unit further comprises a regeneration gas heater, a regeneration gas cooler, a regeneration gas separator and a condensed water recovery device.

[0018] As a further improvement of the present application, a bypass adjustment pipeline is arranged between the outlet of the molecular sieve dehydration unit and the inlet of the MDEA deacidification unit, and when the natural gas purified by the natural gas purification system is substandard or the load of the natural gas purification system needs to be adjusted, the natural gas at the outlet of the molecular sieve dehydration unit is pressurized by the circulating gas compressor and then returned to the inlet of the MDEA deacidification unit to realize circulation.

[0019] As a further improvement of the present application, the natural gas liquefaction system comprises a liquefaction cold box, a refrigerant compression unit, an LNG loading unit and a vaporizer.

[0020] The inlet of the liquefaction cold box is connected with the outlet of the molecular sieve dehydration unit, and the outlet of the liquefaction cold box is divided into two routes, one of which is connected with the refrigerant compression unit, and the other of which is connected with the LNG loading unit.

[0021] The outlet of the refrigerant compression unit is also divided into two routes, one of which is connected with the inlet of the molecular sieve dehydration unit, returns to the inlet of the refrigerant compression unit after passing through the molecular sieve dehydration unit to form a circulation, and the other of which is connected with the liquefaction cold box.

[0022] The BOG outlet of the LNG loading unit is divided into two routes, one of which is connected with the inlet of the vaporizer, and the other of which is connected with the inlet of the tube side of the overhead cooler, and the outlet of the overhead cooler goes to the fuel gas unit, and the outlet of the vaporizer also goes to the fuel gas unit.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] (1) The present application realizes the cascade utilization and recovery of energy through multiple structure design. In the MDEA deacidification unit, the lean-liquid and rich-liquid heat exchanger exchanges heat by using the temperature difference between the rich-liquid and the lean-liquid, reducing the heat source consumption of the reboiler. The overhead cooler uses the low-temperature BOG generated by the LNG loading unit as a cold source to cool the overhead gas of the absorption tower, replacing the traditional additional cold source, and at the same time, recovering the cold energy of the BOG. The bypass adjustment pipeline of the refrigerant compression unit is automatically controlled by the DCS system according to the natural gas flow, avoiding the waste of refrigerant cold energy. In addition, the BOG is sent to the fuel gas unit after being treated by the overhead cooler or vaporizer, realizing the energy recovery of the BOG, reducing energy waste and emissions, and reducing the overall energy consumption of the device.

[0025] (2) The present application adds a pre-dehydration unit to the molecular sieve dehydration unit, which preliminarily removes water by condensation in the condensation column, and improves the pre-dehydration effect by reciprocating scraping and turbulence of the composite scraping ring. At the same time, the solid amine adsorbent adsorbs the residual acid gas, avoiding damage to the molecular sieve bed, reducing the dehydration and regeneration burden of the molecular sieve, and prolonging the service life of the molecular sieve. The overhead cooler in the MDEA deacidification unit cools the overhead gas to below 40℃, further reducing the load of the molecular sieve dehydration unit, reducing the size of the drying tower and the heat load of the regeneration gas, ensuring that the off-spec natural gas is re-purified by the circulating gas compressor, ensuring the quality of the final product, and improving the purification efficiency and equipment operation stability of the system as a whole.

[0026] (3) The present application realizes multi-unit linkage control through the DCS system, and automatically switches the program-controlled valve to complete the continuous operation of the molecular sieve dehydration unit. The refrigerant bypass adjustment valve adjusts the cold energy according to the natural gas flow, and the BOG flow adjustment valve distributes the flow according to the overhead cooling demand. Each unit no longer operates independently, forming an efficient and collaborative whole. The circulating branch of the refrigerant compression unit and the molecular sieve dehydration unit shortens the equipment start-up displacement time, and the circulating process of the circulating gas compressor adapts to changes in system load, reducing the waste of natural gas during the start-up and commissioning phase. These designs enable the system to flexibly respond to fluctuations in raw material gas composition, load changes and other operating conditions, expand the process adaptation range, and improve the flexibility and reliability of system operation. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The system flow chart of the present application;

[0028] Figure 2 The structure diagram of the drying tower of the present application;

[0029] Figure 3 The partial sectional view of the drying tower of the present application;

[0030] Figure 4 The structure diagram of the condensation column of the present application;

[0031] Figure 5Structure diagram of the composite scraping ring of the application;

[0032] Figure 6 Structure diagram of the composite scraping ring of the application.

[0033] The figure marks represent:

[0034] 1, overhead cooler; 2, MDEA acid removal unit; 3, molecular sieve dehydration unit; 31, drying tower; 32, molecular sieve bed; 33, cooling water jacket; 4, circulating gas compressor; 5, liquefaction cold box; 6, refrigerant compression unit; 7, LNG loading unit; 8, vaporizer; 9, pre-dehydration unit; 91, split column; 92, electromagnet module; 93, condensing column; 931, outer condensing layer; 932, inner cooling water pipe; 933, condensing fin; 94, composite scraping ring; 941, moving ring; 942, annular scraping strip; 943, inner reinforcing rib; 944, annular magnetic sheet; 945, protective patch; 946, air-permeable micropore; 947, solid amine adsorbent. DETAILED DESCRIPTION

[0035] The technical solutions of the application will be described clearly and completely below in combination with the drawings of the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the application.

[0036] Embodiment 1:

[0037] Please refer to Figure 1 A recyclable natural gas purification processing system, comprising a natural gas purification system and a natural gas liquefaction system, the natural gas purification system comprising an overhead cooler 1, an MDEA acid removal unit 2, a molecular sieve dehydration unit 3 and a circulating gas compressor 4; the MDEA acid removal unit 2 is connected with raw natural gas at the inlet, the outlet of the MDEA acid removal unit 2 is connected with the inlet of the molecular sieve dehydration unit 3, the outlet of the molecular sieve dehydration unit 3 is connected with the inlet of the circulating gas compressor 4, the outlet of the circulating gas compressor 4 is connected with the inlet of the MDEA acid removal unit 2, to complete the circulation of the natural gas purification system; the shell inlet of the overhead cooler 1 is connected with the outlet of the overhead air cooler in the MDEA acid removal unit 2, and the shell outlet of the overhead cooler 1 is connected with the inlet of the overhead separator in the MDEA acid removal unit 2.

[0038] The overhead cooler 1 is arranged after the overhead air cooler in the MDEA acid removal unit 2, to cool the overhead gas of the absorption tower to below 40℃, reduce the dehydration load of the dehydration unit, reduce the size of the dehydration tower, reduce the heat load of the dehydration regeneration gas, and realize comprehensive utilization of energy.

[0039] The internal connection of the MDEA acid removal unit 2 is as follows:

[0040] The natural gas flow path: the raw gas is heated by the raw gas heat exchanger, and then enters the absorption tower from bottom to top, and is contacted with the MDEA lean liquid from top to bottom to remove the acid gas in the raw gas. The raw gas after the acid removal is cooled by the raw gas heat exchanger, and then enters the top air cooler to be cooled to about 45℃, and then is further cooled by the top cooler, and then enters the top gas-liquid separator of the absorption tower to separate and remove the entrained liquid phase. The liquid phase is depressurized by the pressure reducing valve and sent to the amine solution regeneration process. The gas from the top gas-liquid separator of the absorption tower is sent to the subsequent molecular sieve dehydration unit 3.

[0041] MDEA solution circulation regeneration: the MDEA solution rich liquid from the bottom of the absorption tower, which has absorbed acid gas, is first heat exchanged with the solution lean liquid from the bottom of the regeneration tower in the lean- rich liquid heat exchanger, and then enters the upper part of the regeneration tower after being heated. The solution is sprayed into the tower body and is regenerated by stripping in the regeneration tower until the lean degree of the lean liquid reaches the standard. The reboiler of the regeneration tower is provided with a heat source by a heat conducting oil, and the lower part of the regeneration tower is operated at 110-120℃ to ensure complete desorption and regeneration of the MDEA rich liquid. The lean liquid after regeneration is cooled by the lean-rich liquid heat exchanger after being discharged from the bottom of the regeneration tower, and then is pressurized by the lean liquid circulating pump, and then is further cooled by the lean liquid cooler to return to the upper part of the absorption tower to complete the MDEA solution circulation regeneration process.

[0042] A bypass adjustment pipeline is arranged between the outlet of the molecular sieve dehydration unit 3 and the inlet of the MDEA acid removal unit 2. When the natural gas from the natural gas purification system does not meet the standard or the load of the natural gas purification system needs to be adjusted, the natural gas from the outlet of the molecular sieve dehydration unit 3 is pressurized by the circulating gas compressor 4 and then returned to the inlet of the MDEA acid removal unit 2 to realize circulation.

[0043] The bypass adjustment pipeline can reduce the waste of natural gas and realize comprehensive utilization of resources during equipment commissioning and debugging.

[0044] The natural gas liquefaction system includes a liquefaction cold box 5, a refrigerant compression unit 6, an LNG loading unit 7 and a vaporizer 8. The inlet of the liquefaction cold box 5 is connected with the outlet of the molecular sieve dehydration unit 3. The outlet of the liquefaction cold box 5 is divided into two paths, one of which is connected with the refrigerant compression unit, and the other of which is connected with the LNG loading unit 7. The outlet of the refrigerant compression unit 6 is also divided into two paths, one of which is connected with the inlet of the molecular sieve dehydration unit 3, and the other of which is connected with the liquefaction cold box 5. The BOG outlet of the LNG loading unit 7 is also divided into two paths, one of which is connected with the inlet of the vaporizer 8, and the other of which is connected with the inlet of the tube side of the top cooler 1. The outlet of the top cooler 1 is sent to the fuel gas unit, and the outlet of the vaporizer 8 is also sent to the fuel gas unit.

[0045] A bypass regulating pipeline is arranged between the inlet and outlet of the refrigerant circulation unit 6 in the natural gas liquefaction system, the refrigerant circulation amount is controlled by a regulating valve, the refrigerant cold energy waste is reduced, the comprehensive utilization of energy is realized, and the device energy consumption is reduced.

[0046] The regulating valve in the refrigerant bypass is controlled by a DCS system, the refrigerant circulation amount is automatically controlled according to the natural gas flow at the outlet of the natural gas purification system, the natural gas purification system and the liquefaction system are cooperatively linked, the device energy consumption is reduced, and the adaptability of the processing process to the working condition fluctuation is improved.

[0047] The refrigerant compression unit 6 and the molecular sieve dehydration unit 3 are connected by a pipeline to form a circulation, before the equipment is started, the refrigerant compressor unit 6 is replaced at the water dew point, the use amount of replacement gas such as nitrogen and natural gas is reduced, a dry replacement gas-swept replacement gas dehydration-dry replacement gas circulation process is realized, the replacement gas sweeping dew point time is reduced, the liquefaction equipment production time is accelerated, the natural gas purification system and the natural gas liquefaction system are coupled, and the cooperative efficiency between the equipment is improved.

[0048] The low-temperature BOG in the LNG loading unit 7 goes to the inlet of the tube side of the overhead cooler 1, provides a cold source for the overhead gas cooling of the MDEA deacidification unit 2, and then goes out from the outlet of the tube side of the overhead cooler 1 to the fuel gas unit. This process recovers the low-temperature BOG cold energy, improves the comprehensive utilization of energy, reduces the dehydration load of the dehydration unit, reduces the dehydration tower size, and reduces the dehydration regeneration gas heat load.

[0049] The BOG in the LNG loading unit 7 is also provided with a path to the vaporizer 8. When the overhead cooling of the absorption tower in the MDEA deacidification unit 2 does not require an additional cold source, the low-temperature BOG goes to the vaporizer 8 after being reheated by a control valve, and then goes to the fuel gas unit. The control valve is controlled by a DCS system, and the required cold energy of the overhead gas in the MDEA deacidification unit 2 is adjusted according to the feedback signal of the pre-cooled natural gas temperature sensor, the flow of the BOG in the LNG loading unit 7 in the two paths is adjusted, the applicability and stability of the device are realized.

[0050] Example 2:

[0051] Please refer to Figures 2-3 The molecular sieve dehydration unit 3 includes two drying towers 31, a molecular sieve bed 32 is installed in the middle of the drying tower 31, a cooling water jacket 33 is arranged at the bottom of the side of the drying tower 31, a pre-dehydration unit 9 is installed at the bottom of the drying tower 31, and the pre-dehydration unit 9 is located below the molecular sieve bed 32.

[0052] The tower body of the drying tower 31 is made of stainless steel, which has good corrosion resistance and strength, and can withstand the pressure and temperature changes in the natural gas processing process. A molecular sieve bed 32 is installed in the middle of the drying tower 31, which is filled with 3A molecular sieve. The 3A molecular sieve has the characteristics of small pore size and strong selective adsorption capacity for water molecules, and can efficiently remove water from natural gas. The side of the drying tower 31 is provided with a cooling water jacket 33, which is made of carbon steel and internally passes cooling water to cool the bottom of the drying tower 31 and provide favorable conditions for the subsequent condensation process of the condensation column 93. The bottom of the drying tower 31 is provided with a pre-dehydration unit 9, which is located below the molecular sieve bed 32. The pre-dehydration unit 9 is used to preliminarily dehydrate and remove residual acid gas from the natural gas before it enters the molecular sieve bed 32, thereby reducing the load of the molecular sieve bed 32.

[0053] The pre-dehydration unit 9 includes a flow dividing column 91 fixedly installed at the bottom of the drying tower 31, an electromagnet module 92 integrated at the center of the flow dividing column 91, a plurality of groups of condensation columns 93 arranged in a ring array and fixedly connected between the flow dividing column 91 and the molecular sieve bed 32, and a matching composite scraper ring 94 slidably installed on the condensation column 93.

[0054] The flow dividing column 91 is made of stainless steel and its surface is polished to reduce resistance during the flow of natural gas and prevent corrosion of the flow dividing column 91 by impurities in the natural gas. The flow dividing column 91 is used to divide the natural gas entering from the bottom of the drying tower 31 to the edge of the side, so that the natural gas can uniformly contact the subsequent condensation column 93.

[0055] The electromagnet module 92 includes a core and a coil wound on the core. The core is made of silicon steel sheet with high magnetic permeability, and the coil is made of copper wire. The copper wire has good electrical conductivity and can reduce energy consumption when current passes through. The electromagnet module 92 is powered by a direct current power supply, which provides stable direct current power from the system's direct current power cabinet. The power supply voltage is set according to the power requirement of the electromagnet module 92, usually 24V or 48V. The control mode is automatically controlled by the DCS distributed control system. The DCS system periodically controls the power-on and power-off of the electromagnet module 92 according to the preset program, so that the electromagnet module 92 generates a periodically changing magnetic field, which exerts repulsive and attractive forces on the composite scraper ring 94, and realizes the reciprocating movement of the composite scraper ring 94 on the condensation column 93.

[0056] The natural gas directly enters into the molecular sieve drying tower 31 after being deacidified, and the residual part of the acidic gas will affect the normal dehydration of the molecular sieve, and because the humidity of the natural gas is high at this time, it greatly increases the dehydration and regeneration burden of the molecular sieve, which reduces the overall purification efficiency of the system, so the pre-dehydration unit 9 is added, and the natural gas enters the bottom of the drying tower 31 after being deacidified, is distributed to the edge of the side after passing through the distribution column 91, and is condensed when passing through the condensing column 93 cooled by the cooling water jacket 33, so that the water is intercepted, and the composite scraper ring 94 can be periodically subjected to repulsion and attraction by the electromagnet module 92, so that it reciprocates on the condensing column 93. The composite scraper ring 94 will scrape off the water film formed on the surface of the condensing column 93 during the movement, maintain the dry characteristics of the condensing column surface, so that it can maintain good water interception performance, and the composite scraper ring 94 will also cause turbulence in this area during the movement, prolonging the contact time of the natural gas and the condensing column, thereby fully dehydrating. In addition, the residual acidic gas in the natural gas also contacts the solid amine adsorbent 947 through the gas-permeable micropore 946 to realize chemical adsorption, thereby avoiding affecting the subsequent molecular sieve bed 32.

[0057] Please refer to Figure 4 , the condensing column 93 comprises an outer condensing layer 931, the inner cooling water pipe 932 is inlaidly installed in the inner condensing layer 931, and the inner cooling water pipe 932 is connected with the cooling water jacket 33 and extends to the inside of the cooling water jacket 33. The outer surface of the outer condensing layer 931 is fixedly connected with a plurality of condensing fins 933 arranged in an annular array.

[0058] The inner cooling water pipe 932 is made of copper, which has excellent heat conduction performance and can further improve the cooling efficiency of the condensing column 93. The inner cooling water pipe 932 is connected with the cooling water jacket 33 and extends to the inside of the cooling water jacket 33, and the continuous cooling of the condensing column 93 is realized by passing cooling water into the inner cooling water pipe 932. The outer surface of the outer condensing layer 931 is fixedly connected with a plurality of condensing fins 933 arranged in an annular array, and the condensing fins 933 are also made of stainless steel. Its role is to increase the contact area of the condensing column 93 and the natural gas, improve the condensing efficiency, and better intercept the water in the natural gas.

[0059] Please refer to Figures 5-6 , the composite scraper ring 94 comprises a moving ring 941, the inner side of the moving ring 941 is fixedly installed with an annular scraper strip 942 matched with the condensing column 93, and the inner side of the annular scraper strip 942 is inlaidly installed with an inner reinforcing rib 943.

[0060] The mobile ring 941 is made of engineering plastic material such as polytetrafluoroethylene, has good wear resistance, corrosion resistance and low friction coefficient, and can ensure that the composite wiper ring 94 slides smoothly on the condensing column 93, while avoiding wear on the surface of the condensing column 93. The inner side of the mobile ring 941 is fixedly installed with an annular wiper strip 942 matched with the condensing column 93, the annular wiper strip 942 is made of elastic rubber material, has good elasticity and sealing performance, can tightly fit the outer surface of the condensing column 93, effectively wipe off the water film formed on the surface of the condensing column 93 during movement, maintain the dry characteristics of the surface of the condensing column 93, and ensure its continuous and stable water blocking performance. The inner side of the annular wiper strip 942 is inlaid with an inner reinforcing rib 943 made of stainless steel, which serves to enhance the strength and rigidity of the annular wiper strip 942, prevent the annular wiper strip 942 from deforming or being damaged during long-term use, and ensure the effect of wiping off the water film.

[0061] The annular wiper strip 942 is inlaid with an inner reinforcing rib 943 made of stainless steel, which serves to enhance the strength and rigidity of the annular wiper strip 942, prevent the annular wiper strip 942 from deforming or being damaged during long-term use, and ensure the effect of wiping off the water film.

[0062] The annular wiper strip 942 is inlaid with an inner reinforcing rib 943 made of stainless steel, which serves to enhance the strength and rigidity of the annular wiper strip 942, prevent the annular wiper strip 942 from deforming or being damaged during long-term use, and ensure the effect of wiping off the water film.

[0063] The annular wiper strip 942 is inlaid with an inner reinforcing rib 943 made of stainless steel, which serves to enhance the strength and rigidity of the annular wiper strip 942, prevent the annular wiper strip 942 from deforming or being damaged during long-term use, and ensure the effect of wiping off the water film.

[0064] The annular wiper strip 942 is inlaid with an inner reinforcing rib 943 made of stainless steel, which serves to enhance the strength and rigidity of the annular wiper strip 942, prevent the annular wiper strip 942 from deforming or being damaged during long-term use, and ensure the effect of wiping off the water film.

[0065] The annular wiper strip 942 is inlaid with an inner reinforcing rib 943 made of stainless steel, which serves to enhance the strength and rigidity of the annular wiper strip 942, prevent the annular wiper strip 942 from deforming or being damaged during long-term use, and ensure the effect of wiping off the water film.

[0066] The molecular sieve dehydration unit 3 further comprises a regeneration gas heater, a regeneration gas cooler, a regeneration gas separator, and a condensed water recovery device.

[0067] The regeneration gas heater is electrically or oil heated, and the shell and heating element are made of carbon steel and stainless steel respectively. The regeneration gas heater functions to heat the regeneration gas to about 240°C, providing high temperature conditions for the regeneration of the molecular sieve bed 32 and the solid amine adsorbent 947. The regeneration gas cooler is similar in structure and material to the overhead cooler 1, and is used to cool the high-temperature regeneration gas after regeneration to a suitable temperature, so that the water vapor therein is condensed into liquid water. The regeneration gas separator is made of carbon steel, and is internally provided with a separation baffle, and is used to separate the liquid water and gas in the regeneration gas. The condensed water recovery device is made of stainless steel, and is connected to the bottom of the drying tower 31 through a recovery pipeline and a valve, and is used to collect the liquid water separated by the regeneration gas separator and the condensed water generated at the bottom of the drying tower 31, and to recover and treat the same, so as to realize the rational use of water resources.

[0068] The entire drying process of the molecular sieve dehydration unit 3 is implemented by automatic switching of the program-controlled valves to realize continuous operation. The product gas after drying has a water dew point lower than -76°C.

[0069] Taking one of the drying towers 31 as an example, the process thereof is as follows:

[0070] The adsorption process: the deacidified raw gas from the MDEA deacidification unit 2 enters the drying tower from the bottom through a pressure regulating valve and a bottom program-controlled valve, and the water in the gas is selectively absorbed by the molecular sieve in the tower, and the dried natural gas flows out from the top of the tower and enters the mercury removal tower through a program-controlled valve. The adsorption process lasts for 8 hours, and the purified gas goes to the subsequent liquefaction cold box 5.

[0071] After the adsorption process is completed, the raw gas feeding valve and the outlet valve are automatically closed, the adsorption is stopped, and the drying tower enters the regeneration link.

[0072] The heating process: the regeneration gas is obtained before the pressure regulating valve, enters the auxiliary drying tower for dehydration treatment through a program-controlled valve, and then is heated to about 240°C in the regeneration gas heater, and enters the drying tower from the top through a program-controlled valve under the action of the high-temperature regeneration gas. The water absorbed by the molecular sieve bed 32 is released, and the solid amine adsorbent 947 is also regenerated and desorbs the acid gas, which enters the regeneration gas cooler from the bottom through a program-controlled valve together with the regeneration gas. After cooling, the gas phase returns to the pressure regulating valve after the liquid phase goes to the blowdown main. The heating process lasts for about 4 hours.

[0073] Cooling process: Regeneration gas from the bottom of the tower through the program-controlled valve into the regeneration gas cooler cooling, and then into the regeneration gas separator, liquid phase from the bottom of the separator to the sewage main pipe, gas phase from the top of the separator discharge into the pipeline at the bottom of the drying tower, mixed with raw material gas into the drying tower. When the temperature of the regeneration gas out of the top of the drying tower reaches about 40℃, the cooling process is completed, and the cooling process is about 4 hours.

[0074] When the molecular sieve bed 32 is heated and regenerated, it can be used for the regeneration of solid amine adsorbent 947, which is a deacidification material that can be regenerated with high-temperature, oxygen-free dry gas, which is close to the regeneration environment of the molecular sieve, and matches the movable characteristics of the composite scraping ring 94, so that the acidic gas desorbed during regeneration can be fully taken away for recycling.

[0075] Working principle:

[0076] The raw natural gas first enters the MDEA deacidification unit 2 in the natural gas purification system, and before entering the absorption tower, it is heated and warmed by the raw gas heat exchanger with the deacidification gas from the top of the absorption tower. Then it enters the absorption tower from bottom to top and fully contacts with the MDEA lean liquid sprayed from top to bottom. The MDEA lean liquid chemically reacts with the acidic gas in the raw material gas to remove the acidic gas from the raw material gas. The deacidified raw material gas is discharged from the top of the absorption tower, enters the raw gas heat exchanger again to be cooled, and then enters the shell side of the overhead cooler 1 after being cooled to about 45℃. At this time, the low-temperature BOG generated by the LNG loading unit 7 enters the tube side of the overhead cooler 1, and the temperature of the deacidification gas is reduced to below 40℃ through heat exchange between the shell side and the tube side. The cooled deacidification gas enters the gas-liquid separator at the top of the absorption tower, and the MDEA liquid phase entrained is separated and discharged to the amine liquid regeneration process after being reduced by the pressure reducing valve. The gas phase enters the molecular sieve dehydration unit 3.

[0077] The deacidified gas entering the molecular sieve dehydration unit 3 first enters the bottom of the drying tower 31, is distributed to the side edge under the action of the distribution column 91, and then contacts the condensing column 93 cooled by the cooling water jacket 33. The inner cooling water pipe 932 of the condensing column 93 is connected to cooling water, and the outer condensing layer 931 and the condensing fin 933 transmit heat to the outside, so that the water in the deacidified gas is condensed and adheres to the surface of the condensing column 93. At the same time, the DCS system controls the electromagnetic iron module 92 to be periodically powered on and powered off, generates an alternating magnetic field, and exerts repulsion and attraction on the annular magnetic sheet 944 at both ends of the composite scraper ring 94, so as to drive the composite scraper ring 94 to reciprocate on the condensing column 93: during the movement, the annular scraper strip 942 scrapes off the water film on the surface of the condensing column 93, so as to maintain the condensing efficiency of the condensing column 93, and the movement of the composite scraper ring 94 will cause local turbulence, prolong the contact time of the deacidified gas with the condensing column 93, and improve the pre-dehydration effect; in addition, the residual acid gas in the deacidified gas enters the inside through the air-permeable micropore 946 on the surface of the moving ring 941, and chemically adsorbs the solid amine adsorbent 947, so as to avoid the influence of the residual acid gas on the subsequent molecular sieve bed 32.

[0078] The deacidified gas completing the pre-dehydration continues to enter the molecular sieve bed 32, and under the adsorption action of the 3A molecular sieve, the water is further removed, so that the water dew point of the natural gas is reduced to below -76°C. The dried natural gas is discharged from the top of the drying tower 31 through the process control valve, part of which goes to the subsequent liquefaction cold box 5, and the other part enters the circulating gas compressor 4 if it is detected that the purification index does not meet the standard or the system needs to adjust the load, is pressurized and then returns to the inlet of the MDEA deacidification unit 2 to participate in the deacidification purification cycle again; during the equipment commissioning stage, this circulating process can also reduce the waste of natural gas.

[0079] When one drying tower 31 completes an 8-hour adsorption process, the DCS system automatically closes its raw gas inlet valve and outlet valve, switches to the regeneration link: the regeneration gas is taken out before the pressure regulating valve, enters the auxiliary drying tower after dehydration through the process control valve, is heated to about 240°C in the regeneration gas heater, and then enters the top of the drying tower 31, under the action of high temperature, the water adsorbed by the molecular sieve bed 32 is desorbed, and the solid amine adsorbent 947 in the composite scraper ring 94 also desorbs the acid gas, which is discharged from the bottom of the drying tower 31 with the regeneration gas, enters the regeneration gas cooler to be cooled, and then enters the regeneration gas separator for gas-liquid separation, the separated gas phase returns to the pressure regulating valve to participate in the process again, and the liquid phase goes to the blowdown main; then, the cooling process is entered, the regeneration gas is cooled by the regeneration gas cooler and separated by the regeneration gas separator, and then enters the bottom of the drying tower 31 to cool the drying tower 31, when the temperature of the regeneration gas at the top is reduced to about 40°C, the cooling process is completed, and the drying tower 31 waits for the next adsorption switching, and the other drying tower 31 is synchronously operated, so that continuous dehydration is realized through the automatic switching of the process control valve.

[0080] It should be noted that the acid gas desorbed by the solid amine adsorbent 947 will be mixed with the water vapor desorbed from the molecular sieve bed 32 into the high-temperature regeneration gas, and after being discharged from the bottom of the drying tower 31, it will first enter the regeneration gas cooler. In the cooler, the temperature of the high-temperature regeneration gas is rapidly reduced, and the water vapor in it will be condensed into liquid water, and part of the acid gas such as carbon dioxide and hydrogen sulfide will dissolve in the condensed water due to the reduction of temperature. This step has realized the preliminary separation of acid gas, and the condensed water dissolved with acid gas will enter the regeneration gas separator with the liquid phase, and finally be discharged from the system through the blowdown main, and will not continue to circulate with the gas phase. The gas phase separated from the regeneration gas separator is mainly a small amount of natural gas that has not been condensed and a small amount of acid gas that has not been dissolved, and its return path is not directly into the adsorption process of the molecular sieve dehydration unit 3, but back to the main stream of the raw gas after the pressure regulating valve. This node is located just before the inlet of the MDEA acid removal unit 2. That is, this part of the gas phase containing a small amount of acid gas will be combined with the fresh raw natural gas and re-enter the absorption tower of the MDEA acid removal unit 2 to be contacted with the MDEA lean liquid from top to bottom again. Since the MDEA lean liquid has high selective adsorption capacity for acid gas, the small amount of acid gas in the combined gas will be completely absorbed by the MDEA lean liquid and enter the regeneration tower with the rich liquid for desorption and regeneration, and finally be removed from the system.

[0081] The purified natural gas enters the liquefied cold box 5 of the natural gas liquefaction system and exchanges heat with the low-temperature refrigerant delivered by the refrigerant compression unit 6. The natural gas is gradually cooled to below -160°C and liquefied into LNG. The liquefied LNG is discharged from the outlet of the liquefied cold box 5, stored in the low-temperature storage tank of the LNG loading unit 7, and then loaded into a vehicle through a loading crane. The refrigerant whose temperature has risen after heat exchange with the natural gas returns to the refrigerant compression unit 6 from the other outlet of the liquefied cold box 5, is pressurized by the refrigerant compressor, condensed into a liquid by the refrigerant condenser, and then reduced in pressure by the throttle valve before being delivered to the liquefied cold box 5 again, forming a refrigerant circulation. Before the refrigerant compression unit 6 is started, the circulation branch formed by the molecular sieve dehydration unit 3 is started to dehydrate the displacement gas, reduce the displacement gas consumption, shorten the displacement time, and speed up the equipment commissioning.

[0082] The BOG generated by the LNG loading unit 7 is processed through two outlets: when the MDEA acid removal unit 2 needs a cooling source at the top of the tower, the DCS system adjusts the valve to make the BOG enter the tube side of the tower top cooler 1 to provide a cooling source for the tower top gas, and after heat exchange, the BOG goes to the fuel gas unit; when no additional cooling source is needed, the BOG enters the vaporizer 8, is warmed to room temperature, and is sent to the fuel gas unit. The DCS system automatically adjusts the flow of the two BOGs according to the cooling capacity required by the tower top gas to ensure stable operation of the system.

[0083] It will be obvious to a person skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments and can be implemented in other concrete forms without departing from the spirit or essential characteristics of the application. The embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, as regards the scope of the application.

[0084] Furthermore, it should be understood that, although the present specification describes exemplary embodiments, the present specification does not limit the application to these embodiments alone. The scope of the application is defined by the appended claims. The specification is to be regarded as illustrative, rather than restrictive, of the overall application.

Claims

1. A recyciabie clean natural gas processing system characterized by: The natural gas purification system and the natural gas liquefaction system comprise a tower top cooler (1), an MDEA deacidification unit (2), a molecular sieve dehydration unit (3) and a circulating gas compressor (4); The molecular sieve dehydration unit (3) comprises two drying towers (31), a molecular sieve bed (32) is arranged in the middle of the drying tower (31), a cooling water jacket (33) is arranged at the bottom of the side of the drying tower (31), a pre-dehydration unit (9) is arranged at the bottom of the drying tower (31) and below the molecular sieve bed (32). The pre-dehydration unit (9) comprises a shunt column (91) fixedly arranged at the bottom of the drying tower (31), an electromagnet module (92) is integrated at the center of the shunt column (91), a plurality of groups of condensing columns (93) arranged in annular arrays are fixedly connected between the shunt column (91) and the molecular sieve bed (32), and a matching composite scraping ring (94) is slidably arranged on the condensing column (93). The condensing column (93) comprises an outer condensing layer (931), an inner cooling water pipe (932) is inlaidly arranged in the outer condensing layer (931), the inner cooling water pipe (932) is connected with the cooling water jacket (33) and extends to the inner side of the cooling water jacket (33), a plurality of condensing fins (933) arranged in annular arrays are fixedly connected to the outer surface of the outer condensing layer (931), the composite scraping ring (94) comprises a moving ring (941), an annular scraping strip (942) matched with the condensing column (93) is fixedly arranged on the inner side of the moving ring (941), an inner reinforcing rib (943) is inlaidly arranged on the inner side of the annular scraping strip (942), annular magnetic sheets (944) are fixedly connected to the front and rear ends of the moving ring (941), the outer surface of the annular magnetic sheet (944) is covered with a protective patch (945), the moving ring (941) is a ring-shaped hollow structure, filled with a solid amine adsorbent (947), and a plurality of evenly distributed air-permeable micropores (946) are formed in the outer surface of the moving ring (941).

2. A system for processing a natural gas stream as claimed in claim 1, wherein: The MDEA deacidification unit (2) is connected with raw natural gas at the inlet, the outlet of the MDEA deacidification unit (2) is connected with the inlet of the molecular sieve dehydration unit (3), the outlet of the molecular sieve dehydration unit (3) is connected with the inlet of the circulating gas compressor (4), and the outlet of the circulating gas compressor (4) is connected with the inlet of the MDEA deacidification unit (2), so as to complete the circulation of the natural gas purification system.

3. A system for processing a natural gas stream as claimed in claim 2, wherein: The shell side inlet of the tower top cooler (1) is connected with the outlet of the air cooler of the absorption tower of the MDEA deacidification unit (2), and the shell side outlet of the tower top cooler (1) is connected with the inlet of the tower top separator of the MDEA deacidification unit (2).

4. A system for recycling and purifying natural gas as claimed in claim 1, wherein: The molecular sieve dehydration unit (3) further comprises a regenerated gas heater, a regenerated gas cooler, a regenerated gas separator and a condensed water recovery device.

5. A system for recycling and purifying natural gas as claimed in claim 1, wherein: The bypass regulating pipeline is arranged between the outlet of the molecular sieve dehydration unit (3) and the inlet of the MDEA deacidification unit (2), when the natural gas purified by the natural gas purification system is substandard or the load of the natural gas purification system needs to be regulated, the natural gas at the outlet of the molecular sieve dehydration unit (3) is pressurized by the circulating gas compressor (4) and then returned to the inlet of the MDEA deacidification unit (2), so that the circulation is realized.

6. A system for recycling and purifying natural gas as claimed in claim 1, wherein: The natural gas liquefaction system comprises a liquefaction cold box (5), a refrigerant compression unit (6), an LNG loading unit (7) and a vaporizer (8); The inlet of the liquefaction cold box (5) is connected with the outlet of the molecular sieve dehydration unit (3), the outlet of the liquefaction cold box (5) is divided into two paths, one path is connected with the refrigerant compression unit, and the other path is connected with the LNG loading unit (7); The outlet of the refrigerant compression unit (6) is also divided into two paths, one path is connected with the inlet of the molecular sieve dehydration unit (3), returns to the inlet of the refrigerant compression unit (6) after passing through the molecular sieve dehydration unit (3), so that the circulation is formed, and the other path is connected with the liquefaction cold box (5); The BOG outlet of the LNG loading unit (7) is divided into two paths, one path is connected with the inlet of the vaporizer (8), and the other path is connected with the inlet of the tube side of the overhead cooler (1), the outlet of the overhead cooler (1) goes to a fuel gas unit, and the outlet of the vaporizer (8) also goes to the fuel gas unit.

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