FLNG treatment system convenient to purify and liquefy

Abstract

The invention discloses an FLNG treatment system convenient for purification and liquefaction. The FLNG treatment system comprises a gas production tree for collecting feed gas; the desanding separator is arranged at the output end of the christmas tree to separate impurities of the raw material gas, and a pressure regulating valve is arranged between the desanding separator and the christmas tree; the water bath heater is arranged at the output end of the desanding separator, and the output end of the water bath heater is connected with a three-phase separator for separating dry gas; an absorption tower; according to the technical scheme of FLNG purification and liquefaction, acid gas in raw material gas can be conveniently treated, the purity of liquefied FLNG is improved, the product quality is guaranteed, natural gas exploited in a deep sea gas field can be directly purified till the requirement for CO2 content of cryogenic liquefaction is met, a BOG gas reliquefaction device is designed, and the requirement for CO2 content is met. The evaporation loss of the FLNG is reduced; and the transportation safety is improved.

Description

Technical Field

[0001] The present invention particularly relates to an FLNG processing system that facilitates purification and liquefaction. Background Art

[0002] A floating liquefied natural gas (FLNG) system, or floating liquefied natural gas (LNG) production facility, is a system that utilizes large floating structures to extract, liquefy, store, and transship natural gas directly at sea. These floating structures, typically anchored offshore via a single-point mooring system, are capable of extracting, processing, liquefying, storing, and loading and unloading natural gas. These structures, in conjunction with LNG carriers, facilitate the extraction and transportation of natural gas from offshore fields.

[0003] Existing offshore gas field systems are ineffective at separating acid gas from feedstock, impacting the purity of collected FLNG. During FLNG storage, BOG gas evaporation losses occur, compromising the safety of subsequent transportation. Furthermore, most offshore gas field systems utilize a double expansion cycle, which offers advantages such as simple operation and readily available feedstock. However, compared to mixed refrigerant cycle refrigeration, this system consumes more power and has a smaller operating space, hindering the separation of heavy hydrocarbon components. Therefore, we propose an FLNG processing system that facilitates purification and liquefaction. Summary of the Invention

[0004] The object of the present invention is to provide an FLNG processing system that is convenient for purifying and liquefying, so as to solve the problems raised in the above background technology.

[0005] To achieve the above objectives, the present invention provides the following technical solutions: an FLNG processing system for purifying and liquefying FLNG, comprising:

[0006] A gas tree for collecting raw gas;

[0007] A desander separator is provided at the output end of the gas tree to separate impurities from the raw gas, and a pressure regulating valve is provided between the desander separator and the gas tree;

[0008] A water bath heater is provided at the output end of the desander separator, and the output end of the water bath heater is connected to a three-phase separator for separating dry gas;

[0009] An absorption tower connected to the output end of the three-phase separator for deacidification, and a regeneration module connected to the interior of the absorption tower for refluxing the deacidification absorbent is provided on one side of the absorption tower;

[0010] An FLNG cooler is provided at the output end of the absorption tower, and the output end of the FLNG cooler is connected to an FLNG dehydration unit;

[0011] a cold box, provided at the output end of the FLNG dehydration unit to cool the FLNG using a mixed refrigerant to form liquefied FLNG;

[0012] The FLNG spherical storage tank is connected to the output end of the cold box to store liquefied FLNG, and a liquefaction module for evaporating BOG during storage is provided on one side of the FLNG spherical storage tank.

[0013] Preferably, the upper end of the cold box is connected to a refrigerant compression unit for pressurizing the refrigerant through a pipeline, and the output end of the refrigerant compression unit is connected to the cold box, and the other output end of the refrigerant compression unit is connected to a refrigerant storage tank, and the output end of the refrigerant storage tank is communicated with the lower end of the cold box.

[0014] Preferably, the regeneration module includes an amine liquid flash tank, a heat exchanger, a regeneration tower and a lean liquid cooler. The output end of the absorption tower is connected to an amine liquid flash tank for treating rich amine liquid. The output end of the amine liquid flash tank is sequentially connected to a heat exchanger and a regeneration tower for converting rich amine liquid into lean amine liquid. The output end of the regeneration tower is connected to the inside of the heat exchanger, and the output end of the heat exchanger is provided with a lean liquid cooler for cooling the lean amine liquid for reflux to the absorption tower.

[0015] Preferably, the other output end of the regeneration tower is connected to an acid gas cooler, and a desulfurization unit is provided at one end of the acid gas cooler.

[0016] Preferably, a complex iron solution is provided inside the desulfurization unit to absorb and desulfurize the gas.

[0017] Preferably, the liquefaction module includes a BOG booster and a denitrification flash tank. The BOG booster is connected to the output end of the FLNG spherical storage tank to pressurize the evaporated BOG, and the output end of the BOG booster is connected to the interior of the cold box to cool and liquefy the pressurized BOG. ​​The denitrification flash tank is provided at the other output end of the cold box, and the output end of the denitrification flash tank is connected to the interior of the FLNG spherical storage tank.

[0018] Preferably, the other output end of the denitrification flash tank is provided with a pipeline connected to an external flare to discharge nitrogen.

[0019] Preferably, the pressure regulating valve is provided with multiple valves to adjust the pressure value of the gas.

[0020] Preferably, a sewage pipe is provided at the lower end of the three-phase separator for discharging liquid to the outside during separation.

[0021] Preferably, the mixed refrigerant inside the cold box is nitrogen, methane, carbon dioxide, and isobutane.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention proposes a technical solution for FLNG purification and liquefaction, which facilitates the treatment of acid gas in the feed gas, improves the purity of the liquefied FLNG, and ensures product quality. Natural gas extracted from deep-sea gas fields can be directly purified to meet the CO2 content requirements for cryogenic liquefaction. A mixed refrigerant two-stage expansion refrigeration cycle device is used to improve liquefaction efficiency and reduce energy consumption. At the same time, a BOG gas reliquefaction device is designed to reduce evaporation losses of FLNG and facilitate improved transportation safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the present invention.

[0025] In the figure: 1. Christmas tree; 2. Desander separator; 3. Water bath heater; 4. Three-phase separator; 5. Absorber; 6. FLNG cooler; 7. Amine flash tank; 8. Heat exchanger; 9. Regeneration tower; 10. Acid gas cooler; 11. Desulfurization unit; 12. Lean liquid cooler; 13. FLNG dehydration unit; 14. Cold box; 15. FLNG spherical storage tank; 16. Refrigerant compression unit; 17. Refrigerant storage tank; 18. BOG booster; 19. Denitrification flash tank. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] See also Figure 1 The present invention provides a technical solution: an FLNG processing system that is convenient for purifying liquefaction, comprising:

[0028] A gas tree 1 for collecting raw gas;

[0029] The desander separator 2 is provided at the output end of the gas tree 1 to separate impurities from the raw gas. A pressure regulating valve is provided between the desander separator 2 and the gas tree 1.

[0030] A water bath heater 3 is provided at the output end of the desander separator 2, and the output end of the water bath heater 3 is connected to a three-phase separator 4 for separating dry gas;

[0031] An absorption tower 5 is connected to the output end of the three-phase separator 4 for deacidification, and a regeneration module is provided on one side of the absorption tower 5 for reflux of the deacidification absorbent.

[0032] The FLNG cooler 6 is provided at the output end of the absorption tower 5, and the output end of the FLNG cooler 6 is connected to the FLNG dehydration unit 13;

[0033] A cold box 14 is provided at the output end of the FLNG dehydration unit 13 to cool the mixed refrigerant to form liquefied FLNG;

[0034] The FLNG spherical storage tank 15 is connected to the output end of the cold box 14 to store liquefied FLNG, and a liquefaction module for evaporating BOG during storage is provided on one side of the FLNG spherical storage tank 15 .

[0035] Preferably, the upper end of the cold box 14 is connected to a refrigerant compression unit 16 for pressurizing the refrigerant through a pipeline, and the output end of the refrigerant compression unit 16 is connected to the cold box 14, and the other output end of the refrigerant compression unit 16 is connected to a refrigerant storage tank 17, and the output end of the refrigerant storage tank 17 is communicated with the lower end of the cold box 14.

[0036] Preferably, the regeneration module includes an amine liquid flash tank 7, a heat exchanger 8, a regeneration tower 9 and a lean liquid cooler 12. The output end of the absorption tower 5 is connected to the amine liquid flash tank 7 for treating the rich amine liquid. The output end of the amine liquid flash tank 7 is sequentially connected to the heat exchanger 8 and the regeneration tower 9 for converting the rich amine liquid into a lean amine liquid. The output end of the regeneration tower 9 is connected to the inside of the heat exchanger 8, and the output end of the heat exchanger 8 is provided with a lean liquid cooler 12 for cooling the lean amine liquid for reflux to the absorption tower 5.

[0037] Preferably, the other output end of the regeneration tower 9 is connected to an acid gas cooler 10 , and a desulfurization unit 11 is provided at one end of the acid gas cooler 10 .

[0038] Preferably, a complex iron solution is provided inside the desulfurization unit 11 to absorb and desulfurize the gas.

[0039] Preferably, the liquefaction module includes a BOG booster 18 and a denitrification flash tank 19. The BOG booster 18 is connected to the output end of the FLNG spherical storage tank 15 to pressurize the evaporated BOG, and the output end of the BOG booster 18 is connected to the interior of the cold box 14 to cool and liquefy the pressurized BOG. ​​The denitrification flash tank 19 is arranged at the other output end of the cold box 14, and the output end of the denitrification flash tank 19 is connected to the interior of the FLNG spherical storage tank 15.

[0040] Preferably, the other output end of the denitrification flash tank 19 is provided with a pipeline connected to an external flare to discharge nitrogen.

[0041] Preferably, a plurality of pressure regulating valves are provided to adjust the pressure value of the gas.

[0042] Preferably, a sewage pipe is provided at the lower end of the three-phase separator 4 for discharging liquid to the outside during separation.

[0043] Preferably, the mixed refrigerant inside the cold box 14 is nitrogen, methane, carbon dioxide, and isobutane.

[0044] The working principle and use process of the present invention:

[0045] High-pressure feed gas is delivered from the Christmas tree 1 above the submarine wellhead, where it passes through a regulating valve and is reduced to approximately 20 MPa. It then passes through a desander 2 to separate most of the entrained solid particles. The gas is then heated to room temperature in a water bath 3 and its pressure is raised to 6 MPa. The regulated gas then enters a three-phase separator 4, where it is dried and discharged from the outlet. It then enters a deacidification process.

[0046] Feed gas enters the bottom of acid gas absorption tower 5. Deacidification utilizes a modified MDEA process, using a tailored MDEA solution formulation tailored to the CO2 and H2S content of the feed gas. A single-stage absorption and regeneration process is employed. The feed gas is subjected to countercurrent contact with lean amine solution flowing downward, removing CO2 from the feed gas to below 50 ppm. The solution is then withdrawn from the top of the tower, cooled to approximately 40°C in FLNG cooler 6, and enters FLNG dehydration unit 13. Rich amine, which has absorbed the acid gas, exits the bottom of absorption tower 5 and passes through amine flash tank 7. The waste gas collected at the top of amine flash tank 7 is used for power generation on the FLNG offshore platform. The rich amine exiting the bottom of amine flash tank 7 is heated to 90°C in heat exchanger 8. The rich amine enters the top of regeneration tower 9. The regenerated lean amine passes through lean liquid cooler 12, where it reaches approximately 40°C before entering the top of absorption tower 5, completing the cycle. The high-temperature acidic gas flowing out of the top of regeneration tower 9 is first cooled to approximately 40°C in an acid gas cooler 10, then separated into a liquid phase in an acid gas separator before being fed into a desulfurization unit 11. Desulfurization unit 11 utilizes a complex iron process. The cooled acidic gas enters the desulfurization tower from the bottom, fully contacts the complex iron solution sprayed on the top of the tower, and then flows out from the bottom of the tower. The desulfurization liquid, which has absorbed hydrogen sulfide, enters the oxidation regeneration tower, where it undergoes an oxidation reaction with the blown-in air. The complexed ferrous ions are oxidized to complexed ferric ions, simultaneously generating elemental sulfur. The resulting suspended solution and sulfur slurry are pumped into a plate and frame filter press to obtain sulfur. The regenerated filtrate is then transported to the desulfurization tower to complete the regeneration.

[0047] After dehydration, the acid gas enters the FLNG dehydration unit 13, where it is divided into two paths by a flow control valve. The main path, which undergoes flow regulation and returns from the regeneration gas separator, is directed to a drying tower for adsorption, removing water molecules to below 1 ppm. The dehydrated dry gas then enters the liquefaction unit from the top of the tower. The other path, serving as regeneration gas, first passes through a pre-drying tower to absorb moisture. It is then heated to 240-260°C by a regeneration gas heater and then enters the drying tower at the bottom of the tower requiring regeneration for hot-blow regeneration. After completion of the hot-blow regeneration cycle, the regeneration gas enters the hot tower at the top of the drying tower requiring cold-blow, where it is cooled to the design temperature before switching back to the adsorption state to begin the next cycle.

[0048] The purified gas from the FLNG dehydration unit 13 and the gaseous and liquid refrigerants from the outlet of the refrigerant compression unit 16 enter the upper section of the cold box 14. The raw gas exchanges heat with the throttled mixed refrigerant to approximately -50°C, where it is separated into a liquid phase by a heavy hydrocarbon separator and continues to enter the lower section of the cold box 14. The raw gas exchanges heat with the throttled gaseous refrigerant to -162°C for liquefaction. The liquefied FLNG is throttled by a throttle valve and transferred to the FLNG spherical storage tank 15. The return refrigerant from the liquefaction cold box 14 passes through a filter and enters the refrigerant compression unit 16. The outlet pressure of the low-pressure stage compressor is 1.7 MPa. After cooling and separation, the refrigerant enters the high-pressure stage compressor, where the outlet pressure is 3.4 MPa. After cooling and separation, the high-pressure refrigerant gas enters the cold box 14 or refrigerant storage tank 17, completing the refrigerant circulation process. The refrigerant primarily consists of a nitrogen-methane-carbon dioxide-isobutane mixture. The ratio of these components is adjusted to minimize power consumption throughout the refrigerant cycle. A reliquefaction unit is incorporated into the design to liquefy the evaporated BOG gas from the FLNG spherical storage tank 15. The BOG gas is pressurized to 5 MPa by a BOG booster 18 and then enters the BOG flow channel of the cold box 14 for heat exchange, completing the reliquefaction process. The reliquefied BOG passes through a regulating valve and enters the denitrification flash tank 19. Nitrogen flashes out from the top and is sent to the flare, and the liquid phase returns to the FLNG spherical storage tank 15, completing the cycle.

[0049] This invention proposes a FLNG purification and liquefaction technology solution that can directly purify natural gas extracted from deep-sea gas fields to meet the cryogenic liquefaction requirement of less than 50 ppm CO₂. Using a two-stage expansion refrigeration cycle of nitrogen, methane, carbon dioxide, and isobutane, this system improves liquefaction efficiency and reduces energy consumption. A BOG gas reliquefaction unit is also designed to minimize evaporation losses during FLNG transport and improve transportation safety. Consequently, this invention offers the advantages of high purification purity, low energy consumption, boil-off gas reliquefaction, and a heat recovery system.

[0050] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An FLNG processing system for purifying liquefaction, characterized in that: include: A gas tree (1) for collecting raw gas; A desanding separator (2) is provided at the output end of the gas tree (1) to separate impurities from the raw gas, and a pressure regulating valve is provided between the desanding separator (2) and the gas tree (1); A water bath heater (3) is provided at the output end of the desander separator (2), and the output end of the water bath heater (3) is connected to a three-phase separator (4) for separating dry gas; An absorption tower (5) is connected to the output end of the three-phase separator (4) for deacidification, and a regeneration module is provided on one side of the absorption tower (5) for refluxing the deacidification absorbent. An FLNG cooler (6) is provided at the output end of the absorption tower (5), and the output end of the FLNG cooler (6) is connected to an FLNG dehydration unit (13); A cold box (14) is provided at the output end of the FLNG dehydration unit (13) to cool the mixed refrigerant to form liquefied FLNG; The FLNG spherical storage tank (15) is connected to the output end of the cold box (14) to store liquefied FLNG, and a liquefaction module for evaporating BOG during storage is provided on one side of the FLNG spherical storage tank (15).

2. The FLNG processing system for facilitating purification and liquefaction according to claim 1, characterized in that: The upper end of the cold box (14) is connected to a refrigerant compression unit (16) for pressurizing the refrigerant through a pipeline, and the output end of the refrigerant compression unit (16) is connected to the cold box (14), and the other output end of the refrigerant compression unit (16) is connected to a refrigerant storage tank (17), and the output end of the refrigerant storage tank (17) is communicated with the lower end of the cold box (14).

3. The FLNG processing system for facilitating purification and liquefaction according to claim 2, characterized in that: The regeneration module comprises an amine liquid flash tank (7), a heat exchanger (8), a regeneration tower (9) and a lean liquid cooler (12); the output end of the absorption tower (5) is connected to the amine liquid flash tank (7) for treating rich amine liquid; the output end of the amine liquid flash tank (7) is sequentially connected to the heat exchanger (8) for converting rich amine liquid into lean amine liquid and the regeneration tower (9); the output end of the regeneration tower (9) is connected to the interior of the heat exchanger (8); and the output end of the heat exchanger (8) is provided with a lean liquid cooler (12) for cooling the lean amine liquid for reflux to the absorption tower (5).

4. The FLNG processing system for facilitating purification and liquefaction according to claim 3, characterized in that: The other output end of the regeneration tower (9) is connected to an acid gas cooler (10), and a desulfurization unit (11) is provided at one end of the acid gas cooler (10).

5. The FLNG processing system for facilitating purification and liquefaction according to claim 4, characterized in that: A complex iron solution is provided inside the desulfurization unit (11) to absorb and desulfurize the gas.

6. The FLNG processing system for facilitating purification and liquefaction according to claim 1, characterized in that: The liquefaction module comprises a BOG pressurizing device (18) and a denitrification flash tank (19). The BOG pressurizing device (18) is connected to the output end of the FLNG spherical storage tank (15) to pressurize the evaporated BOG, and the output end of the BOG pressurizing device (18) is connected to the interior of the cold box (14) to cool and liquefy the pressurized BOG. ​​The denitrification flash tank (19) is arranged at the other output end of the cold box (14), and the output end of the denitrification flash tank (19) is connected to the interior of the FLNG spherical storage tank (15).

7. The FLNG processing system for facilitating purification and liquefaction according to claim 6, characterized in that: The other output end of the denitrification flash tank (19) is provided with a pipeline connected to an external flare to discharge nitrogen.

8. The FLNG processing system for facilitating purification and liquefaction according to claim 1, characterized in that: The pressure regulating valve is provided with a plurality of pressure values ​​for adjusting the gas.

9. The FLNG processing system for facilitating purification and liquefaction according to claim 1, characterized in that: The lower end of the three-phase separator (4) is provided with a sewage pipe for discharging liquid to the outside during separation.

10. The FLNG processing system for facilitating purification and liquefaction according to claim 1, characterized in that: The mixed refrigerant inside the cold box (14) is nitrogen, methane, carbon dioxide, and isobutane.

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