A zero-emission scattered gas-liquid recovery and co-production helium extraction system and method

Abstract

This invention discloses a zero-emission scattered gas liquefaction recovery and helium extraction system and method, comprising: an inlet separation unit for gas-liquid separation of the feed gas to obtain a first gas phase; a feed gas pressurization unit for interstage pressurization of the first gas phase to obtain a second gas phase; a feed gas deacidification unit for deacidification of the second gas phase to obtain a third gas phase; a dehydration and mercury removal unit for dehydration and mercury removal of the third gas phase to obtain a fourth gas phase; a heavy hydrocarbon removal unit for re-contact and cryogenic separation of the fourth gas phase after precooling to obtain a fifth gas phase and a heavy hydrocarbon liquid; a denitrification unit for denitrification of the fifth gas phase after liquefaction to obtain LNG and a sixth gas phase; a helium extraction unit for helium extraction from the sixth gas phase to obtain high-purity helium; a hydrocarbon stabilization unit for hydrocarbon stabilization of the heavy hydrocarbon liquid; and a condensate desulfurization unit for gas stripping desulfurization of the sulfur-containing condensate obtained from the previous stage. This invention can improve the recovery rate of scattered gas, reduce operating energy consumption, and reduce investment costs.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical technology and relates to a zero-emission scattered gas liquefaction, recovery, and helium extraction system and method. Specifically, it relates to a zero-emission system and method for liquefaction, denitrification, helium extraction, and sulfur-containing condensate recovery of scattered gas with high sulfur content, high nitrogen content, low helium content, and rich heavy hydrocarbons. It is applicable to scattered gas fields with high sulfur content, high nitrogen content, low helium content, and rich heavy hydrocarbons in remote areas. Background Technology

[0002] Liquefied Natural Gas (LNG) is natural gas that has undergone purification, transforming it from a gaseous state to a liquid state (cryogenically cooled to -162°C). Its volume is approximately 1 / 600th of the volume of standard-state natural gas, and its weight is about 45% of the weight of the same volume of water, giving it advantages in storage, transportation, trade, and application. When used for expanding urban gas distribution systems and peak shaving, it offers advantages over other methods such as underground gas storage facilities and gas holders, including lower investment, shorter construction periods, faster results, and less susceptibility to external factors. As a high-quality vehicle fuel, compared to gasoline, it boasts higher octane ratings, better anti-knock properties, more complete combustion, lower exhaust emissions, longer engine life, and lower operating costs. Compared to compressed natural gas (CNG), it offers higher storage efficiency, longer driving range, lower cylinder pressure, lighter weight, smaller quantity, and its construction is not limited by gas supply networks.

[0003] Natural gas liquefaction (LNG) processes can be broadly categorized into two types based on their working principles: one is the refrigerant refrigeration method, where natural gas is cooled by exchanging heat with a refrigerant. Selecting a suitable refrigerant and using one or more stages of cooling can achieve liquefaction. The other is the expansion refrigeration method, where high-pressure natural gas flows through an expander or throttle valve to reduce its pressure. Simultaneously, isentropic or isenthalpic expansion cools the natural gas, and the resulting low-temperature gas exchanges heat with the feedstock natural gas, forming a cooling cycle that gradually lowers the gas temperature to its liquefaction temperature. Currently, the main industrial liquefaction processes include: stepped refrigeration cycles, mixed refrigerant (MRC) refrigeration cycles, and expander refrigeration cycles. Each liquefaction process has its own characteristics. Among them, the stepped refrigeration cycle has advantages such as low energy consumption, high operational flexibility, and mature and reliable technology. However, it also has disadvantages such as high initial investment, complex process flow, cumbersome operation and maintenance, large footprint, and difficulty in achieving skid-mounted and modular designs. This makes this process more suitable for large-scale natural gas liquefaction plants and less applicable to remote, distributed wells. Expansionist refrigeration cycles can be achieved through the compression and expansion of single-component or multi-component gas streams, primarily employing three forms: ① direct natural gas expansion refrigeration; ② nitrogen expansion refrigeration; ③ N2-CH4 mixed expansion refrigeration. Compared to stepped refrigeration cycles and MRC refrigeration cycles, expansionist refrigeration cycles offer advantages such as simpler and faster start-up and shutdown, but they have higher energy consumption, lower operational flexibility, and are not suitable for remote areas with large production fluctuations during the extraction cycle. Compared to stepped refrigeration cycles, MRC refrigeration cycle liquefaction offers advantages such as lower initial investment, simpler process flow, convenient operation and maintenance, smaller footprint, and easier skid-mounting, making it more suitable for scattered gas liquefaction processes.

[0004] Nitrogen removal is necessary during LNG production to prevent "tumbling" during storage and transportation, while also meeting LNG performance requirements. Existing natural gas denitrification technologies typically use denitrification towers for distillation, which require reboilers and condensers in conjunction with the denitrification tower, resulting in high costs and energy consumption. Therefore, a simpler, more economical, and energy-efficient denitrification method is urgently needed.

[0005] Currently, there are five main natural gas denitrification processes both domestically and internationally: cryogenic separation (CNR), pressure swing adsorption (PSA), membrane separation, solvent absorption, and hydrate separation. Cryogenic denitrification boasts advantages such as large processing capacity, high recovery rate, and high nitrogen removal rate, making it the most widely used natural gas denitrification process. Pressure swing adsorption (PSA) denitrification features low investment, low energy consumption, and a simple process flow, and has already entered the industrial application stage. However, this process suffers from disadvantages such as low adsorption selectivity, limited adsorption capacity, and low methane recovery rate. Membrane separation denitrification technology is less widely used; the performance issues of membrane materials remain a major limiting factor for its application. Solvent absorption denitrification is not extensively used in the natural gas industry; the solvent-based natural gas denitrification technologies already applied in industry mainly use hydrocarbon oils as absorbents to recover methane from natural gas. Hydrate synthesis and separation technology, as a novel separation technology, is currently still in the laboratory research stage.

[0006] Helium is mainly used in cryogenics, aerospace, electronics, biomedicine, and nuclear facilities, and is one of the basic materials for national security and the development of high-tech industries. With the development of my country's national economy, the demand for helium is constantly increasing; however, my country's total natural gas resources are scarce, and the helium content is relatively low, meaning that helium production levels are far from meeting the requirements of scientific and technological development, economic construction, and national defense.

[0007] Existing natural gas helium extraction technologies include non-cryogenic methods and cryogenic methods (deep cryogenic methods). Non-cryogenic methods mainly include physical adsorption, solvent absorption, membrane separation, and pressure swing adsorption (PSA). Cryogenic methods are also known as condensation methods. Among these, PSA, membrane separation, and cryogenic methods are the three main helium extraction methods, with cryogenic methods being the most commonly used. The advantages of PSA are high product purity (up to 99.999%), simple equipment, easy operation and maintenance, no need for heating the regeneration bed, low operating costs, and continuous production using a cyclic process. However, the higher the helium purity, the more complex the process becomes. Additionally, PSA has a short cycle time, typically around 20 minutes, requiring automatic control and placing high demands on equipment valves. Although membranes have good selectivity for helium and methane, the helium content is very low, resulting in low efficiency for single-stage membranes; multi-stage membranes are generally used. In recent years, new membrane materials (hollow fiber permeable membranes) have emerged, indicating a promising future for membrane separation helium extraction. Cryogenic methods utilize the differences in the critical temperatures of various components in natural gas to separate helium. Although cryogenic extraction has low operational flexibility, high equipment investment and energy consumption, it produces high product purity and yield, making it the most widely used helium extraction method. Approximately 90% of helium is extracted through cryogenic extraction.

[0008] In natural gas liquefaction (LNG) processes, if heavy hydrocarbons are not completely removed, they will preferentially liquefy, leading to freezing and blockage in the cold box flow channels. This not only reduces liquefaction efficiency but can also cause unit shutdowns in severe cases. Therefore, a high degree of separation of heavy hydrocarbons from the feed gas is necessary in LNG processes. For associated gas from oilfields or high-pressure gas fields rich in high-sulfur and heavy hydrocarbon content, a large amount of sulfur-containing condensate will precipitate during feed gas pressurization or expansion throttling. To improve the recovery rate of scattered gas in remote areas, it is necessary to effectively treat the sulfur-containing condensate to produce qualified mixed hydrocarbon products and increase product added value.

[0009] Domestic reports on mixed hydrocarbon desulfurization technology in oilfields are scarce, with most applications focused on desulfurization of light hydrocarbons, solvent oils, and liquefied petroleum gas (LPG) in refineries. Common oil desulfurization processes include alkaline washing desulfurization, oxidative desulfurization, hydrodesulfurization, bio-oxidative desulfurization, adsorption desulfurization, extraction desulfurization, and membrane separation. Alkaline washing desulfurization is simple and requires low investment, but suffers from high treatment costs and difficulty in treating high-sulfur wastewater. Other chemical desulfurization processes are not only costly but also require expensive equipment. Adsorption desulfurization primarily uses zinc-based, iron-based, and manganese-based oxides, as well as activated carbon or modified activated carbon, as adsorbents. It has lower operating costs but is mainly used for oils with low sulfur content. Extraction desulfurization is widely used in LPG desulfurization, offering advantages such as high removal efficiency and low operating costs, especially suitable for H2S removal. However, the complex composition of mixed hydrocarbons and the high content of heavy hydrocarbons affect the regeneration of the extractant. Summary of the Invention

[0010] To address the problems of high investment and high energy consumption in existing natural gas liquefaction denitrification and helium extraction technologies, this invention provides a system and method for the liquefaction, denitrification, helium extraction, and sulfur-containing condensate recovery of scattered gas sources with high nitrogen, high sulfur, low helium, and rich heavy hydrocarbons in remote areas, achieving zero emissions. The aim is to improve the recovery rate of scattered gas in remote areas, reduce operating energy consumption, and decrease investment costs.

[0011] This invention discloses a zero-emission scattered gas liquefaction recovery and helium extraction system, comprising: an inlet separation unit, a feed gas pressurization unit, a feed gas acid removal unit, a dehydration and mercury removal unit, a precooling unit, a heavy hydrocarbon removal unit, a liquefaction unit, a denitrification unit, a helium extraction unit, a mixed hydrocarbon stabilization unit, and a condensate desulfurization unit; wherein,

[0012] The inlet separation unit is used to separate the raw material gas into a gas-liquid phase to obtain the first gas phase;

[0013] The raw gas pressurization unit is used to perform interstage pressurization on the first gas phase to obtain the second gas phase and the first sulfur-containing condensate.

[0014] The raw material gas deacidification unit is used to filter and deacidify the second gas phase to obtain a third gas phase and a second sulfur-containing condensate.

[0015] The dehydration and mercury removal unit is used to cool, separate the three phases, adsorb by molecular sieves and remove mercury from all or part of the third gas phase to obtain a fourth gas phase and liquid hydrocarbons.

[0016] The heavy hydrocarbon removal unit is used to re-contact and perform low-temperature separation on all or part of the fourth gas phase after precooling by the precooling unit to obtain the fifth gas phase and heavy hydrocarbon liquid.

[0017] The denitrification unit is used to denitrify the fifth gas phase after liquefaction by the liquefaction unit to obtain LNG and the sixth gas phase.

[0018] The helium extraction unit is used to extract helium from the sixth gas phase after passing through the liquefaction unit, precooling unit, and dehydration and mercury removal unit to obtain high-purity helium.

[0019] The mixed hydrocarbon stabilization unit is used to stabilize the heavy hydrocarbon liquid, with top gas returned to the inlet separation unit and bottom liquid entering the mixed hydrocarbon storage tank.

[0020] The condensate desulfurization unit is used to perform gas stripping desulfurization on the first sulfur-containing condensate, the second sulfur-containing condensate, and the heated liquid hydrocarbons. The top gas is returned to the inlet separation unit, and the bottom liquid enters the mixed hydrocarbon storage tank.

[0021] As a further improvement of the present invention, the inlet separation unit includes an inlet separator, the raw material gas pressurization unit includes a multi-stage compressor and a separation tank arranged at intervals, and the raw material gas deacidification unit includes a filter and an absorption tower;

[0022] The outlet of the inlet separator is connected to the inlet of the pre-separation tank, the outlet of the post-separation tank is connected to the inlet of the filter, the outlet of the filter is connected to the lower inlet of the absorption tower, and the top outlet of the absorption tower is connected to the dehydration and mercury removal unit. The rich amine liquid at the bottom of the absorption tower is regenerated by an external amine liquid regeneration system to obtain a lean amine liquid, which enters the top of the absorption tower and flows counter-currently with the gas phase.

[0023] The liquid phase in the inlet separator and the pre-separation tank enters the sewage discharge unit, and the first sulfur-containing condensate in the remaining separation tank and the second sulfur-containing condensate in the filter enter the condensate desulfurization unit.

[0024] As a further improvement of the present invention, the dehydration and mercury removal unit includes a cooler, a first three-phase separator, a pre-filter, a molecular sieve adsorption tower, a mercury removal tower, and a post-filter;

[0025] The cooler is connected to the outlet of the absorption tower and the inlet of the first three-phase separator. The cold source of the cooler comes from the pre-cooler of the pre-cooling unit. The outlet of the first three-phase separator is sequentially connected to the pre-filter, one or more molecular sieve adsorption towers connected in parallel, mercury removal tower and post-filter. The outlet of the post-filter is connected to the heavy hydrocarbon removal unit after passing through the pre-cooling box of the pre-cooling unit. The liquid hydrocarbon port of the first three-phase separator is connected to the condensate desulfurization unit.

[0026] As a further improvement of the present invention, the heavy hydrocarbon removal unit includes a heavy contact tower and a low-temperature separator, the precooling unit includes a precooling box and a precooler for cooling the precooling box, the denitrification unit includes a denitrification tower, and the liquefaction unit includes a main cold box and a main cooler for cooling the main cold box.

[0027] The lower inlet of the heavy contact tower receives all or part of the fourth gas phase, which has been precooled by the precooling box. The top exhaust of the heavy contact tower is connected to the main cold box for primary cooling. The gas phase after primary cooling enters the cryogenic separator. The liquid phase separated by the cryogenic separator enters the upper liquid inlet of the heavy contact tower. A portion of the separated fifth gas phase is connected to the main cold box for secondary cooling. The liquid phase after secondary cooling is connected to the upper liquid inlet of the denitrification tower. Another portion of the separated fifth gas phase is connected to the lower inlet of the denitrification tower. The liquid phase at the bottom of the denitrification tower is connected to the main cold box for tertiary cooling before being fed into the LNG storage tank.

[0028] As a further improvement of the present invention, the cooling temperature of the secondary or tertiary cooling stage is less than the cooling temperature of the primary cooling stage, which is less than the cooling temperature of the pre-cooling stage; the cooling temperature of the secondary or tertiary cooling stage is lower than -162°C.

[0029] As a further improvement of the present invention, the gas vented from the top of the denitrification tower enters the cold end reflux channel of the main cold box and the precooling box in sequence, and after reheating, it goes to the molecular sieve adsorption tower of the dehydration and mercury removal unit as molecular sieve regeneration gas. The regenerated and cooled helium-containing gas is then introduced into the helium extraction unit.

[0030] As a further improvement of the present invention, the helium extraction unit includes a membrane treatment unit and a pressure swing adsorption purification unit arranged sequentially.

[0031] As a further improvement of the present invention, the mixed hydrocarbon stabilization unit includes an ethane stripper;

[0032] The inlet of the deethaner is connected to the bottom liquid outlet of the heavy contact tower. The top gas from the deethaner is returned to the inlet separator at the front end, and the bottom condensate from the deethaner enters the mixed hydrocarbon storage tank.

[0033] As a further improvement of the present invention, the condensate desulfurization unit includes a second three-phase separator and a condensate desulfurization tower;

[0034] The inlet of the second three-phase separator is connected to the first sulfur-containing condensate and the second sulfur-containing condensate. The gas outlet of the second three-phase separator is returned to the inlet separator at the front end. The liquid phase of the second three-phase separator enters the upper part of the condensate desulfurization tower. The liquid hydrocarbons of the first three-phase separator enter the middle part of the condensate desulfurization tower. The remaining third or fourth gas phase enters the lower part of the condensate desulfurization tower. The condensate at the bottom of the condensate desulfurization tower enters the mixed hydrocarbon storage tank.

[0035] This invention also discloses a zero-emission method for the liquefaction and recovery of scattered gas and the co-production of helium, comprising:

[0036] The inlet separation unit performs gas-liquid separation on the raw material gas to obtain the first gas phase;

[0037] The raw gas pressurization unit performs interstage pressurization on the first gas phase to obtain the second gas phase and the first sulfur-containing condensate.

[0038] The raw gas deacidification unit filters and deacidifies the second gas phase to obtain the third gas phase and the second sulfur-containing condensate;

[0039] The dehydration and mercury removal unit cools, separates, adsorbs and removes mercury from all or part of the third gas phase to obtain a fourth gas phase and liquid hydrocarbons.

[0040] The heavy hydrocarbon removal unit re-contacts and performs low-temperature separation on all or part of the fourth gas phase after precooling by the precooling unit to obtain the fifth gas phase and heavy hydrocarbon liquid.

[0041] The denitrification unit denitrifies the fifth gas phase after liquefaction in the liquefaction unit to obtain LNG and the sixth gas phase.

[0042] The helium extraction unit extracts helium from the sixth gas phase after passing through the liquefaction unit, precooling unit, and dehydration and mercury removal unit to obtain high-purity helium.

[0043] The mixed hydrocarbon stabilization unit stabilizes the heavy hydrocarbon liquid, the top gas is returned to the inlet separation unit, and the bottom liquid enters the mixed hydrocarbon storage tank.

[0044] The condensate desulfurization unit performs gas stripping desulfurization on the first sulfur-containing condensate, the second sulfur-containing condensate, and the heated liquid hydrocarbons. The top gas is returned to the inlet separation unit, and the bottom liquid enters the mixed hydrocarbon storage tank.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] This invention enables the liquefaction and recovery of scattered gases with complex compositions in remote areas, with an operational flexibility of 30-120%, improving the adaptability of raw gas components and expanding the application scope of scattered gas recovery and liquefaction. The invention employs a pre-cooling and gradual condensation process, fully utilizing energy, reducing overall liquefaction energy consumption, and achieving zero emissions of tail gas, thus contributing to energy conservation and carbon reduction. Furthermore, this invention achieves zero emissions while simultaneously extracting helium and increasing the yield of by-products, demonstrating broad prospects for application and promotion. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the zero-emission scattered gas liquefaction recovery and co-production helium extraction system disclosed in this invention.

[0048] In the picture:

[0049] 10. Inbound separation unit; 11. Inbound separator;

[0050] 20. Raw material gas booster unit; 21. Compressor; 22. Separator;

[0051] 30. Raw gas deacidification unit; 31. Filter; 32. Absorption tower;

[0052] 40. Dehydration and mercury removal unit; 41. Cooler; 42. First three-phase separator; 43. Pre-filter; 44. Molecular sieve adsorption tower; 45. Mercury removal tower; 46. Post-filter;

[0053] 50. Heavy hydrocarbon removal unit; 51. Heavy contact tower; 52. Cryogenic separator;

[0054] 60. Liquefaction unit; 61. Main cold box; 62. Main refrigeration unit;

[0055] 70. Denitrification unit; 71. Denitrification tower;

[0056] 80. Helium extraction unit; 81. Membrane treatment unit; 82. Pressure swing adsorption purification unit;

[0057] 90. Mixed hydrocarbon stabilization unit; 91. Ethane removal tower;

[0058] 100. Condensate desulfurization unit; 101. Second and third phase separator; 102. Condensate desulfurization tower;

[0059] 110. Precooling unit; 111. Precooling box; 112. Precooler. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] The present invention will now be described in further detail with reference to the accompanying drawings:

[0062] like Figure 1 As shown, this invention provides a zero-emission scattered gas liquefaction and recovery system with helium extraction, used to achieve liquefaction, denitrification, helium extraction, and sulfur-containing condensate recovery of scattered gas with high sulfur content, high nitrogen content, low helium content, and rich heavy hydrocarbons; it includes: an inlet separation unit 10, a feed gas pressurization unit 20, a feed gas deacidification unit 30, a dehydration and mercury removal unit 40, a heavy hydrocarbon removal unit 50, a liquefaction unit 60, a denitrification unit 70, a helium extraction unit 80, a mixed hydrocarbon stabilization unit 90, a condensate desulfurization unit 100, and a precooling unit 110; wherein,

[0063] The inlet separation unit 10 of the present invention is used to perform gas-liquid separation on the raw material gas to obtain a first gas phase. Specifically, the inlet separation unit 10 includes an inlet separator 11. The inlet of the inlet separator 11 is connected to the raw material gas and the exhaust gas from the de-ethane tower 91, the second three-phase separator 101 and the condensate desulfurization tower 102. The inlet separator 11 separates the mixed gas to obtain a first gas phase and a liquid phase. The liquid phase is treated for sewage discharge.

[0064] The raw gas pressurization unit 20 of the present invention is used to perform interstage pressurization on the first gas phase to obtain a second gas phase and a first sulfur-containing condensate; specifically, the raw gas pressurization unit 20 includes a multi-stage compressor 21 and a separator 22 arranged sequentially at intervals, such as... Figure 1 The two-stage compressor 21 and the three-stage separator 22 shown are connected. The outlet of the inlet separator 11 is connected to the inlet of the front-stage separator, and the outlet of the rear-stage separator is connected to the inlet of the filter 31. The liquid phase of the first-stage separator 22 is discharged. The first sulfur-containing condensate produced by the second and third-stage separators 22 enters the second three-phase separator 101.

[0065] The raw gas deacidification unit 30 of the present invention is used to filter and deacidify the second gas phase to obtain a third gas phase and a second sulfur-containing condensate. Specifically, the raw gas deacidification unit 30 includes a filter 31 and an absorption tower 32 connected in sequence. The outlet of the filter 31 is connected to the lower inlet of the absorption tower 32. The top outlet of the absorption tower 32 is connected to the inlet of the cooler 41 and the condensate desulfurization tower 102. The amine-rich liquid at the bottom of the absorption tower 32 is regenerated by an external amine regeneration system (not shown in the figure) to obtain a lean amine liquid. The lean amine liquid enters the top of the absorption tower 32 and flows counterclockwise with the gas phase. The second sulfur-containing condensate in the filter 31 enters the second three-phase separator 101.

[0066] The dehydration and mercury removal unit 40 of the present invention is used to cool, separate the three phases, adsorb by molecular sieves, and remove mercury from all or part of the third gas phase to obtain a fourth gas phase and liquid hydrocarbons. Specifically, the dehydration and mercury removal unit 40 includes a cooler 41, a first three-phase separator 42, a pre-filter 43, one or more molecular sieve adsorption towers 44 connected in parallel, a mercury removal tower 45, and a post-filter 46 arranged sequentially along the gas processing direction. The outlet of the post-filter 46 is connected to the heavy contact tower 51 after passing through the pre-cooling box 111. The outlet of the post-filter 46 can also be connected to the inlet of the condensate desulfurization tower 102. The liquid hydrocarbon port of the first three-phase separator 42 is connected to the condensate desulfurization tower 102.

[0067] The heavy hydrocarbon removal unit 50 of the present invention is used to perform heavy contact and cryogenic separation on all or part of the fourth gas phase after precooling by the precooling unit to obtain a fifth gas phase and heavy hydrocarbon liquid; the denitrification unit 70 is used to denitrify the fifth gas phase after liquefaction by the liquefaction unit 60 to obtain LNG and a sixth gas phase; specifically, the heavy hydrocarbon removal unit 50 includes a heavy contact tower 51 and a cryogenic separator 52, the precooling unit 110 includes a precooling box 111 and a precooler 112 for cooling the precooling box, the denitrification unit 70 includes a denitrification tower 71, and the liquefaction unit 60 includes a main cold box 61 and a main cooler 62 for cooling the main cold box 61; the lower part of the heavy contact tower 51 is connected to all or part of the fourth gas phase after precooling by the precooling box 111. The exhaust gas from the top of the heavy contact tower 51 is connected to the main cold box 61 for primary cooling. The gas phase after primary cooling enters the cryogenic separator 52. The liquid phase separated by the cryogenic separator 52 enters the upper inlet of the heavy contact tower 51. A portion of the separated fifth gas phase enters the main cold box 61 for secondary cooling. The liquid phase after secondary cooling enters the upper inlet of the denitrification tower 71. Another portion of the separated fifth gas phase enters the lower inlet of the denitrification tower 71. The liquid phase at the bottom of the denitrification tower 71 enters the main cold box 61 for tertiary cooling before being fed into the LNG storage tank. The cooling temperature of the secondary or tertiary cooling is less than the cooling temperature of the primary cooling, which is less than the cooling temperature of the precooling. The cooling temperature of the secondary or tertiary cooling is below -162℃. The exhaust gas from the top of the denitrification tower 71 sequentially enters the cold end reflux channel of the main cold box 61 and the precooling box 111. After reheating, it goes to the molecular sieve adsorption tower 44 of the dehydration and mercury removal unit 40 as molecular sieve regeneration gas. The regenerated and cooled helium-containing gas is then fed into the helium extraction unit 80.

[0068] The helium extraction unit 80 of the present invention is used to extract helium from the sixth gas phase after passing through the liquefaction unit 60, the precooling unit 110, and the dehydration and mercury removal unit 40 to obtain high-purity helium gas; specifically, the helium extraction unit 80 includes a membrane treatment unit 81 and a pressure swing adsorption purification unit 82 arranged sequentially.

[0069] The mixed hydrocarbon stabilization unit 90 of the present invention is used to stabilize heavy hydrocarbon liquids, with the top gas returned to the inlet separation unit and the bottom liquid entering the mixed hydrocarbon storage tank. Specifically, the mixed hydrocarbon stabilization unit 90 includes a deethanizer 91, the inlet of which is connected to the bottom liquid outlet of the heavy contact tower 51, the top gas from the deethanizer 91 is returned to the inlet separator 11 at the front end, and the bottom condensate from the deethanizer 91 enters the mixed hydrocarbon storage tank.

[0070] The condensate desulfurization unit 100 of the present invention is used for gas stripping desulfurization of a first sulfur-containing condensate, a second sulfur-containing condensate, and heated liquid hydrocarbons. The top gas is returned to the inlet separation unit, and the bottom liquid enters the mixed hydrocarbon storage tank. Specifically, the condensate desulfurization unit 100 includes a second three-phase separator 101 and a condensate desulfurization tower 102. The inlet of the second three-phase separator 101 is connected to the first sulfur-containing condensate and the second sulfur-containing condensate. The outlet gas of the second three-phase separator 101 is returned to the inlet separator 11 at the front end. The liquid phase of the second three-phase separator 101 enters the upper part of the condensate desulfurization tower 102, the liquid hydrocarbons of the first three-phase separator 42 enter the middle part of the condensate desulfurization tower 102, and the remaining third or fourth gas phase enters the lower part of the condensate desulfurization tower 102. The bottom condensate of the condensate desulfurization tower 102 enters the mixed hydrocarbon storage tank.

[0071] This invention provides a zero-emission method for the liquefaction, recovery, and helium extraction of scattered gases containing high sulfur, high nitrogen, low helium, and rich in heavy hydrocarbons. The main process scheme employed is "wet acid removal and purification + adsorption dehydration and mercury removal + liquefaction with a pre-cooled mixed refrigerant + gas stripping denitrification + combined method (membrane + PSA) helium extraction"; specifically including:

[0072] S1. The inlet raw gas first enters the inlet separation unit 10 to achieve gas-liquid separation. The separated gas phase is metered and then sent to the raw gas pressurization unit 20. The sulfur-containing condensate generated by the interstage pressurization of the raw gas compressor is treated by the condensate desulfurization unit 100. The pressurized raw gas goes to the raw gas deacidification unit 30, and after being filtered by the filter 31, it enters the absorption tower 32. The raw gas enters from the bottom of the absorption tower 32 and passes through the absorption tower 32 from bottom to top. The fully regenerated lean amine liquid enters from the top of the absorption tower 32 and passes through the absorption tower 32 from top to bottom. The counter-flowing lean amine liquid and the pressurized raw gas are fully contacted in the absorption tower to remove CO2 and H2S from the raw gas, meeting the requirements of CO2≤50ppm and H2S≤4ppm in the purified gas. The rich amine liquid coming out from the bottom of the absorption tower 32 goes to the amine liquid regeneration system.

[0073] S2. After deacidification, the raw gas is cooled by chilled water in cooler 41 and then goes to the first three-phase separator 42, where a large amount of free water and liquid hydrocarbons are separated. The separated liquid hydrocarbons are heated and then go to the condensate desulfurization unit 100. The gas phase of the first three-phase separator 42 passes through the pre-filter 43 to remove impurities and liquid components and enters the molecular sieve adsorption tower 44. In the tower, the liquid components are further removed by adsorbent and protective agent, and then the gas contacts the molecular sieve for dehydration and drying, so that the water content in the raw gas is ≤0.1ppm. The raw gas exits the tower and enters the mercury removal tower 45, where sulfur-impregnated activated carbon is used to remove mercury, so that the Hg in the raw gas is ≤0.01μg / Nm3, preventing problems such as cold box corrosion and leakage.

[0074] S3. The purified raw gas first passes through the precooling unit 110, and after being cooled by chilled water, it enters the heavy hydrocarbon removal unit 50. The precooled raw gas from the bottom of the heavy hydrocarbon removal contact tower 51 comes into contact with the reflux condensate of the low-temperature separator 52 at the top of the tower to remove heavy hydrocarbons. After heavy hydrocarbon removal, the gas phase continues to enter the cryogenic module main cold box 61 of the liquefaction unit 60 for cooling to -50°C. It then enters the low-temperature separator 52 for gas-liquid separation. The separated low-temperature condensate is pumped to the top of the heavy hydrocarbon contact tower 51. A portion of the gas phase from the separator continues to enter the main cold box 61 for cooling to below -162°C and then liquefying. After being throttled and depressurized by the JT valve, it goes to the denitrification unit 70.

[0075] S4. The liquefied natural gas flows from top to bottom to the top of the denitrification tower 71. After contacting another part of the gas from the low-temperature separation gas phase outlet inside the tower, most of the nitrogen and helium are removed. LNG that meets the product index requirements is obtained at the bottom of the tower. It is then returned to the main cold box 61 to be subcooled to below -162°C. After being throttled and depressurized by the JT valve, the LNG product is obtained and sent to the LNG storage tank in the plant area.

[0076] S5. Heavy hydrocarbons at the bottom of the heavy contact tower 51 are depressurized by a throttling valve and then stabilized in the deethaner tower 91 of the mixed hydrocarbon stabilization unit 90. The top gas from the deethaner tower 91 returns to the front-end inlet separator 11, and the condensate from the deethaner tower 91 enters the mixed hydrocarbon storage tank. The nitrogen-rich and helium-rich gas from the top of the denitrification tower 71 enters the reflux channel at the cold end of the main cold box 61. After reheating, it goes to the molecular sieve adsorption tower 43 of the dehydration and mercury removal unit 40 as molecular sieve regeneration gas. The regenerated and cooled helium-containing gas is then introduced into the helium extraction unit 80.

[0077] The main function of S6, the helium extraction unit 80, is to extract helium from the overhead gas of the denitrification tower 71. It mainly consists of a membrane treatment unit 81 and a pressure swing adsorption (PSA) purification unit 82. The reheated nitrogen- and helium-rich gas enters the membrane treatment unit. Due to the different permeabilities of the various components of the feed gas to the special membrane, driven by the pressure difference across the membrane, helium is concentrated using its high permeability. Using a multi-stage membrane separation method, the helium concentration can be increased to 80%–90%. The concentrated crude helium then goes to the PSA helium purification unit. After mixing with air, the crude helium is preheated and catalytically oxidized to remove H2 and hydrocarbons before entering the two-stage PSA unit to remove water, CO2, N2, and O2, yielding 99.999% pure nitrogen.

[0078] S7. All sulfur-containing condensate before the raw material gas deacidification unit 30 is throttled and depressurized, then sent to the condensate desulfurization unit 100. The sulfur-containing condensate enters the three-phase separator 101 for oil-gas-water separation. The gas phase separated by flash evaporation returns to the inlet of the inlet separator. The sulfur-containing condensate flows from top to bottom at the top of the condensate desulfurization tower 102. A portion of the purified gas after deacidification is taken as stripping gas and flows from bottom to top in the lower part of the condensate desulfurization tower. The two gases come into contact and transfer mass inside the condensate desulfurization tower, removing H2S from the sulfur-containing condensate and entering the gas phase. The condensate separated by the three-phase separator 41 in the dehydration and mercury removal unit 40 is heated and throttled before entering the lower part of the condensate desulfurization tower 102 for flash stabilization. The deacidified condensate is pressurized by a pump and enters the mixed hydrocarbon storage tank. The top gas of the condensate desulfurization tower 102 returns to the inlet of the inlet separator.

[0079] further,

[0080] 1) The purified gas from the dehydration and mercury removal unit can also be used as the gas stripping gas in the condensate desulfurization unit 100.

[0081] 2) The stripping gas from the condensate desulfurization unit 100 can be heated before entering the desulfurization tower 102 deacidification tower, thereby reducing the amount of stripping gas used and improving the quality of the condensate.

[0082] 3) The dehydration unit can adopt a two-tower process, a three-tower process, or a two-and-a-half-tower process, provided that the dehydration point index is met.

[0083] 4) The raw gas precooling unit 110 is not limited to water cooling, propane precooling, mixed refrigerant precooling, etc.

[0084] 5) The mixed hydrocarbon stabilization unit 90 can adopt a scheme that simultaneously recovers LPG and stabilizes light hydrocarbons. LPG can be used as a supplement to the mixed refrigerant, reducing the additional amount of propane and butane refrigerant used.

[0085] 6) The denitrification tower can adopt either a half-tower distillation process or a full-tower distillation process.

[0086] The advantages of this invention are:

[0087] 1. This invention is applicable to the gas composition of scattered gases with high sulfur content, high nitrogen content, low helium content, and rich in heavy hydrocarbons. It has strong applicability to a wide range of raw gas components with high impurity content, simplifies the process flow, and expands the application scope of scattered gas recovery and liquefaction.

[0088] 2. This invention adopts a natural gas pre-cooling and gradual condensation process, which improves the yield of mixed hydrocarbon products, fully realizes energy utilization, and reduces the overall liquefaction energy consumption;

[0089] 3. This invention can use LPG products as a refrigerant supplement, innovatively combining the product with refrigerant proportioning technology, taking into account C 3+The yield and liquefaction energy consumption have been optimized, the refrigerant formulation has been improved, raw material self-sufficiency has been achieved, the process has been simplified, and the overall operational flexibility has reached 30% to 120%.

[0090] 4. This invention uses gas stripping desulfurization process to recover sulfur-containing condensate, which significantly reduces energy consumption, improves the yield of mixed hydrocarbons, and achieves full recovery of carbon-containing components in the feed gas.

[0091] 5. In view of the high nitrogen content of the raw gas components, this invention combines the denitrification process to realize the recovery of helium. The helium recovery process takes into account the overall process, makes full use of the cooling capacity of nitrogen-containing and helium-containing gases, saves refrigeration energy consumption, and at the same time, this part of the gas is used as the regeneration gas of the dehydration unit, which improves the processing capacity of the dehydration unit and reduces the regeneration energy consumption.

[0092] 6. The system of the present invention realizes a closed-loop cycle, achieves zero CH4 emissions during operation, improves the utilization efficiency of natural gas, protects the environment, and saves non-renewable resources.

[0093] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A zero-emission scattered gas liquefaction recovery and co-production helium extraction system, characterized in that, include: The system includes an inlet separation unit, a feed gas pressurization unit, a feed gas acid removal unit, a dehydration and mercury removal unit, a precooling unit, a heavy hydrocarbon removal unit, a liquefaction unit, a denitrification unit, a helium extraction unit, a mixed hydrocarbon stabilization unit, and a condensate desulfurization unit; among which, The inlet separation unit is used to separate the raw material gas into a gas-liquid phase to obtain the first gas phase; The raw gas pressurization unit is used to perform interstage pressurization on the first gas phase to obtain the second gas phase and the first sulfur-containing condensate. The raw material gas deacidification unit is used to filter and deacidify the second gas phase to obtain a third gas phase and a second sulfur-containing condensate. The dehydration and mercury removal unit is used to cool, separate the three phases, adsorb by molecular sieves and remove mercury from all or part of the third gas phase to obtain a fourth gas phase and liquid hydrocarbons. The heavy hydrocarbon removal unit is used to re-contact and perform low-temperature separation on all or part of the fourth gas phase after precooling by the precooling unit to obtain the fifth gas phase and heavy hydrocarbon liquid. The denitrification unit is used to denitrify the fifth gas phase after liquefaction by the liquefaction unit to obtain LNG and the sixth gas phase. The helium extraction unit is used to extract helium from the sixth gas phase after passing through the liquefaction unit, precooling unit, and dehydration and mercury removal unit to obtain high-purity helium. The mixed hydrocarbon stabilization unit is used to stabilize the heavy hydrocarbon liquid, with top gas returned to the inlet separation unit and bottom liquid entering the mixed hydrocarbon storage tank. The condensate desulfurization unit is used to perform gas stripping desulfurization on the first sulfur-containing condensate, the second sulfur-containing condensate, and the heated liquid hydrocarbons. The top gas is returned to the inlet separation unit, and the bottom liquid enters the mixed hydrocarbon storage tank.

2. The zero-emission scattered gas liquefaction recovery and co-production helium extraction system as described in claim 1, characterized in that, The inlet separation unit includes an inlet separator, the raw material gas pressurization unit includes a multi-stage compressor and a separation tank arranged at intervals, and the raw material gas deacidification unit includes a filter and an absorption tower; The outlet of the inlet separator is connected to the inlet of the pre-separation tank, the outlet of the post-separation tank is connected to the inlet of the filter, the outlet of the filter is connected to the lower inlet of the absorption tower, and the top outlet of the absorption tower is connected to the dehydration and mercury removal unit. The rich amine liquid at the bottom of the absorption tower is regenerated by an external amine liquid regeneration system to obtain a lean amine liquid, which enters the top of the absorption tower and flows counter-currently with the gas phase. The liquid phase in the inlet separator and the pre-separation tank enters the sludge discharge unit, and the first sulfur-containing condensate in the remaining separation tank and the second sulfur-containing condensate in the filter enter the condensate desulfurization unit.

3. The zero-emission scattered gas liquefaction recovery and co-production helium extraction system as described in claim 2, characterized in that, The dehydration and mercury removal unit includes a cooler, a first three-phase separator, a pre-filter, a molecular sieve adsorption tower, a mercury removal tower, and a post-filter. The cooler is connected to the outlet of the absorption tower and the inlet of the first three-phase separator. The cold source of the cooler comes from the pre-cooler of the pre-cooling unit. The outlet of the first three-phase separator is sequentially connected to the pre-filter, one or more molecular sieve adsorption towers connected in parallel, mercury removal tower and post-filter. The outlet of the post-filter is connected to the heavy hydrocarbon removal unit after passing through the pre-cooling box of the pre-cooling unit. The liquid hydrocarbon port of the first three-phase separator is connected to the condensate desulfurization unit.

4. The zero-emission scattered gas liquefaction recovery and co-production helium extraction system as described in claim 3, characterized in that, The heavy hydrocarbon removal unit includes a heavy contact tower and a cryogenic separator; the precooling unit includes a precooling box and a pre-cooling unit that supplies cooling to the precooling box; the denitrification unit includes a denitrification tower; and the liquefaction unit includes a main cold box and a main refrigeration unit that supplies cooling to the main cold box. The lower inlet of the heavy contact tower receives all or part of the fourth gas phase, which has been precooled by the precooling box. The top exhaust of the heavy contact tower is connected to the main cold box for primary cooling. The gas phase after primary cooling enters the cryogenic separator. The liquid phase separated by the cryogenic separator enters the upper liquid inlet of the heavy contact tower. A portion of the separated fifth gas phase is connected to the main cold box for secondary cooling. The liquid phase after secondary cooling is connected to the upper liquid inlet of the denitrification tower. Another portion of the separated fifth gas phase is connected to the lower inlet of the denitrification tower. The liquid phase at the bottom of the denitrification tower is connected to the main cold box for tertiary cooling before being fed into the LNG storage tank.

5. The zero-emission scattered gas liquefaction recovery and co-production helium extraction system as described in claim 4, characterized in that, The cooling temperature of secondary or tertiary cooling is less than that of primary cooling, which is less than that of pre-cooling; the cooling temperature of secondary or tertiary cooling is below -162℃.

6. The zero-emission scattered gas liquefaction recovery and co-production helium extraction system as described in claim 4, characterized in that, The gas vented from the top of the denitrification tower enters the cold end reflux channel of the main cold box and the precooling box in sequence. After reheating, it goes to the molecular sieve adsorption tower of the dehydration and mercury removal unit as molecular sieve regeneration gas. The regenerated and cooled helium-containing gas is then introduced into the helium extraction unit.

7. The zero-emission scattered gas liquefaction recovery and co-production helium extraction system as described in claim 6, characterized in that, The helium extraction unit includes a membrane processing unit and a pressure swing adsorption purification unit arranged sequentially.

8. The zero-emission scattered gas liquefaction recovery and co-production helium extraction system as described in claim 4, characterized in that, The mixed hydrocarbon stabilization unit includes an ethane stripper; The inlet of the deethaner is connected to the bottom liquid outlet of the heavy contact tower. The top gas from the deethaner is returned to the inlet separator at the front end, and the bottom condensate from the deethaner enters the mixed hydrocarbon storage tank.

9. The zero-emission scattered gas liquefaction recovery and co-production helium extraction system as described in claim 4, characterized in that, The condensate desulfurization unit includes a second three-phase separator and a condensate desulfurization tower; The inlet of the second three-phase separator is connected to the first sulfur-containing condensate and the second sulfur-containing condensate. The gas outlet of the second three-phase separator is returned to the inlet separator at the front end. The liquid phase of the second three-phase separator enters the upper part of the condensate desulfurization tower. The liquid hydrocarbons of the first three-phase separator enter the middle part of the condensate desulfurization tower. The remaining third or fourth gas phase enters the lower part of the condensate desulfurization tower. The condensate at the bottom of the condensate desulfurization tower enters the mixed hydrocarbon storage tank.

10. A zero-emission scattered gas liquefaction recovery and helium co-production method, employing the zero-emission scattered gas liquefaction recovery and helium co-production system as described in any one of claims 1 to 9, characterized in that, include: The inlet separation unit performs gas-liquid separation on the raw material gas to obtain the first gas phase; The raw gas pressurization unit performs interstage pressurization on the first gas phase to obtain the second gas phase and the first sulfur-containing condensate. The raw gas deacidification unit filters and deacidifies the second gas phase to obtain the third gas phase and the second sulfur-containing condensate; The dehydration and mercury removal unit cools, separates, adsorbs and removes mercury from all or part of the third gas phase to obtain a fourth gas phase and liquid hydrocarbons. The heavy hydrocarbon removal unit re-contacts and performs low-temperature separation on all or part of the fourth gas phase after precooling by the precooling unit to obtain the fifth gas phase and heavy hydrocarbon liquid. The denitrification unit denitrifies the fifth gas phase after liquefaction in the liquefaction unit to obtain LNG and the sixth gas phase. The helium extraction unit extracts helium from the sixth gas phase after passing through the liquefaction unit, precooling unit, and dehydration and mercury removal unit to obtain high-purity helium. The mixed hydrocarbon stabilization unit stabilizes the heavy hydrocarbon liquid, the top gas is returned to the inlet separation unit, and the bottom liquid enters the mixed hydrocarbon storage tank. The condensate desulfurization unit performs gas stripping desulfurization on the first sulfur-containing condensate, the second sulfur-containing condensate, and the heated liquid hydrocarbons. The top gas is returned to the inlet separation unit, and the bottom liquid enters the mixed hydrocarbon storage tank.

Images