An integrated membrane separation light hydrocarbon recovery system for shale oil associated gas

Abstract

The invention discloses an integrated membrane separation light hydrocarbon recovery system for shale oil associated gas. The compressed shale oil associated gas is used as the feed gas and is successively heat-exchanged with the materials in the deethanizer tower and passed through a cooler. After cooling, it enters a drying device for dehydration and drying. After being sent to a first-stage spiral tube multi-pass heat exchanger for temperature reduction, it enters a shallow cold condenser for condensation. Then, the non-condensable gas is sent to a low-temperature first-stage separator, and the gas phase of the low-temperature first-stage separator is sent to a second-stage spiral tube multi-pass heat exchanger. After further cooling, it is sent to a low-temperature second-stage separator. The liquid phases of the low-temperature first-stage separator and the low-temperature second-stage separator are respectively sent to the liquid inlet in the middle and upper parts of the deethanizer tower. The heat exchange cold source of this system comes from the shallow cold refrigeration system and the process gas expansion refrigeration. By integrating the membrane separation technology and the condensation process and applying it to the light hydrocarbon recovery in shale oil associated gas, the recovery rate of light hydrocarbons can be significantly increased, and the methane proportion in natural gas can be increased.

Description

Technical Field

[0001] The present invention relates to the field of treatment of associated natural gas in shale oil, and specifically to an integrated membrane separation light hydrocarbon recovery system for associated gas in shale oil. Background Art

[0002] For the recovery of light hydrocarbons from natural gas, three commonly used processes are oil absorption method, adsorption method, and condensation method. Most of the existing light hydrocarbon condensate recovery plants adopt the condensation method. The process of recovering condensate by the condensation method is to condense the C3+ components in natural gas at low temperature under a certain pressure and then perform gas-liquid separation to achieve the recovery purpose. According to the lowest freezing temperature of natural gas in the refrigeration separation system, the condensation separation method is usually divided into two types: shallow refrigeration separation and deep refrigeration separation. The freezing temperature of shallow refrigeration separation is generally between -20°C and -35°C, while the freezing temperature of deep refrigeration separation is generally lower than -45°C, and the lowest can reach below -100°C. Sometimes, only using refrigerant refrigeration is classified as the shallow refrigeration separation process, and using the turbine expander refrigeration method, the combined refrigeration method of refrigerant refrigeration and expansion refrigeration is classified as the deep refrigeration separation process.

[0003] CN206219508U discloses a natural gas treatment technology, which is applied to the treatment of associated gas in oil. This application has made process innovations and is especially applied to the treatment of associated gas in shale oil.

[0004] The membrane separation technology utilizes the organic vapor composite separation membrane to form a selective separation based on the different permeation rates of organic gases with different components through the membrane. Under the driving force of a certain working pressure difference, the hydrocarbon components with high boiling points and large molecules have a much higher permeation rate than the hydrocarbon components with low boiling points and small molecules, so as to achieve the enrichment of C3+ hydrocarbon components on the permeate gas side of the membrane separator, while the non-permeate gas side of the membrane separator becomes lean gas, and methane is further enriched on the non-permeate gas side. Domestic membrane separator products with low temperature resistance and high separation performance are used.

[0005] In shale oil production, there are a large number of scattered wellhead associated gas operation areas with small and medium production in oil fields. The associated gas contains a considerable proportion of saturated and unsaturated light hydrocarbon components, and the recovery of light hydrocarbons has important economic value. Under this background, integrating the membrane separation technology with the condensation process, making full use of the shallow refrigeration system and the deep refrigeration capacity of the expander, and combining the light hydrocarbon concentration ability of the gas membrane separation technology, the coupling effect of the two technologies can significantly improve the light hydrocarbon production capacity, improve the commercial quality of natural gas, and increase the economic benefits of enterprises. Summary of the Invention

[0006] The light hydrocarbon recovery system of the present invention is coupled and integrated with the membrane separation technology and the condensation process, and is applied to the light hydrocarbon recovery and deep processing of associated gas in shale oil, significantly improving the light hydrocarbon production and recovery rate. This system can be designed and applied to a light hydrocarbon plant of a certain scale, or can also be designed and applied to a small-scale skid-mounted light hydrocarbon recycling station.

[0007] The technical solution of the present invention is realized as follows: A shale oil associated gas integrated membrane separation light hydrocarbon recovery system. The shale oil associated gas is used as the raw material gas and passes through a compressor unit. The gas after pressure increase is heat-exchanged at the bottom of the deethanizer (7), and then further cooled by a cooler (6). After cooling, it enters a gas-liquid separator (4). The liquid-phase hydrocarbon of the gas-liquid separator (4) is sent to a storage tank (8). The gas-phase of the gas-liquid separator (4) enters a drying device (3) for drying and dehydration. After dehydration, it is sent to a first-stage spiral wound multi-pass heat exchanger (11) for temperature reduction, and then enters a shallow cold condenser (13) for condensation, and then is sent to a low-temperature first-stage separator (5). The gas-phase of the low-temperature first-stage separator (5) is sent to a second-stage spiral wound multi-pass heat exchanger (14) for further cooling and then sent to a low-temperature second-stage separator (9). The liquid-phase of the low-temperature first-stage separator (5) is sent to the middle liquid inlet of the deethanizer (7). The gas-phase outlet of the low-temperature second-stage separator (9) is connected to the inlet of the membrane separation unit (12) after passing through the second-stage spiral wound multi-pass heat exchanger (14). The liquid-phase outlet of the low-temperature second-stage separator (9) is connected to the upper liquid inlet of the deethanizer (7). The gas-phase outlet at the top of the deethanizer (7) is connected to the inlet of the raw material gas compressor unit after heat exchange through the first-stage spiral wound multi-pass heat exchanger (11). The liquid-phase outlet at the bottom of the deethanizer (7) is connected to the inlet of the liquid hydrocarbon storage tank (8).

[0008] Further, the membrane separation unit comprises a number of membrane separators connected in series or in parallel. The structure of the membrane separator can be of types such as flat plate, spiral wound, stacked, etc., and is designed and manufactured as a low-temperature resistant membrane separator, usually with a minimum operating temperature of -40°C. The permeate gas of the membrane separation unit (12) exchanges heat with the first-stage spiral wound multi-pass heat exchanger (11) to recover cold energy. After the permeate gas is heated up, it is used as a light hydrocarbon enriched gas and sent to the inlet of the recycle compressor unit (10). The recycle gas at the outlet of the recycle compressor is mixed with the raw material gas. The retentate gas of the membrane separation unit (12) is used as lean gas and sent to the expansion end of the expansion unit (15). The cold and dry gas after expansion successively passes through the second-stage spiral wound multi-pass heat exchanger (14) and the first-stage spiral wound multi-pass heat exchanger (11). After recovering cold energy and being pressurized as the braking gas of the expansion unit, it becomes dry gas for external transportation.

[0009] Further, the shallow cold condenser can use refrigerants such as ammonia or propane as the refrigerant and is used as a component device of the first-stage shallow cold refrigeration system; the expansion unit is used as a second-stage deep cold refrigeration device, and obtains deep cold low temperature through the expansion of the process gas to become the second-stage cold source.

[0010] Further, the shale oil associated gas is compressed in two stages by a raw material pre-stage compressor unit (1) and a raw material post-stage compressor unit (2). The gas-phase outlet at the top of the deethanizer (7) is connected to the inlet of the raw material gas post-stage compressor unit (2) after heat exchange through the first-stage spiral wound multi-pass heat exchanger (11).

[0011] Further, the dry gas output from the expansion unit (15) is compressed by a CNG compressor unit (16) to obtain product gas.

[0012] Further, the cooler is an air-cooled or water-cooled heat exchanger. The gas-liquid separator is a vertical or horizontal vessel. The gas phase is non-condensable gas, and the liquid phase includes two materials, water and hydrocarbon liquid. The water and hydrocarbon liquid are output from nozzles at different heights through stratification. The drying equipment usually adopts an adsorption / regeneration twin-tower switching molecular sieve dehydration equipment, which includes necessary heaters, coolers and gas-liquid separation equipment. The regeneration form of the adsorbent is dry gas heating regeneration. The deethanizer is a distillation column used to separate ethane (including lighter components) from heavier hydrocarbon components in cryogenic separation. The expansion unit, as a cryogenic equipment, can be selectively applied according to the basic component conditions of the specific raw gas to meet the project economic principle.

[0013] The beneficial effects of this patent are as follows: making full use of the light hydrocarbon concentration effect of the membrane separation technology and the light hydrocarbon condensation effect of the condensation process, through the combined application of the membrane separation technology and the shallow cooling and deep cooling technologies, the C3+ hydrocarbon components in the associated gas are recovered in depth step by step, and the light hydrocarbon recovery rate is improved. Compared with the existing process, the present invention applies the membrane separation integration technology to the light hydrocarbon recovery field of shale oil associated gas. ① Applying the low-temperature membrane separation group to further separate and recover the light hydrocarbon from the inlet gas of the expander, which not only ensures the cryogenic temperature of the expander refrigeration, but also reduces the dry gas dew point to ensure the safe operation of the expander. ② The top gas of the deethanizer is returned to the inter-stage compression of the compressor unit as recycle gas, and while removing methane and ethane, the C3+ components are further recovered. ③ Using the heat generated by gas compression as the heat source at the bottom of the deethanizer optimizes the energy utilization of the system. Description of the Drawings

[0014] Figure 1 It is the structure diagram of the integrated membrane separation light hydrocarbon recovery system for shale oil associated gas.

[0015] In the figure: 1. Feed gas pre-stage compressor unit; 2. Feed gas post-stage compressor unit; 3. Drying equipment; 4. Gas-liquid separator; 5. Low-temperature first-stage separator; 6. Cooler; 7. Deethanizer; 8. Storage tank; 9. Low-temperature second-stage separator; 10. Recycle gas compressor unit; 11. First-stage spiral-wound multi-pass heat exchanger; 12. Membrane separation group; 13. Shallow cooling condenser; 14. Second-stage spiral-wound multi-pass heat exchanger; 15. Expansion unit; 16. CNG compressor unit. Detailed Embodiments

[0016] The following further explains and illustrates this patent in combination with specific embodiments.

[0017] For a certain shale oil associated gas, Table 1:

[0018] Sampling component <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C3H8]]> <![CDATA[i-C4]]> <![CDATA[i-C5]]> <![CDATA[C6]]> C*= Others (mol %) 60.48 15.35 6.88 2.31 0.98 0.52 2.31 Slightly

[0019] Using the recovery system of the present invention, the light hydrocarbon recovery rate of 80-90% can be achieved under different working conditions.

[0020] As Figure 1 shown, the associated gas, as the feed gas, undergoes multi-stage compression by the pre-stage compressor unit 1 and the post-stage compressor unit 2. The gas after pressure increase is heat-exchanged at the bottom of the deethanizer tower 7 and then further cooled by the cooler 6, and then enters the gas-liquid separator 4 after cooling. The liquid-phase hydrocarbon in the gas-liquid separator is sent to the storage tank 8, and the gas-phase in the gas-liquid separator enters the drying equipment 3 for drying and dehydration. After being cooled down by the first-stage spiral multi-pass heat exchanger 11, it enters the shallow-cooling condenser 13 for condensation (usually the temperature can be cooled to -25°C), and then is sent to the low-temperature first-stage separator 5. The gas-phase in the low-temperature first-stage separator is sent to the second-stage spiral multi-pass heat exchanger 14, and after further cooling, it is sent to the low-temperature second-stage separator 9 (usually the temperature can be cooled to below -45°C); the liquid-phase in the low-temperature first-stage separator 5 is sent to the middle liquid inlet of the deethanizer tower 7. The cold source of the shallow-cooling condenser can be a refrigerant cooling source such as ammonia or propane, serving as the first-stage shallow-cooling equipment; the expansion unit 15 serves as the second-stage deep-cooling refrigeration equipment, obtaining low temperature through the expansion of the process gas and becoming the second-stage deep-cooling refrigeration cold source. The gas-phase outlet of the low-temperature second-stage separator 9 is connected to the gas inlet of the membrane separation unit 12 after passing through the second-stage spiral multi-pass heat exchanger 14, and the liquid-phase outlet is connected to the upper liquid inlet of the deethanizer tower 7. The permeate gas of the membrane separation unit recovers the cold energy through heat exchange with the first-stage spiral multi-pass heat exchanger 11, and after the permeate gas is heated up, it serves as the light-hydrocarbon enriched gas and is sent to the inlet of the recycle compressor unit 10, and the recycle gas at the compressor outlet is mixed with the feed gas. The retentate gas of the membrane separation unit 12 serves as the lean gas and is sent to the expansion end of the expansion unit 15. After expansion, the cold and dry gas passes through the second-stage spiral multi-pass heat exchanger 14 and the first-stage spiral multi-pass heat exchanger 11 successively, and after recovering the cold energy, it is pressurized as the braking gas of the expansion unit and then becomes the dry gas for external transmission. The external transmission dry gas is compressed by the CNG compressor unit 16 to obtain the product gas. The gas-phase outlet at the top of the deethanizer tower 7 is connected to the gas inlet of the post-stage compressor unit 2 of the feed gas after heat exchange through the first-stage spiral multi-pass heat exchanger 11, and the liquid-phase outlet at the bottom of the tower is connected to the liquid inlet of the liquid-hydrocarbon storage tank 8.

[0021] The above is only the preferred specific implementation mode of this patent, but the protection scope of this patent is not limited thereto. Any person skilled in the art within the technical scope disclosed by this patent, according to the technical solution and patent concept of this patent, making equivalent substitutions or changes, should be covered within the protection scope of this patent.

Claims

1. An integrated membrane separation light hydrocarbon recovery system for shale oil associated gas, characterized in that The associated gas of shale oil is used as the feed gas and passes through a compressor train. The gas after pressure boosting is heat-exchanged at the bottom of the deethanizer tower (7), further cooled by a cooler (6), and then enters a gas-liquid separator (4). The liquid-phase hydrocarbon in the gas-liquid separator (4) is sent to a storage tank (8). The gas-phase in the gas-liquid separator (4) enters a drying device (3) for drying and dehydration. After dehydration, it is sent to a first-stage spiral wound multi-pass heat exchanger (11) for temperature reduction and then enters a shallow-cooling condenser (13) for condensation. Then it is sent to a low-temperature first-stage separator (5). The gas-phase in the low-temperature first-stage separator (5) is sent to a second-stage spiral wound multi-pass heat exchanger (14) for further cooling and then sent to a low-temperature second-stage separator (9). The liquid-phase in the low-temperature first-stage separator (5) is sent to the middle liquid inlet of the deethanizer tower (7). The gas-phase outlet of the low-temperature second-stage separator (9) is connected to the inlet of a membrane separation unit (12) after passing through the second-stage spiral wound multi-pass heat exchanger (14). The liquid-phase outlet of the low-temperature second-stage separator (9) is connected to the upper liquid inlet of the deethanizer tower (7). The gas-phase outlet at the top of the deethanizer tower (7) is connected to the inlet of the feed gas compressor train after heat exchange through the first-stage spiral wound multi-pass heat exchanger (11). The liquid-phase outlet at the bottom of the deethanizer tower (7) is connected to the inlet of the liquid hydrocarbon storage tank (8); The permeate gas of the membrane separation unit (12) recovers cold energy through heat exchange with the first-stage spiral wound multi-pass heat exchanger (11). After the permeate gas is heated up, it is used as a light hydrocarbon enriched gas and sent to the inlet of a recycle compressor train (10). The recycle gas at the outlet of the recycle compressor train (10) is mixed with the feed gas; The retentate gas of the membrane separation unit (12) is used as lean gas and sent to the expansion end of an expansion unit (15). The cold and dry gas after expansion passes through the second-stage spiral wound multi-pass heat exchanger (14) and the first-stage spiral wound multi-pass heat exchanger (11) successively. After recovering cold energy, it is used as the braking gas of the expansion unit and is pressurized to become dry gas for external transmission.

2. The integrated membrane separation light hydrocarbon recovery system for shale oil associated gas according to claim 1, wherein The cold source of the shallow-cooling condenser (13) is a shallow-cooling refrigeration cold source using ammonia or propane refrigerant as the refrigerant medium.

3. The integrated membrane separation light hydrocarbon recovery system for shale oil associated gas according to claim 1, wherein The associated gas of shale oil is used as the feed gas and is compressed in two stages by a feed gas pre-stage compressor train (1) and a feed gas post-stage compressor train (2). The gas-phase outlet at the top of the deethanizer tower (7) is connected to the inlet of the feed gas post-stage compressor train (2) after heat exchange through the first-stage spiral wound multi-pass heat exchanger (11).

4. The integrated membrane separation light hydrocarbon recovery system for shale oil associated gas according to claim 1, wherein The dry gas externally transmitted by the expansion unit (15) is compressed by a CNG compressor train (16) to obtain product gas.

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