Device and process method for mixed hydrocarbon co-production of LNG (Liquefied Natural Gas)

Abstract

The invention belongs to the technical field of oil field associated gas recycling, and particularly provides a device and a process method for mixed hydrocarbon co-production of LNG (Liquefied Natural Gas). Comprising a raw material gas metering and separating unit, a raw material gas pressurizing unit, a raw material gas deacidification unit, a raw material gas dehydration unit, a low-temperature separation unit, a mixed hydrocarbon washing and stabilizing unit, a dry gas metering and separating unit, a sewage collecting unit and an LNG separation and storage unit, the method solves the problem of low recycling rate of the existing oil field associated gas, and has the advantages of improving the utilization rate of the associated gas, reducing the oil gas loss of the oil field, improving the production safety, increasing the benefits of the oil field, saving energy and reducing emission.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield associated gas recovery and utilization, and specifically relates to a device and a process method for co-producing LNG by mixing hydrocarbons. Background Art

[0002] After crude oil is extracted from underground, a large amount of associated gas is separated from the crude oil. During the process of viscosity reduction, heating and gathering, if the process is non-closed gathering, most of the light components such as methane, ethane, propane in the crude oil will escape, and at the same time take away a certain amount of butane, pentane, hexane and other light components, causing losses along the way during transportation. The comprehensive utilization of associated gas can effectively reduce crude oil loss, rationally utilize oil and gas resources, improve the level of oilfield development, and achieve good economic and social benefits. It is an important measure to achieve quality improvement, efficiency improvement, safety and environmental protection, energy conservation and emission reduction, and cost reduction and profit creation. It is of great significance to help the country achieve the "dual carbon" strategic goal.

[0003] Domestic light hydrocarbon recovery methods are divided into cold oil absorption method and low temperature condensation method. The cold oil absorption method is to inject absorbent (mainly liquid hydrocarbon) into the top of the deethanizer under shallow cold conditions (-30℃, 1.7MPa), and countercurrently contact with the raw gas entering the middle of the deethanizer to absorb the C3+ components. The low temperature condensation method is also called the direct contact method (DHX method). This process is carried out in the reabsorption tower (DHX tower) (-40℃, 1.3MPa). The gas at the top of the deethanizer is in direct contact with the refrigerated raw gas to condense the C3+ hydrocarbons in the gas. Most of the light hydrocarbon recovery devices built at home and abroad in the past 20 years have adopted the low temperature condensation method. The development of this method has promoted the progress of light hydrocarbon recovery technology.

[0004] However, these current processes only produce liquefied petroleum gas, natural gas condensate and dry gas, with single products. In addition, most of the excess dry gas beyond daily use is burned and discharged without further processing and utilization, resulting in problems such as waste of resources, environmental pollution, and low recovery rate of associated gas.

[0005] Therefore, in order to further improve the utilization rate of associated gas, the present invention proposes a mixed hydrocarbon co-production LNG process and device to achieve the recovery and utilization of oil field associated gas and solve the safety and environmental protection problems in production.

[0006] A Chinese patent document with publication number CN113430026A and publication date September 24, 2021 discloses an oilfield associated gas recovery system, including a pretreatment module, a stable hydrocarbon separation module and a natural gas separation module, the pretreatment module including a filtering device, a boost cooling device and a purification device, the purification device being provided with a CO2 acid gas mixture outlet and a natural gas mixture outlet; the stable hydrocarbon separation module including a cooling and drying device and a three-phase separation device connected in sequence to the CO2 acid gas mixture outlet, the oil phase port of the three-phase separation device being connected to a stable hydrocarbon storage device through a delivery pump; the natural gas separation module including a main cold box, a heavy contact tower, an auxiliary cold box, a deethanizer tower and a liquefied gas tower. When recycling the associated gas, this document needs to first separate the associated gas into two streams, namely a CO2 acid gas mixture and a natural gas mixture, through a purification device, and then extract stable hydrocarbons from the CO2 acid gas mixture and extract LPG products from the natural gas mixture. Although this method can separate, purify and liquefy the oilfield associated gas, realize the joint production of natural gas, petroleum gas and stable hydrocarbons, and improve the recovery efficiency of the oilfield associated gas, the purification device will separate the associated gas into two streams. However, the separation will not be complete when the purification device separates the associated gas into two streams, and a single stream will be mixed with substances in another stream. Since the separation and extraction methods of the two streams are different, the mixed substances to be extracted cannot be recovered, resulting in a low recovery rate of the associated gas, an increase in production equipment, and a high recycling cost. Summary of the invention

[0007] The device and process for co-producing LNG by mixing hydrocarbons provided by the present invention aim to overcome the problem of low recovery rate of associated gas in oil fields in the prior art.

[0008] To this end, the present invention provides a device for co-producing LNG with mixed hydrocarbons, comprising a raw gas metering and separation unit, a raw gas pressurizing unit, a raw gas deacidification unit, a raw gas dehydration unit, a low-temperature separation unit, a mixed hydrocarbon washing and stabilization unit, a dry gas metering and separation unit, a sewage collection unit and an LNG separation and storage unit, wherein the gas outlet of the raw gas metering and separation unit is connected to the inlet of the raw gas pressurizing unit, the raw gas pressurizing unit is connected to the inlet of the raw gas dehydration unit via the raw gas deacidification unit, the gas outlet of the raw gas dehydration unit is connected to the inlet of the low-temperature separation unit, the gas outlet one of the low-temperature separation unit is connected to the LNG separation and storage unit, the gas outlet two of the low-temperature separation unit is connected to the dry gas metering and separation unit, the liquid outlet of the low-temperature separation unit is connected to the inlet of the mixed hydrocarbon washing and stabilization unit, and the gas outlet of the mixed hydrocarbon washing and stabilization unit is connected to the inlet of the low-temperature separation unit; the liquid outlet of the raw gas dehydration unit, the liquid outlet of the raw gas pressurizing unit, the liquid outlet of the mixed hydrocarbon washing and stabilization unit and the liquid outlet of the dry gas metering and separation unit are all connected to the inlet of the sewage collection unit.

[0009] Preferably, the raw gas boosting unit includes a multi-stage compression, cooling and separation device, the gas outlet of the previous stage compression, cooling and separation device is connected to the inlet of the next stage compression, cooling and separation device, and the liquid outlet of each stage compression, cooling and separation device is connected to the sewage collection unit.

[0010] Preferably, the low-temperature separation unit comprises a cold box and a low-temperature separator, the gas outlet of the raw gas dehydration unit is connected to inlet one of the cold box, the gas outlet one of the cold box is connected to the inlet of the low-temperature separator, the gas outlet of the low-temperature separator is connected to inlet two of the cold box, and the gas outlet two of the cold box is connected to the inlet of the LNG separation storage unit (11); the liquid outlet of the low-temperature separator is connected to inlet three of the cold box, and the liquid outlet of the cold box is connected to the inlet of the mixed hydrocarbon washing and stabilization unit.

[0011] Preferably, the mixed hydrocarbon washing stabilization unit includes a mixed hydrocarbon stabilization tower and a mixed hydrocarbon storage tank, the liquid outlet of the cold box is connected to the inlet of the mixed hydrocarbon stabilization tower, the liquid outlet of the mixed hydrocarbon stabilization tower is connected to the mixed hydrocarbon storage tank, the gas outlet of the mixed hydrocarbon stabilization tower is connected to inlet four of the cold box, and the gas outlet three of the cold box is connected to the inlet of the dry gas metering and separation unit.

[0012] Preferably, the device for co-producing LNG by mixing hydrocarbons further comprises a pre-cooling device and a cryogenic device, and the cold air outlet of the pre-cooling device and the cold air outlet of the cryogenic device are both connected to the cold air inlet of the cold box.

[0013] Preferably, the cold box adopts an aluminum plate-fin heat exchanger.

[0014] Preferably, the sewage collection unit includes a heavy hydrocarbon collection tank and a sewage tank, and the liquid outlet of the raw gas dehydration unit, the liquid outlet of the raw gas boosting unit, the liquid outlet of the mixed hydrocarbon washing and stabilization unit and the liquid outlet of the dry gas metering and separation unit are all connected to the sewage tank via the heavy hydrocarbon collection tank.

[0015] Preferably, the LNG separation and storage unit comprises a nitrogen flash tank and an LNG storage tank, and the second gas outlet of the cold box is connected to the LNG storage tank via the nitrogen flash tank.

[0016] A process method for a device for co-producing LNG with mixed hydrocarbons based on any one of the above, comprising the following steps: associated gas enters a raw gas metering and separation unit for gas-liquid separation, the gas separated by the raw gas metering and separation unit enters a raw gas pressurizing unit for pressurization, the pressurized gas enters a raw gas deacidification unit for deacidification, the deacidified gas enters a raw gas dehydration unit for dehydration, the dehydrated gas enters a low-temperature separation unit for cooling and gas-liquid separation, the gas after cooling and separation enters an LNG separation and storage unit for nitrogen flash separation to generate LNG and is stored in an LNG storage tank, the liquid after cooling and separation enters a mixed hydrocarbon washing and stabilization unit for stable separation to generate mixed hydrocarbons and is then stored in a mixed hydrocarbon storage tank; the gas coming out of the mixed hydrocarbon washing and stabilization unit enters a dry gas metering and separation unit for gas-liquid separation after heat exchange in the low-temperature separation unit, and the gas separated by the dry gas metering and separation unit is metered and externally transmitted; the liquid separated by the raw gas metering and separation unit, the raw gas pressurizing unit, the raw gas dehydration unit, the mixed hydrocarbon washing and stabilization unit and the dry gas metering and separation unit is collected by a sewage collection unit.

[0017] Preferably, the raw gas deacidification unit adopts an activated MEDA chemical solvent absorption method for deacidification.

[0018] Beneficial effects of the present invention:

[0019] 1. The device and process method for co-producing LNG with mixed hydrocarbons provided by the present invention are as follows: the associated gas enters the raw gas metering and separation unit for gas-liquid separation, the gas separated by the raw gas metering and separation unit enters the raw gas pressurizing unit for pressurization, the pressurized gas enters the raw gas deacidification unit for deacidification, the deacidified gas enters the raw gas dehydration unit for dehydration, the dehydrated gas enters the low-temperature separation unit for cooling and gas-liquid separation, the cooled and separated gas enters the LNG separation and storage unit for nitrogen flash evaporation to generate LNG for storage in the LNG storage tank, the cooled and separated liquid enters the mixed hydrocarbon washing and stabilization unit for stable separation to generate mixed hydrocarbons, and then goes to the mixed hydrocarbon storage tank for storage; there is no need to divide the associated gas into multiple different streams, the entire device and process method is a processing method, after pressurization, purification, and liquefaction treatment, mixed hydrocarbons are produced and LNG is co-produced, the utilization rate of associated gas is improved, the problem of oil and gas loss in oil fields is solved, production safety is improved, and oil field benefits are increased, so as to meet the needs of Changqing Oilfield for "energy conservation and emission reduction, quality improvement and efficiency enhancement, cost reduction and profit creation".

[0020] 2. The device and process method for co-producing LNG by mixed hydrocarbons provided by the present invention provide cold air for the cold box through a precooling device and a cryogenic device. The refrigerants in the precooling device and the cryogenic device are circulated between the cold boxes, making full use of cold energy and reducing the energy consumption of the device.

[0021] 3. In the device and process method for co-producing LNG by mixed hydrocarbons provided by the present invention, the raw gas is pressurized to the target pressure through a multi-stage compression, cooling and separation device, so as to better meet the load requirements of the back-end device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Figure 1 It is a schematic diagram of the device and process method for co-producing LNG by mixing hydrocarbons.

[0024] Explanation of the reference numerals in the accompanying drawings: 1. Raw gas metering and separation unit; 2. Raw gas pressurizing unit; 3. Raw gas deacidification unit; 4. Raw gas dehydration unit; 5. Low-temperature separation unit; 6. Mixed hydrocarbon washing and stabilization unit; 7. Precooling device; 8. Deep cooling device; 9. Dry gas metering and separation unit; 10. Sewage collection unit; 11. LNG separation and storage unit; 2-1. Compressor; 2-2. Separator; 2-3. Cooler; 5-1. Cold box; 5-2. Low-temperature separator; 6-1. Mixed hydrocarbon stabilization tower; 6-2. Mixed hydrocarbon storage tank; 10-1. Heavy hydrocarbon collection tank; 10-2. Sewage tank; 11-1. Nitrogen flash tank; 11-2. LNG storage tank. DETAILED DESCRIPTION

[0025] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0026] Embodiment 1:

[0027] like Figure 1As shown, a device for co-producing LNG by mixed hydrocarbons comprises a raw gas metering and separation unit 1, a raw gas pressurizing unit 2, a raw gas deacidification unit 3, a raw gas dehydration unit 4, a low-temperature separation unit 5, a mixed hydrocarbon washing and stabilization unit 6, a dry gas metering and separation unit 9, a sewage collection unit 10 and an LNG separation and storage unit 11, wherein the gas outlet of the raw gas metering and separation unit 1 is connected to the inlet of the raw gas pressurizing unit 2, the raw gas pressurizing unit 2 is connected to the inlet of the raw gas dehydration unit 4 via the raw gas deacidification unit 3, and the gas outlet of the raw gas dehydration unit 4 is connected to the low-temperature separation The inlet of the unit 5, the gas outlet 1 of the low-temperature separation unit 5 is connected to the LNG separation storage unit 11, the gas outlet 2 of the low-temperature separation unit 5 is connected to the dry gas metering separation unit 9, the liquid outlet of the low-temperature separation unit 5 is connected to the inlet of the mixed hydrocarbon washing and stabilization unit 6, and the gas outlet of the mixed hydrocarbon washing and stabilization unit 6 is connected to the inlet of the low-temperature separation unit 5; the liquid outlet of the raw gas dehydration unit 4, the liquid outlet of the raw gas boosting unit 2, the liquid outlet of the mixed hydrocarbon washing and stabilization unit 6 and the liquid outlet of the dry gas metering separation unit 9 are all connected to the inlet of the sewage collection unit 10.

[0028] The raw gas metering and separation unit 1 is used to meter the raw gas flow rate and perform gas-liquid separation on the raw gas. Existing devices, including flow meters and gas-liquid separation devices, can be used to achieve metering and gas-liquid separation functions.

[0029] The entire device adopts a process treatment method to process associated gas. There is no need to divide the associated gas into multiple different streams. After pressurization, purification, and liquefaction, mixed hydrocarbons are produced and LNG is co-produced. This improves the utilization rate of associated gas, solves the problem of oil and gas loss in the oil field, improves production safety, and increases oil field benefits to meet the needs of Changqing Oilfield for "energy conservation and emission reduction, quality improvement and efficiency enhancement, cost reduction and profit creation."

[0030] The liquid outlet of the raw gas dehydration unit 4 , the liquid outlet of the raw gas boosting unit 2 , the liquid outlet of the mixed hydrocarbon washing and stabilization unit 6 and the liquid outlet of the dry gas metering and separation unit 9 are all connected to the inlet of the sewage collection unit 10 .

[0031] Preferably, the raw gas boosting unit 2 includes a multi-stage compression, cooling and separation device, the gas outlet of the previous stage compression, cooling and separation device is connected to the inlet of the next stage compression, cooling and separation device, and the liquid outlet of the previous stage compression, cooling and separation device is connected to the sewage collection unit 10.

[0032] The raw gas is pressurized to the target pressure through a multi-stage compression, cooling and separation device to better meet the load requirements of the back-end device.

[0033] Preferably, the multi-stage compression, cooling and separation device is a three-stage compression, cooling and separation device.

[0034] Preferably, each stage of compression, cooling and separation device comprises a compressor 2-1, a separator 2-2 and a cooler 2-3, the gas outlet of the raw gas metering separation unit 1 is connected to the inlet of the first stage compressor 2-1, the outlet of the first stage compressor 2-1 is connected to the inlet of the first stage separator 2-2 through the first stage cooler 2-3, the gas outlet of the first stage separator 2-2 is connected to the inlet of the next stage compressor 2-1, the liquid outlet of the first stage separator 2-2 is connected to the sewage collection unit 10, and so on. The structure is simple and can better meet the load requirements of the back-end device.

[0035] Preferably, a filter is provided between the raw gas pressurizing unit 2 and the raw gas deacidification unit 3. The filter is used to filter the pressurized gas, thereby protecting the raw gas deacidification unit 3 and improving the deacidification efficiency.

[0036] Preferably, the raw gas dehydration unit 4 is used to dehydrate the deacidified gas, and specifically, an existing dehydration device can be used to meet the dehydration requirements.

[0037] Preferably, the low-temperature separation unit 5 includes a cold box 5-1 and a low-temperature separator 5-2, the gas outlet of the raw gas dehydration unit 4 is connected to the inlet one of the cold box 5-1, the gas outlet one of the cold box 5-1 is connected to the inlet of the low-temperature separator 5-2, the gas outlet of the low-temperature separator 5-2 is connected to the inlet two of the cold box 5-1, and the gas outlet two of the cold box 5-1 is connected to the inlet of the LNG separation storage unit 11; the liquid outlet of the low-temperature separator 5-2 is connected to the inlet three of the cold box 5-1, and the liquid outlet of the cold box 5-1 is connected to the inlet of the mixed hydrocarbon washing and stabilization unit 6.

[0038] The cold box 5-1 is used to realize heat exchange between raw natural gas, top gas of the mixed hydrocarbon stabilization tower, low-temperature dry gas, refrigerant and other logistics, and the low-temperature separator 5-2 is used to separate and process the gas after heat exchange.

[0039] Preferably, the cold box 5-1 adopts an aluminum plate-fin heat exchanger, which is used to realize heat exchange between raw natural gas, top gas of the mixed hydrocarbon stabilization tower, low-temperature dry gas, refrigerant and other logistics, and the heat exchange load can reach 1230kW.

[0040] Preferably, the device for co-producing LNG with mixed hydrocarbons further comprises a precooling device 7 and a cryogenic device 8, and the cold air outlet of the precooling device 7 and the cold air outlet of the cryogenic device 8 are both connected to the cold air inlet of the cold box 5-1.

[0041] The precooling device 7 and the deep cooling device 8 provide cold air for the cold box 5-1, and the refrigerants in the precooling device 7 and the deep cooling device 8 are circulated between the cold boxes 5-1, so that the cold energy is fully utilized and the energy consumption of the device is reduced.

[0042] Preferably, the precooling device 7 is a propane refrigeration device, and the cryogenic device 8 is a mixed refrigerant refrigeration device; the cold box cooling capacity is provided by the mixed refrigerant refrigeration device and the propane refrigeration device, the propane first completes the precooling, and the mixed refrigerant then completes the cryogenic cooling, and the mixed refrigerant and the propane refrigerant are circulated between the refrigeration unit (precooling device 7 and cryogenic device 8) and the low-temperature separation unit 5.

[0043] Preferably, the mixed hydrocarbon washing and stabilization unit 6 includes a mixed hydrocarbon stabilization tower 6-1 and a mixed hydrocarbon storage tank 6-2, the liquid outlet of the cold box 5-1 is connected to the inlet of the mixed hydrocarbon stabilization tower 6-1, the liquid outlet of the mixed hydrocarbon stabilization tower 6-1 is connected to the mixed hydrocarbon storage tank 6-2, the gas outlet of the mixed hydrocarbon stabilization tower 6-1 is connected to the inlet four of the cold box 5-1, and the gas outlet three of the cold box 5-1 is connected to the inlet of the dry gas metering and separation unit 9.

[0044] The liquid phase separated by the low-temperature separator 5-2 is depressurized to the target pressure by a depressurizing valve, and then transported to the cold box 5-1 for heat exchange, and finally transported to the mixed hydrocarbon stabilization tower 6-1 for stabilization and cooling to generate mixed hydrocarbons, which are then transported to the mixed hydrocarbon storage tank 6-2 to meet the mixed hydrocarbon product index.

[0045] Preferably, the sewage collection unit 10 includes a heavy hydrocarbon collection tank 10-1 and a sewage tank 10-2, and the liquid outlet of the raw gas dehydration unit 4, the liquid outlet of the raw gas boosting unit 2, the liquid outlet of the mixed hydrocarbon washing and stabilization unit 6 and the liquid outlet of the dry gas metering and separation unit 9 are all connected to the sewage tank 10-2 through the heavy hydrocarbon collection tank 10-1.

[0046] The oily wastewater generated by the raw gas boosting unit 2, the raw gas dehydration unit 4, the mixed hydrocarbon washing and stabilization unit 6 and the dry gas metering and separation unit 9 is transported to the heavy hydrocarbon collection tank 10-1 of the wastewater collection unit 10 for buffering separation, and the hydrocarbon liquid is further recovered. The separated light oil is transported to the storage and transportation unit by a light oil pump at irregular intervals, and the separated wastewater is transported to the wastewater tank 10-2, and then transported to the wastewater tanker by a wastewater pump at irregular intervals to the wastewater treatment station for treatment. It has high utilization rate and convenient operation.

[0047] Preferably, the LNG separation storage unit 11 comprises a nitrogen flash tank 11 - 1 and an LNG storage tank 11 - 2 , and the second gas outlet of the cold box 5 - 1 is connected to the LNG storage tank 11 - 2 via the nitrogen flash tank 11 - 1 .

[0048] After deacidification and dehydration, the raw gas is cooled in the cold box 5-1 and then transported to the low-temperature separator 5-2. The separated gas phase is cooled to the target temperature in the cold box 5-1, and the low-temperature liquefied gas is transported to the nitrogen flash tank 11-1, flash-separated to generate LNG, and transported to the LNG storage tank 11-2. The LNG product index is met.

[0049] Embodiment 2:

[0050] On the basis of Example 1, a process method for a device for co-production of LNG with mixed hydrocarbons based on any one of the above-mentioned embodiments comprises the following steps: associated gas enters a raw gas metering and separation unit 1 for gas-liquid separation, the gas separated by the raw gas metering and separation unit 1 enters a raw gas pressurizing unit 2 for pressurization, the pressurized gas enters a raw gas deacidification unit 3 for deacidification, the deacidified gas enters a raw gas dehydration unit 4 for dehydration, the dehydrated gas enters a low-temperature separation unit 5 for cooling and gas-liquid separation, the gas after cooling and separation enters an LNG separation and storage unit 11 for flash evaporation to separate LNG and then stores the generated LNG, the liquid after cooling and separation enters a mixed hydrocarbon washing and stabilization unit 6 for stable cooling to generate mixed hydrocarbons and then stores the generated mixed hydrocarbons; the gas coming out of the mixed hydrocarbon washing and stabilization unit 6 enters a dry gas metering and separation unit 9 for gas-liquid separation after heat exchange in the low-temperature separation unit 5, and the gas separated by the dry gas metering and separation unit 9 is metered and transported out; the liquids separated by the raw gas pressurizing unit 2, the raw gas dehydration unit 4, the mixed hydrocarbon washing and stabilization unit 6 and the dry gas metering and separation unit 9 are all collected by a sewage collection unit 10.

[0051] The process method of the present invention is mainly aimed at recovering liquefied natural gas (LNG) and mixed hydrocarbons. After pressurization, purification and liquefaction treatment, mixed hydrocarbons are produced and LNG is co-produced at the same time, thereby improving the utilization rate of associated gas, solving the problem of oil and gas loss in oil fields, improving production safety, and increasing oil field benefits, so as to meet the needs of Changqing Oilfield for "energy conservation and emission reduction, quality improvement and efficiency enhancement, cost reduction and profit creation".

[0052] Preferably, the raw gas deacidification unit 3 adopts an activated MEDA chemical solvent absorption method for deacidification. The process flow of the activated MEDA chemical solvent absorption method adopts a conventional absorption + (flash evaporation + stripping) regeneration process scheme.

[0053] Embodiment 3:

[0054] Based on Example 2, the associated gas treatment capacity is 3×10 4 Nm 3 / d is implemented as an example, a process method of the device for co-producing LNG based on any one of the above-mentioned mixed hydrocarbons comprises the following steps:

[0055] The associated gas at 15℃ and 0.1MPa.g from the station enters the raw gas metering and separation unit 1 for gas-liquid separation;

[0056] The gas separated by the raw gas metering and separation unit 1 is metered and enters the raw gas boosting unit 2, where it is boosted to 4.6 MPa.a by a reciprocating compressor in three stages, cooled to 40°C in three stages, and the 4.6 MPa.a, 40°C raw gas separated by the three-stage separator is transported to the raw gas deacidification unit 3 for deacidification (specifically, the raw gas is filtered and separated, and enters the absorption tower for deacidification treatment, and the deacidification is performed to a carbon content of ≤50 ppm in the gas);

[0057] The purified gas after deacidification is then air-cooled, separated and transported to the raw gas dehydration unit 4 (specifically, the 4.1MPa.a, 40°C purified gas generated after deacidification is dehydrated by a molecular sieve drying tower to remove water content of the raw gas to ≤0.1ppm), and then transported to the low-temperature separation unit 5 for cooling and gas-liquid separation (specifically, the 3.97MPa.a, 40°C raw gas after deacidification and dehydration is cooled to 3.97MPa.a, -45°C by a cold box 5-1 and then transported to a low-temperature separator 5-2);

[0058] The gas after cooling and separation enters the LNG separation and storage unit 11 for flash evaporation to separate LNG and then store the generated LNG. The liquid after cooling and separation enters the mixed hydrocarbon washing and stabilization unit 6 for stabilization and cooling to generate mixed hydrocarbons and then store the generated mixed hydrocarbons (specifically: the 3.97MPa.a, -45°C gas phase separated by the low-temperature separator 5-2 is then cooled to -155°C by the cold box 5-1, and the low-temperature liquefied gas is transported to the nitrogen flash tank 11-1, flash-separated to generate LNG (-162°C, nitrogen content ≤1%), and then transported to the LNG storage tank 11-2; the 3.97MPa.a, -45°C liquid phase separated by the low-temperature separator 5-2 is depressurized to 2.67MPa.a by the pressure reducing valve, and then transported to the cold box 5-1 for heat exchange to 2.65MPa.a, 20°C, and finally transported to the mixed hydrocarbon stabilization tower 6-1 for stabilization and cooling to generate mixed hydrocarbons, which are then transported to the mixed hydrocarbon storage tank 6-2;

[0059] The 2.58MPa.a, -31°C gas from the mixed hydrocarbon washing and stabilization unit 6 is transported to a cold box for heat exchange to 2.56MPa.a, 40°C, and then is pressure-regulated to 1.5MPa.a by a pressure regulating valve before entering the dry gas metering and separation unit 9, where the dry gas metering and separation unit 9 performs gas-liquid separation, and the gas separated by the dry gas metering and separation unit 9 is metered and transported outward;

[0060] The liquid separated by the raw gas metering and separation unit 1, the raw gas pressurizing unit 2, the raw gas dehydration unit 4, the mixed hydrocarbon washing and stabilization unit 6 and the dry gas metering and separation unit 9 is transported to the heavy hydrocarbon collection tank 10-1 of the sewage collection unit 10 for buffering separation, and the hydrocarbon liquid is further recovered. The separated light oil is transported to the storage and transportation unit by the light oil pump at irregular intervals, and the separated sewage is transported to the sewage tank 10-2, and then transported to the sewage tanker by the sewage pump at irregular intervals to the sewage treatment station for treatment, with high utilization rate and convenient operation.

[0061] The LNG produced by this process has a methane content of ≥75%, C4+alkanes ≤2%, nitrogen content ≤1%, carbon dioxide content ≤0.01%, and hydrogen sulfide content ≤3.5mg / m 3, meeting the LNG product indicators; the generated mixed hydrocarbon vapor pressure ≤1380kPa, sulfur content ≤0.1%, meeting the mixed hydrocarbon product indicators; the generated dry gas high calorific value>31.4MJ / m 3 , sulfur content ≤ 200mg / m 3 , carbon dioxide content ≤3%, meeting the dry gas product indicators.

[0062] This process can achieve a C2+ recovery rate of up to 95%, generate diversified products (LNG, dry gas, mixed hydrocarbons), achieve 100% utilization of recovered associated gas, and reduce carbon emissions. The newly built associated gas processing capacity of this invention is 3×10 4 Nm 3 / d, it is estimated that about 6227.1t / a of mixed hydrocarbons and 4841.1t / a of LNG can be recovered annually, and annual sales can be increased by about 15 million yuan, achieving the dual goals of energy conservation and emission reduction and efficiency improvement. It has played a leading role in the development of oilfield associated gas recovery and utilization technology at home and abroad, and has broad prospects for promotion and application.

[0063] In the description of the present invention, it should be understood that if there are terms indicating an orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as a limitation on the present invention.

[0064] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A device for co-producing LNG by mixing hydrocarbons, characterized in that: The invention comprises a raw gas metering and separation unit (1), a raw gas pressurizing unit (2), a raw gas deacidification unit (3), a raw gas dehydration unit (4), a low temperature separation unit (5), a mixed hydrocarbon washing and stabilization unit (6), a dry gas metering and separation unit (9), a sewage collection unit (10) and an LNG separation and storage unit (11), wherein the gas outlet of the raw gas metering and separation unit (1) is connected to the inlet of the raw gas pressurizing unit (2), the raw gas pressurizing unit (2) is connected to the inlet of the raw gas dehydration unit (4) via the raw gas deacidification unit (3), and the gas outlet of the raw gas dehydration unit (4) is connected to the inlet of the low temperature separation unit (5). The first gas outlet of the low-temperature separation unit (5) is connected to the LNG separation storage unit (11), the second gas outlet of the low-temperature separation unit (5) is connected to the dry gas metering separation unit (9), the liquid outlet of the low-temperature separation unit (5) is connected to the inlet of the mixed hydrocarbon washing and stabilization unit (6), and the gas outlet of the mixed hydrocarbon washing and stabilization unit (6) is connected to the inlet of the low-temperature separation unit (5); the liquid outlet of the raw gas dehydration unit (4), the liquid outlet of the raw gas boosting unit (2), the liquid outlet of the mixed hydrocarbon washing and stabilization unit (6) and the liquid outlet of the dry gas metering separation unit (9) are all connected to the inlet of the sewage collection unit (10).

2. The device for co-producing LNG by mixing hydrocarbons as claimed in claim 1, characterized in that: The raw gas boosting unit (2) comprises a multi-stage compression, cooling and separation device, wherein the gas outlet of the previous stage compression, cooling and separation device is connected to the inlet of the next stage compression, cooling and separation device, and the liquid outlet of each stage compression, cooling and separation device is connected to the sewage collection unit (10).

3. The device for co-producing LNG by mixing hydrocarbons as claimed in claim 1, characterized in that: The low-temperature separation unit (5) comprises a cold box (5-1) and a low-temperature separator (5-2); the gas outlet of the raw gas dehydration unit (4) is connected to the first inlet of the cold box (5-1); the first gas outlet of the cold box (5-1) is connected to the inlet of the low-temperature separator (5-2); the gas outlet of the low-temperature separator (5-2) is connected to the second inlet of the cold box (5-1); the gas outlet of the cold box (5-1) is connected to the inlet of the LNG separation storage unit (11); the liquid outlet of the low-temperature separator (5-2) is connected to the third inlet of the cold box (5-1); and the liquid outlet of the cold box (5-1) is connected to the inlet of the mixed hydrocarbon washing and stabilization unit (6).

4. The device for co-producing LNG by mixing hydrocarbons as claimed in claim 3, characterized in that: The mixed hydrocarbon washing and stabilization unit (6) comprises a mixed hydrocarbon stabilization tower (6-1) and a mixed hydrocarbon storage tank (6-2); the liquid outlet of the cold box (5-1) is connected to the inlet of the mixed hydrocarbon stabilization tower (6-1); the liquid outlet of the mixed hydrocarbon stabilization tower (6-1) is connected to the mixed hydrocarbon storage tank (6-2); the gas outlet of the mixed hydrocarbon stabilization tower (6-1) is connected to the inlet four of the cold box (5-1); and the gas outlet three of the cold box (5-1) is connected to the inlet of the dry gas metering and separation unit (9).

5. The device for co-producing LNG by mixing hydrocarbons as claimed in claim 3, characterized in that: The device for co-producing LNG from mixed hydrocarbons also includes a pre-cooling device (7) and a cryogenic device (8), and the cold air outlet of the pre-cooling device (7) and the cold air outlet of the cryogenic device (8) are both connected to the cold air inlet of the cold box (5-1).

6. The device for co-producing LNG by mixing hydrocarbons as claimed in claim 3, characterized in that: The cold box (5-1) adopts an aluminum plate-fin heat exchanger.

7. The device for co-producing LNG by mixing hydrocarbons as claimed in claim 1, characterized in that: The sewage collection unit (10) comprises a heavy hydrocarbon collection tank (10-1) and a sewage tank (10-2); the liquid outlet of the raw gas dehydration unit (4), the liquid outlet of the raw gas boosting unit (2), the liquid outlet of the mixed hydrocarbon washing and stabilization unit (6) and the liquid outlet of the dry gas metering and separation unit (9) are all connected to the sewage tank (10-2) via the heavy hydrocarbon collection tank (10-1).

8. The device for co-producing LNG by mixing hydrocarbons as claimed in claim 3, characterized in that: The LNG separation storage unit (11) comprises a nitrogen flash tank (11-1) and an LNG storage tank (11-2), and a second gas outlet of the cold box (5-1) is connected to the LNG storage tank (11-2) via the nitrogen flash tank (11-1).

9. A process method for the device for co-production of LNG by mixed hydrocarbons according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: associated gas enters a raw gas metering and separation unit (1) for gas-liquid separation; the gas separated by the raw gas metering and separation unit (1) enters a raw gas pressurizing unit (2) for pressurization; the pressurized gas enters a raw gas deacidification unit (3) for deacidification; the deacidified gas enters a raw gas dehydration unit (4) for dehydration; the dehydrated gas enters a low-temperature separation unit (5) for cooling and gas-liquid separation; the gas after cooling and separation enters an LNG separation and storage unit (11) for nitrogen flash separation to generate LNG and is sent to an LNG storage tank for storage and cooling. The separated liquid enters the mixed hydrocarbon washing and stabilization unit (6) for stabilization and cooling to generate mixed hydrocarbons, and then is sent to the mixed hydrocarbon storage tank for storage; the gas from the mixed hydrocarbon washing and stabilization unit (6) enters the dry gas metering and separation unit (9) for gas-liquid separation after heat exchange in the low-temperature separation unit (5), and the gas separated by the dry gas metering and separation unit (9) is metered and transported outward; the liquid separated by the raw gas metering and separation unit (1), the raw gas boosting unit (2), the raw gas dehydration unit (4), the mixed hydrocarbon washing and stabilization unit (6) and the dry gas metering and separation unit (9) is collected by the sewage collection unit (10).

10. The process of the device for co-producing LNG by mixing hydrocarbons as claimed in claim 9, characterized in that: The raw gas deacidification unit (3) uses an activated MEDA chemical solvent absorption method to perform deacidification.

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