Device for dealkylation, denitrification, liquefaction and BOG (boil-off gas) recovery of natural gas

Abstract

The utility model relates to a device for dealkylation, denitrification and liquefaction of natural gas and BOG (boil-off gas) recovery. The device comprises a dealkylation unit, a natural gas denitrification and liquefaction unit and a BOG (Boil Off Gas) recovery unit, wherein the dealkylation natural gas is denitrified and liquefied for producing an LNG (Liquefied Natural Gas) product; the low-temperature rectifying tower is adopted to remove redundant nitrogen, so that the heat efficiency is higher, and the required power consumption is lower; the regenerated gas is extracted after heavy hydrocarbon is separated in the cold box by using a low-temperature separation means, and returns to an adsorption assembly in the dealkylation unit for further purification, so that resource waste is avoided; bOG enters the cold box after being pressurized by the compressor, and is converged into an LNG product after being cooled, flashed and denitrified, so that BOG recovery is realized, waste is avoided, and the energy consumption is low.

Description

Technical Field

[0001] The utility model belongs to the field of natural gas liquefaction, and particularly relates to a device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery. Background Technique

[0002] As a clean energy source, natural gas accounts for an increasingly large proportion in the energy structure. During the natural gas liquefaction process, impurities such as heavy hydrocarbons (C5+) and nitrogen will affect the product quality. The heavy hydrocarbon components will condense out first as the temperature decreases. When the temperature continues to drop, the heavy hydrocarbons will freeze, causing blockage of the main heat exchanger channels in the cold box, so they must be removed. A high nitrogen content will reduce the calorific value of liquefied natural gas (LNG) or lead to unqualified products. The "Liquefied Natural Gas" (GB / T38753-2020) requires that the nitrogen content of various types (lean liquid type, conventional type and rich liquid type) of liquefied natural gas be below 1%. BOG is the gas formed after the evaporation and gasification of LNG, mainly composed of methane. If it is not discharged in time, it will cause too high pressure in the tank and unstable operation. If it is directly discharged, it will cause waste and does not conform to the dual-carbon policy.

[0003] Chinese patent document CN111780490A discloses a natural gas liquefaction device and method for simultaneous dehydrocarbonization and denitrification. This patent is not applicable to the treatment of raw gas containing a small amount of heavy hydrocarbons. There are many low-temperature devices and it contains moving devices. Using a de-heavy hydrocarbon tower, it has poor adaptability to fluctuations in the raw gas components. The unqualified gas directly enters the cryogenic section, which will cause freezing and blockage of the cold box. Summary of the Utility Model

[0004] In order to solve the above problems and defects in the prior art, the utility model provides a device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery.

[0005] To solve the above technical problems, the utility model is realized through the following technical solutions:

[0006] The utility model provides a device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery, which includes: a dehydrocarbonization unit, a natural gas denitrification and liquefaction unit, a BOG recovery unit, and a refrigeration cycle unit; among them,

[0007] The dehydrocarbonization unit includes an adsorption assembly, a heater, a cooler, a first precooler, a gas-liquid separator, and a first condensate separator. The adsorption assembly includes a dehydrocarbonization tower,

[0008] The natural gas denitrification and liquefaction unit includes a main heat exchanger, a second precooler, a second condensate separator, a denitrification tower reboiler, a denitrification tower, a denitrification tower top condenser, a denitrification tower reflux tank, and a subcooling heat exchanger,

[0009] The BOG recovery unit includes: a BOG heat exchanger, a BOG compression device, and a flash tank,

[0010] The feed pipeline for the raw gas (equipped with a valve) is connected to the inlet of the dehydrocarbonization tower, the outlet of the dehydrocarbonization tower is connected to the outlet pipeline for the dehydrocarbonized natural gas (equipped with a valve), the refluxed regeneration gas feed pipeline from the natural gas denitrification and liquefaction unit is connected to the feed pipeline for the raw gas or the inlet of the dehydrocarbonization tower, a branch (equipped with a valve) separated from the natural gas outlet pipeline of the dehydrocarbonization tower is connected to the inlet of the heater, and the outlet of the heater returns to the said dehydrocarbonization tower through a pipeline (equipped with a valve); the regenerated gas outlet pipeline after desorption of the dehydrocarbonization tower is successively connected to a cooler, a first precooler, and a gas-liquid separator. The bottom liquid phase outlet of the gas-liquid separator is connected to the heavy hydrocarbon outlet pipeline. The top gas phase outlet of the gas-liquid separator is connected to the inlet of the first heat channel of the main heat exchanger through a pipeline. The outlet of the first heat channel of the main heat exchanger is connected to the inlet of the first condensate separator through a pipeline. The top gas phase outlet of the first condensate separator is connected to the inlet of the first cold channel of the main heat exchanger through a pipeline. The outlet of the first cold channel of the main heat exchanger is connected to the refluxed regeneration gas feed pipeline. The bottom liquid phase outlet of the first condensate separator is connected to the heavy hydrocarbon outlet pipeline;

[0011] The outlet pipeline for the dehydrocarbonized natural gas is connected to the inlet of the second precooler. The outlet of the second precooler is connected to the inlet of the second heat channel of the main heat exchanger through a pipeline. The outlet of the second heat channel of the main heat exchanger is connected to the inlet of the second condensate separator through a pipeline. The bottom liquid phase outlet of the second condensate separator is connected to the heavy hydrocarbon outlet pipeline through a pipeline. The top gas phase outlet of the second condensate separator is connected to the inlet of the third heat channel of the main heat exchanger through a pipeline. The outlet of the third heat channel of the main heat exchanger is connected to the upper inlet of the denitrification tower reboiler through a pipeline. The lower outlet of the denitrification tower reboiler is connected to the inlet of the fifth heat channel of the main heat exchanger through a pipeline. The outlet of the fifth heat channel of the main heat exchanger is connected to the inlet of the denitrification tower through a pipeline. The bottom liquid phase outlet of the denitrification tower is connected to the inlet of the fourth heat channel of the main heat exchanger through a pipeline. The outlet of the fourth heat channel of the main heat exchanger is connected to the LNG product outlet pipeline through a pipeline. The top gas phase outlet of the denitrification tower is connected to the hot side inlet of the denitrification tower top condenser through a pipeline. The hot side outlet of the denitrification tower top condenser is connected to the inlet of the denitrification tower reflux drum. The bottom liquid phase outlet of the denitrification tower reflux drum returns to the denitrification tower through a pipeline. The top gas phase outlet of the denitrification tower reflux drum is connected to the second heat medium inlet of the subcooling heat exchanger through a pipeline. The second heat medium outlet of the subcooling heat exchanger is connected to the inlet of the second cold channel of the main heat exchanger. The outlet of the second cold channel of the main heat exchanger is connected to the rich nitrogen gas outlet pipeline;

[0012] The BOG feed pipeline is connected to the inlet of the first heat exchange channel of the BOG heat exchanger. The outlet of the first heat exchange channel of the BOG heat exchanger is connected to the inlet of the BOG compression device via a pipeline. The outlet of the BOG compression device returns to the inlet of the second heat exchange channel of the BOG heat exchanger via a pipeline. The outlet of the second heat exchange channel of the BOG heat exchanger is connected to the inlet of the sixth heat channel of the main heat exchanger. The outlet of the sixth heat channel of the main heat exchanger is connected to the inlet of the flash tank via a pipeline. The bottom outlet of the flash tank is connected to the LNG product discharge pipeline via a pipeline. The top outlet of the flash tank is connected to the inlet of the third cold channel of the main heat exchanger via a pipeline. The outlet of the third cold channel of the main heat exchanger is connected to the rich nitrogen discharge pipeline via a pipeline.

[0013] Further, the refrigeration cycle unit includes a nitrogen refrigeration cycle unit and a mixed refrigerant refrigeration cycle unit. The nitrogen refrigeration cycle unit includes a nitrogen compression device and a nitrogen precooler. The mixed refrigerant refrigeration cycle unit includes a refrigerant compression device, a refrigerant precooler, and a refrigerant liquid separation tank.

[0014] The nitrogen refrigerant feed pipeline is connected to the inlet of the nitrogen compression device. The outlet of the nitrogen compression device is connected to the inlet of the nitrogen precooler via a pipeline. The outlet of the nitrogen precooler is connected to the inlet of the seventh heat channel of the main heat exchanger via a pipeline. The outlet of the seventh heat channel of the main heat exchanger is connected to the cold medium inlet of the subcooling heat exchanger via a pipeline. The cold medium outlet of the subcooling heat exchanger is connected to the cold side inlet of the denitrification tower condenser via a pipeline. The cold side outlet of the denitrification tower condenser is connected to the first heat medium inlet of the subcooling heat exchanger via a pipeline. The first heat medium outlet of the subcooling heat exchanger is connected to the inlet of the fourth cold channel of the main heat exchanger. The outlet of the fourth cold channel of the main heat exchanger is connected to the nitrogen refrigerant feed pipeline.

[0015] The reflux refrigerant feed pipeline is connected to the inlet of the refrigerant compression device. The outlet of the refrigerant compression device is connected to the inlet of the refrigerant precooler via a pipeline. The outlet of the refrigerant precooler is connected to the inlet of the refrigerant liquid separation tank via a pipeline. The gas phase outlet of the refrigerant liquid separation tank is connected to the inlet of the ninth heat channel of the main heat exchanger via the gas phase mixed refrigerant discharge pipeline. The outlet of the ninth heat channel of the main heat exchanger first exits the main heat exchanger and then is connected to the inlet of the fifth cold channel of the main heat exchanger. The outlet of the fifth cold channel of the main heat exchanger is connected to the reflux refrigerant feed pipeline. The liquid phase outlet of the refrigerant liquid separation tank is connected to the inlet of the eighth heat channel of the main heat exchanger via the liquid phase mixed refrigerant discharge pipeline. The outlet of the eighth heat channel of the main heat exchanger first exits the main heat exchanger and then is connected to the fifth cold channel of the main heat exchanger.

[0016] In the utility model, the dehydrogenation unit adopts the TSA process to adsorb and remove heavy hydrocarbons in the raw gas, and the obtained natural gas is used for subsequent production. The heavy hydrocarbons in the regenerated gas are further cooled and removed by a cold box and returned to the adsorption component; the natural gas after dehydrogenation enters the cold box for cooling and then enters the denitrogenation tower, and the natural gas after denitrogenation goes to the cold box for liquefaction to become an LNG product; BOG is compressed and enters the cold box, and after cooling and flash evaporation and denitrogenation, it is merged into the LNG product to realize BOG recovery.

[0017] Furthermore, the main heat exchanger is a plate-fin heat exchanger, which is provided with a plurality of parallel hot channels and a plurality of parallel cold channels. The hot medium flows in the hot channels and the cold medium flows in the cold channels, thereby achieving heat exchange between the hot medium and the cold medium.

[0018] Furthermore, the cooler and the pre-cooling heat exchanger are both shell and tube heat exchangers, and the cooling media are circulating water and chilled water respectively.

[0019] Furthermore, the refrigeration cycle unit includes nitrogen refrigeration and mixed refrigerant refrigeration, and the refrigerant provides cooling capacity at different positions of the cold box.

[0020] Furthermore, in the above-mentioned natural gas dehydrogenation, denitrification, liquefaction and BOG recovery device, the dehydrogenation tower adopts an isobaric temperature swing adsorption process (TSA), and the interior of the dehydrogenation tower is filled with an adsorbent, and the adsorbent is preferably activated carbon.

[0021] Furthermore, in the above-mentioned natural gas dehydrogenation, denitrification, liquefaction and BOG recovery device, a tower bottom inlet control valve is provided on the tower bottom inlet pipeline of the dehydrogenation tower;

[0022] A tower top outlet control valve is arranged on the tower top outlet pipeline of the dehydrogenation tower.

[0023] In a preferred embodiment, the adsorption assembly includes three parallel dehydrogenation towers, a first dehydrogenation tower, a second dehydrogenation tower, and a third dehydrogenation tower.

[0024] The raw gas feed pipeline is divided into a raw gas pipeline and a cold blow pipeline. The raw gas pipeline is divided into three air intake pipelines after passing through the thirteenth valve (regulating valve) to connect the lower inlet of the first to third dehydrogenation towers. Each air intake pipeline is equipped with the first to third program-controlled valves.

[0025] The cold blowing pipeline is also divided into three routes and connected to the lower inlet of the first to third dehydrogenation towers through the seventh to ninth program-controlled valves respectively.

[0026] Three dehydrogenated natural gas pipelines are led out from the upper outlets of the first to third dehydrogenation towers respectively. The three dehydrogenated natural gas pipelines are respectively provided with the fourth to sixth program-controlled valves and merged into the dehydrogenated natural gas outlet pipeline.

[0027] Three cold blow post-regeneration gas pipelines are respectively led out from the upper outlets of the first to the third dehydrocarbonation towers or from the three dehydrocarbonated natural gas pipelines led out from the upper outlets of the first to the third dehydrocarbonation towers (each with the tenth to the twelfth programmable control valves). After these cold blow post-regeneration gas pipelines converge, they are connected to the post-regeneration gas heater. The post-regeneration gas pipeline led out from the regeneration heater is divided into three post-regeneration gas branches, which then return to the upper outlets of the first to the third dehydrocarbonation towers or are connected to the three dehydrocarbonated natural gas pipelines led out from the upper outlets of the first to the third dehydrocarbonation towers (between the upper outlet and the fourth to the sixth programmable control valves). The three post-regeneration gas branches are respectively equipped with the thirteenth to the fifteenth programmable control valves.

[0028] The post-regeneration gas pipelines are respectively led out from the lower inlets of the first to the third dehydrocarbonation towers or the above three inlet gas pipelines and converge into the post-desorption post-regeneration gas discharge pipeline. Each post-regeneration gas pipeline is equipped with the sixteenth to the eighteenth programmable control valves, and the post-regeneration gas discharge pipeline is equipped with a post-regeneration gas cooler.

[0029] The isobaric temperature swing adsorption process flow is as described below. Taking the first dehydrocarbonation tower as an example:

[0030] The gas after acid removal, mercury removal and dehydration from the raw gas feed pipeline is regulated in flow rate by the thirteenth valve, i.e., the regulating valve, and then directly goes to the first dehydrocarbonation tower through the first programmable control valve. The dehydrocarbonation tower is filled with activated carbon inside. Under the selective adsorption of the adsorbent bed layer, the heavy hydrocarbons (C6 + ) in the raw gas are adsorbed. After passing through the fourth programmable control valve, it is the dehydrocarbonated natural gas, which enters the subsequent unit through the dehydrocarbonated natural gas discharge pipeline. When the mass transfer zone front of the adsorbed impurities reaches the reserved section at the bed layer outlet, the raw gas inlet valve - the first programmable control valve and the outlet valve - the fourth programmable control valve of this dehydrocarbonation tower are closed, and the adsorption stops. The adsorption bed starts to transfer to the regeneration process.

[0031] When the first dehydrocarbonation tower is in the adsorption state, the third dehydrocarbonation tower is in the thermal regeneration process, and the second dehydrocarbonation tower is in the cold blow process.

[0032] During the heating regeneration process, about 25% of the post-regeneration gas in the total amount of the raw gas goes to the post-regeneration gas heater, is heated to about 240 °C and then goes to purge the third dehydrocarbonation tower that needs to be regenerated through the fifteenth programmable control valve, so that the adsorbent is heated up, and the hydrocarbons therein are desorbed. After passing through the eighteenth programmable control valve, it goes to the post-regeneration gas cooler to be cooled to about 45 °C and then is the post-desorption post-regeneration gas, which enters the subsequent unit through the post-desorption post-regeneration gas discharge pipeline. The reflux post-regeneration gas after further dehydrocarbonation returns to the dehydrocarbonation tower through the reflux post-regeneration gas feed pipeline to continue purification; when the temperature of the gas leaving the tower reaches about 180 °C during the regeneration heating process, the heating stops.

[0033] Cold blow process: After the heating regeneration process ends, open the eighth program-controlled valve on the pipeline for cooling regeneration. About 25% of the cold regeneration gas enters the second dehydrocarbonation tower in the cold blow process to purge the adsorbent bed, reducing the bed temperature to about 40°C, and the cold blow process ends. The regeneration gas exiting the second dehydrocarbonation tower goes through the tenth program-controlled valve to the regeneration gas heater for heating and serves as the hot regeneration gas in the aforementioned heating regeneration process. After the cold blow process ends, close the program-controlled valve on the pipeline for cooling regeneration.

[0034] Next, the first dehydrocarbonation tower enters the hot regeneration state, the second dehydrocarbonation tower enters the adsorption state, and the third dehydrocarbonation tower enters the cold blow state. Each dehydrocarbonation tower sequentially undergoes three stages: adsorption, hot regeneration, and cold blow, which constitutes one operation cycle. The implementation of the entire process is automatically switched by the program-controlled valve according to the program, and the operator can adjust the program time according to actual needs to control the dehydrocarbonation process.

[0035] Furthermore, in the above-mentioned device for natural gas dehydrocarbonation, denitrification, liquefaction, and BOG recovery, a first valve is provided on the bottom liquid phase outlet pipeline of the gas-liquid separator, and the first valve is a liquid level regulating valve;

[0036] A second valve is provided on the bottom liquid phase outlet pipeline of the first condensate separator, and the second valve is a liquid level regulating valve;

[0037] A third valve is provided on the bottom liquid phase outlet pipeline of the second condensate separator, and the third valve is a liquid level regulating valve;

[0038] A fourth valve is provided on the outlet pipeline of the fourth heat channel of the main heat exchanger, and the fourth valve is a throttle valve;

[0039] A fifth valve is provided on the pipeline between the outlet of the fifth heat channel of the main heat exchanger and the inlet of the denitrification tower, and the fifth valve is a pressure reducing valve;

[0040] A sixth valve is provided on the outlet pipeline of the third cold channel of the main heat exchanger, and the sixth valve is a pressure reducing valve;

[0041] A seventh valve is provided on the pipeline between the outlet of the sixth heat channel of the main heat exchanger and the inlet of the flash tank, and the seventh valve is a pressure reducing valve;

[0042] An eighth valve is provided on the bottom outlet pipeline of the flash tank, and the eighth valve is a liquid level regulating valve;

[0043] A ninth valve is provided on the outlet pipeline of the second cold channel of the main heat exchanger, and the ninth valve is a pressure reducing valve;

[0044] A tenth valve is provided on the pipeline between the cold medium outlet of the subcooling heat exchanger and the inlet of the denitrification tower condenser, and the tenth valve is a liquid level regulating valve;

[0045] The outlet pipeline of the eighth heat channel of the main heat exchanger is provided with an eleventh valve, and the eleventh valve is a throttle valve;

[0046] The outlet pipeline of the ninth heat channel of the main heat exchanger is provided with a twelfth valve, and the twelfth valve is a throttle valve.

[0047] The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery of the present utility model conducts natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to the following process:

[0048] (1) Dehydrocarbonization: The feed gas is natural gas after acid removal, mercury removal and dehydration (where the CO2 content < 50 ppm, the H2S content < 4 ppm, the Hg content < 0.01 μg / m 3 , and the H2O content < 0.1 ppm; before entering the dehydrocarbonization tower, the content of heavy hydrocarbon components (C6 + ) ≤ 1500 ppm, and the nitrogen content ≤ 8%). The feed gas enters the dehydrocarbonization tower through the feed gas inlet pipeline. The dehydrocarbonization tower is filled with activated carbon inside. Under the selective adsorption of the adsorbent bed layer, the heavy hydrocarbons (C5+) in the feed gas are adsorbed. The dehydrocarbonized natural gas (after being treated by the dehydrocarbonization tower, the content of heavy hydrocarbon components (C6 + ) ≤ 10 ppm) enters the subsequent unit through the outlet pipeline of the dehydrocarbonized natural gas. Another stream of the regenerated gas after desorption enters the cooler through the outlet pipeline of the regenerated gas after desorption and is cooled to 40 ± 5 °C, preferably about 40 °C, and then cooled to 12 ± 2 °C, preferably about 12 °C through the first pre-cooler, and then enters the gas-liquid separator. The liquid phase at the bottom of the gas-liquid separator is heavy hydrocarbon (C6 + ) and is discharged from the system after adjusting the liquid level through the first valve. The gas phase at the top of the gas-liquid separator enters the first heat channel of the main heat exchanger and is further cooled to -50~-60 °C and then extracted, and then enters the first condensate separator. The gas phase at the top of the first condensate separator returns to the first cold channel of the main heat exchanger to be reheated to 5~15 °C and returns to the dehydrocarbonization tower in the adsorption module as the reflux regenerated gas to continue purification. The C6 and heavier hydrocarbon components in the reflux regenerated gas are removed to the extent that they can be dissolved in LNG (≤ 50 ppm). The liquid phase at the bottom of the first condensate separator is heavy hydrocarbon and is discharged from the system after adjusting the liquid level through the second valve;

[0049] (2) Natural gas denitrification and liquefaction: The dehydrogenated natural gas passes through the dehydrogenated natural gas outlet pipeline and is cooled to 12±2°C, preferably about 12°C, and then sent to a cold box for further treatment: first, it enters the second hot channel of the main heat exchanger and is further cooled to -40±5°C, preferably about -40°C, and then is sent to the second condensate separator. The bottom liquid phase of the second condensate separator is heavy hydrocarbons, which are discharged from the system after the liquid level is adjusted by the third valve through the heavy hydrocarbon outlet pipeline. The top gas phase of the second condensate separator returns to the third hot channel of the main heat exchanger and is cooled to -162±5°C, preferably about -162°C, and then is extracted. After extracting heat from the denitrification tower reboiler, it returns to the fifth hot channel of the main heat exchanger and is cooled to -162±5°C, preferably about -162°C, and is reduced in pressure to 0.45±0.05MPaG, preferably about After 0.45MPaG (the nitrogen content in the natural gas before entering the denitrification tower is ≤1%), it enters the denitrification tower; the liquid phase flows out from the bottom of the denitrification tower and returns to the fourth heat channel of the main heat exchanger to be cooled to -162±5℃, preferably about -162℃, and then passes through the fourth valve to become an LNG product and is sent to the subsequent storage and transportation equipment through the LNG product discharge pipeline. The gas phase at the top of the denitrification tower is cooled by the denitrification tower top condenser and the denitrification tower reflux tank and is divided into gas and liquid phases. The liquid phase at the bottom of the denitrification tower reflux tank returns to the denitrification tower for circulation. The gas phase at the top of the denitrification tower reflux tank is nitrogen-rich gas (mainly composed of nitrogen content of 99.5% and methane content of 0.5%, temperature of -177℃, pressure of 0.45MPaG), which passes through the nitrogen-rich gas discharge pipeline, passes through the cold heat exchanger and the main heat exchanger, and is reheated to 8±2℃, preferably about 8℃, and then is reduced to normal pressure through the sixth valve and discharged from the system;

[0050] (3) BOG recovery: BOG (temperature -162°C, atmospheric pressure) from the storage and transportation equipment enters the BOG heat exchanger through the BOG feed pipeline and is heated to 35±2°C, preferably about 35°C. It is then compressed and cooled by the BOG compressor and returned to the BOG heat exchanger for further cooling to -136±5°C, preferably about -136°C. It then enters the sixth hot channel of the main heat exchanger and is cooled to -162±5°C, preferably about -162°C for liquefaction. It is then depressurized to 0.14±0.05MpaG, preferably about 0.14MPaG, through the seventh valve and enters the flash tank. The liquid phase flows out from the bottom of the flash tank and flows into the LNG product discharge pipeline through the eighth valve. The nitrogen-rich gas flows out from the top of the flash tank and enters the second cold channel of the main heat exchanger for reheating to 8±2°C, preferably about 8°C. It is then depressurized to atmospheric pressure through the ninth valve and discharged from the system.

[0051] (4) The refrigeration cycle includes a nitrogen refrigeration cycle and a mixed refrigerant refrigeration cycle.

[0052] ① Nitrogen refrigeration cycle: The nitrogen refrigerant passes through the nitrogen refrigerant feed pipeline, is compressed and cooled by the nitrogen compression device, then goes to the nitrogen pre-cooler for further pre-cooling to 12 ± 2 °C, preferably about 12 °C, enters the seventh heat channel of the main heat exchanger and is cooled to -162 ± 5 °C, preferably about -162 °C to become liquid nitrogen. Then it is sub-cooled to -176 ± 5 °C, preferably about -176 °C through the sub-cooling heat exchanger, enters the top condenser of the denitrification tower through the tenth valve to provide cooling capacity for it, and the nitrogen that changes back to the gas phase passes through the sub-cooling heat exchanger and the fourth cold channel of the main heat exchanger to be reheated to 8 ± 2 °C, preferably about 8 °C and then exits the main heat exchanger, and finally returns to the inlet of the nitrogen compression device for circulation;

[0053] ② Mixed refrigerant refrigeration cycle: The cooling capacity of the natural gas liquefaction unit is provided by a mixed refrigeration cycle composed of methane, ethylene, propane, isopentane and nitrogen. The mixed refrigerant coming out of the cold box is compressed and cooled by the refrigerant compression device, then goes to the refrigerant pre-cooler for further temperature reduction to 12 ± 2 °C, preferably about 12 °C, and then enters the refrigerant liquid separation tank to be separated into gas-liquid two phases. The liquid-phase mixed refrigerant enters the main heat exchanger through the liquid-phase mixed refrigerant discharge pipeline, decompresses and cools at different positions in the cold box, and after coming out, returns to the main heat exchanger through the eleventh valve (temperature about -73 °C, pressure about 0.45 MPaG); The gas-phase mixed refrigerant enters the ninth heat channel of the main heat exchanger through the gas-phase mixed refrigerant discharge pipeline, decompresses and cools at different positions in the cold box, and after coming out, returns to the fifth cold channel of the main heat exchanger through the twelfth control valve (temperature about -73 °C, pressure about 0.45 MPaG). The mixed refrigerant vaporizes and reheats to 8 ± 2 °C, preferably about 8 °C and then exits the main heat exchanger, and the reflux refrigerant returns to the refrigerant compression device through the reflux refrigerant feed pipeline to enter the next cycle.

[0054] The utility model has the following beneficial effects:

[0055] The device for natural gas dehydrocarbonation, denitrification and liquefaction and BOG recovery of the utility model includes a dehydrocarbonation unit, a natural gas denitrification and liquefaction unit, and a BOG recovery unit. The dehydrocarbonated natural gas goes for denitrification and then liquefaction to produce LNG products; The excess nitrogen is removed by a low-temperature rectification tower, with higher thermal efficiency and lower power consumption required; The regenerated gas uses low-temperature separation means in the cold box to separate heavy hydrocarbons and then is drawn out and returned to the adsorption assembly for further purification, without causing waste of resources; The BOG is pressurized by the compression device and then enters the cold box, is cooled and flash-denitrified and then incorporated into the LNG product to achieve BOG recovery, avoiding waste and having low energy consumption.

[0056] This patent uses an isobaric temperature-variable adsorption process to pre-remove heavy hydrocarbons from the raw gas, obtaining a purified gas for subsequent LNG production. Another stream of regenerated gas is further cooled through a cold box to separate heavy hydrocarbons and then extracted, returned to the dehydrocarbon tower for further purification. The cooled regenerated gas with recovered heavy components is used as a heavy hydrocarbon product, all without external discharge, reducing natural gas losses, increasing the liquefaction rate of natural gas, and not causing resource waste. The integration of natural gas dehydrocarbonization, denitrification liquefaction, and BOG recovery has a high overall integration level and no moving equipment, facilitating operation. Description of the Drawings

[0057] To make the content of the present utility model easier to understand clearly, the following further details the present utility model based on specific embodiments of the present utility model in combination with the drawings, where:

[0058] Figure 1 is a schematic structural diagram of the device for natural gas dehydrocarbonization, denitrification liquefaction, and BOG recovery of the present utility model;

[0059] Figure 2 is a schematic diagram of the adsorption component;

[0060] Among them, 1. Adsorption component, 2. Heater, 3. Cooler, 4. First precooler, 5. Gas-liquid separator, 6. Main heat exchanger, 7. First condensate separator, 8. Second precooler, 9. Second condensate separator, 10. Reboiler of the denitrification tower, 11. Denitrification tower, 12. Condenser at the top of the denitrification tower, 13. Reflux drum of the denitrification tower, 14. Subcooling heat exchanger, 15. BOG heat exchanger, 16. BOG compression device, 17. Flash tank, 18. Nitrogen compression device, 19. Nitrogen precooler, 20. Refrigerant compression device, 21. Refrigerant precooler, 22. Refrigerant liquid separation tank, 23. Cold box (including main heat exchanger, flash tank, and related valves and pipelines);

[0061] L1. Raw gas feed pipeline, L2. Outlet pipeline for dehydrocarbonized natural gas, L3. Inlet pipeline for reflux regenerated gas, L4. Outlet pipeline for desorbed regenerated gas, L5. Outlet pipeline for heavy hydrocarbons, L6. Outlet pipeline for LNG product, L7. Outlet pipeline for nitrogen-rich gas, L8. Inlet pipeline for BOG, L9. Inlet pipeline for nitrogen refrigerant, L10. Outlet pipeline for liquid-phase mixed refrigerant, L11. Outlet pipeline for gas-phase mixed refrigerant, L12. Inlet pipeline for reflux refrigerant;

[0062] H1. First heat channel, H2. Second heat channel, H3. Third heat channel, H4. Fourth heat channel, H5. Fifth heat channel, H6. Sixth heat channel, H7. Seventh heat channel, H8. Eighth heat channel, H9. Ninth heat channel, C1. First cold channel, C2. Second cold channel, C3. Third cold channel, C4. Fourth cold channel, C5. Fifth cold channel;

[0063] V1, the first valve; V2, the second valve; V3, the third valve; V4, the fourth valve; V5, the fifth valve; V6, the sixth valve; V7, the seventh valve; V8, the eighth valve; V9, the ninth valve; V10, the tenth valve; V11, the eleventh valve; V12, the twelfth valve; V13, the thirteenth valve;

[0064] KV1A~KV1C, KV2A~KV2C, KV3A~KV3C, KV4A~KV4C, KV5A~KV5C, KV6A~KV6C, the first to the eighteenth programmable control valves. Detailed implementation manners

[0065] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0066] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, terms such as "installation", "provided with", "connection", etc. should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, and it can be the communication inside two components. Terms such as "upper", "middle", "outer", "inner", "lower", "around", "left", "right", "front", "rear", "top", "bottom", etc. indicating the orientation or position relationship are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0067] As Figure 1 shown, the device for natural gas dehydrocarbonization, denitrification, liquefaction and BOG recovery of the present invention includes: a dehydrocarbonization unit, a natural gas denitrification and liquefaction unit, a BOG recovery unit, and a refrigeration cycle unit; wherein,

[0068] The dehydrocarbonization unit includes an adsorption assembly 1, a heater 2, a cooler 3, a first precooler 4, a gas-liquid separator 5, and a first condensate separator 7. The adsorption assembly 1 includes a dehydrocarbon tower.

[0069] The natural gas denitrification and liquefaction unit includes a main heat exchanger 6, a second precooler 8, a second condensate separator 9, a denitrification tower reboiler 10, a denitrification tower 11, a denitrification tower top condenser 12, a denitrification tower reflux drum 13, and a subcooling heat exchanger 14.

[0070] The BOG recovery unit includes a BOG heat exchanger 15, a BOG compression device 16, and a flash tank 17.

[0071] The refrigeration cycle unit includes a nitrogen refrigeration cycle unit and a mixed refrigerant refrigeration cycle unit. The nitrogen refrigeration cycle unit includes a nitrogen compression device 18 and a nitrogen precooler 19. The mixed refrigerant refrigeration cycle unit includes a refrigerant compression device 20, a refrigerant precooler 21, and a refrigerant liquid separation tank 22.

[0072] The raw gas feed pipeline L1 (equipped with a valve) is connected to the inlet of the dehydrocarbonization tower. The outlet of the dehydrocarbonization tower is connected to the dehydrocarbonized natural gas discharge pipeline L2 (equipped with a valve). The return regeneration gas feed pipeline L3 from the natural gas denitrification and liquefaction unit is connected to the raw gas feed pipeline L1 or the inlet of the dehydrocarbonization tower. A branch (equipped with a valve) separated from the natural gas discharge pipeline of the dehydrocarbonization tower is connected to the inlet of the heater 2. The outlet of the heater 2 returns to the dehydrocarbonization tower through a pipeline (equipped with a valve). The desorbed regeneration gas discharge pipeline L4 of the dehydrocarbonization tower is sequentially connected to the cooler 3, the first precooler 4, and the inlet of the gas-liquid separator 5. The bottom liquid phase outlet of the gas-liquid separator 5 is connected to the heavy hydrocarbon discharge pipeline L5. The top gas phase outlet of the gas-liquid separator 5 is connected to the inlet of the first heat channel H1 of the main heat exchanger 6 through a pipeline. The outlet of the first heat channel H1 of the main heat exchanger 6 is connected to the inlet of the first condensate separator 7 through a pipeline. The top gas phase outlet of the first condensate separator 7 is connected to the inlet of the first cold channel C1 of the main heat exchanger 6 through a pipeline. The outlet of the first cold channel C1 of the main heat exchanger 6 is connected to the return regeneration gas feed pipeline L3. The bottom liquid phase outlet of the first condensate separator 7 is connected to the heavy hydrocarbon discharge pipeline L5.

[0073] In a preferred embodiment, as Figure 2 shown, the adsorption assembly 1 includes three parallel dehydrocarbonization towers, the first dehydrocarbonization tower T1, the second dehydrocarbonization tower T2, and the third dehydrocarbonization tower T3.

[0074] KV1A~KV1C, KV2A~KV2C, KV3A~KV3C, KV4A~KV4C, KV5A~KV5C, KV6A~KV6C are the first to eighteenth program-controlled valves, and the thirteenth valve V13 is a regulating valve.

[0075] The feed pipeline L1 of the raw material gas is divided into a raw material gas pipeline and a cold blow pipeline. After passing through the 13th valve V13 (control valve), the raw material gas pipeline is divided into three inlet gas pipelines to connect to the lower inlets of the first to third dehydrocarbonation towers. Each inlet gas pipeline is equipped with the first to third program control valves KV1A~KV1C.

[0076] The cold blow pipeline is also divided into three paths and is respectively connected to the lower inlets of the first to third dehydrocarbonation towers through the seventh to ninth program control valves KV3A~KV3C.

[0077] Three natural gas pipelines after dehydrocarbonation are respectively led out from the upper outlets of the first to third dehydrocarbonation towers. The fourth to sixth program control valves KV2A~KV2C are respectively installed on the three natural gas pipelines after dehydrocarbonation and converge into the natural gas discharge pipeline L2 after dehydrocarbonation.

[0078] Cold blow after-regeneration pipelines (each with the tenth to twelfth program control valves KV4A~KV4C) are respectively led out from the upper outlets of the first to third dehydrocarbonation towers or from the three natural gas pipelines after dehydrocarbonation led out from the upper outlets of the first to third dehydrocarbonation towers. These cold blow after-regeneration pipelines converge and then connect to the after-regeneration heater 2. The after-regeneration gas pipeline led out from the regeneration heater 2 is divided into three after-regeneration gas branches, and the three after-regeneration gas branches return to the upper outlets of the first to third dehydrocarbonation towers or connect to the three natural gas pipelines after dehydrocarbonation led out from the upper outlets of the first to third dehydrocarbonation towers (between the upper outlet and the fourth to sixth valves KV2A~KV2C). The thirteenth to fifteenth program control valves KV4A~KV4C are respectively installed on the three after-regeneration gas branches.

[0079] Regeneration gas pipelines are respectively led out from the lower inlets of the first to third dehydrocarbonation towers or the above three inlet gas pipelines and converge into the desorbed regeneration gas discharge pipeline L4. The sixteenth to eighteenth program control valves KV6A~KV6C are installed on each regeneration gas pipeline, and a regeneration gas cooler 3 is installed on the regeneration gas discharge pipeline L4.

[0080] The isobaric temperature swing adsorption process flow is as described below. Taking the first dehydrocarbonation tower T1 as an example:

[0081] The gas after acid removal, mercury removal and dehydration from the feed pipeline L1 of the raw material gas is regulated in flow rate by the 13th valve, i.e., the control valve V13, and then directly goes to the first dehydrocarbonation tower T1 through the program control valve KV1A. The dehydrocarbonation tower is filled with activated carbon. Under the selective adsorption of the adsorbent bed layer, the heavy hydrocarbons (C6 + ) in the raw material gas are adsorbed. After passing through the fourth program control valve KV2A, it is the natural gas after dehydrocarbonation and enters the subsequent unit through the natural gas discharge pipeline L2 after dehydrocarbonation. When the mass transfer zone front of the adsorbed impurities reaches the reserved section at the bed layer outlet, the raw material gas inlet valve - the first program control valve KV1A and the outlet valve - the fourth program control valve KV2A of the dehydrocarbonation tower are closed, and the adsorption is stopped. The adsorption bed starts to turn into the regeneration process.

[0082] When the first dehydrocarbonization tower T1 is in the adsorption state, the third dehydrocarbonization tower T3 is in the thermal regeneration process, and the second dehydrocarbonization tower T2 is in the cold blow process.

[0083] During the heating regeneration process, about 25% of the total raw gas, the regeneration gas, goes to the regeneration gas heater 2, is heated to about 240 °C, and then goes through the fifteenth program control valve KV5C to purge the third dehydrocarbonization tower T3 that needs to be regenerated, heating up the adsorbent, and the hydrocarbons therein are desorbed. Then it goes through the eighteenth program control valve KV6C to the regeneration gas cooler 3, is cooled to about 45 °C, and then the desorbed regeneration gas enters the subsequent unit through the desorbed regeneration gas discharge pipeline L4. The reflux regeneration gas after further dehydrocarbonization returns to the dehydrocarbonization tower through the reflux regeneration gas feed pipeline L3 to continue purification; when the temperature of the gas leaving the tower reaches about 180 °C during the regeneration heating process, the heating stops.

[0084] Cold blow process: After the heating regeneration process is completed, the eighth program control valve KV3B on the cooling regeneration pipeline is opened, and about 25% of the total gas volume, the cold regeneration gas, enters the second dehydrocarbonization tower T2 in the cold blow process, purging the adsorbent bed layer to reduce the bed layer temperature to about 40 °C, and the cold blow process ends; the regeneration gas leaving the second dehydrocarbonization tower T2 goes through the tenth program control valve KV4B to the regeneration gas heater 2 for heating, serving as the thermal regeneration gas in the aforementioned heating regeneration process; after the cold blow process ends, the program control valve on the cooling regeneration pipeline is closed.

[0085] Next, the first dehydrocarbonization tower T1 enters the thermal regeneration state, the second dehydrocarbonization tower T2 enters the adsorption state, and the third dehydrocarbonization tower T3 enters the cold blow state. Each dehydrocarbonization tower goes through three stages: adsorption, thermal regeneration, and cold blow in sequence, which is an operation cycle. The implementation of the whole process is automatically switched by the program control valve according to the program, and the operator can adjust the program time according to actual needs to control the dehydrocarbonization process.

[0086] The natural gas discharge pipeline L2 after hydrocarbon removal is connected to the inlet of the second precooler 8. The outlet of the second precooler 8 is connected to the inlet of the second heat channel H2 of the main heat exchanger 6 through a pipeline. The outlet of the second heat channel H2 of the main heat exchanger 6 is connected to the inlet of the second condensate separator 9 through a pipeline. The bottom liquid phase outlet of the second condensate separator 9 is connected to the heavy hydrocarbon discharge pipeline L5 through a pipeline. The top gas phase outlet of the second condensate separator 9 is connected to the inlet of the third heat channel H3 of the main heat exchanger 6 through a pipeline. The outlet of the third heat channel H3 of the main heat exchanger 6 is connected to the upper inlet of the denitrification tower reboiler 10 through a pipeline. The lower outlet of the denitrification tower reboiler 10 is connected to the inlet of the fifth heat channel H5 of the main heat exchanger 6 through a pipeline. The outlet of the fifth heat channel H5 of the main heat exchanger 6 is connected to the inlet of the denitrification tower 11 through a pipeline. The bottom liquid phase outlet of the denitrification tower 11 is connected to the inlet of the fourth heat channel H4 of the main heat exchanger 6 through a pipeline. The outlet of the fourth heat channel H4 of the main heat exchanger 6 is connected to the LNG product discharge pipeline L6 through a pipeline. The top gas phase outlet of the denitrification tower 11 is connected to the hot side inlet of the denitrification tower top condenser 12 through a pipeline. The hot side outlet of the denitrification tower top condenser 12 is connected to the inlet of the denitrification tower reflux drum 13. The bottom liquid phase outlet of the denitrification tower reflux drum 13 returns to the denitrification tower 11 through a pipeline. The top gas phase outlet of the denitrification tower reflux drum 13 is connected to the second heat medium inlet of the subcooling heat exchanger 14 through a pipeline. The second heat medium outlet of the subcooling heat exchanger 14 is connected to the inlet of the second cold channel C2 of the main heat exchanger 6. The outlet of the second cold channel C2 of the main heat exchanger 6 is connected to the rich nitrogen gas discharge pipeline L7.

[0087] The BOG feed pipeline L8 is connected to the inlet of the first heat exchange channel of the BOG heat exchanger 15. The outlet of the first heat exchange channel of the BOG heat exchanger 15 is connected to the inlet of the BOG compression device 16 through a pipeline. The outlet of the BOG compression device 16 returns to the inlet of the second heat exchange channel of the BOG heat exchanger 15 through a pipeline. The outlet of the second heat exchange channel of the BOG heat exchanger 15 is connected to the inlet of the sixth heat channel H6 of the main heat exchanger 6 through a pipeline. The outlet of the sixth heat channel H6 of the main heat exchanger 6 is connected to the inlet of the flash tank 17 through a pipeline. The bottom outlet of the flash tank 17 is connected to the LNG product discharge pipeline L6 through a pipeline. The top outlet of the flash tank 17 is connected to the inlet of the third cold channel C3 of the main heat exchanger 6 through a pipeline. The outlet of the third cold channel C3 of the main heat exchanger 6 is connected to the rich nitrogen gas discharge pipeline L7 through a pipeline.

[0088] The nitrogen refrigerant feed pipeline L9 is connected to the inlet of the nitrogen compression device 18. The outlet of the nitrogen compression device 18 is connected to the inlet of the nitrogen pre-cooler 19 through a pipeline. The outlet of the nitrogen pre-cooler 19 is connected to the inlet of the seventh heat channel H7 of the main heat exchanger 6 through a pipeline. The outlet of the seventh heat channel H7 of the main heat exchanger 6 is connected to the cold medium inlet of the sub-cooling heat exchanger 14 through a pipeline. The cold medium outlet of the sub-cooling heat exchanger 14 is connected to the cold side inlet of the denitrification tower condenser 12 through a pipeline. The cold side outlet of the denitrification tower condenser 12 is connected to the first heat medium inlet of the sub-cooling heat exchanger 14 through a pipeline. The first heat medium outlet of the sub-cooling heat exchanger 14 is connected to the inlet of the fourth cold channel C4 of the main heat exchanger 6. The outlet of the fourth cold channel C4 of the main heat exchanger 6 is connected to the nitrogen refrigerant feed pipeline L9.

[0089] The reflux refrigerant feed pipeline L12 is connected to the inlet of the refrigerant compression device 20. The outlet of the refrigerant compression device 20 is connected to the inlet of the refrigerant pre-cooler 21 through a pipeline. The outlet of the refrigerant pre-cooler 21 is connected to the inlet of the refrigerant liquid separation tank 22 through a pipeline. The gas-phase outlet of the refrigerant liquid separation tank 22 is connected to the inlet of the ninth heat channel H9 of the main heat exchanger 6 through the gas-phase mixed refrigerant discharge pipeline L11. The outlet of the ninth heat channel H9 of the main heat exchanger 6 is connected to the inlet of the fifth cold channel C5 of the main heat exchanger 6 through a pipeline after exiting the main heat exchanger 6 first. The outlet of the fifth cold channel C5 of the main heat exchanger 6 is connected to the reflux refrigerant feed pipeline L12. The liquid-phase outlet of the refrigerant liquid separation tank 22 is connected to the inlet of the eighth heat channel H8 of the main heat exchanger 6 through the liquid-phase mixed refrigerant discharge pipeline L10. The outlet of the eighth heat channel H8 of the main heat exchanger 6 is connected to the fifth cold channel C5 of the main heat exchanger 6 through a pipeline after exiting the main heat exchanger 6 first.

[0090] The BOG compression device, the nitrogen compression device, and the refrigerant compression device each include a compressor and an auxiliary cooler.

[0091] In another preferred embodiment, the dehydrocarbonation tower adopts the isobaric temperature swing adsorption process (TSA), and the inside of the dehydrocarbonation tower is filled with adsorbent activated carbon.

[0092] In still another preferred embodiment, a first valve V1 is provided on the bottom liquid-phase outlet pipeline of the gas-liquid separator 5, and the first valve V1 is a liquid level regulating valve;

[0093] A second valve V2 is provided on the bottom liquid-phase outlet pipeline of the first condensate separator 7, and the second valve V2 is a liquid level regulating valve;

[0094] A third valve V3 is provided on the bottom liquid-phase outlet pipeline of the second condensate separator 9, and the third valve V3 is a liquid level regulating valve;

[0095] A fourth valve V4 is provided on the outlet pipeline of the fourth heat channel H4 of the main heat exchanger 6, and the fourth valve V4 is a throttle valve;

[0096] A fifth valve V5 is provided on the pipeline between the outlet of the fifth heat channel H5 of the main heat exchanger 6 and the inlet of the denitrification tower 11, and the fifth valve V5 is a pressure reducing valve;

[0097] A sixth valve V6 is provided on the pipeline of the outlet of the third cold channel C3 of the main heat exchanger 6, and the sixth valve V6 is a pressure reducing valve;

[0098] A seventh valve V7 is provided on the pipeline between the outlet of the sixth heat channel H6 of the main heat exchanger 6 and the inlet of the flash tank 17, and the seventh valve V7 is a pressure reducing valve;

[0099] An eighth valve V8 is provided on the bottom outlet pipeline of the flash tank 17, and the eighth valve V8 is a liquid level regulating valve;

[0100] A ninth valve V9 is provided on the pipeline of the outlet of the second cold channel C2 of the main heat exchanger 6, and the ninth valve V9 is a pressure reducing valve (the outlet pipelines of the third cold channel C3 and the second cold channel C2 converge into the rich nitrogen gas discharge pipeline L7);

[0101] A tenth valve V10 is provided on the pipeline between the cold medium outlet of the subcooling heat exchanger 14 and the inlet of the denitrification tower condenser 12, and the tenth valve V10 is a liquid level regulating valve;

[0102] An eleventh valve V11 is provided on the pipeline of the outlet of the eighth heat channel H8 of the main heat exchanger 6, and the eleventh valve V11 is a throttle valve;

[0103] A twelfth valve V12 is provided on the pipeline of the outlet of the ninth heat channel H9 of the main heat exchanger 6, and the twelfth valve V12 is a throttle valve.

[0104] The natural gas dehydrocarbonation, denitrification liquefaction and BOG recovery device of this embodiment conducts natural gas dehydrocarbonation, denitrification liquefaction and BOG recovery according to the following process:

[0105] (1) Dehydrocarbonation: The raw material gas is natural gas after acid removal, mercury removal and dehydration (where the CO2 content < 50 ppm, the H2S content < 4 ppm, the Hg content < 0.01 μg / m 3 , and the H2O content < 0.1 ppm; before entering the dehydrocarbonation tower, the content of heavy hydrocarbon components (C6 + ) ≤ 1500 ppm, and the nitrogen content ≤ 8%), the raw material gas enters the dehydrocarbonation tower through the raw material gas feed pipeline L1. Activated carbon is filled inside the dehydrocarbonation tower. Under the selective adsorption of the adsorbent bed layer, the heavy hydrocarbons (C5+) in the raw material gas are adsorbed, and the dehydrocarbonated natural gas (after being treated by the dehydrocarbonation tower, the heavy hydrocarbon components (C6 +The natural gas after hydrocarbon removal (with a content ≤ 10 ppm) enters the subsequent unit through the natural gas discharge pipeline L2. The adsorbed activated carbon is regenerated by the reverse flow regeneration gas in the reverse flow regeneration gas feed pipeline L3. The reverse flow regeneration gas comes from the liquefaction unit. The reverse flow regeneration gas (with a flow rate of about 20% of the total raw gas volume) first enters the hydrocarbon removal tower of the adsorption module 1 through the reverse flow regeneration gas feed pipeline L3 for hydrocarbon removal, and then enters the heater 2 to be heated to about 240 °C to purge the activated carbon that needs to be regenerated in the hydrocarbon removal tower, raising the temperature of the adsorbent activated carbon, and thus enabling the adsorbed heavy hydrocarbon components to be desorbed into the regeneration gas. The regeneration gas after desorption enters the cooler 3 through the regeneration gas discharge pipeline L4 after desorption and is cooled to about 40 °C, cooled to about 12 °C through the first pre-cooler 4, and then enters the gas-liquid separator 5. The liquid phase at the bottom of the gas-liquid separator 5 is heavy hydrocarbons, which are discharged from the system through the heavy hydrocarbon discharge pipeline L5 after the liquid level is adjusted by the first valve V1. The gas phase at the top of the gas-liquid separator 5 enters the first heat channel H1 of the main heat exchanger 6 and continues to be cooled to -50 to -60 °C and then withdrawn, and then enters the first condensate separator 7. The gas phase at the top of the first condensate separator 7 returns to the first cold channel C1 of the main heat exchanger 6 for reheating to 5 to 15 °C and serves as the reverse flow regeneration gas to return to the hydrocarbon removal tower in the adsorption module 1. The heavy hydrocarbon components C6 + (C6 and heavy hydrocarbon components above C6) are removed to the extent that they can be dissolved in LNG (≤ 50 ppm). The liquid phase at the bottom of the first condensate separator 7 is heavy hydrocarbons, which are discharged from the system through the heavy hydrocarbon discharge pipeline L5 after the liquid level is adjusted by the second valve V2;

[0106] (2) Natural gas denitrification and liquefaction: The dehydrogenated natural gas is cooled to about 12°C through the dehydrogenated natural gas outlet pipeline L2 and the second precooler 8, and then sent to the cold box 23 for further treatment: first, it enters the second hot channel H2 of the main heat exchanger 6 and is further cooled to about -40°C, and then sent to the second condensate separator 9. The bottom liquid phase of the second condensate separator 9 is heavy hydrocarbons, which are discharged from the system after the liquid level is adjusted through the heavy hydrocarbon outlet pipeline L5 by the third valve V3. The top gas phase of the second condensate separator 9 returns to the third hot channel H3 of the main heat exchanger 6 and is cooled to about -162°C and then extracted. After extracting heat through the denitrification tower reboiler 10, it returns to the fifth hot channel H5 of the main heat exchanger 6 and is cooled to about -162°C. After the pressure is reduced to 0.45MPaG by the fifth valve V5 (the gas in the denitrification tower before entering the denitrification tower) The nitrogen content is ≤1%) and enters the denitrification tower 11; the liquid phase flows out from the bottom of the denitrification tower 11 and returns to the fourth heat channel H4 of the main heat exchanger 6, and is cooled to about -162°C. After passing through the fourth valve V4, it becomes an LNG product and is sent to the subsequent storage and transportation equipment through the LNG product discharge pipeline L6. The gas phase at the top of the denitrification tower 11 is cooled by the denitrification tower top condenser 12 and the denitrification tower reflux tank 13 and is divided into gas and liquid phases. The liquid phase at the bottom of the denitrification tower reflux tank 13 returns to the denitrification tower 11 for circulation. The gas phase at the top of the denitrification tower reflux tank 13 is nitrogen-rich gas (mainly composed of nitrogen content of 99.5% and methane content of 0.5%, temperature of -177°C, pressure of 0.45MPaG), passes through the nitrogen-rich gas discharge pipeline L7, passes through the cold heat exchanger 14 and the main heat exchanger 6, and is reheated to about 8°C, and then is reduced to normal pressure through the sixth valve V6 and discharged from the system;

[0107] (3) BOG recovery: BOG (temperature -162°C, atmospheric pressure) from the storage and transportation equipment enters the BOG heat exchanger 15 through the BOG feed pipeline L8 and is heated to about 35°C. It is then compressed and cooled by the BOG compressor 16 and returns to the BOG heat exchanger 15 for further cooling to about -136°C. It then enters the sixth hot channel H6 of the main heat exchanger 6 and is cooled to about -162°C for liquefaction. It is then depressurized to about 0.14 MPaG through the seventh valve V7 and enters the flash tank 17. The liquid phase flows out from the bottom of the flash tank 17 and flows through the eighth valve V8 into the LNG product discharge pipeline L6. The nitrogen-rich gas L7 flows out from the top of the flash tank 17 and enters the second cold channel C2 of the main heat exchanger 6 for reheating to about 8°C. It is then depressurized to atmospheric pressure through the ninth valve V9 and discharged into the system.

[0108] (4) The refrigeration cycle includes a nitrogen refrigeration cycle and a mixed refrigerant refrigeration cycle.

[0109] ① Nitrogen refrigeration cycle: The nitrogen refrigerant is compressed and cooled by the nitrogen compression device 18 through the nitrogen refrigerant feed pipeline L9, then further precooled to about 12°C in the nitrogen precooler 19, enters the seventh heat channel H7 of the main heat exchanger 6 and is cooled to about -162°C to become liquid nitrogen. Then it is subcooled to about -176°C in the subcooler 14, and enters the top condenser 12 of the denitrification tower through the tenth valve V10 to provide cooling capacity. The nitrogen that turns back into the gas phase passes through the subcooler 14 and the fourth cold channel C4 of the main heat exchanger 6 in sequence, and is reheated to about 8°C before being led out of the main heat exchanger 6 and finally returning to the inlet of the nitrogen compression device 18 for circulation;

[0110] ② Mixed refrigerant refrigeration cycle: The cooling capacity of the natural gas liquefaction unit is provided by a mixed refrigeration cycle composed of methane, ethylene, propane, isopentane and nitrogen. The mixed refrigerant coming out of the cold box 23 is compressed and cooled by the refrigerant compression device 20, then further cooled to about 12°C in the refrigerant precooler 21, and then enters the refrigerant liquid separation tank 22 to be separated into gas-liquid two phases. The liquid-phase mixed refrigerant enters the main heat exchanger 6 through the liquid-phase mixed refrigerant discharge pipeline L10, is depressurized and cooled at different positions in the cold box 23, and then returns to the main heat exchanger 6 through the eleventh valve V11 (temperature -73°C, pressure 0.45MPaG) after coming out. The gas-phase mixed refrigerant enters the ninth heat channel H9 of the main heat exchanger 6 through the gas-phase mixed refrigerant discharge pipeline L11, is depressurized and cooled at different positions in the cold box 23, and then returns to the fifth cold channel C5 of the main heat exchanger 6 through the twelfth control valve V12 (temperature -73°C, pressure 0.45MPaG) after coming out. After the mixed refrigerant vaporizes and reheats to 8°C, it exits the main heat exchanger 6, and the reflux refrigerant returns to the refrigerant compression device 20 through the reflux refrigerant feed pipeline L12 to enter the next cycle.

[0111] Obviously, the above embodiments are only examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. An apparatus for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery, characterized in that, It includes: a dehydrocarbonation unit, a natural gas denitrification and liquefaction unit, a BOG recovery unit, and a refrigeration cycle unit; among them, the dehydrocarbonation unit includes an adsorption assembly (1), a heater (2), a cooler (3), a first precooler (4), a gas-liquid separator (5), and a first condensate separator (7), and the adsorption assembly (1) includes a dehydrocarbonation tower, the natural gas denitrification and liquefaction unit includes a main heat exchanger (6), a second precooler (8), a second condensate separator (9), a denitrification tower reboiler (10), a denitrification tower (11), a denitrification tower top condenser (12), a denitrification tower reflux drum (13), and a subcooled heat exchanger (14), the BOG recovery unit includes a BOG heat exchanger (15), a BOG compression device (16), and a flash tank (17), The raw gas feed pipeline (L1) is connected to the inlet of the dehydrocarbonation tower, the outlet of the dehydrocarbonation tower is connected to the dehydrocarbonated natural gas discharge pipeline (L2), the refluxed regeneration gas feed pipeline (L3) from the natural gas denitrification and liquefaction unit is connected to the raw gas feed pipeline (L1) or the inlet of the dehydrocarbonation tower, a branch line separated from the natural gas discharge pipeline of the dehydrocarbonation tower is connected to the inlet of the heater (2), and the outlet of the heater (2) returns to the dehydrocarbonation tower through a pipeline; the desorbed regeneration gas discharge pipeline (L4) of the dehydrocarbonation tower is sequentially connected to the inlet of the cooler (3), the first precooler (4), and the gas-liquid separator (5), the bottom liquid phase outlet of the gas-liquid separator (5) is connected to the heavy hydrocarbon discharge pipeline (L5), the top gas phase outlet of the gas-liquid separator (5) is connected to the inlet of the first heat channel (H1) of the main heat exchanger (6) through a pipeline, the outlet of the first heat channel (H1) of the main heat exchanger (6) is connected to the inlet of the first condensate separator (7) through a pipeline, the top gas phase outlet of the first condensate separator (7) is connected to the inlet of the first cold channel (C1) of the main heat exchanger (6) through a pipeline, the outlet of the first cold channel (C1) of the main heat exchanger (6) is connected to the refluxed regeneration gas feed pipeline (L3), and the bottom liquid phase outlet of the first condensate separator (7) is connected to the heavy hydrocarbon discharge pipeline (L5); The natural gas outlet pipeline (L2) after hydrocarbon removal is connected to the inlet of the second precooler (8). The outlet of the second precooler (8) is connected to the inlet of the second heat channel (H2) of the main heat exchanger (6) through a pipeline. The outlet of the second heat channel (H2) of the main heat exchanger (6) is connected to the inlet of the second condensate separator (9) through a pipeline. The bottom liquid phase outlet of the second condensate separator (9) is connected to the heavy hydrocarbon outlet pipeline (L5) through a pipeline. The top gas phase outlet of the second condensate separator (9) is connected to the inlet of the third heat channel (H3) of the main heat exchanger (6) through a pipeline. The outlet of the third heat channel (H3) of the main heat exchanger (6) is connected to the upper inlet of the denitrification tower reboiler (10) through a pipeline. The lower outlet of the denitrification tower reboiler (10) is connected to the inlet of the fifth heat channel (H5) of the main heat exchanger (6) through a pipeline. The outlet of the fifth heat channel (H5) of the main heat exchanger (6) is connected to the inlet of the denitrification tower (11) through a pipeline. The bottom liquid phase outlet of the denitrification tower (11) is connected to the inlet of the fourth heat channel (H4) of the main heat exchanger (6) through a pipeline. The outlet of the fourth heat channel (H4) of the main heat exchanger (6) is connected to the LNG product outlet pipeline (L6) through a pipeline. The top gas phase outlet of the denitrification tower (11) is connected to the hot side inlet of the denitrification tower top condenser (12) through a pipeline. The hot side outlet of the denitrification tower top condenser (12) is connected to the inlet of the denitrification tower reflux drum (13). The bottom liquid phase outlet of the denitrification tower reflux drum (13) returns to the denitrification tower (11) through a pipeline. The top gas phase outlet of the denitrification tower reflux drum (13) is connected to the second heat medium inlet of the subcooling heat exchanger (14) through a pipeline. The second heat medium outlet of the subcooling heat exchanger (14) is connected to the inlet of the second cold channel (C2) of the main heat exchanger (6). The outlet of the second cold channel (C2) of the main heat exchanger (6) is connected to the rich nitrogen gas outlet pipeline (L7); The BOG feed pipeline (L8) is connected to the inlet of the first heat exchange channel of the BOG heat exchanger (15). The outlet of the first heat exchange channel of the BOG heat exchanger (15) is connected to the inlet of the BOG compression device (16) through a pipeline. The outlet of the BOG compression device (16) returns to the inlet of the second heat exchange channel of the BOG heat exchanger (15) through a pipeline. The outlet of the second heat exchange channel of the BOG heat exchanger (15) is connected to the inlet of the sixth heat channel (H6) of the main heat exchanger (6). The outlet of the sixth heat channel (H6) of the main heat exchanger (6) is connected to the inlet of the flash tank (17) through a pipeline. The bottom outlet of the flash tank (17) is connected to the LNG product outlet pipeline (L6) through a pipeline. The top outlet of the flash tank (17) is connected to the inlet of the third cold channel (C3) of the main heat exchanger (6). The outlet of the third cold channel (C3) of the main heat exchanger (6) is connected to the rich nitrogen gas outlet pipeline (L7) through a pipeline.

2. The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to claim 1, characterized in that, The refrigeration cycle unit includes a nitrogen refrigeration cycle unit and a mixed refrigerant refrigeration cycle unit. The nitrogen refrigeration cycle unit includes a nitrogen compression device (18) and a nitrogen pre-cooler (19). The mixed refrigerant refrigeration cycle unit includes a refrigerant compression device (20), a refrigerant pre-cooler (21), and a refrigerant liquid separation tank (22). The nitrogen refrigerant feed pipeline (L9) is connected to the inlet of the nitrogen compression device (18). The outlet of the nitrogen compression device (18) is connected to the inlet of the nitrogen pre-cooler (19) through a pipeline. The outlet of the nitrogen pre-cooler (19) is connected to the inlet of the seventh heat channel (H7) of the main heat exchanger (6) through a pipeline. The outlet of the seventh heat channel (H7) of the main heat exchanger (6) is connected to the cold medium inlet of the sub-cooling heat exchanger (14) through a pipeline. The cold medium outlet of the sub-cooling heat exchanger (14) is connected to the cold side inlet of the denitrification tower condenser (12) through a pipeline. The cold side outlet of the denitrification tower condenser (12) is connected to the first heat medium inlet of the sub-cooling heat exchanger (14) through a pipeline. The first heat medium outlet of the sub-cooling heat exchanger (14) is connected to the inlet of the fourth cold channel (C4) of the main heat exchanger (6). The outlet of the fourth cold channel (C4) of the main heat exchanger (6) is connected to the nitrogen refrigerant feed pipeline (L9). The reflux refrigerant feed pipeline (L12) is connected to the inlet of the refrigerant compression device (20). The outlet of the refrigerant compression device (20) is connected to the inlet of the refrigerant pre-cooler (21) through a pipeline. The outlet of the refrigerant pre-cooler (21) is connected to the inlet of the refrigerant liquid separation tank (22) through a pipeline. The gas phase outlet of the refrigerant liquid separation tank (22) is connected to the inlet of the ninth heat channel (H9) of the main heat exchanger (6) through the gas phase mixed refrigerant discharge pipeline (L11). The outlet of the ninth heat channel (H9) of the main heat exchanger (6) is connected to the inlet of the fifth cold channel (C5) of the main heat exchanger (6) through a pipeline after leaving the main heat exchanger (6). The outlet of the fifth cold channel (C5) of the main heat exchanger (6) is connected to the reflux refrigerant feed pipeline (L12). The liquid phase outlet of the refrigerant liquid separation tank (22) is connected to the inlet of the eighth heat channel (H8) of the main heat exchanger (6) through the liquid phase mixed refrigerant discharge pipeline (L10). The outlet of the eighth heat channel (H8) of the main heat exchanger (6) is connected to the fifth cold channel (C5) of the main heat exchanger (6) through a pipeline after leaving the main heat exchanger (6).

3. The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to claim 1 or 2, characterized in that, The adsorption assembly (1) includes three parallel hydrocarbon removal towers, the first hydrocarbon removal tower (T1), the second hydrocarbon removal tower (T2), and the third hydrocarbon removal tower (T3). The raw gas feed pipeline (L1) is divided into a raw gas pipeline and a cold blow pipeline. The raw gas pipeline is divided into three inlet pipelines after passing through the thirteenth valve (V13) and is connected to the lower inlets of the first to third hydrocarbon removal towers. Each inlet pipeline is provided with a first programmable valve (KV1A) to a third programmable valve (KV1C). The cold blow pipeline is also divided into three paths and is respectively connected to the lower inlets of the first to third hydrocarbon removal towers through the seventh programmable valve (KV3A) to the ninth valve (KV3C). Three natural gas pipelines after dehydrocarbonation are respectively led out from the upper outlets of the first to third dehydrocarbonation towers. The fourth to sixth program-controlled valves (KV2A - KV2C) are respectively installed on the three natural gas pipelines after dehydrocarbonation and converge into the natural gas discharge pipeline (L2) after dehydrocarbonation. Cold blow regeneration gas pipelines are respectively led out from the upper outlets of the first to third dehydrocarbonation towers or from the three natural gas pipelines after dehydrocarbonation led out from the upper outlets of the first to third dehydrocarbonation towers. Each is equipped with the tenth to twelfth program-controlled valves (KV4A - KV4C). After these cold blow regeneration gas pipelines converge, they are connected to the regeneration gas heater (2). The regeneration gas pipeline led out from the regeneration heater (2) is divided into three regeneration gas branch pipes. The three regeneration gas branch pipes return to the upper outlets of the first to third dehydrocarbonation towers or are connected to the three natural gas pipelines after dehydrocarbonation led out from the upper outlets of the first to third dehydrocarbonation towers. The thirteenth to fifteenth program-controlled valves (KV4A - KV4C) are respectively installed on the three regeneration gas branch pipes. Regeneration gas pipelines are respectively led out from the lower inlets of the first to third dehydrocarbonation towers or from the above three inlet gas pipelines and converge into the regenerated gas discharge pipeline (L4) after desorption. The sixteenth to eighteenth program-controlled valves (KV6A - KV6C) are installed on each regeneration gas pipeline. A regeneration gas cooler (3) is installed on the regenerated gas discharge pipeline (L4).

4. The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to claim 3, characterized in that, The inside of the dehydrocarbonation tower is filled with adsorbent, and the adsorbent is activated carbon.

5. The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to claim 3, characterized in that, A first valve (V1) is installed on the bottom liquid phase outlet pipeline of the gas - liquid separator (5), and the first valve (V1) is a liquid level regulating valve. A second valve (V2) is installed on the bottom liquid phase outlet pipeline of the first condensate separator (7), and the second valve (V2) is a liquid level regulating valve. A third valve (V3) is installed on the bottom liquid phase outlet pipeline of the second condensate separator (9), and the third valve (V3) is a liquid level regulating valve.

6. The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to claim 5, wherein, A fourth valve (V4) is installed on the outlet pipeline of the fourth heat channel (H4) of the main heat exchanger (6), and the fourth valve (V4) is a throttle valve. A fifth valve (V5) is installed on the pipeline between the outlet of the fifth heat channel (H5) of the main heat exchanger (6) and the inlet of the denitrification tower (11), and the fifth valve (V5) is a pressure reducing valve. A sixth valve (V6) is installed on the outlet pipeline of the third cold channel (C3) of the main heat exchanger (6), and the sixth valve (V6) is a pressure reducing valve. A seventh valve (V7) is installed on the pipeline between the outlet of the sixth heat channel (H6) of the main heat exchanger (6) and the inlet of the flash tank (17), and the seventh valve (V7) is a pressure reducing valve.

7. The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to claim 6, characterized in that, An eighth valve (V8) is installed on the bottom outlet pipeline of the flash tank (17), and the eighth valve (V8) is a liquid level regulating valve.

8. The device for natural gas dehydrocarbonation, denitrification, liquefaction and BOG recovery according to claim 7, characterized in that A ninth valve (V9) is installed on the outlet pipeline of the second cold channel (C2) of the main heat exchanger (6), and the ninth valve (V9) is a pressure reducing valve. A tenth valve (V10) is installed on the pipeline between the cold medium outlet of the sub - cooled heat exchanger (14) and the inlet of the denitrification tower condenser (12), and the tenth valve (V10) is a liquid level regulating valve. The outlet pipe of the eighth heat channel (H8) of the main heat exchanger (6) is provided with an eleventh valve (V11), and the eleventh valve (V11) is a throttle valve; The outlet pipe of the ninth heat channel (H9) of the main heat exchanger (6) is provided with a twelfth valve (V12), and the twelfth valve (V12) is a throttle valve.

9. The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to claim 3, wherein, The main heat exchanger is a plate-fin heat exchanger.

10. The device for natural gas dehydrocarbonization, denitrification liquefaction and BOG recovery according to claim 3, characterized in that, Both the cooler and the pre-cooling heat exchanger are shell-and-tube heat exchangers.

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