Device for preparing liquefied natural gas from semi-coke tail gas

Abstract

The utility model relates to a device for preparing liquefied natural gas from semi-coke tail gas, which comprises a first compression device, a pre-purification device, a second compression device, a deacidification device, a methane synthesis device, a deamination device, a dehydration device and a liquefaction device which are sequentially connected through pipelines, a steam outlet pipeline of the methane synthesis device is divided into three branches, the first branch is connected with the pre-purification device, the second branch is connected with the deacidification device, and the third branch is connected with the dehydration device and used for supplying heat to the pre-purification device, the deacidification device and the dehydration device.

Description

Technical Field

[0001] The utility model relates to the field of gas purification and natural gas preparation, and in particular to a device for preparing liquefied natural gas from semi-coke tail gas. Background Art

[0002] Semi-coke tail gas is a gas produced during the production of semi-coke. Its main components include nitrogen (N2), methane (CH4), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). Compared with coke oven gas, semi-coke tail gas contains more carbon monoxide and carbon dioxide, but less hydrogen. Too low a hydrogen-carbon ratio is not conducive to methane synthesis. It is necessary to remove excess carbon dioxide from semi-coke tail gas to meet the hydrogen-carbon ratio required for methane synthesis.

[0003] Patent CN108034464A discloses a method for producing liquefied natural gas from semi-coke tail gas, which removes coke, benzene and naphthalene from the semi-coke tail gas, and then sends it to a low-temperature methanol washing unit for purification and desulfurization. The desulfurized semi-coke tail gas is mixed with methane-rich gas and sent to a methanation unit for methanation to obtain a crude methane product gas, which is then sent to a low-temperature methanol washing unit for purification and decarbonization, and finally nitrogen is removed by deep cold separation to obtain liquefied natural gas. The low-temperature methanol washing process used in this patented technology has a large demand for low-temperature cold sources, and the selective absorption rate of methanol as a physical absorbent for carbon dioxide and hydrogen sulfide is not high, and part of the methane in the raw gas will also be absorbed. The above means high energy consumption and more equipment, which will eventually lead to high investment and operating costs.

[0004] Patent CN 108977243A discloses a process for preparing liquefied natural gas from semi-coke tail gas, in which the semi-coke tail gas after buffering in the gas tank is subjected to wet desulfurization, water washing purification, gas pressurization, and methanation treatment to convert CO and CO2 in the semi-coke tail gas into CH4, and then the synthesis gas after methanation is subjected to decarbonization and deep cold liquefaction to liquefy CH4 into liquefied natural gas. The patent uses water washing to remove most of the benzene, naphthalene, and tar in the semi-coke tail gas, but the solubility of benzene and naphthalene in water is extremely low, and it is unrealistic to remove them to the index specified in the patent, and the treatment of water that absorbs benzene, naphthalene, and tar is also a considerable problem.

[0005] The above patents are all technologies for preparing liquefied natural gas from lignite tail gas, and they all have shortcomings in different aspects. Utility Model Content

[0006] In view of the above problems existing in the prior art, the utility model proposes a relatively simple, low-cost, low-energy method for preparing liquefied natural gas from semi-coke tail gas.

[0007] The utility model provides a device for preparing liquefied natural gas from semi-coke tail gas, which comprises a first compression device, a pre-purification device, a second compression device, a deacidification device, a methane synthesis device, a deammoniation device, a dehydration device and a liquefaction device which are sequentially connected via pipelines, the first compression device is connected with a semi-coke tail gas feed pipeline, a methane synthesis device steam outlet pipeline is divided into three branches, a first branch of the methane synthesis device steam outlet pipeline is connected with the pre-purification device, a second branch of the methane synthesis device steam outlet pipeline is connected with the deacidification device and a third branch of the methane synthesis device steam outlet pipeline is connected with the dehydration device, which are respectively used for supplying heat to the pre-purification device, the deacidification device and the dehydration device.

[0008] Preferably, the first compression device is a screw compressor.

[0009] Preferably, the second compression device is a centrifugal compressor.

[0010] Furthermore, the nitrogen-rich tail gas pipeline of the liquefaction device is divided into two branches, the first branch of the nitrogen-rich tail gas pipeline of the liquefaction device is connected to the dehydration device, and the second branch of the nitrogen-rich tail gas pipeline of the liquefaction device is a direct discharge pipeline.

[0011] Furthermore, the pre-purification device comprises a detarring tower and a debenzene and denaphthalene tower connected in series.

[0012] Further, the deacidification device includes an amine absorber, a first cooler, a first gas-liquid separator, a first pressure reducing valve, a flash tank, a first heat exchanger, a second heat exchanger, an amine regeneration tower, a first reboiler, a second cooler, a second gas-liquid separator, a reflux pump, a third cooler, a semi-lean liquid pump, a fourth cooler and a lean liquid pump.

[0013] The blue carbon gas feed pipe is connected to the lower or bottom gas inlet of the amine absorber, the lean liquid feed pipe is connected to the top or upper liquid inlet of the amine absorber, the semi-lean liquid feed pipe is connected to the middle liquid inlet of the amine absorber, the bottom liquid outlet of the amine absorber is connected to the amine liquid discharge pipe, and the top gas outlet of the amine absorber is connected to the top outlet pipeline.

[0014] The top outlet pipeline is connected to the inlet of the first gas-liquid separator through the first cooler. The first gas-liquid separator is provided with a first gas-liquid separator top outlet pipeline.

[0015] The amine liquid discharge pipe is connected to the flash tank inlet through the first pressure reducing valve. The bottom of the flash tank is provided with a flash tank liquid phase outlet pipe.

[0016] The flash tank liquid phase outlet pipeline at the bottom of the flash tank is divided into two branches, wherein the first branch of the flash tank outlet pipeline of one branch is connected to a heat exchange channel of the first heat exchanger, and the second branch of the flash tank outlet pipeline of the other branch is connected to a heat exchange channel of the second heat exchanger. The two branches after heat exchange merge into the amine regeneration tower feed pipe, which is connected to the upper part or top of the amine regeneration tower.

[0017] The top outlet pipeline of the amine regeneration tower is connected to the second gas-liquid separator via the second cooler (CO2 cooler). The second gas-liquid separator is provided with a gas-liquid separator gas phase outlet pipeline and a gas-liquid separator liquid phase outlet pipeline. The gas-liquid separator liquid phase outlet pipeline is returned to the amine regeneration tower via a reflux pump.

[0018] The amine regeneration tower is provided with a first reboiler to heat the bottom liquid to provide stripping steam. The bottom liquid outlet pipeline of the amine regeneration tower is connected to the top of the amine absorption tower via the first heat exchanger, the fourth cooler and the lean liquid pump.

[0019] The middle liquid outlet of the amine regeneration tower is connected to the semi-lean liquid outlet pipeline, and the semi-lean liquid outlet pipeline returns to the middle of the amine absorption tower through the second heat exchanger, the third cooler, and the semi-lean liquid pump.

[0020] Further, the methane synthesis unit includes a third heat exchanger, a fourth heat exchanger, a primary reactor, a primary waste boiler, a secondary reactor, a secondary waste boiler, a fifth heat exchanger, a tertiary reactor, a sixth heat exchanger, a fifth cooler, a third gas-liquid separator, a seventh heat exchanger, a fourth gas-liquid separator, a compressor, and a pump.

[0021] The deacidified gas feed pipeline is divided into two branches after passing through the third heat exchanger, namely, the first deacidified gas branch pipe and the second deacidified gas branch pipe. The first deacidified gas branch pipe is connected to a heat exchange channel of the heat exchanger after merging with the circulating gas pipeline and the circulating liquid pipeline. After exiting the heat exchange channel, it is connected to the first reactor through the first reactor feed pipe.

[0022] The first reactor outlet pipe of the first reactor is connected to the inlet of the second reactor through the first waste boiler, the fourth heat exchanger and the second branch pipe of the deacidified gas.

[0023] The secondary reactor outlet pipeline passes through the secondary waste boiler, the fifth heat exchanger, the third heat exchanger, the seventh heat exchanger, and then connects to the fourth gas-liquid separator.

[0024] The gas phase outlet pipeline of the fourth gas-liquid separator is divided into two branches. The first branch of the gas phase outlet is connected to the feed port of the third-stage reactor via the fifth heat exchanger, and the second branch of the gas phase outlet is connected to the compressor inlet. The compressor outlet pipeline is connected to the seventh heat exchanger. The circulating gas pipeline after the seventh heat exchanger is connected to the circulating liquid pipeline and the first branch of the deacidified gas via the fourth heat exchanger. Connected to the feed port of the first reactor,

[0025] The outlet pipeline of the tertiary reactor is connected to the third gas-liquid separator via the sixth heat exchanger and the fifth cooler. The gas phase outlet pipeline of the third gas-liquid separator is the output product gas pipeline of the methane synthesis unit. The liquid phase outlet pipeline of the third gas-liquid separator is connected to the pump after merging with the liquid outlet pipeline of the fourth gas-liquid separator. The circulating liquid pipeline coming out of the pump is merged with the circulating gas pipeline and the first branch pipe of the deacidified gas.

[0026] The deoxygenated water pipeline of the input device is connected to the sixth heat exchanger, and is respectively connected to the first-level waste boiler and the second-level waste boiler after exiting the sixth heat exchanger, and then outputs the device through the steam pipeline.

[0027] Furthermore, the deamine device adopts a water washing process, including a water washing tower, a water washing tower feed pipe is connected to the lower part of the water washing tower, a desalted water pipeline is connected to the upper part of the water washing tower, a water washing tower top outlet pipeline is provided at the top of the water washing tower, and a water washing tower bottom outlet pipeline is provided at the bottom of the water washing tower.

[0028] Furthermore, the dehydration device adopts a pressure swing temperature adsorption process, including a heater, a sixth cooler, a fifth gas-liquid separator, a dehydration tower integrated by three dehydration towers: a first dehydration tower, a second dehydration tower, a third dehydration tower and a programmable valve, the dehydration device input pipeline is divided into three branches, each branch is provided with a programmable valve, respectively connected to the synthesis gas inlet of the first, second and third dehydration towers, the synthesis gas outlet branches of the first, second and third dehydration towers respectively provided with programmable valves are merged into the device output pipeline, the low-pressure regeneration gas pipeline is divided into three branches, each branch is provided with a programmable valve, respectively connected to the first, second and third dehydration towers The regeneration gas inlets of the second and third dehydration towers and the dehydration regeneration gas output branch pipes of the three dehydration towers respectively provided with programmable valves are merged into a dehydration regeneration gas output pipeline, and then connected to the heater inlet, the heater outlet is connected to the hot regeneration gas input pipeline, the hot regeneration gas input pipeline is branched into three hot regeneration gas input branch pipes provided with programmable valves, which are respectively connected to the regeneration gas inlets of the first, second and third dehydration towers, the regeneration gas output branch pipes provided with programmable valves out of the dehydration towers are merged into a regeneration gas output pipeline, and then connected to the sixth cooler inlet, the sixth cooler outlet is connected to the fifth gas-liquid separator via the fifth gas-liquid separator inlet pipeline.

[0029] Further, the liquefaction device includes a raw gas precooler, a cold box, a main heat exchanger, a second reboiler, a second pressure reducing valve, a denitrification tower, a condenser, a sixth gas-liquid separator, a first throttle valve, a mixed refrigerant compressor, a mixed refrigerant precooler, a seventh gas-liquid separator, a second throttle valve, a third throttle valve, a nitrogen compressor and a nitrogen precooler,

[0030] The discharge pipe of the dehydration device is connected to the first heat exchange channel of the main heat exchanger in the cold box through the raw gas precooler. The outlet of the first heat exchange channel is connected to the second heat exchange channel of the main heat exchanger after passing through a heat exchange channel of the reboiler. The outlet of the second heat exchange channel is connected to the inlet of the denitrification tower through the second pressure reducing valve.

[0031] The denitrogenation tower reboiler is provided with heat by the aforementioned flow in the connecting pipeline between the outlet of the first heat exchange channel and the reboiler. The outlet gas pipeline at the top of the denitrogenation tower passes through a heat exchange channel of the condenser and is connected to the sixth gas-liquid separator. The gas phase outlet pipeline of the sixth gas-liquid separator returns to the third heat exchange channel of the main heat exchanger, and exits the cold box from the hot end of the third heat exchange channel of the main heat exchanger, and exits the liquefaction device through the nitrogen-rich tail gas pipeline as nitrogen-rich tail gas.

[0032] The liquid phase outlet pipeline of the sixth gas-liquid separator flows back into the upper part or top of the denitrification tower.

[0033] The liquid outlet pipeline at the bottom of the denitrification tower is connected to the fourth heat exchange channel of the main heat exchanger. The outlet pipeline of the fourth heat exchange channel leaves the main heat exchanger and is output to the liquefaction device through the first throttle valve and the liquefied natural gas product pipeline.

[0034] Furthermore, the mixed refrigerant cycle is used to provide the cooling capacity required for liquefaction. The low-pressure mixed refrigerant outlet pipeline of the main heat exchanger is connected to the inlet of the mixed refrigerant compressor. The outlet pipeline of the mixed refrigerant compressor is connected to the mixed refrigerant precooler and the seventh gas-liquid separator in sequence. The gas phase outlet pipeline of the seventh gas-liquid separator is connected to the inlet of the fifth heat exchange channel of the main heat exchanger. The outlet pipeline of the fifth heat exchange channel returns to the sixth heat exchange channel of the main heat exchanger after passing through the third throttle valve; the liquid phase outlet pipeline of the seventh gas-liquid separator is connected to the seventh heat exchange channel of the main heat exchanger, and returns to the sixth heat exchange channel of the main heat exchanger after passing through the outlet pipeline of the seventh heat exchange channel and passing through the second throttle valve. The outlet of the sixth heat exchange channel is connected to the inlet of the mixed refrigerant compressor through the low-pressure mixed refrigerant outlet pipeline.

[0035] The outlet pipe of the eighth heat exchange channel of the main heat exchanger is connected to the inlet of the nitrogen compressor, the outlet pipe of the nitrogen compressor is connected to the nitrogen precooler, the outlet pipe of the nitrogen precooler is connected to the ninth heat exchange channel of the main heat exchanger, the outlet pipe of the ninth heat exchange channel is connected to another heat exchange channel of the condenser through a throttle valve, and returns to the eighth heat exchange channel of the main heat exchanger after exiting the heat exchange channel, and the outlet pipe of the eighth heat exchange channel returns to the inlet of the nitrogen compressor.

[0036] The present application further provides a process for preparing liquefied natural gas from blue coal tail gas, comprising the following steps:

[0037] The semi-coke tail gas is pressurized to 0.75±0.20MPa, preferably 0.75±0.10MPa, by the first compression device. The pressurized semi-coke tail gas enters the pre-purification device for detarring, debenzening and denaphthalening, and the tar and naphthalene content in the semi-coke tail gas is reduced to no more than 1mg / Nm 3 , benzene content is not higher than 20mg / Nm 3 ;

[0038] The pre-purified semi-coke tail gas is further pressurized to 2.1±0.20MPa, preferably 2.1±0.10MPa, by a second compression device, and the further pressurized semi-coke tail gas is transported to a deacidification device for deacidification. The carbon dioxide content in the semi-coke tail gas after treatment by the deacidification device is not higher than 50ppm, and the hydrogen sulfide content is not higher than 0.1ppm;

[0039] The deacidified semi-coke tail gas is sent to the methane synthesis unit through the feed pipe of the methane synthesis unit for methane synthesis reaction. The methane synthesis unit is composed of three reactors in series. The reaction heat is recovered to generate steam. A part of the semi-coke tail gas is mixed with the circulating gas and water to undergo a methanation reaction in the primary reactor. The outlet temperature is controlled at 540±10°C. After the waste heat is recovered, the outlet gas is mixed with another part of the semi-coke tail gas and enters the secondary reactor for a methanation reaction. The outlet temperature is controlled at 470±10°C. The outlet gas is divided into two parts after the waste heat is recovered. One part is sent to the primary reactor as the circulating gas through the compressor for pressurization, and the other part enters the tertiary reactor for a methanation reaction. The outlet gas becomes synthesis gas after cooling and liquid separation. The reaction heat in the methane synthesis unit is recovered by the waste heat recovery system and used for the by-product steam of 2.5±0.5MPa. A part of the steam is sent to the pre-purification unit for the regeneration heat source of the adsorbent therein, a part is sent to the deacidification unit for the regeneration heat source of the MDEA solution therein, and a part is sent to the dehydration unit for the regeneration heat source of the molecular sieve therein.

[0040] The synthesis gas produced by the methane synthesis unit is sent to the deamination unit to remove trace ammonia in the synthesis gas. The deamination unit adopts a water washing process, and the ammonia content in the final output gas flow is no more than 1ppm;

[0041] The synthesis gas after deammoniation by the deammoniation unit is sent to the dehydration unit for drying. The dehydration unit adopts the molecular sieve pressure and temperature swing adsorption (PTSA) process to ultimately make the water content in the output gas flow no higher than 1ppm. A part of the nitrogen-rich tail gas from the liquefaction unit is introduced into this unit as the regeneration gas of the molecular sieve. The regenerated tail gas after the molecular sieve regeneration is the nitrogen-rich tail gas discharged from the unit through the regeneration tail gas pipeline of the dehydration unit. The heating heat source of the regeneration gas is the steam produced by the methane synthesis unit.

[0042] The dehydrated and dried synthesis gas is sent to the liquefaction unit for deep cold separation to produce liquefied natural gas that meets the indicators. The liquefaction unit adopts a cryogenic distillation process with precooling, including a precooler, a cold box, a refrigerant compressor and a nitrogen compressor. The synthesis gas is first precooled to 12±2℃ by the precooler, and then enters the cold box to complete cryogenic distillation. The synthesis gas entering the cold box is initially cooled to -95℃~-105℃ by the main heat exchanger in the cold box and then extracted. After passing through the tower kettle evaporator of the denitrification tower as a heat source, it returns to the main heat exchanger and continues to cool to -145℃~-150℃, and then passes through the pressure reducing valve After being reduced in pressure to 0.6±0.1MPa, it enters the denitrification tower, where the nitrogen and hydrogen components flow out from the top of the tower in the form of gas as nitrogen-rich tail gas, and the remaining methane flows out from the bottom of the tower in the form of liquid as liquefied natural gas. The nitrogen-rich tail gas is reheated by the main heat exchanger and then leaves the unit. The reheated nitrogen-rich tail gas is divided into two parts, one part is sent to the dehydration unit as regenerated gas and then discharged, and the other part is directly discharged. The nitrogen content of the liquefied natural gas flowing out of the bottom of the denitrification tower is not higher than 1%. It is supercooled to -162±5℃ by the main heat exchanger and then sent to the cold box. After throttling, it is output from the liquefaction unit as a liquefied natural gas product.

[0043] Preferably, the pre-purification device uses no less than 4 adsorption towers, using adsorbents to physically adsorb impurities such as tar, benzene, naphthalene, etc. contained in the lignite tail gas, and a portion of the steam by-product of the methane synthesis unit is used for thermal regeneration of the adsorbent.

[0044] Preferably, the deacidification device adopts a two-stage absorption process of MDEA (methyldiethanolamine), using MDEA solution to absorb and remove carbon dioxide and hydrogen sulfide in the semi-coke tail gas. The heat required for the regeneration of the MDEA solution is provided by the steam produced by the methane synthesis unit.

[0045] Advantages of this application:

[0046] The device for preparing liquefied natural gas from lignite tail gas of the present application is relatively simple, low-cost, low-energy consumption, and the product has a high methane content, thus avoiding the problems of both high investment and operating costs in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of a device for producing liquefied natural gas from semi-coke tail gas according to the utility model;

[0048] Figure 2 It is a schematic diagram of a deacidification device;

[0049] Figure 3 This is a schematic diagram of a methane synthesis unit;

[0050] Figure 4 It is a schematic diagram of a deammoniation unit;

[0051] Figure 5 It is a schematic diagram of the dehydration device;

[0052] Figure 6 Schematic diagram of the liquefaction device.

[0053] Description of reference numerals:

[0054] B1: first compression unit, B2: pre-purification unit, B3: second compression unit, B4: deacidification unit, B5: methane synthesis unit, B6: deammoniation unit, B7: dehydration unit, B8: liquefaction unit;

[0055] A01: amine absorption tower, A02: first cooler, A03: first gas-liquid separator, A04: first pressure reducing valve, A05: flash tank, A06: first heat exchanger, A07: second heat exchanger, A08: amine regeneration tower, A09: first reboiler, A10: second cooler, A11: second gas-liquid separator, A12: reflux pump, A13: third cooler, A14: semi-lean liquid pump, A15: fourth cooler, A16: lean liquid pump;

[0056] S01: Raw semi-coke tail gas feed pipeline, S02: Pre-purification device feed pipe (semi-coke tail gas compressed to 0.75MPa), S03: Second compression device feed pipe (semi-coke tail gas after pre-purification), S04: Deacidification device feed pipe (semi-coke tail gas compressed to 2.1MPa), S05: Methane synthesis device feed pipe (semi-coke tail gas after deacidification), S06: Deamination device feed pipe (synthesis gas), S07: Dehydration device feed pipe (synthesis gas after deamination), S08: Liquefaction device feed pipe (synthesis gas after dehydration), S09: Liquefaction device discharge pipe (liquefied natural gas product), S10: Methane synthesis device steam outlet pipeline (2.5MPa saturated steam), S 11: The first branch of the steam outlet pipeline of the methane synthesis unit (steam used for regeneration of the pre-purification unit), S12: The second branch of the steam outlet pipeline of the methane synthesis unit (steam used as the regeneration heat source of the MDEA solution), S13: The third branch of the steam outlet pipeline of the methane synthesis unit (steam used as the regeneration heat source of the molecular sieve of the dehydration unit), S14: The nitrogen-rich tail gas pipeline of the liquefaction unit (nitrogen-rich tail gas), S15: The second branch of the nitrogen-rich tail gas pipeline of the liquefaction unit (the discharged nitrogen-rich tail gas), S16: The first branch of the nitrogen-rich tail gas pipeline of the liquefaction unit (the regenerated gas (nitrogen-rich tail gas) entering the dehydration unit), S17: The regenerated tail gas pipeline of the dehydration unit (the regenerated tail gas (nitrogen-rich tail gas) discharged through the dehydration unit). DETAILED DESCRIPTION

[0057] The present invention will be further described below with reference to the accompanying drawings.

[0058] like Figure 1As shown, a device for preparing liquefied natural gas from semi-coke tail gas includes a first compression device B1, a pre-purification device B2, a second compression device B3, a deacidification device B4, a methane synthesis device B5, a deamination device B6, a dehydration device B7 and a liquefaction device B8 which are sequentially connected via pipelines, the first compression device B1 is connected to a semi-coke tail gas feed pipeline S01, a methane synthesis device steam outlet pipeline S10 is divided into three branches, a first branch S11 of the methane synthesis device steam outlet pipeline is connected to the pre-purification device B2, a second branch S12 of the methane synthesis device steam outlet pipeline is connected to the deacidification device B4 and a third branch S13 of the methane synthesis device steam outlet pipeline is connected to the dehydration device B7, which are respectively used to supply heat to the pre-purification device B2, the deacidification device B4 and the dehydration device B7.

[0059] The nitrogen-rich tail gas pipeline S14 of the liquefaction device is divided into two branches. The first branch S16 of the nitrogen-rich tail gas pipeline of the liquefaction device is connected to the dehydration device, and the second branch S15 of the nitrogen-rich tail gas pipeline of the liquefaction device is a direct discharge pipeline.

[0060] The pre-purification device B2 includes a detarring tower and a debenzene and denaphthalene tower connected in series, which may be an existing detarring tower and a debenzene and denaphthalene tower, and is operated according to existing process conditions.

[0061] like Figure 2 As shown, the deacidification unit B4 adopts a two-stage absorption process of MDEA (methyldiethanolamine), including an amine absorption tower A01, a first cooler A02, a first gas-liquid separator A03, a first pressure reducing valve A04, a flash tank A05, a first heat exchanger A06, a second heat exchanger A07, an amine regeneration tower A08, a first reboiler A09, a second cooler A10, a second gas-liquid separator A11, a reflux pump A12, a third cooler A13, a semi-lean liquid pump A14, a fourth cooler A15 and a lean liquid pump A16.

[0062] The feed of the deacidification device is the semi-coke gas pressurized by the compression device, which enters from the bottom gas inlet of the amine absorber A01 through the semi-coke gas feed pipe 401, the lean liquid (lean MDEA solution) enters from the top liquid inlet of the amine absorber A01 through the lean liquid feed pipe 422, and the semi-lean liquid (semi-lean MDEA solution) enters from the middle liquid inlet of the amine absorber A01 through the semi-lean liquid feed pipe 421. After the lean liquid, semi-lean liquid and the gas entering the bottom are fully contacted in the tower for heat and mass transfer, carbon dioxide and hydrogen sulfide are absorbed by the amine liquid. The amine liquid that absorbs carbon dioxide and hydrogen sulfide is discharged from the bottom liquid outlet of the amine absorber A01 through the amine liquid discharge pipe 404. The deacidified gas (gas with carbon dioxide and hydrogen sulfide removed) is discharged from the top gas outlet of the amine absorber A01 through the top outlet pipe 402.

[0063] After the deacidified gas is cooled to 40±5°C, for example, about 40°C, by the first cooler A02, it enters the first gas-liquid separator A03 to separate the condensed free water, and the remaining gas is output from the deacidification device through the outlet pipe 403 at the top of the first gas-liquid separator. The carbon dioxide content in the output gas is not higher than 50ppm, and the hydrogen sulfide content is not higher than 0.1ppm.

[0064] The rich amine liquid (amine liquid that has absorbed carbon dioxide and hydrogen sulfide) is depressurized to 0.5 MPa by the first pressure reducing valve A04 and then enters the flash tank A05 for gas-liquid separation. The liquid phase is discharged from the bottom of the flash tank A05 through the flash tank outlet pipe 405.

[0065] The liquid discharged from the bottom of the flash tank A05 is divided into two parts, one part of the fluid enters the first heat exchanger A06 through the first branch pipe 406 of the flash tank outlet pipe for heat exchange, and the other part of the fluid enters the second heat exchanger A07 through the second branch pipe 407 of the flash tank outlet pipe for heat exchange. After the heat exchange, the two branches merge into the amine regeneration tower feed pipe 408 and enter the top of the amine regeneration tower A08.

[0066] The rich amine liquid enters the amine regeneration tower A08 through the amine regeneration tower feed pipe 408 and flows downward, and contacts with the stripping steam from bottom to top in countercurrent for heat and mass transfer. The carbon dioxide and hydrogen sulfide in the rich amine solution are resolved from the rich amine solution and discharged from the top gas outlet of the amine regeneration tower A08. The top gas is cooled to 40±5°C, for example, about 40°C, through the second cooler A10 (CO2 cooler) from the top outlet pipe 409 of the amine regeneration tower, and then enters the second gas-liquid separator A11. The separated gas is discharged from the device through the gas-liquid separator gas phase outlet pipe 410, and the separated liquid is sent back to the amine regeneration tower A08 through the gas-liquid separator liquid phase outlet pipe 411 and the reflux pump A12.

[0067] The first reboiler A09 of the amine regeneration tower A08 heats the bottom liquid to provide stripping steam. The steam produced by the synthesis unit is introduced into the first reboiler A09 through the steam pipeline 415 to provide the heat required for the regeneration of the amine liquid.

[0068] The rich amine liquid from which carbon dioxide and hydrogen sulfide have been removed is discharged from the liquid outlet pipe 413 at the bottom of the amine regeneration tower A08, which is called the lean liquid. The lean liquid is heat exchanged with the rich amine liquid from the first branch pipe 406 of the flash tank outlet pipe through the first heat exchanger A06, and then cooled to 40±5°C, for example, about 40°C, through the fourth cooler A15, and is sent to the top of the amine absorption tower A01 through the lean liquid pump A16.

[0069] The rich amine liquid from which carbon dioxide is partially removed is referred to as semi-lean liquid. The semi-lean liquid is discharged from the middle liquid outlet of the amine regeneration tower A08 through the semi-lean liquid outlet pipe 414, and after heat exchange with the rich amine liquid from the second branch pipe 407 of the flash tank outlet pipe through the second heat exchanger A07, it is cooled to 40±5°C, for example, about 40°C, through the third cooler A13, and is sent to the middle of the amine absorption tower A01 through the semi-lean liquid pump A14.

[0070] like Figure 3 As shown, the methane synthesis unit mainly includes a third heat exchanger Y01, a fourth heat exchanger Y02, a primary reactor Y03, a primary waste boiler Y04, a secondary reactor Y05, a secondary waste boiler Y06, a fifth heat exchanger Y07, a tertiary reactor Y08, a sixth heat exchanger Y09, a fifth cooler Y10, a third gas-liquid separator Y11, a seventh heat exchanger Y12, a fourth gas-liquid separator Y13, a compressor Y14, and a pump Y15.

[0071] The deacidified gas output by the deacidification unit is the feed of the methane synthesis unit. After being preheated by the third heat exchanger Y01 from the deacidified gas feed pipeline 501, it is divided into two parts. One part is mixed with the circulating gas from the circulating gas pipeline 521 and the circulating liquid from the circulating liquid pipeline 524 through the first branch pipe 502 of the deacidified gas and then enters the heat exchanger Y02 to be heated to 280±10℃, for example, about 280℃. The heated gas flow enters the primary reactor Y03 through the primary reactor feed pipe 504, and a methanogenic reaction occurs in the reactor. Carbon monoxide, carbon dioxide and hydrogen in the gas flow react and convert into methane and water under the action of high temperature and catalyst. It is converted into an exothermic reaction.

[0072] Methane synthesis reaction equation:

[0073] CO+3H2=CH4+H2O

[0074] CO2+4H2=CH4+2H2O.

[0075] The outlet gas flow of the first reactor Y03 enters the first waste boiler Y04 through the first reactor outlet pipe 505 to recover heat. The gas flow after heat recovery enters the heat exchanger Y02 through the circulation pipe 506 to exchange heat with the aforementioned feed. The gas flow after heat exchange passes through the first reactor product pipe 507 and is mixed with another part of the preheated feed from the second branch pipe 503 of the deacidified gas. The mixing temperature is about 280±10°C, for example, about 280°C. The gas flows into the second reactor Y05 to continue the methanation reaction in the reactor.

[0076] The gas flow at the outlet of the secondary reactor enters the secondary waste boiler Y06 through the secondary reactor outlet pipe 508 for heat exchange and heat recovery. The gas flow after heat recovery enters the fifth heat exchanger Y07 through the secondary waste boiler and the fifth heat exchanger connecting pipe 509 for heat exchange with the gas flow from the first branch pipe 513 of the gas phase outlet of the fourth gas-liquid separator. The gas flow after heat exchange enters the third heat exchanger Y01 through the fifth heat exchanger and the third heat exchanger connecting pipe 510 for heat exchange with the gas flow of the deacidified gas feed pipe 501. The gas flow after heat exchange enters the seventh heat exchanger Y12 through the third heat exchanger and the seventh heat exchanger connecting pipe 511 for heat exchange with the gas flow of the compressor outlet pipe 520. The gas flow temperature after heat exchange is about 110±10℃ and enters the fourth gas-liquid separator Y13 through the fourth gas-liquid separator inlet pipe 512.

[0077] The outlet gas flow of the fourth gas-liquid separator is divided into two parts, one of which flows through the second branch pipe 514 of the gas phase outlet of the fourth gas-liquid separator as circulating gas to enter the compressor Y14 for pressurization, and the pressurized circulating gas enters the seventh heat exchanger Y12 through the compressor outlet pipe 520 to exchange heat with the gas flow (discharge product of the secondary reactor) from the connecting pipe 511 between the third heat exchanger and the seventh heat exchanger, and the gas flow after heat exchange is mixed with the circulating liquid from the circulating liquid pipe 524 and the main gas flow of the first branch pipe 502 of the deacidified gas through the circulating gas pipe 521 and then enters the primary reactor Y03. The other part of the gas flow enters the fifth heat exchanger Y07 through the first branch pipe 513 of the gas phase outlet of the fourth gas-liquid separator to exchange heat with the gas flow from the connecting pipe 509 between the secondary waste boiler and the fifth heat exchanger for preheating, and the gas flow 515 preheated to 270±10℃ (e.g., about 270℃) enters the tertiary reactor Y08, and continues to undergo methanation reaction in the reactor.

[0078] The outlet gas flow of the tertiary reactor Y08 enters the sixth heat exchanger Y09 through the tertiary reactor outlet pipe 516 to exchange heat with the deoxygenated water input into the device through the deoxygenated water pipe 525. The gas flow after heat exchange enters the fifth cooler Y10 through the sixth heat exchanger and the fifth cooler connecting pipe 517 to be cooled to 40±5°C, for example, about 40°C. The cooled gas enters the third gas-liquid separator Y11 through the third gas-liquid separator feed pipe 518 to complete gas-liquid separation. The separated gas is discharged from the third gas-liquid separator gas phase outlet pipe 519 as the output product gas of the methane synthesis unit (referred to as synthesis gas); the separated liquid is combined with the liquid from the fourth gas-liquid separator Y13 liquid outlet pipe 523 through the third gas-liquid separator liquid phase outlet pipe 522 to form a circulating liquid, which is pressurized by pump Y15. The pressurized circulating liquid is mixed with the circulating gas from the circulating gas pipe 521 and the main gas flow of the first branch pipe 502 of the deacidified gas through the circulating liquid pipe 524.

[0079] The methane synthesis reaction is an exothermic reaction, and the heat released by the reaction is used to generate steam. The deoxygenated water input into the device is preheated by the sixth heat exchanger Y09, and then injected into the reaction heat through the first-level waste boiler Y04 and the second-level waste boiler Y06 to become steam, and then output from the device through the steam pipeline 526.

[0080] like Figure 4 As shown, the deamine device adopts a water washing process, including a water washing tower M01, preferably a plate tower. The synthesis gas output by the methane synthesis device enters the lower part of the water washing tower M01 through the water washing tower feed pipe 601, and contacts the desalted water entering from the upper part of the water washing tower M01 through the desalted water pipeline 602 in reverse, and the trace ammonia remaining in the synthesis gas is absorbed by water. The deammonified synthesis gas is discharged from the top of the water washing tower M01 through the water washing tower top outlet pipeline 603, and the absorbed ammonia aqueous solution is discharged from the bottom of the water washing tower M01 through the water washing tower bottom outlet pipeline 604.

[0081] like Figure 5 As shown, the dehydration device adopts a pressure swing temperature adsorption process. In one embodiment, it includes a heater D02, a sixth cooler D03, a fifth gas-liquid separator D04, a dehydration tower assembly D01 consisting of three dehydration towers (the first dehydration tower T1, the second dehydration tower T2, and the third dehydration tower T3) and a programmable valve. The gas flow from the dehydration device input pipeline 701 is the synthesis gas output by the deammoniation device. The dehydration tower is filled with molecular sieves to adsorb water in the synthesis gas, so that the water content in the dry gas flow of the device output pipeline 703 is not higher than 1ppm. The molecular sieve that has completed adsorption needs to be regenerated using low-pressure regeneration gas. The low-pressure regeneration gas of the low-pressure regeneration gas pipeline 702 comes from the nitrogen-rich tail gas discharged from the liquefaction device. The regeneration gas flow rate is about 20±5% of the synthesis gas flow rate entering the device. The regeneration gas is first dehydrated by a dehydration tower. The regeneration gas after the dehydration tower (dehydration regeneration gas output pipeline 704) is heated to about 240±10°C by a heater D02. The hot regeneration gas enters the dehydration tower through a hot regeneration gas input pipeline 705 to regenerate the molecular sieve. The regeneration gas out of the dehydration tower enters the sixth cooler D03 through the regeneration gas output pipeline 706 and is cooled to about 40±5°C, for example, about 40°C. The cooled gas enters the fifth gas-liquid separator D04 through the fifth gas-liquid separator inlet pipeline 707 to separate the condensed water, and the tail gas is discharged from the dehydration device through the tail gas exhaust pipe 708.

[0082] The regeneration gas heater D02 uses steam to heat the regeneration gas, and the steam input through the steam pipeline 710 is produced from the methane synthesis unit.

[0083] like Figure 6As shown, the liquefaction device includes a raw gas precooler L01, a cold box L02, a main heat exchanger L03, a second reboiler L04, a second pressure reducing valve L05, a denitrogenation tower L06, a condenser L07, a sixth gas-liquid separator L08, a first throttle valve L09, a mixed refrigerant compressor L21, a mixed refrigerant precooler L22, a seventh gas-liquid separator L23, a second throttle valve L24, a third throttle valve L25, a nitrogen compressor L31 and a nitrogen precooler L32.

[0084] The dry synthesis gas output from the dehydration device discharge pipe 801 is cooled to 12±3°C by the raw gas precooler L01. The cooled synthesis gas enters the first heat exchange channel of the main heat exchanger L03 in the cold box L02 through the synthesis gas feed pipe 802 for initial cooling, and leaves the main heat exchanger after initial cooling to -95°C~-105°C. The synthesis gas leaving the main heat exchanger L03 enters the reboiler L04 for heating through the outlet of the first heat exchange channel and the reboiler connecting pipe 803. The synthesis gas after heating enters the second heat exchange channel of the main heat exchanger L03 through the reboiler and the second heat exchange channel connecting pipe 804 and is cooled to -145 to -150°C. The synthesis gas leaving the main heat exchanger enters the denitrification tower L06 after being reduced in pressure to 0.53±0.05MPa through the second pressure reducing valve L05 through the outlet of the second heat exchange channel and the denitrification tower connecting pipe 805.

[0085] The denitrification tower L06 purifies the methane in the feed by distillation. The denitrification tower reboiler L04 is provided with heat by the aforementioned logistics from the outlet of the first heat exchange channel and the reboiler connecting pipe 803. The nitrogen in the feed is discharged from the top of the tower. The outlet gas of the tower top outlet pipe 809 is cooled to -176±5°C by the condenser L07, and then enters the sixth gas-liquid separator L08 through the condenser cold channel outlet pipe 810. The separated gas phase returns to the third heat exchange channel of the main heat exchanger L03 through the sixth gas-liquid separator gas phase outlet pipe 812. After reheating, it is discharged from the cold box from the hot end of the third heat exchange channel of the main heat exchanger, and discharged from the liquefaction device as nitrogen-rich tail gas through the nitrogen-rich tail gas pipe 813. The liquid phase discharged from the liquid outlet of the sixth gas-liquid separator L08 flows back into the denitrification tower L06 through the sixth gas-liquid separator liquid phase outlet pipe 811. The bottom liquid of the denitrification tower L06 (the bottom liquid outlet pipeline 806 of the denitrification tower) is cooled to -163±10°C, preferably -163±5°C, through the fourth heat exchange channel of the main heat exchanger L03. This liquid leaves the main heat exchanger through the fourth heat exchange channel outlet pipeline 807, and after throttling by the first throttle valve L09, it is output to the liquefaction device as a liquefied natural gas product (through the liquefied natural gas product pipeline 808).

[0086] The reboiler heat required for the distillation of the denitrogenation tower L06 comes from the initially cooled synthesis gas (from the pipe 803 connecting the outlet of the first heat exchange channel and the reboiler), and the required condensing cooling capacity comes from liquid nitrogen.

[0087] The mixed refrigerant cycle is used to provide the cooling capacity required for liquefaction. The mixed refrigerant is composed of nitrogen, methane, ethylene, propane and isopentane. The low-pressure mixed refrigerant comes from (the low-pressure mixed refrigerant outlet pipe 821 of the main heat exchanger L03) and is pressurized by the mixed refrigerant compressor L21. The pressurized high-pressure mixed refrigerant enters the mixed refrigerant precooler L22 through the mixed refrigerant compressor outlet pipe 822 to cool to about 12±5℃, and then enters the seventh gas-liquid separator L23 through the seventh gas-liquid separator inlet pipe 823. The separated gas phase mixed refrigerant enters the inlet of the fifth heat exchange channel of the cold box L02 through the seventh gas-liquid separator gas phase outlet pipe 826, and is cooled to -163±10℃ by the main heat exchanger. After leaving the refrigeration heat exchanger, The liquid mixed refrigerant separated by the seventh gas-liquid separator L23 enters the cold box L02 through the seventh heat exchange channel 824 of the main heat exchanger, is cooled to -40±5℃ by the main heat exchanger, leaves the main heat exchanger through the seventh heat exchange channel outlet pipe 825, and then is throttled, depressurized and cooled by the second throttle valve L24, returns to the sixth heat exchange channel of the main heat exchanger, merges with the aforementioned reflux low-pressure mixed refrigerant to transfer cold, and is finally discharged from the hot end of the main heat exchanger L03 to become the low-pressure mixed refrigerant outlet pipe 821, and re-enters the mixed refrigerant compressor L21.

[0088] The low-pressure nitrogen from the outlet pipe 831 of the eighth heat exchange channel of the main heat exchanger is pressurized by the nitrogen compressor L31, and the pressurized high-pressure nitrogen enters the nitrogen precooler L32 through the nitrogen compressor outlet pipe 832 and is precooled to 12±5°C. The precooled high-pressure nitrogen enters the ninth heat exchange channel of the cold box L02 through the nitrogen precooler outlet pipe 833, is cooled to -174±10°C through the main heat exchanger L03 to become high-pressure liquid nitrogen and leaves the main heat exchanger. The high-pressure liquid nitrogen leaving the main heat exchanger passes through the outlet pipe 834 of the ninth heat exchange channel and is reduced in pressure and temperature by the throttle valve L33 to become low-pressure liquid nitrogen, becomes low-pressure nitrogen after the condenser L07 provides cooling capacity, returns to the eighth heat exchange channel of the main heat exchanger L03 through the condenser hot channel outlet pipe 835, and is discharged from its hot end (the outlet pipe 831 of the eighth heat exchange channel of the main heat exchanger), and re-enters the nitrogen compressor L31 as low-pressure nitrogen. Example 1

[0089] The flow rate of the blue carbon tail gas used as raw material in the embodiment is 100000 Nm 3 / h, the components are as follows:

[0090] Components V% <![CDATA[H2]]> 28.36 CO 14.14 <![CDATA[CO2]]> 11.59 <![CDATA[CH4]]> 5.66 <![CDATA[N2]]> 38.82 <![CDATA[C2H6]]> 0.50 <![CDATA[O2]]> 0.75 <![CDATA[C3H8]]> 0.12 <![CDATA[i-C4H 10 ]]> 0.01 <![CDATA[n-C4H 10 ]]> 0.04 <![CDATA[n-C5H 12 ]]> 0.01

[0091] The semi-coke tail gas is first pressurized to 0.75MPa through the semi-coke tail gas feed pipe S01 through the first compression device B1. The compressor is a screw compressor. The pressurized semi-coke tail gas enters the pre-purification device B2 through the pre-purification device feed pipe S02 for detarring, debenzening and denaphthalening. The pre-purification unit uses no less than 4 adsorption towers, and uses adsorbents to physically adsorb tar, benzene, naphthalene and other impurities contained in the semi-coke tail gas, and finally reduces the tar and naphthalene content in the semi-coke tail gas to no more than 1mg / Nm 3 , benzene content is not higher than 20mg / Nm 3 A portion of the steam produced as a byproduct of the methane synthesis unit B5 is used for thermal regeneration of the adsorbent through the first branch S11 of the methane synthesis unit steam outlet pipeline.

[0092] The pre-purified blue coke tail gas is further pressurized to 2.1 MPa through the second compression device feed pipe S03 and the second compression device B3, and the compressor is a centrifugal compressor. The further pressurized blue coke tail gas is transported to the deacidification device B4 through the deacidification device feed pipe S04.

[0093] The deacidification device B4 adopts the MDEA (methyldiethanolamine) two-stage absorption process, using MDEA solution to absorb and remove carbon dioxide and hydrogen sulfide in the semi-coke tail gas. The carbon dioxide content in the semi-coke tail gas after treatment by the deacidification device is not higher than 50ppm, and the hydrogen sulfide is not higher than 0.1ppm. The heat required for the regeneration of the MDEA solution is provided by the steam produced by the methane synthesis device B5 (through the second branch S12 of the steam outlet pipeline of the methane synthesis device).

[0094] The deacidified semi-coke tail gas is sent to the methane synthesis unit B5 through the methane synthesis unit feed pipe S05 for methane synthesis reaction. The methane synthesis unit consists of three reactors in series, and the reaction heat is recovered to produce steam. A part of the semi-coke tail gas is mixed with the circulating gas and water to undergo a methanogenic reaction in the primary reactor. The outlet temperature is controlled at 540°C. After the outlet gas is recovered by waste heat, it is mixed with another part of the semi-coke tail gas and enters the secondary reactor for a methanogenic reaction. The outlet temperature is controlled at 470°C. After the waste heat is recovered, the outlet gas is divided into two parts. One part is sent to the primary reactor as circulating gas through a compressor for boosting, and the other part enters the tertiary reactor for a methanogenic reaction. The outlet gas becomes synthesis gas after cooling and liquid separation. The reaction heat in the methane synthesis unit is recovered by the waste heat recovery system and used to produce 2.5MPa steam as a by-product. Part of the steam is sent to the pre-purification unit through the first branch S11 of the steam outlet pipe of the methane synthesis unit to be used as the adsorbent regeneration heat source therein, part of it is sent to the deacidification unit through the second branch S12 of the steam outlet pipe of the methane synthesis unit to be used as the regeneration heat source of the MDEA solution therein, and part of it is sent to the dehydration unit through the third branch S13 of the steam outlet pipe of the methane synthesis unit to be used as the regeneration heat source of the molecular sieve therein.

[0095] The synthesis gas produced by the methane synthesis unit is sent to the deamination unit B6 through the deamination unit feed pipe S06 to remove trace ammonia in the synthesis gas. The deamination unit adopts a water washing process, and the ammonia content in the final output gas flow is not higher than 1ppm.

[0096] The synthesis gas after deammoniation by the deamination unit is sent to the dehydration unit B7 through the dehydration unit feed pipe S07 for drying. The dehydration unit adopts the molecular sieve pressure and temperature swing adsorption (PTSA) process. The synthesis gas is continuously dried by the periodic adsorption of three dehydration towers, and the water content in the output gas flow is finally reduced to no more than 1ppm. A part of the nitrogen-rich tail gas from the liquefaction unit is introduced into this unit through the first branch S16 of the nitrogen-rich tail gas pipeline of the liquefaction unit as the regeneration gas of the molecular sieve. The regenerated tail gas (nitrogen-rich tail gas) after the molecular sieve regeneration is discharged from the unit through the dehydration unit regeneration tail gas pipeline S17. The heating heat source of the regenerated gas is the steam produced by the methane synthesis unit.

[0097] The dehydrated and dried synthesis gas is sent to the liquefaction unit B8 through the liquefaction unit feed pipe S08 for deep cold separation to produce liquefied natural gas that meets the index. The liquefaction unit adopts a cryogenic distillation process with precooling, which is composed of components such as a precooler, a cold box, a refrigerant compressor and a nitrogen compressor. The synthesis gas is first precooled to 12°C by the precooler, and then enters the cold box to complete cryogenic distillation. The synthesis gas entering the cold box is initially cooled to -95°C~-105°C by the main heat exchanger (plate-fin heat exchanger) in the cold box and then extracted. After passing through the tower kettle evaporator of the denitrification tower as a heat source, it returns to the main heat exchanger to continue cooling to -145°C~-150°C, and then enters the denitrification tower after being reduced to 0.6MPa through the pressure reducing valve. The nitrogen, hydrogen and other components flow out from the top of the tower in the form of gas as nitrogen-rich tail gas, and the remaining methane flows out from the bottom of the tower in the form of liquid as liquefied natural gas. The nitrogen-rich tail gas is reheated by the main heat exchanger and then discharged from the unit. The reheated nitrogen-rich tail gas is divided into two parts. One part is sent to the dehydration unit through the first branch S16 of the nitrogen-rich tail gas pipeline of the liquefaction unit as regeneration gas and then discharged. The other part is directly discharged through the second branch S15 of the nitrogen-rich tail gas pipeline of the liquefaction unit. The nitrogen content of the liquefied natural gas flowing out of the bottom of the denitrogenation tower is not higher than 1%. It is sent out of the cold box after being supercooled to about -162℃ by the main heat exchanger, and after throttling, it is output as a liquefied natural gas product through the liquefaction unit discharge pipe S09 to the liquefaction unit.

[0098] The cooling capacity required for the low-temperature distillation of the liquefaction unit is provided by a mixed refrigerant circulation system and a nitrogen refrigeration circulation system.

[0099] Taking the raw material blue charcoal tail gas in the embodiment as raw material, the flow rate of liquefied natural gas product produced by this method is 16984 Nm 3 / h, its components are as follows:

[0100] Components V% <![CDATA[CH4]]> 99.28 <![CDATA[N2]]> 0.72

[0101] The solution of this patent does not have the problems of patents CN108034464A and CN108977243A, and has the advantages of relatively simple device, low cost and low energy consumption.

[0102] The above describes the preferred embodiments of the present invention, however, the above description is not intended to be limiting. A person skilled in the art may make many changes or modifications to the present invention without departing from the spirit and scope of the present invention. The changes or modifications should be included in the scope of the appended claims.

Claims

1. A device for preparing liquefied natural gas from semi-coke tail gas, characterized in that: The invention comprises a first compression device (B1), a pre-purification device (B2), a second compression device (B3), a deacidification device (B4), a methane synthesis device (B5), a deamination device (B6), a dehydration device (B7) and a liquefaction device (B8) which are connected in sequence via pipelines. The first compression device (B1) is connected to a blue coke tail gas feed pipeline (S01). A steam outlet pipeline (S10) of a methane synthesis device is divided into three branches. A first branch (S11) of the steam outlet pipeline of the methane synthesis device is connected to the pre-purification device (B2). A second branch (S12) of the steam outlet pipeline of the methane synthesis device is connected to the deacidification device (B4). A third branch (S13) of the steam outlet pipeline of the methane synthesis device is connected to the dehydration device (B7), which are used to supply heat to the pre-purification device (B2), the deacidification device (B4) and the dehydration device (B7), respectively.

2. The device for producing liquefied natural gas from semi-coke tail gas according to claim 1, characterized in that: The nitrogen-rich tail gas pipeline (S14) of the liquefaction unit is divided into two branches, the first branch (S16) of the nitrogen-rich tail gas pipeline of the liquefaction unit is connected to the dehydration unit, and the second branch (S15) of the nitrogen-rich tail gas pipeline of the liquefaction unit is a direct discharge pipeline; and / or The pre-purification device (B2) comprises a detarring tower and a debenzene and denaphthalene tower connected in series.

3. The device for preparing liquefied natural gas from blue coke tail gas according to claim 1 or 2, characterized in that: The deacidification device (B4) includes an amine absorption tower (A01), a first cooler (A02), a first gas-liquid separator (A03), a first pressure reducing valve (A04), a flash tank (A05), a first heat exchanger (A06), a second heat exchanger (A07), an amine regeneration tower (A08), a first reboiler (A09), a second cooler (A10), a second gas-liquid separator (A11), a reflux pump (A12), a third cooler (A13), a semi-lean liquid pump (A14), a fourth cooler (A15) and a lean liquid pump (A16). The blue carbon gas feed pipe (401) is connected to the lower or bottom gas inlet of the amine absorber (A01), the lean liquid feed pipe (422) is connected to the top or upper liquid inlet of the amine absorber (A01), the semi-lean liquid feed pipe (421) is connected to the middle liquid inlet of the amine absorber (A01), the bottom liquid outlet of the amine absorber (A01) is connected to the amine liquid discharge pipe (404), and the top gas outlet of the amine absorber (A01) is connected to the top outlet pipe (402). The top outlet pipe (402) is connected to the inlet of the first gas-liquid separator (A03) via the first cooler (A02). The first gas-liquid separator (A03) is provided with a first gas-liquid separator top outlet pipe (403). The amine liquid discharge pipe (404) is connected to the inlet of the flash tank (A05) through the first pressure reducing valve (A04). The bottom of the flash tank (A05) is provided with a flash tank liquid phase outlet pipe (405). The flash tank liquid phase outlet pipe (405) at the bottom of the flash tank (A05) is divided into two branches, wherein the first branch pipe (406) of the flash tank outlet pipe is connected to a heat exchange channel of the first heat exchanger (A06), and the second branch pipe (407) of the flash tank outlet pipe is connected to a heat exchange channel of the second heat exchanger (A07). After the heat exchange, the two branches are merged into an amine regeneration tower feed pipe (408), which is connected to the upper part or top of the amine regeneration tower (A08). The tower top outlet pipe (409) of the amine regeneration tower (A08) is connected to the second gas-liquid separator (A11) via the second cooler (A10). The second gas-liquid separator (A11) is provided with a gas-liquid separator gas phase outlet pipe (410) and a gas-liquid separator liquid phase outlet pipe (411). The gas-liquid separator liquid phase outlet pipe (411) returns to the amine regeneration tower (A08) via a reflux pump (A12). The amine regeneration tower (A08) is provided with a first reboiler (A09) for heating the bottom liquid to provide stripping steam, and the bottom liquid outlet pipeline (413) of the amine regeneration tower (A08) is connected to the top or upper part of the amine absorption tower (A01) via the first heat exchanger (A06), the fourth cooler (A15), and the lean liquid pump (A16); The middle liquid outlet of the amine regeneration tower (A08) is connected to the semi-lean liquid outlet pipe (414), and the semi-lean liquid outlet pipe (414) returns to the middle of the amine absorption tower (A01) through the second heat exchanger (A07), the third cooler (A13), and the semi-lean liquid pump (A14).

4. The device for preparing liquefied natural gas from semi-coke tail gas according to claim 3, characterized in that: The methane synthesis unit includes a third heat exchanger (Y01), a fourth heat exchanger (Y02), a primary reactor (Y03), a primary waste boiler (Y04), a secondary reactor (Y05), a secondary waste boiler (Y06), a fifth heat exchanger (Y07), a tertiary reactor (Y08), a sixth heat exchanger (Y09), a fifth cooler (Y10), a third gas-liquid separator (Y11), a seventh heat exchanger (Y12), a fourth gas-liquid separator (Y13), a compressor (Y14), and a pump (Y15). The deacidified gas feed pipe (501) is divided into two branch pipes after passing through the third heat exchanger (Y01), namely, a first deacidified gas branch pipe (502) and a second deacidified gas branch pipe (503). The first deacidified gas branch pipe (502) is connected to a heat exchange channel of the heat exchanger (Y02) after merging with the circulating gas pipe (521) and the circulating liquid pipe (524). After exiting the heat exchange channel, the first deacidified gas branch pipe is connected to the first reactor (Y03) through the first reactor feed pipe (504). The first reactor outlet pipe (505) of the first reactor (Y03) passes through the first waste boiler (Y04), the fourth heat exchanger (Y02), and then is connected to the inlet of the second reactor (Y05) together with the second branch pipe (503) of the deacidified gas. The secondary reactor outlet pipe (508) passes through the secondary waste boiler (Y06), the fifth heat exchanger (Y07), the third heat exchanger (Y01), the seventh heat exchanger (Y12), and then connects to the fourth gas-liquid separator (Y13). The gas phase outlet pipeline of the fourth gas-liquid separator (Y13) is divided into two branches. The first branch pipe (513) of the gas phase outlet is connected to the feed port of the third-stage reactor (Y08) via the fifth heat exchanger (Y07). The second branch pipe (514) of the gas phase outlet is connected to the inlet of the compressor (Y14). The compressor outlet pipeline (520) is connected to the seventh heat exchanger (Y12). The circulating gas pipeline (521) after the seventh heat exchanger is merged with the circulating liquid pipeline (524) and the first branch pipe (502) of the deacidified gas and then connected to the feed port of the first-stage reactor (Y03) via the fourth heat exchanger (Y02). The outlet pipe (516) of the tertiary reactor (Y08) is connected to the third gas-liquid separator (Y11) via the sixth heat exchanger (Y09) and the fifth cooler (Y10). The gas phase outlet pipe (51) of the third gas-liquid separator is the output product gas pipe of the methane synthesis unit. The liquid phase outlet pipe (522) of the third gas-liquid separator is connected to the pump (Y15) after merging with the liquid outlet pipe (523) of the fourth gas-liquid separator (Y13). The circulating liquid pipe (524) coming out of the pump is connected to the circulating gas pipe (521) and the first branch pipe (502) of the deacidified gas. The deoxygenated water pipeline of the input device is connected to the sixth heat exchanger (Y09), and after exiting the sixth heat exchanger, it is respectively connected to the first waste boiler (Y04) and the second waste boiler (Y06), and then output to the device through the steam pipeline (526).

5. The device for preparing liquefied natural gas from semi-coke tail gas according to claim 4, characterized in that: The deamine device adopts a water washing process, including a water washing tower (M01), the lower part of the water washing tower (M01) is connected to a water washing tower feed pipe (601), the upper part of the water washing tower (M01) is connected to a desalted water pipeline (602), the top of the water washing tower (M01) is provided with a water washing tower top outlet pipeline (603), and the bottom of the water washing tower (M01) is provided with a water washing tower bottom outlet pipeline (604).

6. The device for preparing liquefied natural gas from semi-coke tail gas according to claim 5, characterized in that: The dehydration device adopts a pressure swing temperature swing adsorption process, including a heater (D02), a sixth cooler (D03), a fifth gas-liquid separator (D04), a dehydration tower assembly (D01) consisting of three dehydration towers: a first dehydration tower (T1), a second dehydration tower (T2), and a third dehydration tower (T3) and a programmable valve. The dehydration device input pipeline (701) is divided into three branches, each branch is provided with a programmable valve, and is respectively connected to the synthesis gas inlet of the first, second and third dehydration towers. The synthesis gas outlet branch pipes of the first, second and third dehydration towers, which are respectively provided with program-controlled valves, are combined into the device output pipeline (703). The low-pressure regeneration gas pipeline (702) is divided into three branches, each of which is provided with a program-controlled valve, and is respectively connected to the regeneration gas inlet of the first, second and third dehydration towers. The dehydration regeneration gas output branch pipes of the three dehydration towers, each of which is provided with a program-controlled valve, are merged into a dehydration regeneration gas output pipeline (704), which is then connected to the inlet of the heater (D02). The outlet of the heater (D02) is connected to the hot regeneration gas input pipeline (705). The hot regeneration gas input pipeline (705) is branched into three hot regeneration gas input branch pipes provided with program-controlled valves, which are respectively connected to the regeneration gas inlet of the first, second and third dehydration towers. The regeneration gas output branch pipes with programmable valves out of the dehydration tower are combined into a regeneration gas output pipeline (706), which is then connected to the inlet of the sixth cooler (D03). The outlet of the sixth cooler (D03) is connected to the fifth gas-liquid separator (D04) via the fifth gas-liquid separator inlet pipeline (707).

7. The device for preparing liquefied natural gas from semi-coke tail gas according to claim 6, characterized in that: The liquefaction device includes a raw gas precooler (L01), a cold box (L02), a main heat exchanger (L03), a second reboiler (L04), a second pressure reducing valve (L05), a denitrification tower (L06), a condenser (L07), a sixth gas-liquid separator (L08), a first throttle valve (L09), a mixed refrigerant compressor (L21), a mixed refrigerant precooler (L22), a seventh gas-liquid separator (L23), a second throttle valve (L24), a third throttle valve (L25), a nitrogen compressor (L31) and a nitrogen precooler (L32). The dehydration device discharge pipe (801) is connected to the first heat exchange channel of the main heat exchanger (L03) in the cold box (L02) through the raw gas precooler (L01), the outlet of the first heat exchange channel passes through a heat exchange channel of the reboiler (L04) and is connected to the second heat exchange channel of the main heat exchanger (L03), and the outlet of the second heat exchange channel is connected to the inlet of the denitrification tower (L06) through the second pressure reducing valve (L05). The denitrogenation tower reboiler (L04) is provided with heat by the aforementioned flow in the connecting pipeline between the outlet of the first heat exchange channel and the denitrogenation tower reboiler. The denitrogenation tower top gas outlet pipeline (809) passes through a heat exchange channel of the condenser (L07) and is connected to the sixth gas-liquid separator (L08). The gas phase outlet pipeline (812) of the sixth gas-liquid separator returns to the third heat exchange channel of the main heat exchanger (L03), and exits the cold box from the hot end of the third heat exchange channel of the main heat exchanger, and exits the liquefaction device as nitrogen-rich tail gas through the nitrogen-rich tail gas pipeline (813). The liquid phase outlet pipe (811) of the sixth gas-liquid separator flows back into the upper part or top of the denitrification tower (L06). The liquid outlet pipeline (806) at the bottom of the denitrification tower is connected to the fourth heat exchange channel of the main heat exchanger (L03), and the fourth heat exchange channel outlet pipeline (807) leaves the main heat exchanger and is output to the liquefaction device through the first throttle valve (L09) and the liquefied natural gas product pipeline (808).

8. The device for preparing liquefied natural gas from semi-coke tail gas according to claim 7, characterized in that: The mixed refrigerant cycle is used to provide the cooling capacity required for liquefaction. The low-pressure mixed refrigerant outlet pipe (821) of the main heat exchanger (L03) is connected to the inlet of the mixed refrigerant compressor (L21). The mixed refrigerant compressor outlet pipe (822) is connected to the mixed refrigerant precooler (L22) and the seventh gas-liquid separator (L23) in sequence. The gas phase outlet pipe (826) of the seventh gas-liquid separator is connected to the inlet of the fifth heat exchange channel of the main heat exchanger (L03). The fifth heat exchange channel outlet pipe (827) returns to the sixth heat exchange channel of the main heat exchanger (L03) after passing through the third throttle valve (L25). The liquid phase outlet pipe of the seventh gas-liquid separator (L23) is connected to the seventh heat exchange channel of the main heat exchanger. After passing through the seventh heat exchange channel outlet pipe (825) and the second throttle valve (L24), it returns to the sixth heat exchange channel of the main heat exchanger (L23). The outlet of the sixth heat exchange channel is connected to the inlet of the mixed refrigerant compressor (L21) through the low-pressure mixed refrigerant outlet pipe (821). The outlet pipe (831) of the eighth heat exchange channel of the main heat exchanger is connected to the inlet of the nitrogen compressor (L31), the outlet pipe (832) of the nitrogen compressor is connected to the nitrogen precooler (L32), the outlet pipe (833) of the nitrogen precooler is connected to the ninth heat exchange channel of the main heat exchanger (L03), the outlet pipe (834) of the ninth heat exchange channel is connected to another heat exchange channel of the condenser (L07) via a throttle valve (L33), and returns to the eighth heat exchange channel of the main heat exchanger (L03) after exiting the heat exchange channel, and the outlet pipe (831) of the eighth heat exchange channel returns to the inlet of the nitrogen compressor (L31).

Images