A method for converting and decarbonizing gasified coke tail gas to produce LNG

Abstract

The present invention belongs to the technical field of producing LNG (liquefied natural gas) from the tail gas of gasified coke, and particularly relates to a method for converting and decarbonizing the tail gas of gasified coke to produce LNG. After the tail gas of gasified coke sequentially passes through a pretreatment unit, a compression unit, an oil and naphthalene removal unit, and a benzene and ammonia removal unit, a part of the gas sequentially enters a sulfur-tolerant conversion unit, a converted gas desulfurization unit, and a converted gas wet decarbonization unit for treatment. The decarbonized gas after treatment is mixed with another part of the gas and then enters a mixed gas fine desulfurization unit, a mixed gas methanation unit, and a cryogenic separation unit for methanated gas to produce an LNG product. In the present invention, the requirement of the methanation reaction for the hydrogen-carbon ratio is satisfied; after the mixed gas is finely desulfurized, a methanation reaction is carried out to cause the CO, CO2, and H2 therein to react to form CH4, and then the LNG product is obtained through cryogenic separation. It has a simple structure, low cost, and high efficiency.

Description

Technical Field

[0001] The patent of the present invention belongs to the technical field of producing LNG (liquefied natural gas) from gasified coke tail gas, and in particular relates to a method for converting and decarbonizing gasified coke tail gas to produce LNG. Background Art

[0002] Generally, coking enterprises produce metallurgical coke, and the typical composition of coke oven gas is as follows:

[0003] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) 6.20 2.20 0.60 26.00 58.00 4.50 2.50 100.00

[0004] However, due to different market demands, some coking enterprises now also produce gasified coke. The typical composition of gasified coke tail gas during the production of gasified coke is as follows:

[0005] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) 15.03 5.13 0.46 20.84 52.86 2.71 2.97 100.00

[0006] When producing metallurgical coke, the content of CO and CO2 in coke oven gas is relatively small, and the content of H2 is relatively high. The so-called hydrogen-carbon ratio (3 molecules of H2 are consumed for every 1 molecule of CO, 4 molecules of H2 are consumed for every 1 molecule of CO2, and 2 molecules of H2 are consumed for every 1 molecule of O2) is about 2, which is more favorable for the use of methanation catalysts and the conversion effect of CO and CO2. After being compressed and the harmful impurities are removed, the coke oven gas can be directly subjected to methanation reaction, so that the CO, CO2 and H2 react to generate CH4, and then the LNG product (liquefied natural gas) is obtained through deep cold separation.

[0007] When producing gasification coke, the CO and CO2 in the tail gas of gasification coke are much higher than those in the production of metallurgical coke, and the H2 is less than that in the production of metallurgical coke. The so-called hydrogen-carbon ratio (3 molecules of H2 are consumed for every 1 molecule of CO, 4 molecules of H2 are consumed for every 1 molecule of CO2, and 2 molecules of H2 are consumed for every 1 molecule of O2) is less than 80% of the theoretical value, which is unfavorable and not feasible for the use of methanation catalysts, the conversion effects of CO and CO2, and other aspects.

[0008] Invention patent content

[0009] In order to solve the above technical problems, the present invention provides a method for producing LNG by conversion and decarbonization of gasified coke tail gas, which adds conversion, desulfurization and decarbonization units, and then performs methanation reaction after fine desulfurization, and deep cold separation to produce LNG products (liquefied natural gas). After conversion and decarbonization of gasified coke tail gas, the process of producing LNG from gasified coke tail gas is opened up, making it possible. It will inevitably lead to cost reduction, increased economic and social benefits.

[0010] The method for producing LNG by shifting and decarbonizing gasified coke tail gas in the present invention, which solves the above technical problems, is characterized in that: after the gasified coke tail gas is sequentially processed by a pretreatment unit, a compression unit, a deoiling and naphthalene removal unit, and a benzene and ammonia removal unit, a portion of the gas enters a sulfur-resistant shift unit, a shift gas desulfurization unit, and a shift gas wet decarbonization unit for treatment, and the treated decarbonized gas is mixed with another portion of the gas and then enters a mixed gas fine desulfurization unit, a mixed gas methanation unit, and a methanation gas cryogenic separation unit to generate LNG products. The decarbonized tail gas is output from the shift gas wet decarbonization unit, and the cryogenic tail gas is output from the methanation gas cryogenic separation unit.

[0011] The gasified coke tail gas after debenzening and deamination in the debenzening and deamination unit is divided into two routes. One route is to the gasified coke tail gas sulfur-resistant conversion unit, the conversion gas desulfurization unit, and the conversion gas wet decarbonization unit, and decarbonized gas is obtained after conversion, desulfurization, and wet decarbonization; the other route of gasified coke tail gas is directly mixed with the decarbonized gas to form a mixed gas, and the mixed gas enters the mixed gas fine desulfurization unit; the relative gas volumes of the two routes of gasified coke tail gas can be adjusted to adjust the hydrogen-carbon ratio of the mixed gas.

[0012] The deconverted gasification coke tail gas in the two gasification coke tail gases accounts for about 73% of the total gas volume (it will change with the change of the composition of the gasification coke tail gas).

[0013] The two gas volumes are used mainly to adjust the amount of gasification coke tail gas to be converted, thereby adjusting the hydrogen-carbon ratio of the mixed gas.

[0014] The pretreatment unit adopts a carbon-based adsorbent with strong adsorption capacity for tar and naphthalene in the gasification coke tail gas, and after adsorbing the tar and naphthalene in the gasification coke tail gas, steam is purged and regenerated once every period of time, and the regenerated wastewater is decoked. The carbon-based adsorbent has a high removal rate for tar and naphthalene, and the adsorption conditions are mild (under normal temperature and pressure).

[0015] At least two carbon-based adsorbents are used, such as coke and activated carbon (activated carbon can be divided into many combinations according to different pore sizes, and the carbon-based adsorbent is selected according to its properties, and adsorption is carried out at room temperature and pressure (6-7 kPa).

[0016] The operation mode of steam purge regeneration is: first pass steam to gradually increase the temperature, when the temperature rises to above 150℃, seal the tank for a period of time, then release the pressure and discharge the waste liquid; the regeneration interval is determined by the content of tar and naphthalene in the tail gas of gasification coke, that is, test the tar and naphthalene content at the outlet, and regenerate if it does not meet the standard. Generally 7-10 days.

[0017] In the present invention, adsorption is carried out at room temperature and pressure (6-7 kPa); regeneration is carried out at temperature and pressure, and the temperature must be raised to above 150° C., otherwise the regeneration is not complete, which will affect the adsorption effect next time.

[0018] The compression unit may use a reciprocating compressor for compression processing, or a compression device combining a screw compressor and a centrifugal compressor, and the pressure of the gasified coke tail gas after compression is 0.8-6.0 MPa.

[0019] The de-oiling and naphthalene removal unit uses carbon-based composite agents and silicate composite agents to further remove the naphthalene to reduce the impact on subsequent units. The carbon-based composite agent is different from the carbon-based adsorbent. It mainly selects activated carbon with higher removal accuracy and no coke. The silicate composite agent is characterized by better de-oiling (including tar and compressor lubricating oil) effect, and a suitable model can be selected and purchased from the market.

[0020] The gas compressed by the gasification coke tail gas compressor still contains a small amount of impurities such as naphthalene, oil, and water, which need to be treated.

[0021] After adsorbing oil and naphthalene, carbon-based composite agents, silicate composite agents, etc. are regenerated by steam purge at regular intervals depending on the operating conditions, and the regenerated wastewater is decoked. The regeneration by steam purge at regular intervals here is the same as the steam regeneration method, but the regeneration interval is different, which is determined by the tar and naphthalene content in the gasification coke tail gas, that is, the tar and naphthalene content at the outlet is tested, and regeneration is performed if it does not meet the standard. Generally 10-15 days.

[0022] The debenzene and deammoniation unit uses the temperature swing adsorption (TSA) method to remove benzene and ammonia from the gasification coke tail gas to reduce the impact on subsequent units. The regeneration gas of the temperature swing adsorption (TSA) is the tail gas separated by deep cold or the self-purified gas. After steam heating, the adsorption tower is purged to regenerate the adsorbent. After removing benzene and ammonia, the benzene in the gasification coke tail gas is ≤10PPm and the ammonia is ≤10PPm.

[0023] The device structure and operation steps of temperature swing adsorption (TSA) are conventional operations, and the selected adsorbent has better selective adsorption of benzene and ammonia. Adsorption is at room temperature, and the regeneration temperature is 150-180°C; there is no special requirement for the regeneration pressure, as long as it can be sent out of the boundary.

[0024] The temperature of the regenerated gas after steam heating is about 180-200°C, with the purpose of heating the adsorption bed layer to 150-180°C.

[0025] The sulfur-resistant conversion unit for gasified coke tail gas is to separate a part of the compressed, de-oiled, de-naphthalened, de-benzened and de-ammonified gasified coke tail gas, heat it to 220°C, mix it with added water vapor and then enter the upper layer of the conversion reactor to remove harmful impurities such as oxygen and olefins in the gasified coke tail gas. At the same time, the temperature of the gasified coke tail gas is increased, and it is sprayed with water to cool it down to 210°C before entering the lower layer of the conversion reactor. The CO in the gasified coke tail gas undergoes a conversion reaction to generate CO2 and H2, and the CO dry basis concentration is reduced to ~3.0%v.

[0026] The sulfur-resistant conversion unit is a process in which a proper amount of water vapor is added to the compressed gasification coke tail gas, and most of the CO is converted into CO2 and H2 under the action of the sulfur-resistant conversion catalyst. The conversion reaction is an exothermic reaction, and appropriate measures (intermediate heat exchange and / or cold shock) are taken in the reactor to control the catalyst bed temperature to prevent the catalyst from overheating and causing sintering and deactivation, or even damage to the equipment.

[0027] The sulfur-resistant conversion unit includes more than 10 equipment such as the conversion reactor, and the conversion reaction is carried out in the conversion reactor.

[0028] The temperature entering the shift reactor is 210-220℃ (slightly different at the beginning and end of the catalyst). When it rises to 310℃, the reaction is exothermic; it is extracted for heat exchange and / or cold shock to 210-220℃ in the middle, and then enters the shift reactor for better shift reaction. The outlet temperature of the second-stage outlet shift gas is 320℃. The added water vapor comes from outside the boundary and is mixed in a device called a gas-steam mixer. The added water vapor is about 21% (V / V) of the gasification coke tail gas entering the shift.

[0029] The conversion gas desulfurization unit removes H2S converted from organic sulfur during the conversion process through a solid desulfurizer under the conversion gas outlet temperature condition, so that the sulfur content of the decarbonization tail gas of the conversion gas wet decarbonization unit can meet the emission standards or be convenient for other uses.

[0030] The shift gas wet decarbonization unit uses the regenerated decarbonization liquid to remove CO2 from the shift gas, so as to adjust the hydrogen-carbon ratio after mixing with the unshifted gasified coke tail gas, and the loss of effective components in wet decarbonization is small. The decarbonization liquid that absorbs CO2 can be recycled by heating and regenerating, and the decarbonized tail gas generated by regeneration can be directly discharged or used for other purposes.

[0031] In the present invention, regeneration is a process in which the decarbonization liquid that absorbs CO2 is heated to drive out the CO2, and the regenerated decarbonization liquid is recycled.

[0032] The shift gas wet decarbonization mainly includes more than 10 equipments such as absorption tower, regeneration tower, reboiler, circulation pump, etc., which are connected and recycled.

[0033] The mixed gas fine desulfurization unit, according to the characteristics that most of the inorganic sulfur (H2S) in the gasification coke tail gas (or mixed gas) has been removed, but the content of organic sulfur (sulfur oxide carbon, carbon disulfide, mercaptan, sulfide, thiophene, etc.) is still relatively high, pre-hydrogenates the organic sulfur through a solid catalyst, converts it into inorganic sulfur (H2S) through a primary hydrogenation, removes the generated inorganic sulfur (H2S) through a solid desulfurizer, and then converts the remaining organic sulfur into inorganic sulfur (H2S) through a secondary hydrogenation, and removes it through a solid desulfurizer. At this time, the total sulfur in the gasification coke tail gas (or mixed gas) has been removed to ≤0.1ppm. It is further treated with an ultra-fine purifier to remove the total sulfur in the outlet gasification coke tail gas (or mixed gas) to <0.05ppm. The conversion gas after desulfurization by the solid desulfurizer heats the raw gasification coke tail gas and cools itself, and the dehumidification method decarbonization unit regeneration tower is used as a part of the heat source.

[0034] The mixed gas fine desulfurization unit of the present invention is a mixed gas that undergoes organic sulfur pre-conversion, primary conversion, primary fine desulfurization, secondary conversion, and secondary fine desulfurization. The solid catalysts for pre-conversion, primary conversion, and secondary conversion are Co-Mo, Fe-Mo, and Ni-Mo catalysts, which are optional and have good organic sulfur conversion effects; the solid catalysts for primary fine desulfurization and secondary fine desulfurization are zinc oxide desulfurizers, which are optional and have good desulfurization effects. The pre-conversion tank, primary conversion tank, primary fine desulfurization tank, secondary conversion tank, and secondary fine desulfurization tank are mainly used in connection.

[0035] The mixed gas methanation unit reacts CO and CO2 in the gasified coke tail gas (or mixed gas) with H2 to generate CH4.

[0036] On the one hand, it increases the production of CH4, and at the same time removes CO and CO2 from the gasification coke tail gas, reducing the difficulty of subsequent separation and toxic hazards. Since the methanation reaction is a highly exothermic reaction, a three-stage methanation process with circulation (patent pending technology) is used in the process setting to control the temperature of each catalyst bed to prevent the catalyst from overheating and sintering deactivation, or even damage to the equipment. The gasification coke tail gas (or mixed gas) can be made to meet the CO2 concentration requirement of ≤30ppm when LNG is subjected to low-temperature separation through the three-stage methanation reaction, without the need for additional decarbonization equipment.

[0037] The methanogenic gas cryogenic separation unit is a process in which the methane-rich gas obtained from the methanogenic unit is cryogenically separated to obtain LNG products and cryogenic tail gas. Before cryogenic separation, precise filtration and drying and dehydration are required (precision filtration and drying and dehydration are necessary before the methanogenic gas enters the cryogenic unit, otherwise it will be blocked, which can be considered as equipment in the cryogenic unit) to separate impurities larger than 1μm and make the water content ≤1ppm.

[0038] The cryogenic separation unit may adopt processes such as step-type refrigeration liquefaction, mixed refrigerant (MRC) refrigeration liquefaction or expansion mechanism refrigeration liquefaction, etc. These processes are conventional technologies.

[0039] Instruction Manual

[0040] Figure 1 and Figure 2 Schematic diagram of the preparation process of the present invention DETAILED DESCRIPTION

[0041] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0042] Example 1

[0043] The process of a method for converting and decarbonizing the tail gas of gasified coke to produce LNG in this embodiment is as follows:

[0044] With 38000Nm 3 / h gasification coke tail gas to LNG device as an example, the gasification coke tail gas at pressure 6 ~ 7kPa and room temperature is 38000Nm 3 / h, the composition is shown in the following table:

[0045] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) 15.03 5.13 0.46 20.84 52.86 2.71 2.97 100.00

[0046] The impurity content is shown in the following table:

[0047] Components <![CDATA[H2S]]> Organic sulfur Naphthalene Tar+Dust <![CDATA[NH3]]> BTX (Benzene) HCN <![CDATA[Content (mg / Nm 3 )]]> ≤20 ≤150 ≤300 ≤50 ≤50 ≤3000 ≤100

[0048] First, the gasification coke tail gas pretreatment unit uses carbon-based adsorbent to adsorb tar and naphthalene in the gasification coke tail gas. After pretreatment, the gasification coke tail gas contains: tar + dust ≤ 10mg / Nm 3 , naphthalene≤20mg / Nm 3 .

[0049] Then, two reciprocating compressors are used to compress the pre-treated gasification coke tail gas to 2.4MPa in four stages. Then, carbon-based composite agents and silicate composite agents are used to further remove oil and naphthalene. After de-oiling and naphthalene removal, the gasification coke tail gas contains: tar + dust ≤ 1mg / Nm 3 , naphthalene≤2mg / Nm 3 .

[0050] The benzene and ammonia in the gasification coke tail gas are removed by temperature swing adsorption (TSA). After removal of benzene and ammonia, the benzene in the gasification coke tail gas is ≤10PPm and the ammonia is ≤10PPm. The temperature swing adsorption (TSA) adopts a three-tower process, one tower for adsorption, one tower for heating and regeneration, and one tower for cold blowing and cooling. The nitrogen and hydrogen tail gas separated by deep cold is used as the regeneration gas source. The regenerated gas is heated by steam and then purged and heated to the adsorption tower to regenerate the adsorbent, and then cold blowing and cooling are performed to restore the adsorption capacity of the adsorbent. The three towers are used in turn and the whole process is carried out continuously.

[0051] The gasification coke tail gas after debenzene and deamination is separated into 28000Nm 3 / h for sulfur-resistant conversion. The gasified coke tail gas is first heated to 220°C by hot conversion gas, mixed with 4700kg / h of water vapor and then enters the upper layer of the conversion reactor to remove harmful impurities such as oxygen and olefins in the gasified coke tail gas. Oxygen and olefins react with hydrogen to release a large amount of heat. The gasified coke tail gas is heated to ~310°C, enters the water spray cooler to be cooled to 210°C by water spray, and then enters the lower layer of the conversion reactor, where the CO in the gasified coke tail gas undergoes conversion reaction to produce CO2 and H2, reducing the CO dry basis concentration to ~3.0%v and the temperature to ~320°C. At this temperature, the conversion gas enters the fine desulfurization tank, and the solid desulfurizer removes the H2S in the conversion gas to ≤1PPm. The raw gasification coke tail gas is then heated to cool itself down, and then goes to the wet decarbonization regeneration tower as part of the heat source and enters the water cooler to be cooled to ≤40℃ (the water cooler is a device in the conversion unit, which is after the fine desulfurization tank, raw gas heater, wet decarbonization reboiler, and before wet decarbonization.), and is sent to the conversion gas wet decarbonization unit after separating the condensed water.

[0052] The shift gas composition is as follows:

[0053] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) 3.00 15.26 - 18.90 57.68 2.46 2.70 100.00

[0054] Conversion gas volume: 30940Nm 3 / h.

[0055] The above-mentioned desulfurized and cooled shift gas enters the absorption tower and is washed with a decarbonization solution. After the semi-lean liquid washing and lean liquid washing, the CO2 content in the gas is reduced to below 0.5%v. After cooling and separation to remove the trace amount of decarbonization solution in the gas, it is mixed with another 10000Nm 3 / h of gasified coke tail gas after debenzene and deamination is mixed to form a mixed gas. By adjusting the relative gas volume of the two gasified coke tail gases, the hydrogen-carbon ratio of the mixed gas can be adjusted.

[0056] The rich liquid coming out of the bottom of the absorption tower enters the top of the regeneration tower and is depressurized to 0.1MPa and is stripped by steam from the bottom of the tower. The gas stripped from the top of the regeneration tower is cooled to below 40℃, and the separated condensate is returned to the top of the regeneration tower as reflux liquid. The cooled CO2 meets the emission standards or is used outside the boundary.

[0057] The decarbonized solution coming out from the bottom of the upper section of the regeneration tower is a semi-lean solution, which is divided into two streams. Most of the semi-lean solution is pressurized and circulated to the middle of the absorption tower; the remaining semi-lean solution is preheated and sent to the lower section of the regeneration tower for further regeneration. The decarbonized solution coming out from the bottom of the lower section of the regeneration tower is a lean solution, which is sent to the upper part of the absorption tower for circulation and absorption after cooling. Part of the heat of the reboiler of the regeneration tower is provided by the aforementioned conversion gas, and the insufficient part is supplemented by steam.

[0058] The composition of decarbonized gas is as follows:

[0059] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) 3.53 0.50 - 22.20 67.75 2.89 3.13 100.00

[0060] Decarburization gas volume: 26350Nm 3 / h.

[0061] The gas mixture is composed as follows:

[0062] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) 6.89 1.85 0.13 21.81 63.39 2.84 3.09 100.00

[0063] Mixed gas volume: 36350Nm 3 / h.

[0064] The mixed gas formed by the gasification coke tail gas after debenzene and deamination and the decarbonized gas enters the mixed gas fine desulfurization unit for fine desulfurization. After the mixed gas and the gas after fine desulfurization are heated up by heat exchange, they enter two pre-hydrogenation tanks that can be used in parallel or separately, mainly to hydrogenate the unsaturated hydrocarbons in the mixed gas and react to remove the oxygen in the mixed gas. At the same time, a small amount of organic desulfurization is hydrogenated and converted into inorganic sulfur (H2S).

[0065] The pre-hydrogenated mixed gas enters the first-stage hydrogenation tank, where the organic desulfurization in the mixed gas is further hydrogenated and converted, and then enters two first-stage fine desulfurization tanks that can be used in series or in parallel or separately to remove the H2S generated by the hydrogenation conversion. In order to further reduce the organic sulfur and inorganic sulfur in the mixed gas, the mixed gas enters the second-stage hydrogenation tank and two second-stage fine desulfurization tanks. When the previous hydrodesulfurization can meet the total sulfur requirements of the process, the purified mixed gas bypasses (without the second-stage hydrodesulfurization). The aforementioned purified gas enters the ultra-fine purifier after cooling to ensure that the total sulfur content in the outlet purified gas is less than 0.05ppm.

[0066] The aforementioned ultra-fine purified gas is divided into two paths in proportion, one for demethanation in the first reactor and the other for methanation in the second reactor.

[0067] The mixed gas fine desulfurization unit mainly includes a pre-conversion tank, a primary conversion tank, a primary fine desulfurization tank, a secondary conversion tank, and a secondary fine desulfurization tank, which are connected in series. The conversion unit and the decarbonization unit are set up to make the gasification coke tail gas be used to produce LNG.

[0068] The purified gas from the first demethanation reactor is mixed with the circulating gas pressurized by the circulating compressor, heated to ≥250°C, and enters the first methanation reactor for methanation reaction. The high-temperature reaction gas from the first methanation reactor is 505°C, and the temperature drops to 360-400°C after the by-product 2.5MPa steam. After heat exchange and cooling, it is mixed with the purified gas from the second demethanation reactor. The mixed gas temperature is 250-300°C and enters the second methanation reactor to continue the methanation reaction.

[0069] The high-temperature reaction gas at the outlet of the second-stage methanation reactor is 505°C, and the temperature drops to 360°C after the by-product 2.5MPa steam. It is preheated into the process gas and the first-stage raw gas of the third-stage methanation reactor, and is divided into two paths after heat recovery. One path is cooled to ≤40°C, condensed water is separated, and heated before entering the third-stage methanation reactor. The concentration of CO2 in the reaction gas coming out of the third-stage methanation reactor is ≤30ppm. After cooling to ≤40°C and separating condensed water, it goes to the deep cold separation unit to produce LNG products.

[0070] The other route is cooled to ≤60℃, condensed water is separated, and then pressurized by the circulating gas compressor and returned to the inlet of the methanation unit to dilute the raw gas.

[0071] The composition of methanogen gas is as follows:

[0072] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) - - - 53.47 42.17 4.11 0.25 100.00

[0073] Methanation gas volume: 25050Nm 3 / h.

[0074] The methanogenized gas enters the cryogenic separation unit, and is cryogenically separated to produce LNG products and cryogenic tail gas. Before cryogenic separation, it is first subjected to precision filtration and drying and dehydration to separate impurities larger than 1 μm and to reduce the water content to ≤ 1 ppm.

[0075] The above-mentioned methanogenized gas enters the liquefied cold box, is cooled to a certain temperature by the mixed refrigerant, is extracted from the heat exchanger to the reboiler at the bottom of the distillation tower as a heat source, and then returns to the liquefied heat exchanger to be cooled and condensed by the mixed refrigerant, and then enters the flash tank after throttling. The hydrogen-rich tail gas coming out of the flash tank is throttled and returned to the liquefied heat exchanger for reheating and then exits the cold box. The liquid coming out of the flash tank enters the distillation tower, and the nitrogen-rich tail gas is throttled and reheated at the top of the tower after distillation, and then exits the cold box. LNG is obtained at the bottom of the tower and enters the liquefied heat exchanger for supercooling. The LNG is throttled to normal pressure by the throttle valve and sent out of the cold box into the LNG storage tank.

[0076] Part of the hydrogen-rich tail gas and nitrogen-rich tail gas (i.e., cryogenic tail gas) exiting the cold box is used as the regeneration gas for drying and dehydration of this unit, and then used together with the remaining cryogenic tail gas as the gas source for debenzene and deamination regeneration.

[0077] LNG is composed of:

[0078] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) - - - 98.54 - 0.99 0.47 100.00

[0079] LNG production: 13200Nm 3 / h.

[0080] The composition of deep-cooled exhaust gas is as follows:

[0081] Components CO <![CDATA[CO2]]> <![CDATA[O2]]> <![CDATA[CH4]]> <![CDATA[H2]]> <![CDATA[N2]]> <![CDATA[C n H m ]]> total content(%) - - - 3.27 89.14 7.59 - 100.00

[0082] Deep-cooled exhaust gas volume: 11850Nm 3 / h.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing LNG by shifting and decarbonizing gasified coke tail gas, characterized in that: After the gasification coke tail gas passes through the pretreatment unit, compression unit, de-oiling and naphthalene removal unit and benzene and deamination unit in sequence, a part of the gas enters the sulfur-resistant conversion unit, the conversion gas desulfurization unit and the conversion gas wet decarbonization unit in sequence for treatment, and the treated decarbonized gas is mixed with another part of the gas and then enters the mixed gas fine desulfurization unit, the mixed gas methanation unit and the methanation gas cryogenic separation unit to generate LNG products; The gasification coke tail gas pretreatment unit uses a carbon-based adsorbent to preliminarily remove tar and naphthalene from the gasification coke tail gas, and uses steam for regeneration; the pressure of the gasification coke tail gas compressed in the compression unit is 0.8-6.0 MPa; The sulfur-resistant conversion unit for gasified coke tail gas separates a portion of the compressed, de-oiled, de-naphthalene, de-benzened and de-ammoniated gasified coke tail gas, heats it to 220°C, mixes it with added water vapor and then enters the upper layer of the conversion reactor to remove oxygen and olefin harmful impurities in the gasified coke tail gas. At the same time, the temperature of the gasified coke tail gas is increased, sprayed with water to cool it down to 210°C and then enters the lower layer of the conversion reactor. CO in the gasified coke tail gas undergoes a conversion reaction to generate CO2 and H2, and the CO dry basis concentration is reduced to 3.0%v. The outlet temperature of the sulfur-resistant conversion unit is ≤40°C; The shift gas wet decarbonization unit uses the regenerated decarbonization liquid to remove CO2 from the shift gas, so as to adjust the hydrogen-carbon ratio after mixing with the unshifted gasification coke tail gas; The mixed gas methanation unit adopts a three-stage methanation process with circulation, and the gasified coke tail gas or mixed gas undergoes a three-stage methanation reaction to make the CO2 concentration reach the requirement of ≤30ppm; The nitrogen and hydrogen tail gas produced in the cryogenic separation unit is returned to the debenzene and deamination unit as a regeneration gas source. The nitrogen and hydrogen tail gas needs to be heated to 150-180°C in the debenzene and deamination unit.

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