Method and system for producing natural gas by methanation of coke oven gas

Abstract

The present invention relates to the field of comprehensive utilization of coal gasification, and discloses a method and a system for producing natural gas by methanation of coke oven gas. The method includes: carrying out a first-stage isothermal methanation reaction on the coke oven gas in the presence of catalyst I; carrying out first-stage condensation gas-liquid separation on the obtained first-stage reaction gas to obtain a first-stage gas phase and a first-stage liquid phase; mixing the first-stage gas phase with carbon dioxide, and carrying out a second-stage isothermal methanation reaction on the obtained mixed gas in the presence of catalyst II; carrying out second-stage condensation gas-liquid separation on the obtained second-stage reaction gas to obtain a methane product gas and a second-stage liquid phase; catalyst I and catalyst II are the same or different, and each independently is a methanation catalyst, and the methanation catalyst includes a carrier and an active component and a promoter supported on the carrier, wherein the active component is amorphous nickel, and the promoter is selected from oxides of La and / or Ce. The method and the system are beneficial to reducing carbon oxides in the methane product gas, realizing the resource utilization of excess hydrogen and CO2, and increasing the yield of the methane product gas.

Description

Technical Field

[0001] The invention relates to the field of comprehensive application of coal gasification, and in particular to a method and system for producing natural gas by methanation of coke oven gas. Background Art

[0002] Coke oven gas is composed of CH4, H2, CO, and CO2, and is an ideal raw material gas for the production of SNG / LNG. The investment in converting the exhaust coke oven gas into natural gas is about 1 / 5 of that of the same scale of synthetic natural gas produced from coal, which can generate good economic and social benefits. In view of the composition of coke oven gas, due to its excess hydrogen, by supplementing CO2, developing a suitable coke oven gas CO2 supplementation methane technology is an effective way to realize the utilization of excess hydrogen in coke oven gas and the resource utilization of CO2, which is of great significance.

[0003] CN109111967A discloses a methanogenic system and method for producing natural gas from coke oven gas. The method uses a temperature-isolating reactor with a cold shock distributor in series with an adiabatic reactor. After the coke oven gas is supplemented with CO2, it enters the temperature-isolating reactor. The unheated coke oven gas can also enter the temperature-isolating reactor through the cold shock device to cool it down. After that, an adiabatic reactor is connected in series to further refine the product gas. Although the method has a constant operating temperature, is energy-saving and easy to operate, and can better protect the methanogenic catalyst, since the carbon supplementation position is located in the first reactor, the methanogenic reaction load is mostly distributed in the first reactor, and the isothermal reactor has higher requirements for its production, material, heat capacity and circulation volume of the heat removal fluid. In addition, an adiabatic reactor is used for methane refining in the subsequent process, and the precision of the refining is greatly affected by the reaction temperature rise.

[0004] CN103881780A discloses a process for preparing liquefied natural gas by supplementing coke oven gas with carbon dioxide. The main process is to first purify and pre-clean the CO2-rich gas to obtain CO2 gas with a CO2 (vol%) content greater than or equal to 95%, and then mix the gas with hydrogen-rich gas for deep hydrogenation and desulfurization to obtain a mixed gas rich in CO2 and H2 with a total sulfur content less than 0.05ppm; at the same time, the coke oven gas after pretreatment, compression and purification enters a primary methanation reactor, and the gas at the outlet of the primary methanation reactor is supplemented with the above-mentioned desulfurized fresh CO2 and H2 mixed gas, and then enters a secondary methanation reactor, and the gas at the outlet of the secondary methanation reactor is then subjected to multi-stage adiabatic methanation reactions in sequence for purification to obtain methane-rich gas. Although this process increases the output of liquefied natural gas, the reaction and refining are both carried out in an adiabatic reactor. Due to the limitation of adiabatic equilibrium, the refining process is equipped with more refining reactors, the process is longer, the heat exchange between stages requires a large number of heat exchangers, there are many control points, and the operation is cumbersome.

[0005] CN103820183A discloses a method for producing synthetic natural gas by directly supplementing coke oven gas with carbon dioxide. The main processes of the method include coke oven gas compression, purification, CO2 gasification, methanation and membrane separation. Among them, the purification process consists of a primary desulfurization section, a TSA deep purification section and a fine desulfurization section. The methanation process adopts a three-stage methanation reaction system consisting of a first-stage methanation reactor, a second-stage methanation reactor and a third-stage methanation reactor, and each stage of the methanation reactor adopts an adiabatic reactor; the coke oven gas supplemented with CO2 from the fine desulfurization section can enter the first-stage methanation reactor and the second-stage methanation reactor respectively; a dilution mixer is provided in front of the first-stage methanation reactor, and the low-concentration gas after the reaction of the second-stage methanation reactor can be sent to the dilution mixer and mixed with fresh gas to reduce the gas concentration entering the first-stage methanation reactor and reduce the temperature rise. Although this method can increase the production of CH4 in synthetic natural gas, the process sends the outlet product of the second-stage reactor to the inlet of the first-stage reactor as dilution gas, and requires a circulating compressor to establish gas circulation. As a circulating compressor of dynamic equipment, the investment, failure rate and safety risk are all high. In addition, the temperature of the first reactor of this process is relatively high, and the catalyst has the problems of rapid thermal deactivation rate and carbon deposition rate.

[0006] At present, the coke oven gas methanation process is equipped with at least one adiabatic reactor. The advantages of the adiabatic reactor are large carbon oxide processing capacity, high outlet gas temperature, and inter-stage heat exchange to produce high-pressure steam. The disadvantages are high reaction temperature, low heat balance, and high outlet carbon oxides. If carbon is added from the outlet of the first reactor, the load of the second reactor will increase. The catalysts in the first and second reactors are prone to carbon accumulation and thermal deactivation due to high temperature, and must be equipped with a circulating compressor for circulating cooling. In addition, multiple heat exchangers are required for inter-stage heat exchange, and the second reactor needs to be equipped with one or two reactors for deep refining. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems in the prior art of producing natural gas by methanation of coke oven gas, such as long process, high preparation cost, and high carbon oxide content in the produced methane product gas. A method and system for producing natural gas by methanation of coke oven gas are provided to shorten the coke oven gas methanation process, reduce costs, reduce carbon oxides in the methane product gas, and realize the utilization of surplus hydrogen in the coke oven gas and the resource utilization of CO2, thereby increasing the output of methane product gas.

[0008] In order to achieve the above object, the present invention provides a method for producing natural gas by methanation of coke oven gas in a first aspect, the method comprising:

[0009] (1) in the presence of a catalyst I, subjecting coke oven gas to a primary isothermal methanation reaction to obtain a primary reaction gas; subjecting the primary reaction gas to a primary condensation, and obtaining a primary gas phase and a primary liquid phase after gas-liquid separation;

[0010] (2) mixing the primary gas phase with carbon dioxide to obtain a mixed gas; then subjecting the mixed gas to a secondary isothermal methanation reaction in the presence of catalyst II to obtain a secondary reaction gas; subjecting the secondary reaction gas to a secondary condensation and gas-liquid separation to obtain a methane product gas and a secondary liquid phase;

[0011] Wherein, the catalyst I is the same as or different from the catalyst II, and each is independently a methanation catalyst, and the methanation catalyst includes a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from oxides of La and / or Ce.

[0012] A second aspect of the present invention provides a system for producing natural gas by methanation of coke oven gas, the system comprising at least one methanation unit, wherein the methanation unit comprises a first isothermal reactor, a first gas-liquid separator, a second isothermal reactor and a second gas-liquid separator connected in sequence.

[0013] Through the above technical scheme, the method and system for producing natural gas by methanation of coke oven gas provided by the present invention adopts a two-stage isothermal reactor combination connected in series, without an adiabatic reactor, and shortens the coke oven gas methanation process, and does not require a circulating compressor, so the equipment investment and operating costs are low. The heat is directly removed from the isothermal reactor by a heat-conducting medium, and there is no need for inter-stage heat exchange, thus saving a heat exchanger. The lower reaction temperature of the isothermal reactor can slow down the carbon deposition and high-temperature thermal deactivation rate of the catalyst due to high temperature, and extend the service life of the catalyst. While reducing the carbon oxides in the methane product gas, the excess hydrogen in the coke oven gas is rationally utilized through the carbon replenishment process, which is beneficial to increase the output of the methane product gas and realize the resource utilization of CO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of a method and system for producing natural gas by methanation of coke oven gas according to an embodiment of the present invention.

[0015] Description of Reference Numerals

[0016] 1. Preheater 2. First isothermal reactor 3. First gas-liquid separator

[0017] 4. Heater 5. Second isothermal reactor 6. Second gas-liquid separator DETAILED DESCRIPTION

[0018] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0019] A first aspect of the present invention provides a method for producing natural gas by methanation of coke oven gas, the method comprising:

[0020] (1) in the presence of a catalyst I, subjecting coke oven gas to a primary isothermal methanation reaction to obtain a primary reaction gas; subjecting the primary reaction gas to a primary condensation, and obtaining a primary gas phase and a primary liquid phase after gas-liquid separation;

[0021] (2) mixing the primary gas phase with carbon dioxide to obtain a mixed gas; then subjecting the mixed gas to a secondary isothermal methanation reaction in the presence of catalyst II to obtain a secondary reaction gas; subjecting the secondary reaction gas to a secondary condensation and gas-liquid separation to obtain a methane product gas and a secondary liquid phase;

[0022] Wherein, the catalyst I is the same as or different from the catalyst II, and each is independently a methanation catalyst, and the methanation catalyst includes a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from oxides of La and / or Ce.

[0023] According to some embodiments of the present invention, the catalyst I is the same as or different from the catalyst II, and each is independently a methanation catalyst, and the methanation catalyst includes a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from La and / or Ce oxides. In order to further improve the conversion rate of hydrogen and carbon oxides and reduce the content of carbon oxides in the methane product gas, preferably, the catalyst I is the same as the catalyst II, and includes a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from La and / or Ce oxides.

[0024] According to some embodiments of the present invention, the active component in the methanation catalyst is amorphous nickel, which has a stronger hydrogenation capacity. Preferably, in the XRD spectrum of the methanation catalyst, there is a broad diffraction peak with a peak width greater than 5° at 2θ=45°. The broad diffraction peak is a diffuse peak type formed by amorphous diffuse reflection, which is the main characteristic diffraction peak of amorphous nickel. The short and wide diffuse peak indicates that the nickel in the methanation catalyst exists in an amorphous structure.

[0025] According to some embodiments of the present invention, the carrier can be a carrier suitable for supported catalysts conventionally used in the art, as long as it can load active components and additives, the purpose of the present invention can be achieved to a certain extent. Preferably, the carrier is selected from at least one of alumina, zirconia and magnesium aluminum spinel.

[0026] According to some embodiments of the present invention, preferably, based on the total weight of the methanation catalyst, the content of the active component is 10-55% by weight, the content of the auxiliary agent is 0.3-2% by weight, and the content of the carrier is 40-90% by weight;

[0027] More preferably, based on the total weight of the methanation catalyst, the content of the active component is 15-50% by weight, the content of the auxiliary agent is 0.35-1.7% by weight, and the content of the carrier is 45-85% by weight.

[0028] According to some embodiments of the present invention, preferably, the method for preparing the methanation catalyst comprises the following steps:

[0029] (a) in the presence of a first solvent, contacting the precursor I and the precursor II with a reducing agent to perform a reduction reaction to obtain a reduction product;

[0030] (b) mixing the reduced product with a carrier and cellulose in the presence of a second solvent to obtain a suspension;

[0031] (c) removing the second solvent from the suspension, and then calcining the obtained solid under an inert atmosphere to obtain a methanation catalyst;

[0032] Wherein, the precursor I is a compound containing nickel, and the precursor II is selected from compounds containing lanthanum and / or cerium.

[0033] According to some embodiments of the present invention, in step (a), in the presence of a first solvent, the precursor I and the precursor II are contacted with a reducing agent to perform a reduction reaction to obtain a reduced product. This step can reduce the nickel element in the precursor I and the precursor II to metal, and finally obtain a reduced product containing amorphous elemental nickel and lanthanum and / or cerium hydroxide in the solution. The present invention does not particularly limit the type of the reducing agent, and can be a conventional choice in the art, as long as the nickel element in the precursor I can be reduced to amorphous nickel. Preferably, the reducing agent is a borohydride, more preferably sodium borohydride and / or potassium borohydride.

[0034] According to some embodiments of the present invention, the precursor I is a compound containing nickel. There is no particular limitation on the type of the precursor I, which can be a conventional choice in the art, for example, a conventional water-soluble nickel salt in the art. Preferably, the precursor I is selected from at least one of nickel nitrate, nickel chloride and nickel acetate, more preferably nickel nitrate.

[0035] According to some embodiments of the present invention, the precursor II is selected from compounds containing lanthanum and / or cerium. There is no particular limitation on the type of the precursor II, which can be a conventional choice in the art, for example, a conventional water-soluble lanthanum salt and / or a water-soluble cerium salt in the art. Preferably, the precursor II is selected from nitrates and / or chlorides containing lanthanum and / or cerium, more preferably nitrates containing lanthanum and / or cerium.

[0036] According to some embodiments of the present invention, preferably, in terms of metal elements, the mass ratio of the precursor I to the precursor II is (20-110): 1, more preferably (20-100): 1. The above preferred embodiments are conducive to further reducing the content of carbon monoxide and carbon dioxide in the methane product gas.

[0037] According to some embodiments of the present invention, preferably, the molar ratio of the reducing agent to the total amount of the precursor I and the precursor II calculated as metal elements is (1-2.5): 1, preferably (1.5-2): 1. The above preferred embodiments can further promote the formation of amorphous nickel particles and lanthanum and / or cerium hydroxides by chemical reduction.

[0038] According to some embodiments of the present invention, preferably, the first solvent is water.

[0039] According to some embodiments of the present invention, preferably, the precursor I, precursor II and reducing agent are provided in the form of a solution. There is no particular limitation on the order of adding the precursor I, precursor II and reducing agent, and they can be mixed in any order. Preferably, the precursor I and the precursor II are first dissolved in water, and then contacted with a solution containing a reducing agent for reduction reaction. More preferably, the mixed solution containing the precursor I and the precursor II is dripped into the solution containing the reducing agent in a dropwise manner for contact, and the dripping speed can be 4-6 drops / second. Further preferably, in the solution containing the reducing agent, the concentration of the reducing agent is 1-3mol / L; in the mixed solution containing the precursor I and the precursor II, the concentration of the precursor I and the precursor II is 0.5-2mol / L.

[0040] According to some embodiments of the present invention, preferably, the conditions of the reduction reaction include: a temperature of 15-25° C. and a time of 1-3 h. In order to remove oxygen from the solution, further promote the formation of the reduction product, and improve the dispersion of the reduction product, more preferably, the reduction reaction is carried out under high-frequency oscillation. The conditions and methods of the high-frequency oscillation can be conventionally selected in the art and are not particularly limited thereto.

[0041] According to some embodiments of the present invention, in order to better precipitate and separate the reduction product, preferably, a magnetic substance or device may be used during the reduction reaction to assist in the precipitation of the reduction product.

[0042] According to some embodiments of the present invention, preferably, the method further comprises subjecting the reduction product obtained in step (a) to solid-liquid separation and washing. The present invention does not particularly limit the method of solid-liquid separation, and it can be a conventional choice in the art, for example, it can be at least one of filtration, centrifugation and gravity sedimentation, preferably using centrifugation to remove the supernatant liquid for solid-liquid separation. The washing can be carried out using a washing liquid conventionally used in the art, such as deionized water. Preferably, washing is carried out by repeatedly adding deionized water and removing the supernatant liquid until the washing liquid is neutral.

[0043] According to some embodiments of the present invention, in step (b), in the presence of a second solvent, the reduced product is mixed with a carrier and cellulose to obtain a suspension. This step can load the amorphous nickel in the reduced product and the hydroxide of lanthanum and / or cerium on the carrier. The cellulose can not only play the role of thickening and pore-making, but also fully mix the carrier with the reduced product, and will not cause precipitation and stratification due to different particle settling speeds, promote the dispersion of amorphous nickel and the hydroxide of lanthanum and / or cerium on the carrier, so as to further improve the catalytic activity of the catalyst. At the same time, the adhesion between the amorphous nickel and the hydroxide of lanthanum and / or cerium in the reduced product and the carrier can also be increased to make it more closely combined. Preferably, the second solvent is water. More preferably, the mixing process can be carried out under stirring. The stirring conditions and methods can be conventionally selected in the art, and there is no particular limitation on this. Further preferably, the stirring is carried out using non-ferromagnetic equipment.

[0044] According to some embodiments of the present invention, the type of the carrier can be selected with reference to the above, and will not be described in detail here.

[0045] According to some embodiments of the present invention, preferably, the mass ratio of the precursor I to the carrier in terms of metal element is (0.1-1.5): 1, preferably (0.176-1): 1. The above preferred embodiments are conducive to further improving the dispersion of amorphous nickel on the carrier, so that the methanation catalyst has a certain microscopic morphology, while providing a reaction environment of different acidity when the catalyst is methanated, and fully supporting the active components and additives, thereby increasing the contact area between the catalyst and the airflow diffusion.

[0046] According to some embodiments of the present invention, preferably, the mass ratio of the cellulose to the second solvent is (0.5-1.5): 100, preferably (0.8-1.2): 100. The above preferred embodiments are conducive to further promoting uniform mixing of the reduction product and the carrier, and further improving the adhesion of the amorphous nickel and lanthanum and / or cerium hydroxides on the carrier.

[0047] According to some embodiments of the present invention, in step (c), the second solvent in the suspension is removed, and then the obtained solid is calcined under an inert atmosphere to obtain a methanation catalyst. The step can convert the hydroxide of lanthanum and / or cerium supported on the carrier into an oxide of lanthanum and / or cerium. Preferably, the second solvent in the suspension can be removed by drying. The drying conditions and methods can be conventionally selected in the art and are not particularly limited thereto.

[0048] According to some embodiments of the present invention, preferably, the calcination conditions include: a heating rate of 1-5°C / min, preferably 2-4°C / min; a temperature of 300-400°C, preferably 330-350°C; and a time of 1-10h, preferably 2-5h.

[0049] According to some embodiments of the present invention, preferably, the method is carried out under an inert atmosphere.

[0050] According to some embodiments of the present invention, preferably, the inert atmosphere is provided by at least one of nitrogen, argon, helium and neon.

[0051] According to some embodiments of the present invention, preferably, the method further comprises crushing and molding the methanation catalyst obtained in step (c) so that the methanation catalyst has a certain strength and morphology. More preferably, the crushing and molding are completed within 1 hour after completing step (c) to obtain a molded catalyst product. In order to prevent the molded catalyst product from being oxidized, it is preferably stored in a sealed state under an inert atmosphere.

[0052] According to some embodiments of the present invention, preferably, the method further comprises, before performing step (1), purifying and desulfurizing the coke oven gas to obtain purified coke oven gas.

[0053] According to some embodiments of the present invention, preferably, in step (1), the temperature of the coke oven gas is 250-350°C, preferably 260-300°C.

[0054] According to some embodiments of the present invention, preferably, the conditions of the primary isothermal methanation reaction include: temperature not exceeding 350°C, preferably 300-350°C; pressure of 1-4MPa, preferably 1.5-3.5MPa; volume space velocity of 3000-25000h -1 , preferably 6000-15000h -1 .

[0055] According to some embodiments of the present invention, preferably, based on the total amount of the primary gas phase, the content of hydrogen in the primary gas phase is 25-50 volume %; the content of methane is 40-65 volume %; and the content of carbon oxides does not exceed 0.01 volume %.

[0056] According to some embodiments of the present invention, preferably, in step (2), the temperature of the mixed gas is 250-400°C, preferably 260-300°C.

[0057] According to some embodiments of the present invention, in step (2), the primary gas phase is mixed with carbon dioxide to obtain a mixed gas. By adding carbon dioxide, the excess hydrogen in the coke oven gas is rationally utilized, which is beneficial to increase the output of methane product gas and realize the resource utilization of CO2. The amount of carbon dioxide can be calculated based on the content of hydrogen in the primary gas phase and the stoichiometric ratio of the methanation reaction of carbon dioxide and hydrogen. Preferably, based on the total amount of the primary gas phase, the amount of carbon dioxide is 6-13% by volume, preferably 6.25-12.5% ​​by volume, and more preferably 7-12% by volume.

[0058] According to some embodiments of the present invention, preferably, the conditions of the secondary isothermal methanation reaction include: temperature not exceeding 350°C, preferably 300-350°C; pressure of 1-4MPa, preferably 1.5-3.5MPa; volume space velocity of 3000-25000h -1 , preferably 6000-15000h -1 .

[0059] According to some embodiments of the present invention, preferably, the maximum reaction temperature of the primary isothermal methanation reaction and the secondary isothermal methanation reaction are both controlled to be no more than 350°C. A lower reaction temperature is beneficial to promoting the equilibrium of the methanation reaction to move in a positive direction and improving the conversion rate of hydrogen and carbon oxides.

[0060] According to some embodiments of the present invention, preferably, based on the total amount of the methane product gas, the hydrogen content in the methane product gas does not exceed 0.5 volume %; the methane content is greater than 80 volume %, preferably 80.1-90 volume %; the carbon oxide content is less than 0.02 volume %, preferably not more than 0.01 volume %.

[0061] According to a particularly preferred embodiment of the present invention, the method for producing natural gas by methanation of coke oven gas comprises:

[0062] (1-1) purifying and desulfurizing the coke oven gas to obtain purified coke oven gas;

[0063] (2-1) in the presence of catalyst I, subjecting purified coke oven gas to a primary isothermal methanation reaction to obtain a primary reaction gas; subjecting the primary reaction gas to a primary condensation, and obtaining a primary gas phase and a primary liquid phase after gas-liquid separation; the temperature of the primary isothermal methanation reaction does not exceed 350° C.;

[0064] (3-1) mixing the primary gas phase with carbon dioxide to obtain a mixed gas; then subjecting the mixed gas to a secondary isothermal methanation reaction in the presence of catalyst II to obtain a secondary reaction gas; subjecting the secondary reaction gas to a secondary condensation, and obtaining a methane product gas and a secondary liquid phase after gas-liquid separation; the temperature of the secondary isothermal methanation reaction does not exceed 350° C.;

[0065] Wherein, the catalyst I and the catalyst II are methanation catalysts, and the methanation catalyst comprises a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from oxides of La and / or Ce.

[0066] A second aspect of the present invention provides a system for producing natural gas by methanation of coke oven gas, the system comprising at least one methanation unit, wherein the methanation unit comprises a first isothermal reactor, a first gas-liquid separator, a second isothermal reactor and a second gas-liquid separator connected in sequence.

[0067] According to some embodiments of the present invention, preferably, the first isothermal reactor is filled with catalyst I, and the second isothermal reactor is filled with catalyst II; the catalyst I is the same as or different from the catalyst II, and each is independently a methanation catalyst, and the methanation catalyst includes a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from oxides of La and / or Ce.

[0068] Preferably, the catalyst I is the same as the catalyst II and comprises a carrier and an active component and an auxiliary agent supported on the carrier, wherein the active component is amorphous nickel and the auxiliary agent is selected from oxides of La and / or Ce.

[0069] According to some embodiments of the present invention, the methanation catalyst and the method for preparing the methanation catalyst can be selected with reference to the above, and will not be described in detail here.

[0070] According to some embodiments of the present invention, preferably, the methanation unit further includes a preheater and a heater, wherein the preheater is arranged before the first isothermal reactor to heat the coke oven gas; and the heater is arranged between the first gas-liquid separator and the second isothermal reactor to heat the mixed gas.

[0071] According to some embodiments of the present invention, preferably, the system further comprises a pretreatment unit, and the pretreatment unit is used to purify and desulfurize the coke oven gas to obtain purified coke oven gas.

[0072] According to a particularly preferred embodiment of the present invention, the system for producing natural gas by methanation of coke oven gas includes at least one methanation unit, wherein the methanation unit includes a first isothermal reactor, a first gas-liquid separator, a second isothermal reactor and a second gas-liquid separator connected in sequence. The first isothermal reactor is filled with catalyst I, and the second isothermal reactor is filled with catalyst II; the catalyst I and the catalyst II are methanation catalysts, and the methanation catalyst includes a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from oxides of La and / or Ce. The methanation unit also includes a preheater and a heater, wherein the preheater is arranged before the first isothermal reactor; and the heater is arranged between the first gas-liquid separator and the second isothermal reactor. The system also includes a pretreatment unit, which is used to purify and desulfurize the coke oven gas to obtain purified coke oven gas.

[0073] The method and system for producing natural gas by methanation of coke oven gas provided by the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0074] The present invention illustratively provides a method and system schematic diagram of producing natural gas by methanation of coke oven gas according to an embodiment, as shown in FIG. Figure 1As shown. The system includes a pretreatment unit and a methanation unit, wherein the methanation unit includes a preheater 1, a first isothermal reactor 2, a first gas-liquid separator 3, a heater 4, a second isothermal reactor 5 and a second gas-liquid separator 6 connected in sequence. The first isothermal reactor 2 is filled with a catalyst I, and the second isothermal reactor 5 is filled with a catalyst II; the catalyst I and the catalyst II are methanation catalysts, and the methanation catalyst includes a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from La and / or Ce oxides. The method for producing natural gas by methanation of coke oven gas comprises:

[0075] (S1) sending the coke oven gas into the pretreatment unit for purification and desulfurization to obtain purified coke oven gas;

[0076] (S2) After the purified coke oven gas is heated by a preheater 1, it is sent to a first isothermal reactor 2 for a primary isothermal methanation reaction to obtain a primary reaction gas;

[0077] (S3) sending the primary reaction gas into the first gas-liquid separator 3 for primary condensation, and obtaining a primary gas phase and a primary liquid phase after gas-liquid separation;

[0078] (S4) mixing the primary gas phase with carbon dioxide to obtain a mixed gas; heating the mixed gas by a heater 4, and then sending the mixed gas to a second isothermal reactor 5 for a secondary isothermal methanation reaction to obtain a secondary reaction gas;

[0079] (S5) The secondary reaction gas is sent to the second gas-liquid separator 6 for secondary condensation, and after gas-liquid separation, a methane product gas and a secondary liquid phase are obtained.

[0080] In the present invention, the pressures are all gauge pressures.

[0081] The present invention will be described in detail below through examples.

[0082] In the following preparation examples, embodiments and comparative examples, unless otherwise specified, all raw materials can be obtained from commercial sources.

[0083] The composition of the catalyst was determined by a ZSX Primus II X-ray fluorescence spectrometer (XRF) from Rigaku;

[0084] The XRD spectrum of the catalyst was measured by an X-ray diffractometer. The powder X-ray diffractometer was purchased from Bruker Company and its model was D8 advance.

[0085] Preparation Example

[0086] This preparation example is used to illustrate the methanation catalyst and its preparation method

[0087] 200 g of nickel nitrate pentahydrate was dissolved in 500 mL of deionized water, and 1.01 g of lanthanum nitrate was added to prepare a mixed solution (wherein the mass ratio of nickel element to lanthanum element was 100:1). The mixed solution was dripped into a 2 mol / L sodium borohydride solution (the molar ratio of sodium borohydride to the total amount of nickel and lanthanum was 1.5:1) at a rate of 4 drops / second, the solution temperature was maintained at 20℃±2℃, high-frequency oscillation was turned on, and the black substance produced during the dripping process was dispersed. After the dripping was completed (the entire reduction process took 2 hours), the product was allowed to precipitate freely, and magnetic substances were used to assist precipitation at the bottom. The supernatant was skimmed off, and deionized water was added to wash the precipitate several times until the solution was neutral. The amount of deionized water above the precipitate was controlled to about 500mL, 80.27g of alumina powder (the mass ratio of nickel to alumina was 0.54:1) was added, and non-ferromagnetic equipment was used to stir for 1 minute, and 5g of cellulose (the mass ratio of cellulose to deionized water above the precipitate was 1:100) was added, and stirring was continued to make all powdered substances uniformly distributed and suspended in the viscous liquid to obtain a suspension. The suspension was placed in a 60℃ oven, and the water was evaporated under nitrogen protection until it was dried. The dried block was placed in a sealed bag and crushed, taken out and placed in a muffle furnace, protected by argon, and programmed to heat at a rate of 3°C / min, calcined at 350°C for 4 hours, and then cooled to room temperature. The cooled block was broken in a sealed bag and formed into φ4*4 cylindrical tablets within 1 hour to obtain a methanation catalyst, which was sealed and filled with nitrogen and recorded as sample 1. Among them, the content of nickel was 35% by weight, the content of lanthanum in terms of oxide was 0.35% by weight, and the content of aluminum oxide was 64.65% by weight.

[0088] XRD detection shows that the active component nickel in the methanation catalyst is amorphous nickel.

[0089] Comparative Preparation Example

[0090] Using the same precursor as in the preparation example, with alumina powder as the carrier raw material, the alumina powder was prepared into a φ4*4 carrier by a conventional molding method, 100g of the carrier was excessively impregnated with a nickel nitrate solution of ρ=1.6g / mL for 2h, dried at 120°C for 6h, and calcined at 400°C for 4h, and then the above impregnation, drying, and calcination methods were repeated for a second impregnation. After two impregnations and two calcinations, the increment of nickel oxide on 100g of the carrier was 68.44g. Then, according to the water absorption rate, an equal volume of 2.93g of lanthanum nitrate solution was impregnated with the solute, dried at 120°C for 6h, calcined at 450°C for 4h, and pre-reduced with pure hydrogen at 450°C for 6h to obtain a methanation catalyst, which was recorded as D1. Among them, the content of nickel was 35% by weight, the content of lanthanum in terms of oxide was 0.35% by weight, and the content of alumina was 64.65% by weight.

[0091] XRD detection shows that the active component nickel in the methanation catalyst is crystalline nickel.

[0092] Examples 1-5 are used to illustrate the method and system for producing natural gas by methanation of coke oven gas provided by the present invention.

[0093] Example 1

[0094] This embodiment adopts Figure 1 The coke oven gas methanogenic system for producing natural gas shown in the figure comprises a methanogenic unit, wherein the methanogenic unit comprises a preheater 1, a first isothermal reactor 2, a first gas-liquid separator 3, a heater 4, a second isothermal reactor 5 and a second gas-liquid separator 6 connected in sequence; the first isothermal reactor 2 and the second isothermal reactor 5 are respectively filled with the methanogenic catalyst prepared in the preparation example, and the filling amounts are 100 mL and 50 mL respectively. The method for producing natural gas by methanogenic coke oven gas is as follows:

[0095] The clean coke oven gas from upstream has a pressure of 3.2 MPa, a temperature of 40°C, and a volume space velocity of 15000 h -1 , the volume composition is 55% hydrogen, 27% methane, 8% carbon monoxide, 3% carbon dioxide, 3% nitrogen, and 4% unsaturated hydrocarbons above C2. The purified coke oven gas is preheated to 260°C by the preheater 1 and enters the first isothermal reactor 2 for reaction. The flow rate of the heat transfer medium is adjusted to control the temperature of the catalyst bed in the first isothermal reactor 2 to be lower than 350°C during the reaction. After the mixed gas at the outlet of the first isothermal reactor 2 is condensed and separated by gas and liquid by the first gas-liquid separator 3, the volume composition of the outlet dry gas is about 29.5% hydrogen, about 60.097% methane, 0% carbon monoxide, 0.003% carbon dioxide, about 4.4% nitrogen, and about 6% unsaturated hydrocarbons above C2. According to the hydrogen content of 29.5%, carbon dioxide with a hydrogen content of 1 / 4 is added, that is, carbon dioxide with a flow rate of 7.37% of the total flow rate of the outlet dry gas is added. The added dry gas is heated to 260°C by the heater 4 and enters the second isothermal reactor 5 for reaction. The temperature of the catalyst bed in the second isothermal reactor 5 is controlled to be lower than 350°C, and the outlet gas of the second isothermal reactor 5 is condensed and separated by the second gas-liquid separator 6 to obtain methane product gas. The volume composition of the methane product gas is 0.3% hydrogen, about 86.596% methane, 0% carbon monoxide, 0.004% carbon dioxide, about 5.6% nitrogen, and about 7.5% unsaturated hydrocarbons above C2.

[0096] In this embodiment, the target product flow rate at the outlet of the first isothermal reactor 2 is 570NL / h in terms of methane, and the target product flow rate at the outlet of the second isothermal reactor 5 is 641.25NL / h in terms of methane. The methane production increased by adding carbon dioxide is 71.25NL / h, which increases the methane production by 12.5%.

[0097] Example 2

[0098] This embodiment adopts Figure 1 The coke oven gas methanation system for producing natural gas shown in the figure includes a methanation unit, wherein the methanation unit includes a preheater 1, a first isothermal reactor 2, a first gas-liquid separator 3, a heater 4, a second isothermal reactor 5 and a second gas-liquid separator 6 connected in sequence; the first isothermal reactor 2 and the second isothermal reactor 5 are respectively filled with the methanation catalyst prepared in the preparation example, and the filling amounts are 120mL and 60mL respectively. The method for producing natural gas by methanation of coke oven gas is as follows:

[0099] The clean coke oven gas from upstream has a pressure of 3.2 MPa, a temperature of 40°C, and a volume space velocity of 6000 h -1 , the volume composition is 60% hydrogen, 23% methane, 6.5% carbon monoxide, 1.5% carbon dioxide, 7% nitrogen, and 2% unsaturated hydrocarbons above C2. After being preheated to 290°C by preheater 1, the gas enters the first isothermal reactor for reaction. The flow rate of the heat transfer medium is adjusted to control the catalyst bed temperature in the reactor to be lower than 350°C during the reaction. After the gas-liquid separation of the mixed gas at the outlet of the first reactor, the volume composition of the outlet dry gas is about 46.3% hydrogen, about 41.697% methane, 0% carbon monoxide, 0.003% carbon dioxide, about 9.3% nitrogen, and about 2.7% unsaturated hydrocarbons above C2. According to the hydrogen content of 46.3%, carbon dioxide with a hydrogen content of 1 / 4 is added, that is, carbon dioxide with a flow rate of 11.58% of the total flow rate of the outlet dry gas is added. The added dry gas is heated to 260°C by heater 4 and enters the second isothermal reactor for reaction. The catalyst bed temperature in the second reactor is controlled to be lower than 350°C, and the outlet gas of the second isothermal reactor is separated by gas and liquid to obtain methane product gas. The volume composition of the methane product gas is 0.2% hydrogen, about 81.593% methane, 0% carbon monoxide, 0.007% carbon dioxide, about 14.1% nitrogen, and about 4.1% unsaturated hydrocarbons above C2.

[0100] In this embodiment, the target product flow rate at the outlet of the first isothermal reactor 2 is 223.2NL / h in terms of methane, and the target product flow rate at the outlet of the second isothermal reactor 5 is 285.3NL / h in terms of methane. The methane production increased by carbon dioxide supplementation is 62.1NL / h, which increases the methane production by 27.8%.

[0101] Example 3

[0102] This embodiment adopts Figure 1The coke oven gas methanation system for producing natural gas shown in the figure includes a methanation unit, wherein the methanation unit includes a preheater 1, a first isothermal reactor 2, a first gas-liquid separator 3, a heater 4, a second isothermal reactor 5 and a second gas-liquid separator 6 connected in sequence; the first isothermal reactor 2 and the second isothermal reactor 5 are respectively filled with the methanation catalyst prepared in the preparation example, and the filling amount is 80mL and 40mL respectively. The method for producing natural gas by methanation of coke oven gas is as follows:

[0103] The clean coke oven gas from upstream has a pressure of 1.5 MPa, a temperature of 40°C, and a volumetric air velocity of 10,000 h -1 The volume composition is 58% hydrogen, 26% methane, 5% carbon monoxide, 2% carbon dioxide, 6% nitrogen, and 3% unsaturated hydrocarbons above C2. After being preheated to 270°C by preheater 1, the gas enters the first isothermal reactor for reaction. The flow rate of the heat transfer medium is adjusted to control the catalyst bed temperature in the reactor to be lower than 350°C during the reaction. After the mixed gas at the outlet of the first reactor is separated by gas and liquid, the volume composition of the outlet dry gas is about 45.4% hydrogen, about 42.89% methane, 0% carbon monoxide, 0.01% carbon dioxide, about 9.1% nitrogen, and about 2.6% unsaturated hydrocarbons above C2. According to the hydrogen content of 45.4%, carbon dioxide with a hydrogen content of 1 / 4 is added, that is, carbon dioxide with a flow rate of 11.40% of the total flow rate of the outlet dry gas is added. The added dry gas is heated to 270°C by heater 4 and enters the second isothermal reactor for reaction. The catalyst bed temperature in the second reactor is controlled to be lower than 350°C, and the outlet gas of the second isothermal reactor is separated into gas and liquid to obtain methane product gas. The volume composition of the methane product gas is 0.50% hydrogen, about 82.29% methane, 0% carbon monoxide, 0.01% carbon dioxide, about 13.30% nitrogen, and about 3.9% unsaturated hydrocarbons above C2.

[0104] In this embodiment, the target product flow rate at the outlet of the first isothermal reactor 2 is 264NL / h in terms of methane, and the target product flow rate at the outlet of the second isothermal reactor 5 is 334NL / h in terms of methane. The methane production increased by carbon dioxide supplementation is 70NL / h, which increases the methane production by 26.5%.

[0105] Example 4

[0106] This embodiment adopts Figure 1 The coke oven gas methanation system for producing natural gas shown in the figure includes a methanation unit, wherein the methanation unit includes a preheater 1, a first isothermal reactor 2, a first gas-liquid separator 3, a heater 4, a second isothermal reactor 5 and a second gas-liquid separator 6 connected in sequence; the first isothermal reactor 2 and the second isothermal reactor 5 are respectively filled with the methanation catalyst prepared in the preparation example, and the filling amounts are 140mL and 70mL respectively. The method for producing natural gas by methanation of coke oven gas is as follows:

[0107] The clean coke oven gas from upstream has a pressure of 2.5 MPa, a temperature of 40°C, and a volumetric air velocity of 9000 h -1 The volume composition is 56% hydrogen, 27% methane, 5% carbon monoxide, 1.5% carbon dioxide, 7% nitrogen, and 3.5% unsaturated hydrocarbons above C2. After being preheated to 280°C by preheater 1, the gas enters the first isothermal reactor for reaction. The flow rate of the heat transfer medium is adjusted to control the catalyst bed temperature in the reactor to be lower than 350°C during the reaction. After the mixed gas at the outlet of the first reactor is separated by gas and liquid, the volume composition of the outlet dry gas is about 45.0% hydrogen, about 41.598% methane, 0% carbon monoxide, 0.002% carbon dioxide, about 9.0% nitrogen, and about 4.4% unsaturated hydrocarbons above C2. According to the hydrogen content of 45.0%, carbon dioxide with a hydrogen content of 1 / 4 is added, that is, carbon dioxide with a flow rate of 11.20% of the total flow rate of the outlet dry gas is added. The added dry gas is heated to 270°C by heater 4 and enters the second isothermal reactor for reaction. The catalyst bed temperature in the second reactor is controlled to be lower than 350°C, and the outlet gas of the second isothermal reactor is separated by gas and liquid to obtain methane product gas. The volume composition of the methane product gas is 0.399% hydrogen, about 80.1% methane, 0% carbon monoxide, 0.01% carbon dioxide, about 12.9% nitrogen, and about 6.6% unsaturated hydrocarbons above C2.

[0108] In this embodiment, the target product flow rate at the outlet of the first isothermal reactor 2 is 422.1NL / h in terms of methane, and the target product flow rate at the outlet of the second isothermal reactor 5 is 532.35NL / h in terms of methane. The methane production increased by carbon dioxide supplementation is 110.25NL / h, an increase of 26.1% in methane production.

[0109] Example 5

[0110] This embodiment adopts Figure 1 The coke oven gas methanogenic system for producing natural gas shown in the figure comprises a methanogenic unit, wherein the methanogenic unit comprises a preheater 1, a first isothermal reactor 2, a first gas-liquid separator 3, a heater 4, a second isothermal reactor 5 and a second gas-liquid separator 6 connected in sequence; the first isothermal reactor 2 and the second isothermal reactor 5 are respectively filled with the methanogenic catalyst prepared in the preparation example, and the filling amounts are 100 mL and 50 mL respectively. The method for producing natural gas by methanogenic coke oven gas is as follows:

[0111] The clean coke oven gas from upstream has a pressure of 2.0 MPa, a temperature of 40°C, and a volume space velocity of 15000 h -1The volume composition is 55% hydrogen, 27% methane, 8% carbon monoxide, 3% carbon dioxide, 5% nitrogen, and 2% unsaturated hydrocarbons above C2. After being preheated to 260°C by preheater 1, the gas enters the first isothermal reactor for reaction. The flow rate of the heat transfer medium is adjusted to control the catalyst bed temperature in the reactor to be lower than 350°C during the reaction. After the mixed gas at the outlet of the first reactor is separated by gas and liquid, the volume composition of the outlet dry gas is about 30% hydrogen, about 59.094% methane, 0% carbon monoxide, 0.006% carbon dioxide, about 7.8% nitrogen, and about 3.1% unsaturated hydrocarbons above C2. According to the hydrogen content of 30%, carbon dioxide with a hydrogen content of 1 / 4 is added, that is, carbon dioxide with a flow rate of 7.5% of the total flow rate of the outlet dry gas is added. The added dry gas is heated to 300°C by heater 4 and enters the second isothermal reactor for reaction. The catalyst bed temperature in the second reactor is controlled to be lower than 350°C, and the methane product gas is obtained after the gas-liquid separation of the outlet gas of the second isothermal reactor. The volume composition of the methane product gas is 0.3% hydrogen, about 85.699% methane, 0% carbon monoxide, 0.001% carbon dioxide, about 10.0% nitrogen, and about 4.0% unsaturated hydrocarbons above C2.

[0112] In this embodiment, the target product flow rate at the outlet of the first isothermal reactor 2 is 570NL / h in terms of methane, and the target product flow rate at the outlet of the second isothermal reactor 5 is 641.25NL / h in terms of methane. The methane production increased by adding carbon dioxide is 71.25NL / h, which increases the methane production by 12.5%.

[0113] Comparative Example 1

[0114] According to the method of Example 1, using Figure 1 The coke oven gas methanation system for producing natural gas shown in the figure is different in that the first isothermal reactor 2 and the second isothermal reactor 5 are respectively filled with the methanation catalyst prepared in the comparative preparation example, and the filling amounts are 100 mL and 50 mL, respectively. The method for producing natural gas by methanation of coke oven gas is the same as that in Example 1, wherein the outlet mixed gas of the first isothermal reactor 2 is condensed and separated by gas and liquid by the first gas-liquid separator 3, and the outlet dry gas volume composition is about 30.43% hydrogen, about 59.097% methane, 0.003% carbon monoxide, 0.07% carbon dioxide, about 4.4% nitrogen, and about 6% unsaturated hydrocarbons above C2; ​​the amount of carbon dioxide added is 7.5% of the outlet dry gas flow rate; the outlet gas of the second isothermal reactor 5 is condensed and separated by gas and liquid by the second gas-liquid separator 6 to obtain methane product gas. The volume composition of methane product gas is 1.52% hydrogen, about 85.22% methane, 0% carbon monoxide, 0.36% carbon dioxide, about 5.5% nitrogen, and about 7.4% unsaturated hydrocarbons above C2.

[0115] In this comparative example, the target product flow rate at the outlet of the first isothermal reactor 2 is 570NL / h in terms of methane, and the target product flow rate at the outlet of the second isothermal reactor 5 is 638NL / h in terms of methane. The methane production increased by carbon dioxide supplementation is 68NL / h, an increase of 11.9% in methane production.

[0116] It can be seen from the above results that the method and system for producing natural gas by methanation of coke oven gas provided by the present invention can shorten the coke oven gas methanation process and reduce costs, while reducing carbon oxides in the methane product gas, and realizing the utilization of surplus hydrogen in the coke oven gas and the resource utilization of CO2, thereby increasing the output of methane product gas, and the volume content of hydrogen in the methane product gas does not exceed 0.5%, the total volume content of carbon oxides does not exceed 0.01%, and the methane content is greater than 80%.

[0117] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for producing natural gas by methanation of coke oven gas, characterized in that: The method includes: (1) in the presence of a catalyst I, subjecting coke oven gas to a primary isothermal methanation reaction to obtain a primary reaction gas; subjecting the primary reaction gas to a primary condensation, and obtaining a primary gas phase and a primary liquid phase after gas-liquid separation; (2) mixing the primary gas phase with carbon dioxide to obtain a mixed gas; then subjecting the mixed gas to a secondary isothermal methanation reaction in the presence of catalyst II to obtain a secondary reaction gas; subjecting the secondary reaction gas to a secondary condensation and gas-liquid separation to obtain a methane product gas and a secondary liquid phase; Wherein, the catalyst I is the same as or different from the catalyst II, and each is independently a methanation catalyst, and the methanation catalyst comprises a carrier and an active component and an auxiliary agent supported on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from oxides of La and / or Ce; The method for preparing the methanation catalyst comprises the following steps: (a) in the presence of a first solvent, contacting the precursor I and the precursor II with a reducing agent to perform a reduction reaction to obtain a reduction product; (b) mixing the reduced product with a carrier and cellulose in the presence of a second solvent to obtain a suspension; (c) removing the second solvent from the suspension, and then calcining the obtained solid under an inert atmosphere to obtain a methanation catalyst; Wherein, the precursor I is a compound containing nickel, and the precursor II is selected from compounds containing lanthanum and / or cerium.

2. The method according to claim 1, wherein: The catalyst I is the same as the catalyst II; and / or, in the XRD spectrum of the methanation catalyst, there is a broad diffraction peak with a peak width greater than 5° at 2θ=45°; And / or, based on the total weight of the methanation catalyst, the content of the active component is 10-55% by weight, the content of the auxiliary agent is 0.3-2% by weight, and the content of the carrier is 40-90% by weight.

3. The method according to claim 2, wherein: Based on the total weight of the methanation catalyst, the content of the active component is 15-50% by weight, the content of the auxiliary agent is 0.35-1.7% by weight, and the content of the carrier is 45-85% by weight.

4. The method according to claim 1, wherein: In step (a), the reducing agent is a borohydride; and / or the precursor I is selected from at least one of nickel nitrate, nickel chloride and nickel acetate; and / or the precursor II is selected from nitrates and / or chlorides containing lanthanum and / or cerium; And / or, in terms of metal elements, the mass ratio of the precursor I to the precursor II is (20-110):1; and / or, the molar ratio of the reducing agent to the total amount of the precursor I and the precursor II calculated as metal elements is (1-2.5):1; and / or, the precursor I, precursor II and reducing agent are provided in the form of a solution; And / or, the reduction reaction conditions include: temperature of 15-25° C. and time of 1-3 h.

5. The method according to claim 4, wherein: In step (a), the reducing agent is sodium borohydride and / or potassium borohydride; and / or the precursor I is nickel nitrate; and / or the precursor II is selected from nitrates containing lanthanum and / or cerium; And / or, in terms of metal elements, the mass ratio of the precursor I to the precursor II is (20-100):1; And / or, the molar ratio of the reducing agent to the total amount of the precursor I and the precursor II calculated as metal elements is (1.5-2):

1.

6. The method according to claim 1, wherein: In step (b), the carrier is selected from at least one of alumina, zirconia and magnesium aluminum spinel; and / or The mass ratio of the precursor I to the carrier, calculated as the metal element, is (0.1-1.5):1; and / or The mass ratio of the cellulose to the second solvent is (0.5-1.5):100; and / or In step (c), the calcination conditions include: a heating rate of 1-5°C / min; a temperature of 300-400°C; and a time of 1-10h; and / or, the inert atmosphere is provided by at least one of nitrogen, argon, helium and neon; and / or, the first solvent and the second solvent are water; And / or, the method further comprises performing solid-liquid separation and washing on the reduction product.

7. The method according to claim 6, wherein: In step (b), The mass ratio of the precursor I to the carrier, calculated as the metal element, is (0.176-1):1; and / or The mass ratio of the cellulose to the second solvent is (0.8-1.2):100; and / or In step (c), the calcination conditions include: a heating rate of 2-4°C / min; a temperature of 330-350°C; and a calcination time of 2-5h; And / or, the method is carried out under an inert atmosphere.

8. The method according to claim 1, wherein: The method further comprises, before performing step (1), purifying and desulfurizing the coke oven gas to obtain purified coke oven gas; And / or, in step (1), the temperature of the coke oven gas is 250-350°C; And / or, the conditions of the primary isothermal methanation reaction include: temperature not exceeding 350°C; pressure of 1-4 MPa; volume space velocity of 3000-25000 h -1 ; And / or, based on the total amount of the primary gas phase, the content of hydrogen in the primary gas phase is 25-50 volume %; the content of methane is 40-65 volume %; and the content of carbon oxides does not exceed 0.01 volume %.

9. The method according to claim 8, wherein: In step (1), the temperature of the coke oven gas is 260-300° C.; And / or, the conditions of the primary isothermal methanation reaction include: temperature of 300-350°C; pressure of 1.5-3.5 MPa; volume space velocity of 6000-15000 h -1 .

10. The method according to claim 1, wherein: In step (2), the temperature of the mixed gas is 250-400° C.; and / or, based on the total amount of the primary gas phase, the amount of the carbon dioxide is 6-13% by volume; And / or, the conditions of the secondary isothermal methanation reaction include: temperature not exceeding 350°C; pressure of 1-4 MPa; volume space velocity of 3000-25000 h -1 ; And / or, based on the total amount of the methane product gas, the hydrogen content in the methane product gas does not exceed 0.5 volume %; the methane content is greater than 80 volume %; and the carbon oxide content is less than 0.02 volume %.

11. The method according to claim 10, wherein: In step (2), the temperature of the mixed gas is 260-300°C; and / or, based on the total amount of the primary gas phase, the amount of the carbon dioxide is 6.25-12.5 volume %; And / or, the conditions of the secondary isothermal methanation reaction include: temperature of 300-350° C.; pressure of 1.5-3.5 MPa; Volume space velocity is 6000-15000h -1 ; And / or, the content of methane is 80.1-90 volume %; the content of carbon oxides does not exceed 0.01 volume %.

12. The method according to claim 11, wherein: In step (2), Based on the total amount of the primary gas phase, the amount of the carbon dioxide used is 7-12% by volume.

13. A system for producing natural gas from coke oven gas by methanation according to any one of claims 1 to 12, characterized in that: The system comprises at least one methanation unit, wherein the methanation unit comprises a first isothermal reactor, a first gas-liquid separator, a second isothermal reactor and a second gas-liquid separator which are connected in sequence.

14. The system according to claim 13, wherein: The first isothermal reactor is filled with catalyst I, and the second isothermal reactor is filled with catalyst II; the catalyst I is the same as or different from the catalyst II, and each is independently a methanation catalyst, and the methanation catalyst includes a carrier and an active component and an auxiliary agent loaded on the carrier, wherein the active component is amorphous nickel, and the auxiliary agent is selected from oxides of La and / or Ce.

15. The system of claim 14, wherein: The catalyst I is the same as the catalyst II.

16. The system of claim 14, wherein: In the XRD spectrum of the methanation catalyst, there is a broad diffraction peak with a peak width greater than 5° at 2θ=45°; And / or, based on the total weight of the methanation catalyst, the content of the active component is 10-55% by weight, the content of the auxiliary agent is 0.3-2% by weight, and the content of the carrier is 40-90% by weight.

17. The system of claim 16, wherein: Based on the total weight of the methanation catalyst, the content of the active component is 15-50% by weight, the content of the auxiliary agent is 0.35-1.7% by weight, and the content of the carrier is 45-85% by weight.

18. The system of claim 14, wherein: The method for preparing the methanation catalyst comprises the following steps: (a) in the presence of a first solvent, contacting the precursor I and the precursor II with a reducing agent to perform a reduction reaction to obtain a reduction product; (b) mixing the reduced product with a carrier and cellulose in the presence of a second solvent to obtain a suspension; (c) removing the second solvent from the suspension, and then calcining the obtained solid under an inert atmosphere to obtain a methanation catalyst; Wherein, the precursor I is a compound containing nickel, and the precursor II is selected from compounds containing lanthanum and / or cerium.

19. The system of claim 18, wherein: In step (a), the reducing agent is a borohydride; and / or the precursor I is selected from at least one of nickel nitrate, nickel chloride and nickel acetate; and / or the precursor II is selected from nitrates and / or chlorides containing lanthanum and / or cerium; And / or, in terms of metal elements, the mass ratio of the precursor I to the precursor II is (20-110):1; and / or, the molar ratio of the reducing agent to the total amount of the precursor I and the precursor II calculated as metal elements is (1-2.5):1; and / or, the precursor I, precursor II and reducing agent are provided in the form of a solution; And / or, the reduction reaction conditions include: temperature of 15-25° C. and time of 1-3 h.

20. The system of claim 19, wherein: In step (a), the reducing agent is sodium borohydride and / or potassium borohydride; and / or the precursor I is nickel nitrate; and / or the precursor II is selected from nitrates containing lanthanum and / or cerium; And / or, in terms of metal elements, the mass ratio of the precursor I to the precursor II is (20-100):1; And / or, the molar ratio of the reducing agent to the total amount of the precursor I and the precursor II calculated as metal elements is (1.5-2):

1.

21. The system of claim 18, wherein: In step (b), the carrier is selected from at least one of alumina, zirconia and magnesium aluminum spinel; and / or The mass ratio of the precursor I to the carrier, calculated as the metal element, is (0.1-1.5):1; and / or The mass ratio of the cellulose to the second solvent is (0.5-1.5):100; and / or In step (c), the calcination conditions include: a heating rate of 1-5°C / min; a temperature of 300-400°C; and a time of 1-10h; and / or, the inert atmosphere is provided by at least one of nitrogen, argon, helium and neon; and / or, the first solvent and the second solvent are water; And / or, the method further comprises performing solid-liquid separation and washing on the reduction product.

22. The system of claim 21, wherein: In step (b), The mass ratio of the precursor I to the carrier, calculated as the metal element, is (0.176-1):1; and / or The mass ratio of the cellulose to the second solvent is (0.8-1.2):100; and / or In step (c), the calcination conditions include: a heating rate of 2-4°C / min; a temperature of 330-350°C; and a calcination time of 2-5h; And / or, the method is carried out under an inert atmosphere.

23. The system of claim 13, wherein: The methanation unit further comprises a preheater and a heater, wherein the preheater is arranged before the first isothermal reactor; and the heater is arranged between the first gas-liquid separator and the second isothermal reactor.

24. The system of claim 13, wherein: The system further comprises a pretreatment unit, which is used for purifying and desulfurizing the coke oven gas to obtain purified coke oven gas.

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