Underground gasification method for generating methane through reaction of hydrogen and underground coal seam and application

Abstract

The invention provides an underground gasification method for generating methane through reaction of hydrogen and an underground coal seam and application, and relates to the technical field of underground in-situ methane production of coal. According to the method, hydrogen is injected into the underground coal seam and reacts in the presence of a catalyst under the heating and pressurizing conditions, methane-rich gas is directly generated, the methane content is 95% mol-98.5% mol, the H2 content is 0.1% mol-3% mol, and CO2 is smaller than or equal to 0.1% mol. The underground gasification method does not involve tedious steps of oxygen oxidation, carbon dioxide reduction and the like, coal is directly converted into methane, and simple production of methane is achieved; according to the method, the traditional coal mining process is changed fundamentally, the deep underground methane direct mining is really realized, the direct coal mining is converted into the direct gasification methane production, and the technical blank of generating the methane through the in-situ reaction of the hydrogen and the underground coal seam is filled.

Description

Technical Field

[0001] The invention belongs to the technical field of underground in-situ methane production from coal, and specifically relates to an underground gasification method and application of methane generated by the reaction of hydrogen and underground coal seams. Background Art

[0002] When mining coal wells, there are many safety risks due to the influence of disasters such as water, fire, gas, coal dust, and roof, and safety accidents occur from time to time; the demand for coal for economic development has maintained a steady growth, resulting in a continuous decrease in the amount of mineable coal resources; coal resources below one thousand meters are difficult or even impossible to mine; with the reduction of hydrogen production costs, it is necessary and possible to carry out research on new quality productivity of new coal mining methods.

[0003] Underground coal gasification refers to the process of producing combustible gas through thermal and chemical reactions on underground coal. Compared with traditional coal mining methods, underground coal gasification eliminates the need for coal mining, transportation, washing, gasification and other process equipment, and has the advantages of good safety, low investment and high efficiency.

[0004] The existing underground coal gasification technology is to inject oxygen or air and water into the underground coal seam to generate synthetic gases such as carbon monoxide, hydrogen, and methane through the combustion of coal; due to the complex reaction, the reaction process is difficult to control and therefore cannot be promoted and applied. In the existing technology, in order to improve the total carbon conversion rate, water vapor is usually added during the reaction process, and the reaction temperature is as high as 1000°C or above; although the total carbon conversion rate is improved in this process, due to the high reaction temperature, the methane product reacts with water vapor at high temperature and cracks, which reduces the methane yield.

[0005] Chinese invention patent CN102952598A discloses a methanation process for producing natural gas based on underground coal gasification, comprising the following steps: preheating the raw gas and then dividing it into two streams, the first stream of raw gas and part of the synthesis gas from the third-stage reactor entering the first-stage reactor together for methanation reaction; the second stream of raw gas and the synthesis gas from the first-stage reactor entering the second-stage reactor together for methanation reaction; the synthesis gas from the second-stage reactor after cooling enters the third-stage reactor for further methanation reaction; part of the synthesis gas from the third-stage reactor is cooled and circulated to the first-stage reactor, and the remaining part of the synthesis gas enters the fourth-stage reactor after cooling for methanation reaction, and the gas from the fourth-stage reactor is cooled and separated to obtain synthetic natural gas after condensate is separated; the raw gas is obtained by obtaining raw coal gas from underground coal gasification production through purification pretreatment, compression, debenzene and denaphthalene, CO conversion, and desulfurization and decarbonization treatment. Although this invention utilizes underground coal and synthesizes natural gas through a series of reactions with synthesis gas, this invention does not directly generate methane from coal underground, but rather reacts the gas produced by coal gasification with other reaction gases to undergo a methanation reaction; this invention adds an underground gasification step and does not achieve the purpose of producing methane through direct in-situ reaction of raw coal.

[0006] Chinese invention patent CN118360344A discloses a method of using biomass to promote coal seam CO 2 Circular storage and conversion of CH 4 A system and method for pre-treating biomass to form a biomass liquefied liquid or a derivative thereof, which is then injected into a CO 2 In deep coal seams that are geologically sealed, the biomass liquefied liquid or its derivatives are converted into hydrogen by hydrogen-producing microorganisms under in-situ conditions in the coal seams, and then the CO is converted into hydrogen by methanogenic microorganisms. 2 Convert to CH 4 hydrogen source, promoting the CO 2 Converted to CH 4 ; Then the converted CH 4 Extract and utilize at each node and recapture the generated CO 2 Seal in the in-situ coal seam to achieve CO 2 Circular storage and conversion of CH 4 . This effectively solves the problem of geological storage of CO in coal seams. 2 Bioconversion to CH 4 The lack of hydrogen required for CO 2 Circular storage and conversion of CH 4 However, the methane production reaction involved in the invention is actually based on CO 2The methane production process for raw gas does not involve the process of in-situ reaction of underground coal seams. In addition, the invention uses hydrogen-producing microorganisms to produce hydrogen, which requires the control of the cultivation process of functional microbial flora. The hydrogen production effect of microorganisms is limited, and the methane production process is slow. The methane concentration is only 70% on the 90th day.

[0007] In view of this, the present invention provides a method for directly producing high-purity, high-yield methane from coal through underground gasification technology, fundamentally changing the traditional coal mining process, changing the deep underground methane mining process, and realizing the process of converting direct coal mining into direct gasification to produce methane, filling the technical gap of directly reacting hydrogen with underground coal seams in situ to generate high-purity methane. Summary of the invention

[0008] The present invention aims to solve the problems in the prior art and provides an underground gasification method and application for generating methane by reacting hydrogen with underground coal seams. Hydrogen is injected into underground coal seams and reacted under catalyst, heating and pressurizing conditions to directly generate methane-rich gas. The underground gasification method of the present invention does not involve cumbersome oxygen oxidation, carbon dioxide reduction and other steps, directly converts coal into methane, realizes simple methane production, and provides a new technology for direct utilization of underground coal.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] Firstly, the present invention provides an underground gasification method for in-situ reaction of hydrogen and underground coal seams to generate methane, comprising the steps of injecting hydrogen into the underground coal seam, reacting with coal and a catalyst under heating and pressurizing conditions to obtain methane.

[0011] The underground gasification method of the present invention has the following reaction equation:

[0012]

[0013] Preferably, the mass ratio of the catalyst to coal is 1:1000-3000.

[0014] Further preferably, the mass ratio of the catalyst to coal is 1:2000.

[0015] Preferably, the underground gasification method comprises the steps of:

[0016] (1) The Fe-Ni based catalyst is introduced into the underground coal seam, the reaction environment temperature of the underground coal seam is controlled at 120-300°C, and then N 2 ;

[0017] (2) H 2Injected into the underground coal seam of step (1), the gas pressure of the underground coal seam is controlled at 10-20 MPa, and hydrogen and coal undergo reduction reaction in the gasification channel at a reaction temperature of 600-800° C. to obtain methane.

[0018] Further preferably, in step (1), the mass ratio of Fe to Ni in the Fe-Ni based catalyst is 2-5:1.

[0019] More preferably, in step (1), the mass ratio of Fe to Ni in the Fe-Ni based catalyst is 4:1.

[0020] More preferably, in step (1), the Fe is derived from ferroferric oxide, and the Ni is derived from Raney nickel.

[0021] Further preferably, in step (1), the reaction environment temperature is 160-250°C.

[0022] More preferably, in step (1), the reaction environment temperature is 200°C.

[0023] In step (1) of the present invention, N is introduced into the underground coal seam. 2 , the gas (including oxygen, carbon monoxide and carbon dioxide) in the underground coal seam is discharged, the oxygen is isolated, and the safety of hydrogen introduction is ensured; at the reaction environment temperature of step (1), the water in the underground coal seam is consumed, providing environmental conditions suitable for the direct reaction of coal and hydrogen to produce methane.

[0024] Further preferably, in step (2), the gas pressure of the underground coal seam is 15 MPa.

[0025] Further preferably, in step (2), the reaction temperature is 700-750°C.

[0026] More preferably, in step (2), the reaction temperature is 750°C.

[0027] More preferably, in step (2), the reaction time is 0.1-40 min.

[0028] More preferably, in step (2), the reaction time is: 5-20 seconds to start the reaction and 25-35 minutes to end the reaction.

[0029] More preferably, in step (2), the reaction time is: 10 seconds to start the reaction and 30 minutes to end the reaction.

[0030] In step (2) of the present invention, H 2 Injected into underground coal seams to make H 2 Filling the entire reaction underground coal seam, H2 Direct in-situ reaction with coal to generate high-purity methane.

[0031] In the present invention, the injected H 2 The source of H is not limited; in some embodiments, the H used 2 H produced locally 2 , such as H produced by wind energy and geothermal energy in coal mining areas 2 , saving transportation costs, producing H 2 It is applied in situ to the underground gasification method of the present invention to directly produce methane by contacting with coal.

[0032] Through the underground gasification method of the present invention, underground in-situ coal gasification and gas and heat production can be achieved; hydrogen and coal in underground coal seams directly react to not only produce high-purity methane, but also the generated heat energy can be recycled for underground gasification; or the generated heat energy can be converted into electrical energy; or the generated heat energy can be converted into energy for preparing hydrogen, thereby realizing the recycling of energy.

[0033] Then, the present invention provides a methane-rich natural gas directly prepared by the above underground gasification method.

[0034] Preferably, in the natural gas, methane (CH 4 ) content is 95% mol-98.5% mol, H 2 The content is 0.1% mol-3% mol, CO 2 ≤0.1%mol.

[0035] Finally, the present invention provides the application of the underground gasification method in the direct methane production process of underground coal seams.

[0036] Preferably, in the application, the gasification method is to inject hydrogen directly into the underground coal seam to react directly with the coal in situ to generate high-purity methane.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The underground gasification method of the present invention directly injects hydrogen into the underground coal seam through a pipeline, heats and pressurizes it in the presence of a catalyst, and directly reacts with coal to generate methane. The methane content in the obtained gas product is 95% mol-98.5% mol. The underground gasification method of the present invention not only realizes the direct conversion of underground coal seams to methane, but also has a high methane content in the obtained gas; the present invention uses hydrogen to directly react with coal in situ, replacing the traditional injection of oxygen or air and water to react to generate synthetic gases such as carbon monoxide, hydrogen, and methane. The present invention only performs a one-step reaction to generate high-yield, high-purity methane gas.

[0039] 2. The underground gasification method of the present invention can fully develop and utilize the coal that is difficult to mine below one kilometer, creatively transform traditional physical mining into highly economical chemical mining, transform coal fields into gas fields, and realize the direct reaction of coal and hydrogen to generate high-purity methane.

[0040] 3. The underground gasification method of the present invention uses hydrogen produced on-site at the coal mining site. By coupling with new energy hydrogen production and other methods and applying it to underground gasification technology, the utilization efficiency of renewable energy can be effectively improved, thereby alleviating the problem of new energy consumption, and the overall carbon emissions can be reduced by 30%-50%. DETAILED DESCRIPTION

[0041] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is merely an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, which should also fall within the scope of the present invention.

[0042] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those generally understood by those of ordinary skill in the art to which the present invention belongs.

[0043] The present invention is further described below by way of specific examples. The various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels unless otherwise specified. Unless otherwise specified, raw materials from different manufacturers have no significant effect on the effects.

[0044] Example 1

[0045] An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams:

[0046] (1) Select an underground coal seam with a burial depth greater than 1000 m and good sealing effect; uniformly introduce 0.5 kg of catalyst per ton of coal seam, and control the reaction environment temperature of the underground coal seam to 200 °C; introduce N 2 , discharge gases such as oxygen, carbon monoxide and carbon dioxide in underground coal seams; the catalyst is an Fe-Ni based catalyst, and the mass ratio of Fe to Ni in the catalyst is 4:1;

[0047] (2) Injecting the hydrogen produced on site through a pipeline into the underground coal seam that has been heated to 200° C. and contains a catalyst in step (1), so that the underground coal seam is filled with hydrogen; the gas pressure of the underground coal seam is 15 MPa, and the underground coal seam is heated to 700° C. under this pressure. At a reaction environment temperature of 700° C., hydrogen and coal undergo a reduction reaction, which starts in about 10 seconds and ends after 30 minutes, thereby obtaining methane; and the methane is extracted to the ground through an extraction process.

[0048] Example 2

[0049] An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams:

[0050] (1) Select an underground coal seam with a burial depth greater than 1000 m and good sealing effect; uniformly introduce 0.5 kg of catalyst per ton of coal seam, and control the reaction environment temperature of the underground coal seam to 200 °C; introduce N 2 , discharge gases such as oxygen, carbon monoxide and carbon dioxide in underground coal seams; the catalyst is an Fe-Ni based catalyst, and the mass ratio of Fe to Ni in the catalyst is 2:1;

[0051] (2) Same as Example 1.

[0052] Example 3

[0053] An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams:

[0054] (1) Select an underground coal seam with a burial depth greater than 1000 m and good sealing effect; uniformly introduce 0.5 kg of catalyst per ton of coal seam, and control the reaction environment temperature of the underground coal seam to 200 °C; introduce N 2 , discharge gases such as oxygen, carbon monoxide and carbon dioxide in underground coal seams; the catalyst is an Fe-Ni based catalyst, and the mass ratio of Fe to Ni in the catalyst is 5:1;

[0055] (2) Same as Example 1.

[0056] Example 4

[0057] An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams:

[0058] (1) Same as Example 1;

[0059] (2) Injecting the hydrogen produced on site through a pipeline into the underground coal seam which has been heated to 200° C. and contains a catalyst in step (1), so that the underground coal seam is filled with hydrogen; the gas pressure of the underground coal seam is 10 MPa, and the underground coal seam is heated to 800° C. under this pressure. At a reaction environment temperature of 800° C., hydrogen and coal undergo a reduction reaction, which starts in about 10 seconds and ends after 30 minutes, thereby obtaining methane; and the methane is extracted to the ground through an extraction process.

[0060] Example 5

[0061] An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams:

[0062] (1) Same as Example 1;

[0063] (2) Injecting the hydrogen produced on site through a pipeline into the underground coal seam that has been heated to 200° C. and contains a catalyst in step (1), so that the underground coal seam is filled with hydrogen; the gas pressure of the underground coal seam is 20 MPa, and the underground coal seam is heated to 600° C. under this pressure. At a reaction environment temperature of 600° C., hydrogen and coal undergo a reduction reaction, which starts in about 10 seconds and ends after 30 minutes, thereby obtaining methane; and the methane is extracted to the ground through an extraction process.

[0064] Example 6

[0065] An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams:

[0066] (1) Select an underground coal seam with a burial depth greater than 1000 m and good sealing effect; uniformly introduce 0.35 kg of catalyst per ton of coal seam, and control the reaction environment temperature of the underground coal seam to 200 °C; introduce N 2 , discharge gases such as oxygen, carbon monoxide and carbon dioxide in underground coal seams; the catalyst is an Fe-Ni based catalyst, and the mass ratio of Fe to Ni in the catalyst is 4:1;

[0067] (2) Injecting the hydrogen produced on site through a pipeline into the underground coal seam that has been heated to 200° C. and contains a catalyst in step (1), so that the underground coal seam is filled with hydrogen; the gas pressure of the underground coal seam is 15 MPa, and the underground coal seam is heated to 800° C. under this pressure. At a reaction environment temperature of 800° C., hydrogen and coal undergo a reduction reaction, which starts in about 10 seconds and ends after 35 minutes, thereby obtaining methane; and the methane is extracted to the ground through an extraction process.

[0068] Example 7

[0069] An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams:

[0070] (1) Select an underground coal seam with a burial depth greater than 1000 m and good sealing effect; uniformly introduce 2.0 kg of catalyst per ton of coal seam, and control the reaction environment temperature of the underground coal seam to 200 °C; introduce N 2 , discharge gases such as oxygen, carbon monoxide and carbon dioxide in underground coal seams; the catalyst is an Fe-Ni based catalyst, and the mass ratio of Fe to Ni in the catalyst is 4:1;

[0071] (2) Injecting the hydrogen produced on site through a pipeline into the underground coal seam that has been heated to 200° C. and contains a catalyst in step (1), so that the underground coal seam is filled with hydrogen; the gas pressure of the underground coal seam is 15 MPa, and the underground coal seam is heated to 600° C. under this pressure. At a reaction environment temperature of 600° C., hydrogen and coal undergo a reduction reaction, which starts in about 10 seconds and ends after 25 minutes, thereby obtaining methane; and the methane is extracted to the ground through an extraction process.

[0072] Comparative Example 1

[0073] The difference from Example 1 is that the hydrogen in step (2) is replaced by a mixed gas: (H 2 -CO 2 ) / (CO+CO 2 )=3.0.

[0074] The rest are the same as in Example 1.

[0075] Comparative Example 2

[0076] An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams:

[0077] (1) Selecting an underground coal seam with a burial depth greater than 1000 m and good sealing effect; uniformly introducing 0.5 kg of catalyst per ton of coal seam to seal the gas and water in the underground coal seam; the catalyst is an Fe-Ni based catalyst, and the mass ratio of Fe to Ni in the catalyst is 4:1;

[0078] (2) Injecting the hydrogen produced on site into the underground coal seam of step (1) through a pipeline; the gas pressure of the underground coal seam is 15 MPa, H 2 The content is ≥85%. Under this pressure, the underground coal seam is heated to 700℃. In the reaction environment temperature of 700℃, hydrogen and coal undergo reduction reaction. The reaction starts in about 10 seconds and ends after 30 minutes to obtain methane. The methane is extracted to the ground through an extraction process.

[0079] Comparative Example 3

[0080] The difference from Example 1 is that the reaction environment temperature in step (2) is different. The reaction environment temperature is increased from 700°C to 1000°C.

[0081] The rest are the same as in Example 1.

[0082] Comparative Example 4

[0083] The difference from Example 1 is that the Fe-Ni based catalyst in step (1) is replaced by ferrosoferric oxide, and the added amount is: 0.4 kg ferrosoferric oxide is uniformly introduced into each ton of coal seam.

[0084] The rest are the same as in Example 1.

[0085] Comparative Example 5

[0086] The difference from Example 1 is that the Fe-Ni based catalyst in step (1) is replaced by Raney nickel. The amount of catalyst added is: 0.1 kg of Raney nickel is uniformly introduced into each ton of coal seam.

[0087] The rest are the same as in Example 1.

[0088] Comparative Example 6

[0089] Different from Example 1, the gas pressure and reaction time of step (2) are different.

[0090] Step (1): same as in Example 1;

[0091] Step (2): injecting the hydrogen produced on site through a pipeline into the underground coal seam which has been heated to 200°C and contains a catalyst in step (1), so that the underground coal seam is filled with hydrogen; the gas pressure of the underground coal seam is 5MPa, and the underground coal seam is heated to 700°C under this pressure. At the reaction environment temperature of 700°C, the hydrogen and coal undergo a reduction reaction, the reaction starts in about 10 seconds, and the reaction ends after 15 minutes, thereby obtaining methane; and the methane is extracted to the ground through an extraction process.

[0092] Test 1 High heat detection

[0093] According to the detection method in GB 17820-2018 Natural Gas, the gas product pumped to the ground is tested for high calorific value (MJ / m 3 The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096] As can be seen from Table 1, the method of the present invention for directly generating methane by in-situ reaction of hydrogen with underground coal seams can obtain a gas product with a relatively high calorific value, which meets the quality requirements of Class I natural gas.

[0097] It can be seen from Comparative Example 1 that when mixed gas is used to prepare methane, due to the presence of CO in the gas product, 2, CO and other gases, therefore, the high calorific value is low; it can be seen from Comparative Example 2 that when the underground coal seam is sealed before the hydrogen is injected, the underground coal seam contains CO 2 , CO, H 2 Mixed gases such as carbon and hydrogen can reduce the hydrogen concentration, which further affects the in-situ reaction process of carbon and hydrogen to generate methane, and the obtained gas product has low methane concentration and low calorific value.

[0098] It can be seen from Comparative Examples 3 to 6 that the type of catalyst, reaction pressure, reaction temperature and reaction time in the reaction process all have a significant impact on the quality of methane.

[0099] Test 2 Gas component content

[0100] The components and purity of the gases obtained in the embodiments and comparative examples were tested. The test results are shown in Table 2.

[0101] Table 2

[0102] <![CDATA[CH 4 (%mol)]]> <![CDATA[H 2 (%mol)]]> <![CDATA[CO 2 (%mol)]]> Example 1 98.3 1.1 0.01 Example 2 98.0 1.2 0.01 Example 3 97.2 1.5 0.02 Example 4 97.0 1.3 0.03 Example 5 97.6 1.6 0.01 Example 6 95.0 2.0 0.04 Example 7 97.8 1.1 0.02 Comparative Example 1 76.3 10.2 6.14 Comparative Example 2 70.2 3.6 10.82 Comparative Example 3 86.5 2.3 0.05 Comparative Example 4 55.5 34.0 0.06 Comparative Example 5 22.8 62.9 0.08 Comparative Example 6 43.7 49.9 0.02

[0103] As can be seen from Table 2, the method of the present invention for directly generating methane by in-situ reaction of hydrogen with underground coal seams, in the obtained gas products, the proportion of methane is more than 95 mol%, CO 2 The content is extremely small; the reaction between coal and hydrogen underground is thorough.

[0104] It can be seen from Comparative Example 1 that when the reaction gas is a mixed gas, the hydrogen and CO in the obtained gas product are 2 As the content increases, the corresponding methane content decreases significantly, and the methane purity is low, which does not meet the standard requirements.

[0105] It can be seen from Comparative Example 2 that when the underground coal seam contains other gases such as carbon dioxide, carbon monoxide and water, the generation of methane is affected, the methane content is significantly reduced, and the content of water and carbon-containing gas is increased.

[0106] It can be seen from Comparative Example 3 that when the reaction temperature is increased to a high temperature of 1000° C., the methane content is reduced due to reactions such as cracking.

[0107] It can be seen from Comparative Examples 4 and 5 that the present invention uses an Fe-Ni composite catalyst to participate in the reaction of preparing methane from carbon and hydrogen, which significantly promotes the reaction and makes the reaction complete; when the type and amount of the catalyst are changed, the reaction is incomplete, the methane production performance is significantly reduced, and the methane production is significantly reduced.

[0108] It can be seen from Comparative Example 6 that the reaction pressure and reaction time of coal and hydrogen have a significant impact on the methane yield and purity. When the reaction conditions are changed, the reaction between the underground coal seam and hydrogen is incomplete, the methane content is reduced, and it does not meet the standards of high-quality natural gas.

[0109] The present invention aims at high methane yield and high methane content, and obtains a gas product with high methane yield and purity and simple gas composition by controlling factors such as reaction temperature, reaction pressure, reaction atmosphere, reaction time, catalyst, etc.

[0110] The reaction of coal hydrogenation to produce methane is a highly exothermic process, and methane is prone to cracking under high temperature conditions, and the system methane equilibrium concentration decreases significantly with the increase of temperature. The present invention is spontaneously carried out under the condition of 600-800°C, without the need for coal combustion process, so it can ensure that the reaction process is isolated from oxygen and ensure the safety of hydrogen introduction. Traditional underground coal gasification requires a large amount of water to participate in the gasification reaction. The reaction process of the present invention does not involve water, which reduces water pollution and improves the quality of gas products.

[0111] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. An underground gasification method for generating methane by in-situ reaction of hydrogen with underground coal seams, characterized in that: The method comprises the following steps: injecting hydrogen into an underground coal seam, reacting with coal and a catalyst under heating and pressurizing conditions to obtain methane.

2. The underground gasification method according to claim 1, characterized in that: The mass ratio of the catalyst to the coal is 1:1000-3000.

3. The underground gasification method according to claim 2, characterized in that: The mass ratio of the catalyst to coal is 1:2000.

4. The underground gasification method according to any one of claims 1 to 3, characterized in that: Includes steps: (1) introducing an Fe-Ni-based catalyst into an underground coal seam, controlling the reaction environment temperature of the underground coal seam to 120-300° C., and then introducing N2; (2) Injecting H2 into the underground coal seam of step (1), controlling the gas pressure of the underground coal seam to 10-20 MPa, and allowing hydrogen to react with coal in a gasification channel at a reaction temperature of 600-800°C to obtain methane.

5. The underground gasification method according to claim 4, characterized in that: In step (1), the mass ratio of Fe to Ni in the Fe-Ni based catalyst is 2-5:1; in step (1), the reaction environment temperature is 160-250°C.

6. The underground gasification method according to claim 5, characterized in that: In step (1), the mass ratio of Fe to Ni in the Fe-Ni based catalyst is 4:1; in step (1), the reaction environment temperature is 200°C.

7. The underground gasification method according to claim 4, characterized in that: In step (2), the gas pressure of the underground coal seam is 15 MPa, the reaction temperature is 700-750° C., and the reaction time is 0.1-40 min.

8. The underground gasification method according to claim 7, characterized in that: In step (2), the reaction temperature is 750° C., and the reaction time is: 5-20 seconds to start the reaction and 25-35 minutes to complete the reaction.

9. A natural gas rich in methane, characterized in that: It is directly prepared by the underground gasification method described in any one of claims 1 to 8.

10. Application of the underground gasification method according to any one of claims 1 to 8 in a process for direct methane production from underground coal seams.

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