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CN-121975553-A - Method and system for preparing methane-rich gas by underground gasification of deep coal

CN121975553ACN 121975553 ACN121975553 ACN 121975553ACN-121975553-A

Abstract

The invention belongs to the technical field of underground coal gasification, and discloses a method and a system for preparing methane-rich coal gas by underground deep coal gasification. After the underground coal gasification enters a normal gasification stage, under the conditions of relatively low temperature and high pressure, the underground gasification furnace is injected with the waste water containing the catalyst, and the volume percentage of methane in the coal gas is kept above 35% by adjusting the gas-water ratio and/or the position of the gas injection point. The system for realizing the method comprises an underground gasification furnace, a double-layer continuous pipe, an injection device thereof, a variable-frequency water injection pump and a UCG regulation and control unit, wherein an air inlet of the continuous pipe is connected with a gasifying agent storage device, a water inlet of the continuous pipe is connected with the variable-frequency water injection pump, the underground gasification furnace is connected with the UCG regulation and control unit, and the variable-frequency water injection pump is communicated with a catalytic wastewater pool. The invention forms a set of stable and necessary process control method and operating system for maintaining the gasification coal bed to produce methane-rich gas, and the prepared gas has high methane content.

Inventors

  • YANG LANHE

Assignees

  • 中国矿业大学

Dates

Publication Date
20260505
Application Date
20260407

Claims (13)

  1. 1. A method for preparing methane-rich gas by underground gasification of deep coal is characterized in that after the underground gasification of coal enters a normal gasification stage, the underground gasification furnace is injected with waste water containing catalyst under the conditions of relatively low temperature and high pressure, and the volume percentage of methane in the gas is kept above 35% by adjusting the gas-water ratio and/or the position of a gas injection point.
  2. 2. The method for preparing methane-rich gas by underground gasification of deep coal as claimed in claim 1, wherein the normal gasification stage is that the volume percentage of CO in the gas component is more than 10%, and the volume percentage of H 2 is less than 30%.
  3. 3. The method for preparing methane-rich gas by underground gasification of deep coal according to claim 1, wherein the relatively low temperature is 700-1000 ℃, and the high pressure is 7-12 mpa.
  4. 4. The method for preparing methane-rich gas by underground gasification of deep coal according to claim 1, wherein the wastewater is one or more selected from condensed water obtained by purifying underground gasification gas on the ground, underground water pumped from an underground gasification furnace, coal washing wastewater and wastewater generated in the coal chemical production process.
  5. 5. The method for preparing methane-rich gas by underground gasification of deep coal as claimed in claim 1, wherein the catalyst is a potassium-sodium composite catalyst and/or a potassium-calcium composite catalyst, wherein the mass ratio of elements is potassium to sodium is 0.1:1-2:0.1, potassium to calcium is 0.1:1-2:0.1, and sodium to calcium is 10:1-1:10.
  6. 6. The method for preparing methane-rich gas by underground gasification of deep coal according to claim 5, wherein the mass ratio of the catalyst in the wastewater to the coal is 3:100-10:100 in unit time; the air-water ratio is that the volume ratio of the gasifying agent to the wastewater is 550:1-750:1.
  7. 7. The method for preparing methane-rich gas by underground gasification of deep coal according to claim 1, wherein the specific operation of adjusting the gas-water ratio and/or the position of the gas injection point and keeping the methane content in the gas above 35% by volume is that when the gas-water ratio reaches 600:1, the gas composition at the gas hole top and the temperature of the gasifying agent injection nozzle are detected, wherein, When the volume percentage of the effective gas in the gas component is more than or equal to 60%, the gas-water ratio is adjusted or maintained; when the volume percentage of the effective gas in the gas component is less than 60 percent and the methane content is more than 35 percent, the gas-water ratio is adjusted by combining the temperature of the gasifying agent injection nozzle, or the operation is not performed, or the cooling efficiency of the gasifying agent injection nozzle is enhanced; when the volume percentage of the effective gas in the gas component is less than 60 percent and the methane content is less than 35 percent, the gas-water ratio is adjusted to be more than 550:1, and/or the gasification progress is combined, and the gas injection point is retracted.
  8. 8. The method for producing methane-rich gas by underground gasification of deep coal according to claim 7, wherein the cooling efficiency is adjusted by circulating flow rate of cooling water.
  9. 9. The method for producing methane-rich gas by underground gasification of deep coal according to claim 7, wherein the back-off distance is 0.5m to lm, wherein L is the maximum back-off distance and is 1 to 5 times the thickness of the coal seam.
  10. 10. The system for preparing methane-rich gas by underground gasification of deep coal is characterized by comprising an underground gasification furnace, a double-layer continuous pipe and an injection device thereof, a variable-frequency water injection pump and a UCG regulation and control unit; the double-layer continuous pipe consists of an inner pipe and an outer pipe, wherein the front end of the inner pipe is provided with a continuous pipe air inlet which is connected with the gasifying agent storage device through a pipeline; The underground gasification furnace is provided with an air outlet hole, the air outlet hole is provided with a gas component sensor, the gas component sensor is electrically or communicatively connected with the UCG regulation and control unit, the inlet of the variable-frequency water injection pump is communicated with a catalytic wastewater tank storing catalyst-containing wastewater through a pipeline, and the variable-frequency water injection pump is electrically or communicatively connected with the UCG regulation and control unit.
  11. 11. The system for preparing methane-rich gas by underground gasification of deep coal according to claim 10, wherein the continuous pipe nozzle is provided with a temperature measuring element, and the temperature measuring element is electrically connected or in communication with the UCG regulating unit.
  12. 12. The system for preparing methane-rich gas by underground gasification of deep coal according to claim 10, further comprising a cooling structure arranged on the continuous pipe nozzle, wherein the cooling structure is communicated with a variable-frequency cooling water pump, the variable-frequency cooling water pump is communicated with a cooling water source, and meanwhile, the variable-frequency cooling water pump is electrically connected or in communication with the UCG regulation and control unit.
  13. 13. The system for producing methane-rich gas by underground gasification of deep coal according to claim 10, further comprising through holes arranged on the axial end face and the radial side wall of the outer tube of the continuous tube nozzle.

Description

Method and system for preparing methane-rich gas by underground gasification of deep coal Technical Field The invention relates to the technical field of underground coal gasification, in particular to a method and a system for preparing methane-rich coal gas by underground deep coal gasification. Background Methane is an important energy fuel and chemical raw material in the 21 st century, the preparation of methane (namely, the main component of natural gas) from coal is a feasible path, the development of coal methanation process at home and abroad is mainly based on the preparation of natural gas by ground catalytic gasification, and the research on the preparation of methane by underground coal gasification is less. For example, chinese patent application CN104927922a (process and apparatus for producing methane-rich gas by moving bed pressurized coal gasification) requires directly adding coal blocks into a moving bed gasification furnace, and pressurizing and reacting at high temperature in the furnace to produce methane-rich gas. Chinese patent application CN107099348a (method for producing synthetic natural gas by using underground gasification product gas of coal) mainly uses the gas produced by underground gasification to synthesize methane on the ground. Another method, such as chinese patent application CN119308654a (underground gasification method and application of methane produced by reaction of hydrogen and underground coal), can be adopted, hydrogen is injected into underground coal, and the reaction is performed under the conditions of catalyst and heating and pressurizing, so as to directly produce methane-rich gas. The technology adopts hydrogen to directly perform in-situ reaction on coal at high temperature to replace the traditional injection of oxygen or air and water to perform coal gasification reaction to generate synthesis gas such as carbon monoxide, hydrogen, methane and the like, and at present, the technology has obvious technical problems on the temperature rise and related regulation of an underground coal seam. In summary, the existing underground coal gasification methane production method generally has the technical problems that the underground gasification gas is collected and then methanized on the ground, or the volume percentage of methane in the gas produced by the underground gasification furnace is relatively low (not more than 25%), or the regulation and control of the underground gasification furnace producing methane-rich gas are difficult, mainly because the stable and necessary conditions and regulation and control systems for maintaining the gasification coal bed to produce methane-rich gas cannot be formed in the underground gasification furnace, for example, the operation temperature, the pressure, the composition of gasifying agent and the like of the underground coal gasification do not reach the preferred parameters of synthesizing methane, or the suitability of gasification equipment is poor. For this reason, the application will combine the underground gasification theory condition which is beneficial to methane generation with necessary equipment, and proposes a method and a system for preparing methane-rich coal gas by underground gasification of deep coal. Disclosure of Invention In view of this, the invention provides a method and a system for preparing methane-rich gas by underground gasification of deep coal. The invention aims to provide a method for preparing methane-rich gas by underground gasification of deep coal, which comprises the following specific operation that after the underground gasification of coal enters a normal gasification stage, waste water containing catalyst is injected into an underground gasification furnace under the conditions of relatively low temperature and high pressure, and the volume percentage of methane in the gas is kept above 35% by adjusting the gas-water ratio (gasifying agent and waste water ratio) and/or the position of a gas injection point. Preferably, the normal gasification stage is that the volume percentage of CO in the gas component is more than 10 percent and the volume percentage of H 2 is less than 30 percent. Preferably, the relatively low temperature is 700-1000 ℃, and the high pressure is 7-12 MPa. Preferably, the wastewater is selected from one or more of condensed water obtained by purifying underground gasified coal gas on the ground, underground water pumped out from an underground gasification furnace, coal washing wastewater and wastewater generated in the coal chemical production process. Preferably, the catalyst is a potassium-sodium composite catalyst and/or a potassium-calcium composite catalyst, wherein the mass ratio of elements is potassium to sodium is 0.1:1-2:0.1, potassium to calcium is 0.1:1-2:0.1, and sodium to calcium is 10:1-1:10. Preferably, the gasifying agent is an oxygen-enriched gasifying agent with the oxygen volume fraction of not less than 60%. Preferably, each t