Method for extracting methane contained in low-concentration oxygen-containing coal-seam gas

Abstract

The invention discloses a method for extracting methane contained in a low-concentration oxygen-containing coal-seam gas, and the method comprises the following procedures of: (1) a coal-seam gas storage procedure: storing the low-concentration oxygen-containing coal-seam gas by adopting a gas holder; (2) a coal-seam gas compression procedure: pressurizing and compressing the coal-seam gas output from the gas holder to 0.35-0.4 MPG, and keeping the temperature of the coal-seam gas lower than 80 DEG C in a pressurizing and compressing process; (3) a coal-seam gas purifying procedure: sequentially carrying out demercuration, desulfuration, decarbonation and dewatering treatment on the coal-seam gas; (4) a coal-seam gas cooling procedure: cooling the coal-seam gas to -140-160 DEG C, wherein the liquid molar fraction is not more than 15%; (5) a coal-seam gas rectification and separation procedure: delivering the coal-seam gas into a rectification tower, accessing methane liquid obtained through liquification and separation into a reboiler positioned at the bottom of the rectification tower so that nitrogen and oxygen are evaporated, and accessing the nitrogen and the oxygen which are obtained through the liquification and the separation into a condenser positioned on the top of the rectification tower so that the methane is refluxed to the rectification tower after being liquefied and separated; and (6) a liquefied methane storage procedure: storing the liquefied methane into a liquefied methane storage tank.

Description

technical field [0001] The invention belongs to the technical field of liquefying, solidifying or separating gas or gas mixture through pressurization and cooling treatment, and in particular relates to a method for extracting methane in low-concentration oxygen-containing coal bed gas. Background technique [0002] CBM belongs to the associated gas in coal mine production. Before coal mining, it is necessary to extract coalbed methane on the ground in advance; while mining coal mines, it is necessary to extract coalbed methane in mine tunnels. Coalbed methane extracted from the ground has high methane content, low oxygen content, good safety, and can be directly pressurized for transportation or used for other purposes. But more is for the safety of coal mining, coalbed methane extracted in mines that have already been mined and produced. The methane content of the coalbed methane extracted in the mine is low, usually between 30% and 70%. This kind of coalbed methane cont...

AI Technical Summary

Problems solved by technology

[0005] In the technical methods reported so far, the following measures are mainly taken to ensure safety: First, the oxygen in the low-concentration oxygen-containing coalbed methane is firstly removed by means of catalysis, pressure swing adsorption, membrane separation, and solution absorption, and then the methane is extracted. The second is to ensure that the concentration of methane is higher than the upper limit of explosion throughout the extraction process; or some technical methods do not mention the impact of oxygen on safety, and only describe the method of extracting methane from the technical point of view of gas separation

[0006] Although these methods have improved the safety in the process of extracting methane from low-concentration oxygen-containing coalbed methane to a certain extent, they still have the following disadvantages: in the method of first removing oxygen and then extracting methane, it is necessary to increase the deoxygenation equipment, which increases the equipment cost. Investment and operating costs; control the methane content above the upper explosive limit throughout the extraction process to ensure safety at the expense of methane recovery

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