What is mine gas?
Mine gas is a methane-based harmful gas mainly composed of coalbed methane in the mine. Sometimes referred to separately as methane (biogas). It is a gas associated with the formation of coal and the deterioration of coal. The gas generated in the process of coal formation is the initial stage of the accumulation of coal into ancient coal, and the cellulose and organic matter are decomposed by the action of anaerobic bacteria. In addition, in a high-temperature, high-pressure environment, while coal is formed, gas is continuously generated due to physical and chemical action.
Gas is a colorless, odorless, odorless gas, but sometimes it smells like apple, which is due to the simultaneous emission of aromatic hydrocarbon gas and gas. The relative density of gas to air is 0.554. Under standard conditions, the density of gas is 0.716kg, so it often accumulates in the upper part and the top of the roadway. The gas permeability of gas is 1.6 times that of air. It is hardly soluble in water, does not support combustion, and cannot maintain breathing. When it reaches a certain concentration, it can cause people to suffocate due to lack of oxygen, and can burn or explode. The burning and explosiveness of gas is one of the major disasters in the mine.
Gas is present in the free and sorbed state in the coal or surrounding rock.
The free state is also called the free state. This gas exists in the free gas state in the cracks and pores of the coal or surrounding rock. The amount of the gas is mainly determined by the volume, pressure and temperature of the storage space.
The sorption state is also called the combined state, which is characterized in that gas is integrated with coal or certain rocks and is no longer in the form of free gas. According to its combination, it can be divided into two types: adsorption and absorption. The adsorption state is due to the molecular attraction between the solid particles and the gas molecules, so that the gas molecules are closely attached to a thin layer on the surface of the solid particles; the absorption state is that the gas molecules have entered the interior of the coal molecular group.
Gas in several states is in constant dynamic balance and will transform each other under certain conditions. When the pressure and temperature change, the free gas is converted into sorption gas called adsorption, and the adsorption gas is converted into free gas called desorption.