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Coal Mine Gas (CMG), also known as colliery gas, It is associated gas of coal mining. Coal mine gas is released from seams of coal during mining activities. We distinguish between four kinds of coal mine gas:
1. Coalbed Methane (CBM), that is, Methane exhausted from unexplored coal beds, refers to hydrocarbon gases stored in coal seams which is mainly composed of methane, and adsorbed on the surface of coal matrix particles, and partially free in coal pore or dissolved in coal seam water. It is associated gas of coal mining and belongs to unconventional natural gas. The calorific value of one cubic meter pure coalbed methane is equivalent to 1.13 kg gasoline or 1.21 kg standard coal. The methane (CH4) content of surface pumped CBM is generally greater than 95%. When the methane content is 97.8%, the low calorific value is 34.5964 MJ/Nm3 (about 8263 kcal/Nm3) and the high calorific value 38.9311 MJ/Nm3 (about 9299 kcal/Nm3) at 0 ℃ and 101.325 kPa. Its calorific value is equal to that of natural gas. It can be mixed with natural gas and is an ideal fuel for power generation.
2. Coal Mine Methane (CMM), Methane coming from active underground mining. The calorific value of Coal mine gas is related to methane (CH4) content. Generally, methane (CH4) content is adjusted to 30% or below before being utilized in underground gas extraction, At 0 ℃ and 101.325 kPa, the low calorific value is 14.63 MJ/m3 (about 3494 kcal/Nm3) and the high calorific value 16.24 MJ/m3 (about 3878 kcal/Nm3). Therefore, coal mine gas is divided into high concentration gas and low concentration one, and there are differences in the selection of power generation equipment compared to CBM;
3. Abandoned Mine Methane (AMM), Methane exhausted from abandoned mines;
4. Lean gas, Only lean gas cannot be used for energy generation, because of the low methane content of 0.2 – 1.5%.
The commonly used coal mine gas refers to Class 2 and Class 3 gases, namely CMM and AMM. Due to the high methane content of 30 to 95 %, especially CBM, CMM and AMM are suitabl the utilization e forin gas engines, and is an ideal fuel for power generation.
Mine gas contains high concentration gas and low concentration gas. High concentration gas refers to gas whose methane concentration is more than 30%, and low concentration gas refers to gas whose mathane concentration is less than 30%. More than 60% of the colliery gas in China is low concentration gas containing less than 30% methane. According to the requirements of coal mine safety regulations, the colliery gas whose methane concentration is below 25% can not be stored and transported. Our company adopts water mist conveying system for low concentration colliery gas, which has multi-level fire protection transportation, with explosion venting, explosion suppression and explosion-proof protection to ensure safety conveying of low concentration colliery gas. It is suitable for generating electricity from coalbed methane with methane concentration above 8%.
Gas requirement of Coal Mine Gas：
● Methane content (Volume) ≥ 8%; Methane concentration change rate ≤ 2 %/min.
● Methane and oxygen ≥ 26%; Oxygen (Volume) ≥ 16%.
● Gas temperature ≤ 40℃; Gas pressure 2.5～10 kPa; Pressure change rate ≤ 1 kPa/min.
● Moisture content ≤ 40 g/Nm³, no free water.
● Impurity content ≤ 30 mg/Nm³; Impurity size ≤ 5 μm.
● Sulfur content ≤ 100 mg/Nm³.
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