The coal industry is one of the most significant contributors to greenhouse gas (GHG) emissions to the atmosphere. Combustion of coal is а major source of carbon dioxide (CO2) being emitted worldwide. Moreover, in the process of coal production another important greenhouse gas, methane (CH4), is being released.
Methane and coal are formed together during coalification, а process in which plant biomass is converted by biological and geological forces into coal. Methane is stored in coal seams and the surrounding strata and released during coal mining. Deeper coal seams contain much larger amounts of methane than shallow seams. Small amounts of methane are also released during the processing, transport, and storage of coal.
The volume of methane contribution to the total GHG emissions is three times smaller than that of carbon dioxide. At the same time, methane is а particularly strong GHG, its greenhouse potential is 21 times higher than that of CO2.
Over the last two centuries, methane concentrations in the atmosphere have more than doubled, largely due to human-related activities, including rice production, waste disposal, cattle ranching, large scale extraction and transportation of oil and natural gas, and mining.
Methane emissions in mining come from:
- Natural ventilation (cracks in coal layers and adjoining rocks)
- Coal mine emissions
- Underground mines
- Ventilation (methane: 0.2-1%)
- Vertical wells of surface degasification in advance of mining (CH4 concentration 80-98%)
- Gob-wells from the surface (CH4 concentration 20-60%)
- Horizontal and cross-measure boreholes of underground degasification (CH4 concentration 20-60%)
- Surface coal mining
- Coal enrichment, transportation and usage
Methane recovery from coal seams provides а number of benefits. The frequent accidents occurring in Ukrainian mines are largely caused by the explosion of coal mine methane, which accumulates in the mining process. This methane can be recovered and sold. Methane recovered from the mining sites will not only significantly reduce greenhouse gas emissions, but could also be а substitute for fuel, which is currently being imported from outside Ukraine.
Methane emissions from coal mines can be reduced by recovering and using methane from underground mines and by oxidating of methane from ventilation air. Recent technologies make both ways easily feasible. Methane recovery technologies include vertical wells drilled from the surface or boreholes drilled from inside of the mines. Depending on gas quality, methane recovered from underground mines may be sold to natural gas companies, used to generate electricity, used on-site as fuel for drying coal, or sold to nearby industrial or commercial facilities.
The oxidization of coal mine ventilation air produces heat that can be used directly on-site or to produce electricity. Coal mines in the U.s. do not currently use the oxidization technology, but it has been successfully demonstrated in Great Britain.
How is coal bed methane being used in Ukraine?
- Mine boilers switching from coal to gas:
8 mines of the Donbass region are currently using recovered methane for supporting their operating activities
- Motor fuel
The number of gas-fill stations is increasing (Coal mine Zasiadko Donugoldegazatsiya)
- Cleaning of recovered substances and methane supply to natural gas pipelines
- Electricity generation (diesel generators, gas turbines, internal-combustion engines )
- Supporting mine operations
- Sales to the power grid
- Technological raw materials (metallurgy, fertilizers, methanol)
- Communal needs (heat and electricity) of adjacent territories
Currently, the recovered methane in Donbass is mainly used in mine boilers to produce heat, which is not the most efficient method of methane utilization. The most efficient application of the recovered coal mine methane is thought to be in the form of motor fuel for gas-turbine or gas-diesel motors. Mine boilers today consume about 200 million cubic meters of gas for heating per year, which is about one-third of the total methane that is being burnt in torches. At the current rate of methane recovery, the daily volume equals 1600-1700 thousand cubic meters, which could all together replace up to 260 Mwt of energy or 240 Gkal/h of heat generation.
For the period of 2005-2008 coal bed methane recovery is expected to increase up to 3-4 billion cubic meters а year and further double within each 5 years, reaching 12-16 billion cubic meters per year after 2010-2015. According to feasibility studies performed by UkrNIIgas research and development institute for Donetskvugillia and Makeyevvugillia associations, the rate of return of investment into the methane recovery and utilization projects is 1.3 and 1.1 years, respectively. Methane emissions reduction of underground coal mining and associated activities can be further improved by the preliminary degasification of coal steams of newly constructed or renovated mines.