Speaking at the National CSM-CMM summit in Brisbane last week SaarEnergie managing director Peter Fuchs said the company has been involved with mine gas extraction since 1948. This was the first time in Germany mine gas released during coal mining was systematically exhausted directly at its point of escape.
SaarEnergie specialises in extracting, exhausting and compressing gas released during mining. It operates a total of 12 coal mine methane (CMM) facilities and in 2001 extracted 372 million m3 of mine gas with an average CH4 content of 47%. Average annual CMM extraction for the next ten years has been calculated at 285 million m3 (allowing for 50% CH4).
Historically the group operated in the Saarland but the increasing depths of current coal reserves - at depths of around 1,750m – means that mining in the area will continue declining in the next few years.
Fuchs said there were considerable fluctuations in the CH4 content of the extractable gas across the entire extraction area, ranging from 30% to 90%.
The primary method of extract gas is through boreholes drilled through the roof into the secondary rock of the coal seam. The boreholes are then sealed, cased and connected to an exhaustion line.
SaarEnergie believes that quantities of mine gas will decrease only slightly across its CMM projects, even following mine closures. The greatest unknown factor is how quickly water levels in a mine will rise and block the degassing process of the coal after drainage is stopped.
Attempts to degas prospective mining areas in advance using coal seam methane methods, have not been successful. The quality of the extractable gas was satisfactory but the quantity was not, attributed to the low porosity and permeability of the Saar deposit.
CMM was given a major boost in 2000 with the introduction of the “Renewable Energy Law,” setting down guaranteed minimum prices for energy generated from regenerative sources of energy. The utilisation of CMM for electricity generation was promoted along with other sources such as geothermal, biomass, etc.
In Australia, CMM development has become a growing area of concern to Australian underground coal mining operations, driven by a range of issues including making mining safer and mitigation of greenhouse gases. About 320 kilometres of in-seam drilling is conducted annually in Australian coal mines with around 200 million cubic metres of CH4 drained, much of which is vented to the atmosphere.
