Recent research has highlighted the possibility of burying, or sequestering carbon dioxide in deep, disused coal mines. Not only might this allow us to reduce atmospheric carbon dioxide levels but the process would displace usable methane (natural gas) from the coal and extend the length of time we will have this resource available to us as a fuel and chemical feedstock.
However, I felt that the while the concept sounds viable initially, there are several loopholes in the whole carbon burial argument, especially when releasing methane is also brought into the equation. I asked team leader Thomas Brown of the US Department of Energy’s National Energy Technology Laboratory about my concerns.
First the whole process will require its own energy supply, which will in turn release CO2, as well as being expensive to undertake in practice. Moreover, most of the methane retrieved in this way will end up being burned as fossil fuel and adding still further to the global carbon footprint.
“You are correct,” Brown told me, “Cost projections for CO2 sequestration indicate it will be expensive and a great deal of research is currently underway to bring these costs down.” He points out the methane release process is quite encouraging because for every 2-4 units, or moles, of CO2 trapped, just one unit of methane is released.
“This suggests that [the process] has the potential to be more cost effective than the [alternative approach] of sequestration in deep saline aquifers,” Brown adds.
The coal bed methane will certainly be useful nevertheless and Brown points out that CO2 released by burning it will in turn have CO2 capture systems in place. “It is an additional energy source that can be utilized instead of venting it from coal seams to the atmosphere,” he says, “it also provides some offset for the cost of sequestering CO2 – methane is much more detrimental to the environment as a greenhouse gas than CO2.”
He adds that sequestration in coal seams my not be a viable option owing to low permeability values and swelling of the coal itself, which he discusses in his research paper. “More R&D is required,” he told me.