Research for future in situ conversion of coal

In situ coal conversion in seams of great depth is very important for future energy supply, because resources in deep seams greatly exceed mineable coal reserves. Research should cover all possible coal conversion techniques and has to be based on coal properties and conditions prevailing in seams of great depth. Proceeding on coal properties such as permeability, which is dependent on depth, and reactivity, which is dependent on rank, an assessment of coal conversion reactions is made regarding in situ conversion, and steps of research for developing alternative in situ conversion processes are outlined. Evaluating recent results of coal research reveals some signs that microbiological techniques could have significance for future in situ conversion of coal into methane. Although there are still difficulties in treating coal by microbiological techniques, the progress of recent research is considerable. Microorganisms have been found that develop on coal as sole carbon source, pyritic and organic sulphur can be removed by biochemical techniques, and microorganisms are able to grow, in principle, in narrow pore systems of solids. Also the conversion of aromatics is possible. Steps of microbiological research are outlined beginning with laboratory investigations of model substances and finely ground coal particles, progressing to experiments in large lumps and in field tests.