There's no reason why clean coal should not be used for energy. It is not the best solution, nor is it a truly sustainable solution over the long-term, but there is no reason to not use what we've got while we're developing more sustainable technologies.

Coal cannot be used as a source of energy as coal is not in plenty and extracting coal is a bot of a costly affair which will raise the costprice of coal .. And dependance of coal is risky as it is going to be perished fast.