Why do coal power stations run by creating steam rather than from the expansion due to combustion?
I understand that in order to generate electricity in a coal power plant, steam is usually produced by burning coal, and using the heat to boil water. The steam then moves through a turbine which generates the electricity. However, in an internal combustion, a similar thing occurs except that the expansion of air due to combustion directly causes movement of the pistons or turbines. So why do coal power stations not bypass the steam generation stage, and generate movement of the turbines directly from the combustion of coal? It seems less inefficient to require this intermediate step.