Fluid solutions

A process using solvents to strip away minerals from coal to remove impurities could lead to more efficient power stations, according to researchers at Nottingham University.

The most efficient way to use any fossil fuel in a power station is the combined cycle firing system, where the hot gases from burning the fuel are used to drive a turbine, then to raise steam which drives a second turbine. Most new gas-fired stations use this mechanism. However, worries about the availability and price of gas are leading energy researchers to look at ways of adapting the technique for fuels such as coal.

Large reserves are still available, but coal-fired stations are far less efficient than gas-fired ones and, as Nottingham researcher Karen Steel explained, coal can't currently be used for combined-cycle generation.

Even if it is gasified, she said, it contains mineral impurities, such as silica and sulphur, which survive the gasification process. When the gas is burned, these minerals can remain in the combustion gas stream as abrasive particles, or are converted into acidic gases. Both of these cause damage to the turbine blades as the gases pass through.