UK researchers claim to be the first in the world to cut the level of harmful minerals in all types of coal by a factor of more than 100.
The development, carried out at the University of Nottingham, could allow clean coal production techniques to be introduced that halve carbon dioxide emissions.
Fears over the future supply of natural gas have renewed interest in making coal-fired power stations more efficient.
Existing power stations burn coal to generate steam, which is in turn used to power turbines. If this steam stage could be removed, and the combustion gases from burning coal used directly to drive the turbines, the CO2 produced for the amount of coal burnt could be reduced by 30–50 per cent.
However, this has so far not been possible as the minerals released from the burning coal would destroy the turbine blades. So the researchers have developed a method to leach these harmful minerals from the coal before using it to directly power the turbines.
Although a rival team of researchers in Australia has also developed a technique to cut the level of minerals in coal, Nottingham’s process results in both less mineral matter and less CO2 when the coal is burned, according to the technique’s developer Dr Karen Steel, a lecturer at the Nottingham Fuel and Energy Centre.
Steel said the process produces cleaner coal than the Australian technique because it uses hydrofluoric acid rather than sodium hydroxide to leach the minerals out of the coal. ‘We looked at the CO2 balance [of the Australian technique] and I just thought, “No way”. The fact that you are producing this CO2 has to be offset against the efficiency gains.’ she said.
However, while Steel’s process is cleaner than existing technology, it would still be unusable unless the leaching agent is recycled. Hydrofluoric acid is so dangerous that power generators would be banned from owning sufficient acid to operate a power station. And, as Steel pointed out, the fluoride waste can no longer be disposed of because of effects on the environment.
In the Nottingham process, once the harmful minerals, including silica, have been extracted from the coal the hydrofluoric acid remains and can be re-used.
By removing the need to heat water into steam, Steel’s process could work in much smaller power stations. It could also be used all over the world because HF can clean any type of coal, while the Australian leaching agent only works with lignite.