Ultra-clean coal – could the price now be right to help fight climate change?

A new chemical process for removing unwanted minerals from coal could lead to reductions in carbon dioxide emissions from coal-fired power stations.

There is already a way of burning coal in a cleaner, more efficient fashion that would reduce carbon dioxide emissions: this is where the coal is turned into a gas and used to drive a turbine. However, problems with cleaning the coal before it is burnt have made generating electricity in this way very expensive. This new chemical process could make it more commercially viable.

Under development by a University of Nottingham team with EPSRC funding, the new approach involves using chemicals to dissolve unwanted minerals in the coal and then regenerating the chemicals again for re-use. This avoids the expense of using fresh chemicals each time, as well as the need to dispose of them, which can have an environmental impact. By removing unwanted minerals before the coal enters the power plant the new process helps protect the turbines from corrosive particles.

The aim is to cut unwanted minerals in coal from around 10% to below 0.05%, making the coal ‘ultra clean’. Removing these minerals before using the coal to generate power prevents the formation of harmful particles during electricity production. To do this, the team is using specific chemicals to react with the minerals to form soluble products which can be separated from the coal by filtration. This process is known as ‘leaching’. Hydrofluoric acid is the main chemical being tested. The chemicals not only dissolve the minerals but are also easy to regenerate from the reaction products, so they are constantly recycled. It is this aspect that has largely been overlooked in past research, but is virtually essential if chemical coal-cleaning is to be environmentally and commercially viable.

Dr Karen Steel of the School of Chemical, Environmental and Mining Engineering is leading the project. “A lot of research took place in the 1970s and 1980s to see if coal-cleaning was viable,” she says. “The conclusion was that it was too expensive. With the environment high on the global agenda and coal certain to remain a key energy source for decades, it makes sense to see if the perception is still justified today.”

If it proves technically viable and economically competitive, the new process could help ensure that world coal reserves are harnessed with less impact on climate change.

(As part of National Science Week, EPSRC – the Engineering and Physical Sciences Research Council – is highlighting pioneering energy research to assist global efforts to combat climate change.)