Can ‘clean coal’ save the world?

What is clean coal?
An oxymoron... for now. Coal is still what it always was: cheap and dirty. The most carbon-intensive fossil fuel, it accounts for nearly 40 per cent of the world's CO2 emissions, yet its use is rising, not falling. Coal-fired power stations provide 41 per cent of the world's elec-tricity, a proportion forecast to rise to 44 per cent by 2030. With the huge increase in energy demand, the amount of electricity generated from coal in that same period is expected to rise 23 per cent in the US, 172 per cent in China and 258 per cent in India. If coal stays dirty, its CO2 emissions will almost quadruple. That's why 'clean coal' technology is being so urgently embraced by governments around the world.

What does that technology involve?
A process called 'carbon capture and storage', or CCS, under which a power plant's CO2 emissions are chemically diverted (or 'scrubbed') before they have a chance to escape into the atmosphere, then stored as a liquid, out of harm's way. That, in theory, would reduce the quantity of CO2 emitted by as much 90 per cent. But in practice that presupposes the solving of a huge problem associated with CCS - where to store all those emissions.

What are the storage options being considered?
The two main contenders are injecting CO2 into depleted oil and gas fields or burying it in saline aquifers - porous rocks full of salty water - deep below the surface. But whatever solutions are chosen, the scale of the storage problem is daunting. One estimate says that by 2030 the US alone would have to drill more than 100,000 wells, perhaps as many as 300,000, to keep its CO2 emissions at 2005 levels. And there are still questions about how stable the CO2 would be underground. Any leakage - and green groups say that the gas would have to remain sealed forever - would defeat the whole purpose of storage.

But is the process of CCS technically feasible?
Very much so. Each of the various stages has been successfully tried, just never put together. Energy companies have been transporting and pumping liquefied CO2 into oil and gas fields for decades to help flush out precious fossil fuels. Norway's state oil company, meanwhile, has been storing CO2 in deep, off-shore aquifers since 1996. And the key bit of the process - 'scrubbing' emissions from power stations - has been operating at the world's first CCS demonstration plant in Germany since last September. "There do not appear to be unresolvable open technical issues," was the conclusion of a major study on the future of coal by the Massachusetts Institute of Technology in 2007. The big issues are time and cost: even proponents of CCS don't expect