We hear a lot about the threat of climate change, but could we ever do without coal? Last year the world burned 5.3 billion tons of it, representing an 8.8% increase over the previous year and 92% growth over the past 25 years.

Coal is vital – not just to economic growth but for keeping the lights on and people warm. There is growing interest in technologies that might make coal, along with gas and oil, into a green fuel. Here we look at how some of them might work.

Carbon sequestration

Carbon capture and storage (CCS) is the great white hope of the fossil fuel industries. If it can be made to work economically then, in theory, we could continue burning carbon-based fuels such as coal and gas without accelerating global warming.

In principle CCS is simple. First, CO2 is separated from its sources, such as flue gases, then it’s transported away from where it was generated and finally buried away from the atmosphere, ideally for millions of years. In practice, each of those stages has problems – and underlying them is the issue of how much energy they cost. There is little point in generating carbon-free power if a large chunk of it goes into extracting and pumping to its final resting place. CO2 Robin Irons, who works for E.ON Engineering, the energy company, is tackling such issues. A chemical engineer, he is applying his skills to try to minimise the energy losses of 10%-40% that can result when a traditionally fuelled power station has to deal with its own pollution.

The focus of CCS is going to be on new or refurbished stations. E.ON has planning permission to build a coal-fired plant at Kingsnorth, Kent, one of a generation that will be made ready for carbon capture – although the kit to do this will be fitted only once government policy has become clear, and the final decision to approve the project lies with the Department for Business, Enterprise and Regulatory Reform.

Irons, 45, took a degree and PhD at Imperial College London, following which he worked in engineering and research departments providing technical support to coal-fired power stations. He found his role changing as the construction of a new generation of cleaner power stations began to loom large. “We’re having to consider building large chemical plants to strip CO2 from flue gases, and that’s a new departure for the industry,” says Irons.

Six of Britain’s coal-fired power stations are getting upgrades that will lift their efficiency and make them ready for fitting with carbon capture technology. Elsewhere, progress is slow. Last spring Progressive Energy, a venture involving Centrica, owner of British Gas, announced plans to build the first CCS power station in Britain. The coal-fired plant, to be built on Teesside, needed government support to get off the ground. But six months later the government published its technical requirements for supporting such projects, which excluded the approach planned by Progressive. “It was a great disappointment and now it looks as if the project will never happen,” says a Centrica spokesman.

There are other problems. Designing and building sequestration plants on the scale needed would require huge investment. And sequestration is useful only on large combustion plants and would never be viable for cars, homes or businesses – the source of about 70% of emissions.

Coal gasification

In gasification, coal is heated in the presence of steam and a restricted amount of oxygen. This means that, rather than burning, the coal breaks down, producing “syngas”, containing mainly hydrogen plus some carbon monoxide. This can then be burned in a gas turbine to make electricity.

The system can be made more efficient by capturing waste heat from the gas turbine to drive a steam turbine. This can push efficiency levels well over 50% – comparable with gas. The CO2 emerges as a concentrated gas stream, making it easier to capture and sequester underground. Other pollutants are easily removed.

That’s the theory – and interest in it is growing. A recent report by the former Department of Trade and Industry says: “UK coal resources suitable for deep-seam gasification on land are estimated at 17 billion tons (300 years’ supply at current consumption) and this excludes at least a similar tonnage where the coal is unverifiable. The largest areas are in Yorkshire, Lincolnshire, the Dee area and Warwickshire, with smaller deposits in central Scotland and south Wales.”

There are two basic ways of gasifying coal. One is to dig it up, take it to the surface and treat it in combustion chambers. Adapting to this technique would be within the abilities of Britain’s power utilities. The other is to burn the coal underground by pumping oxygen and steam into a seam, igniting it and then capturing the resulting gases. This would require precision drilling but we have the relevant skills thanks to the North Sea oil and gas industry.

The Coal Authority, which oversees the British coal industry, says: “The concept of gasifying coal underground and bringing the energy to the surface as a gas for use in heating or power generation has considerable attraction. Underground coal gasification has the potential to provide a clean source of energy from seams where traditional mining methods are impossible or uneconomical.”

RWE, the German owner of Npower, one of Britain’s leading generators, plans an underground gasification trial plant in Germany. Kevin Akhurst works for RWE Npower, generator of about 10% of Britain’s power, where he oversees the development of renewable and clean energy.

New technologies that extract energy from coal without releasing carbon will be crucial, he believes: “In Britain, our focus is on absorption postcombustion CO2 is stripped technology [where CO2 from flue gases].”

Coal-bed methane

Methane explosions have been the bane of the coal mining industry for centuries. The gas forms, alongside coal, from the decay of organic matter and is released by mining operations, causing a serious hazard.

Even today, when most deep coal mines have closed, the gas is a problem. Reports commissioned by the Department for Environment, Food and Rural Affairs from environmental consultants White Young Green in 2005 found that the UK’s abandoned coal mines emit more than 60,000 tons of methane per year. Since methane is a powerful global warming gas, these emissions are equivalent to approximately 1.4m tons of CO2 Such reserves are proving a valuable resource in their own right, with private sector operators tapping the methane from a number of abandoned coal mines around Britain to generate electricity. There is greater potential in extracting methane from unworked coal deposits – so-called coal-bed methane. There are vast reserves of this gas trapped in the billions of tons of coal still lying under Britain.

Until now it has been too difficult to access but the engineering and drilling techniques perfected in the North Sea for accessing deep deposits of oil and gas are changing that. UK Coal, Britain’s largest producer, with four deep mines, seven surface mines and more than 3,000 employees, has been using both approaches. “We have developed and implemented projects to maximise savings, generate revenue and significantly reduce coal mine greenhouse gas emissions,” it says.

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