Coal is a plentiful and relatively cheap source of fuel, which is why it is used to generate about 40 per cent of the world’s electricity, compared with about 10 per cent each for gas and nuclear.
But it is also dirty, producing both carbon dioxide and sulphur dioxide, contributing to global warming and acid rain.
The challenge facing governments and energy companies today is how to keep burning coal while reining in its environmental impact. In the European Union, companies now have to pay for the carbon dioxide they produce through the Emissions Trading Scheme. Although carbon prices have dropped from their peak of about €30 a tonne in April to the current price of approximately €13 a tonne, there is still a financial incentive for energy companies to emit less carbon.
This has led to a growing interest in the field of “clean coal” technology. From power station boilers with improved efficiency to processes for catching and storing carbon dioxide emissions, there are several projects around the world developing clean coal technology.
In the UK, coal accounts for 33 per cent of generation capacity, and is especially important in meeting peaks of demand in the winter. But many of the plants are ageing and relatively dirty, and will close over the next decade. The UK government has said it would like coal to remain as part of the country’s energy mix, however, and is encouraging research into clean coal technology.
Earlier this month, Eon of Germany announced that it was looking at spending at least £1bn on building two new 800 Megawatt coal-fired plants at its Kingsnorth site in Kent. If the project goes ahead, the plants would be the first new coal-fired capacity to be built in the UK for many years, and would be fitted with more efficient “super-critical” boilers which should reduce the plants’ carbon dioxide emissions. Instead of getting about 36 per cent of the energy from the coal, as in existing coal boilers, the super-critical boilers would be 45 per cent efficient, says Eon. This would reduce Eon’s carbon emissions by up to 1.8m tonnes a year.
There are already four coal-fired units owned by Eon at Kingsnorth, but these will close down by 2015 in line with the European Union’s Large Plant Combustion Directive. This directive is designed to crack down on sulphur dioxide emissions, and comes into force in 2008.
After this, coal-fired plants that have not fitted equipment to clean up the power stations’ emissions – known as flue gas desulphurisation technology (FGD) – will be forced to close after 20,000 hours of operation or by the end of 2015, whichever is soonest.
Several UK energy companies have fitted FGD equipment to their coal-fired plants, such as International Power at its Rugely plant and Npower at Aberthaw, but others have decided it is not worth making such an investment in ageing plants, and will let them close. Eon says it prefers to invest in new power projects rather than “retro-fitting” old plants, hence the planned investment at Kingsnorth. If Eon succeeds in getting planning permission for the two new units, they will replace the four existing units. “It will be a straight swap, with the same output,” says an Eon spokesman.
Coal can also be burnt more efficiently in plants using a so-called integrated gasification combined cycle. Coal is converted into gas and used to drive a turbine producing electricity, then burned to heat water and drive a separate steam turbine, also producing electricity, so less energy is wasted. RWE of Germany has been investigating this technology.
Beyond fitting more efficient boilers and FGD equipment to remove sulphur, the next step in clean coal technology is to build power plants that do not allow emissions to escape into the atmosphere. Several energy companies are looking at plans for ‘carbon capture’ plants, where the carbon dioxide produced from burning coal (or gas) is tapped and turned into a liquid. It can then be stored, for instance in depleted gas fields or oil wells, in a process known as “carbon sequestration”.
This technology is expensive and relatively untested. Carbon sequestration has yet to be approved by safety authorities around the world, and is therefore illegal. Analysts estimate that carbon capture plants are at least 10 years away in the UK, putting them in the same time frame as the construction of new nuclear plants.
One of the first of these projects could be built by RWE. In April the group said it planned to build a pioneering £800m carbon capture plant at Tilbury on the Thames estuary, to open in 2016.
Meanwhile Eon is studying options for its own advanced clean-coal power station in Lincolnshire.
RWE says it is looking at two possible technologies to make it easier to capture carbon dioxide.
One is oxyfuel combustion, whereby pulverised coal is burned in pure oxygen, producing a much more pure stream of carbon dioxide that can be more easily compressed to a liquid to be pumped underground.
In the second, coal is burned in air, then the gases are passed through water containing dissolved amine compounds, which absorb carbon dioxide. The process can be reversed by heating the solution, releasing the carbon dioxide for storage.
As with many renewable energy technologies, energy companies are weighing up whether clean-coal plants will prove competitive with other forms of energy generation. According to Lueder Schumacher, a utilities analyst at investment bank Dresdner Kleinwort, clean coal technology is economically viable at current coal and electricity prices.
“However, the technology is still at an early stage as far as large-scale projects are concerned and there are legal problems with the storage of the carbon. Nevertheless, in our view, clean coal is set to take over as the new entrant fuel of choice, provided expectations of the oil price remain above $60 a barrel.”