The clean coal revolution
Clean coal: a non-renewable solution to the energy crisis?
The UK is facing a carbon paradox. As the Government strives to cut carbon dioxide emissions by 60% by 2050, the demand for energy is increasing and so too is our dependence on carbon dioxide-producing power stations.
Over the next 20 years, almost all our existing nuclear power stations and most coal-fired power stations will close as they reach the end of their operating lives. Then, the UK will have to rely on imported energy such as gas and oil, often from politically unstable countries. To reduce our reliance on imports, the Government has invested in renewable energy sources such as wind power, which promise cleaner energy without the carbon emissions.
Wind farms are high on the Government’s agenda. Controversial wind turbines have sprung up across Britain’s countryside and there are plans for a further 2,000 by 2010 at a total cost of around £9bn. Despite being ‘green’, wind turbines have met with considerable resistance. Opponents argue they are ruining some of Britain’s best-loved landscapes and are an unreliable source of energy.
One such critic, David Anderson, who chairs the energy board at the Institution of Civil Engineers, refutes the claim that wind power will reduce greenhouse gas emissions. He calculates that turbines could only reduce Britain’s greenhouse gas emissions by a maximum of 5%.
There are alternatives: another solution to curb emissions and maintain a reliable energy supply would be to clean up the act of the well-established coal derived energy.
Coal-fuelled power stations currently supply 30% of the UK’s electricity. Equally, they are responsible for releasing over a third of the total carbon dioxide produced in Britain. Coal is easy to store and transport, and is accessible from diverse suppliers both here and abroad. Loads in coal-fired stations can also be varied easily, so coal-fired generation is particularly useful in meeting peak demand or covering for supply intermittencies in other fuels. Developing cleaner coal that releases less carbon dioxide would therefore have huge benefits.
Various clean coal technologies already exist and aim to use coal in an environmentally friendly and economic way. Clean coal can be achieved either by targeting the pollutants that result from burning coal, or by developing more thermally efficient systems so that less coal generates the same power. There are also improved techniques for gas cleaning, effluent treatment and residue use or disposal.
A new possibility is the development of ultra-clean coal. “Ultra-clean coal is seen as something of a Holy Grail in energy generation,” said Dr Karen Steel of the School of Chemical Environmental and Mining Engineering, University of Nottingham. “It is a very efficient way of producing electricity and it is also much less harmful for the environment.” Her team have just been awarded £120,000 to help them kick start the development of ultra-clean coal which they believe could make power generation 50% more efficient and reduce carbon dioxide release by a third.
Mined coal contains about 15% mineral matter including sulphates, oxides, clays, quartz and carbonates, which restrict its use. By definition, ultra clean coals are coals with less than 1% ash and from which naturally occurring minerals have been removed by chemical cleaning.
CSIRO (the Commonwealth Scientific and Industrial Research Organisation) in Australia is the only other organisation looking into the manufacture of ultra-clean coal. They have invested $15m into a pilot-scale ultra-clean coal operation that has already yielded positive results demonstrating a reduction in greenhouse gas emissions.
The ultra-clean coal process developed by CSIRO utilises alkali/acid digestion to dissolve the minerals out of the coal under moderate temperature and pressure conditions, without the loss of coal’s properties. The dissolved minerals are then precipitated as gypsum and aluminium silicates, which are used in the building and ceramics industries, while the alkalis are regenerated for reuse.
Dr Steel and her team are hoping to develop a similar chemical leaching process that has the potential to reduce the mineral content of coal to less than 0.1%. This ensures a much greater efficiency per tonne of coal and up to a third less carbon dioxide pollution.
Most conventional coal-fired power stations burn coal to produce steam, which turns turbines linked to a generator. This process is only around 37% efficient, which means just over a third of the energy potential of the coal is converted into electricity. Unlike normal coal, ultra-clean coal can be burnt directly in gas turbines. Gas turbines are similar to aircraft jet engines and are a muchmore efficient way of using coal to make electricity – but normal coal cannot be used in them because their impurities damage the turbine blades. Ultra-clean coal is therefore around 50% more efficient than normal coal.
Commenting on the cost of implementing this new technology, Dr Steel said: “There has been an assumption that it would be too expensive to produce ultra-clean coal. But our aim is to do it cheap, so the coal will sell at about the usual price.”
Ultra-clean coal could also help reduce the world’s dependence on oil, according to Dr Steel. There are greater untapped reserves of coal, and they are generally located away from the politically turbulent Middle East. For example, China and the USA both have large reserves of coal, but not much oil. Coal will also remain the dominant generating fuel in large parts of the developing world such as China and India for many years to come. This could be beneficial for UK industry, which could develop business initiatives to promote and install cleaner coal technologies in developing countries.
Ultra-clean coal also will be up against nuclear power. The zero carbon emissions associated with nuclear plants are proving tempting for the re-elected government. But nuclear power stations tend to generate electricity at the same rate all the time. This would provide a baseline rate of power, but would be too inflexible to deal with sharp fluctuations in consumer demand. The age-old problem of storing radioactive waste has also yet to be solved.
Every method of energy production has its pitfalls. The only way the country can keep up with the increasing energy demand is to ensure diversity in energy production, some renewable, some not. Although people were quick to reject fossil fuels as dirty fuels in favour of greener more renewable sources, ultra-clean coal could ensure that coal is back in the game.
