Clean air action

Clean coal technology is likely to be a vital part of power generation at home and abroad. But government support is vital, as Mike Farley of Mitsui Babcock tells Stuart Nathan.

The UK energy industry is facing difficult times. Large power stations face imminent closures with no clear policies for their replacement, the nuclear vs renewables and fossil fuels argument is still raging, and gas prices seem to be defying gravity.

According to Mike Farley, director of technology policy utilisation at generating plant specialist Mitsui Babcock (MB), the situation is, if anything, more urgent than it appears.

‘The estimations of how much plant will be needed by the end of 2015 have been underestimated,’ he said. That date is important, he explained, because by then, eight gigawatts of UK generating capacity will have disappeared because of decommissioning of nuclear plants, and the closures of the coal-fired plants that have opted out of the EU’s Large Combustion Plant Directive. ‘If you add those together with projected growth in energy demand, you can get from 18-29GW of plant needed by the end of 2015.’

This tight deadline virtually dictates what kind of generating capacity will be needed, said Farley. ‘It can’t all be renewables — we know that for certain. It can’t be nuclear, because according to the industry the next-generation reactor technology is at least 10 years away.

‘It could conceivably be gas, but only if we increase the proportion of gas-fired generation in the mix from 39 up to 59 per cent, which is very unlikely. So that leaves coal. And if it’s going to be coal, we need to make sure it’s much cleaner coal than has been in the past.’

Coal also has advantages for security of supply. ‘In retrospect, the Dash For Gas policy [in the 1980s and 90s] has to be seen as the wrong thing to do,’ he said. ‘From a sustainability point of view, it’s got to be a concern that so much gas is being burned for power over and above heating; and on a similar basis, the world enery outlook says that at current usage rates we’ve got 66 years of gas and more than 200 years of coal.

‘If you look at future projections of usage rates, there’s a great danger that the 66 years will become 33.’ Increasing coal-fired generation will lead to more coal imports, ‘but half the coal we use at the moment comes from the UK, which is pretty high compared with the proportion of UK gas, and the half that’s imported comes from diverse sources including very stable countries like Australia.’

It is this conclusion that has led MB to focus on clean coal technology in its latest energy review, produced last month. ‘Clean coal technology is the only short-term solution to environmental, economic and security of supply challenges with a vital role as a long-term solution within a diverse energy portfolio,’ the review states. However, Farley warned, the only way for the technology to be in place in time to meet demand and replace lost capacity is for the government to push its development, through a programme of investment, subsidies and legislation.

There are two aspects to clean coal technology, Farley explained. The first is ensuring that the plants themselves are as efficient as possible, producing the greatest amount of power from the smallest amount of coal, and therefore the lowest emissions of carbon dioxide.

The second, and where the technology will ultimately lead, is through carbon capture and storage, effectively eliminating the emission of CO2 to the atmosphere altogether. This, he believes, is likely to be some decades off. but with power stations generally designed to last about 50 years, the new capacity must be built so that it is ‘capture ready’. even this still requires some technology development. ‘We think that until about 2012, or even right up to 2015, there will be a series of demonstrations of capture technologies and storage options, but they won’t be in time for the plants that need to be built by 2015,’ he said.

For efficiency, Farley believes that the best option for the UK‘s timescale needs is plants using both supercritical boilers and turbines, which operate at higher temperatures and pressures than the previous generation of coal-fired plant. ‘Advanced supercritical offers 42 percent efficiency under UK conditions, which will give around a 20 per cent reduction in CO2 emissions over current plant,’ he said.

MB’s advanced supercritical technology uses a vertical tube boiler design known as Posiflow, with furnace walls made from small-bore ribbed tubes to improve the efficiency of heat transfer. Moreover, these boilers can be adapted for firing with up to 20 per cent biomass in the fuel mixture. ‘With that, you’d have about a 40 per cent reduction in CO2 emissions, and you’d be getting down to levels that are a few per cent higher than gas-fired plants.’

Farley said these boilers could be retrofitted to existing power stations. ‘We could take almost any of the coal-fired UK power plants and replace the boilers, turbines and pipework to provide and use higher temperature and pressure steam — thus achieving that improved efficiency. We’re absolutely confident that we can do it, but there is a technical risk and there are certainly project risks in retrofit that are different from those you would encounter in building a new plant.’

Advanced supercritical is only one option for improving the efficiency of coal-fired plant. in the US, for example, the main thrust of research is into coal gasification so that it can be used to fire integrated gas combined cycle (IGCC) systems. These use the hot flue gases from fuel combustion to operate one set of turbines, then use the residual heat in the gases to raise steam for a second set.

Although these are theoretically more efficient than advanced supercritical, Farley believes that they are ‘an option for the future’ rather than a practical solution to the immediate problem. ‘Until a number of gasification plants have been built and shown themselves to be economical and reliable, we don’t see a large proportion of this as new build or replacement. The plants that have been built aren’t economic or reliable, and they take a long time to build and commission.’

There are also competing technologies for carbon capture, but in this case MB is involved in the development of both. The options, Farley explained, are oxyfuel firing, where the furnace is fed by pure oxygen rather than air, making the CO2 much easier to separate from the flue gas; and amine scrubbing, where the CO2 is captured by passing the gas through an amine solution, converting it to an amide from where it can be recovered chemically.

‘All our attempts to differentiate between the two at the moment lead to similar capital and running costs, and it’s going to be some time before we see what emerges as the best option,’ said Farley. ‘I think that both will end up being used for some considerable time — a bit like the Betamax and VHS battle.’

Farley is particularly keen to have new technology up and running, in part because this will help considerably with export efforts. ‘We sell coal-fired plants in China, and we’re seeing an enormous number being built — not just ours but other people’s as well. And the Chinese always look to see whether you’re using the technology you’re selling in your home market. With that in place, we’re very confident that we could build these plants there.’

However, Farley warns, government action is vital. The government has earmarked £35m to support demonstration projects for low-carbon power generation, he said, ‘but that’s relatively modest. You’ve got to compare that with the US, which is spending billions of dollars in that area.

‘We’re not saying we need to spend billions, but somewhere more in the hundreds of millions is needed.’ Moreover, he said, there is still a great deal of confusion over the emissions trading system. ‘At the moment, if you invested in a lower CO2 plant, you don’t know that in a few years, your allocation will be reduced and you’d cease to have any benefit from the investment.

‘We’re arguing that new plant or refurbished meeting best available technology standard should have an allowance that lets it have a high load factor for an extended period so it can recover its investment costs. That rule has been applied in Germany, where it is a success.’