Down to zero

The constant news stories about wind farm protests and new nuclear power stations are obscuring an important fact — the method of large-scale energy generation will remain much the same in the future. The timescale of industrial investment, the huge expansion of generating capacity in China and India and historical engineering experience mean fossil fuel technology will be a major contributor to power generation well into this century.

‘We know that we’re going to need a mixture of sources, with contributions from everything — new nuclear, renewables and fossil fuels,’ said Colin Snape, director of the Energy Technologies Research Institute (ETRI) at Nottingham University. ‘But that means we’re going to have to make the fossil fuel generation as near to zero-emission as we possibly can. And that’s a huge challenge.’

ETRI is one of the largest centres for energy research in the UK. Pulling together research from physics, chemistry, geography and biosciences and the engineering disciplines, it was formed last year to co-ordinate the university’s research on clean fossil fuel and carbon abatement, energy infrastructure, wind and biomass technologies and hydrogen generation and fuel cells.

Snape has been working in coal technologies since the mid-1970s, when he started work for the Coal Research Establishment of what was then the National Coal Board. His research focused on methods for characterising coal using spectroscopy (the interaction of the molecular components of coal with different types of radiation) and chromatography (separating out the components using liquid and gaseous solvents) and on processes to convert the carbon in coal into compounds useful as fuels and chemical feedstock. After leaving the CRE in 1987, he moved to the University of Strathclyde, then moved his research group to Nottingham in 2000.

Clean coal remains at the heart of Snape’s research and he sees it as an important area for energy researchers. ‘It’s driven by the far east,’ he said. ‘China opens a new power station every couple of weeks and is using pulverised fuel (PF) technology — they’ve got a lot of coal and they’re going to use it. The challenge is to make sure they’re as efficient as possible and to develop effective carbon capture and storage (CCS) technologies to minimise greenhouse gas emissions.’

He describes CCS as ‘inexorably linked’ to large-scale power generation with fossil fuels. There’s a perception that such technologies already exist and can be rolled out but this is not the case, he said.

‘It’s the efficiency that’s important,’ he said. ‘At the moment, we can get 35 per cent efficiency from pure combustion of PF but we need to get it up to around 50 per cent.’

One reason for this is that carbon capture reduces the overall efficiency of the power station. ‘For PF, you’ll take a hit of maybe 10 percentage points and that’s with relatively simple techniques like amine scrubbing, which are really designed for removing pollutants, rather than specifically to remove CO₂.’

The drive for ETRI’s research on CCS is therefore to reduce the cost. Snape notes that 30-40 per cent of coal and gas-fuelled generating capacity in Europe is due to close by 2015 and this will open up a 2GW generating gap in the UK. ‘We’re needing to just find ways of keeping the lights on,’ he said.

On these timescales, the only option for maintaining the necessary capacity is to replace the current fleet of gas-fuelled stations. ‘There isn’t going to be new nuclear by 2020; the political and fiscal framework isn’t there,’ he said. ‘And given that fossil fuels are a part of the energy mix, the continued use of coal and gas will have to be coupled with CCS.’

The goal of the capture part of CCS is to purify the CO₂from the combustion process to remove harmful oxides of sulphur and nitrogen. Among the CCS technologies being investigated at ETRI are pressure-swing adsorption, where the flue gases from the furnaces pass through a porous adsorbent which retains the CO₂; membrane techniques; and a process known as oxyfuel.

‘You separate the air at the front end of the process to give you pure oxygen; you mix that with the flue gases; and that gives you pure carbon dioxide on combustion,’ said Snape.

The storage part of the equation is also under investigation. While most research is concentrating on pumping the CO₂ into deep saline acquifers in the North Sea, some of the institute’s research is looking at mineral carbonisation — developing a CO₂ sequestration module that will pump the gas into seams of silicate minerals underground and convert it into a solid, stable form. ‘We’re looking at the fundamentals of the reactions that need to occur,’ Snape said. ‘There’s a logistical factor here in getting the CO₂ to a suitable location but we need to work out the right temperature and pressure conditions for the silicate/CO₂ reaction.’

One problem with storing sequestered carbon is ensuring that it stays sequestered. Pumping the gas into an old oil well or gas field is relatively simple but the geology can often contain natural faults and cracks, or be pierced by old drill-holes.

One of ETRI’s research strands, which demonstrates the multi- disciplinary nature of environmental technologies, is at Nottingham’s agricultural sciences department, where a team of geographers and bioscientists are looking at what happens if a CO₂ reservoir springs a leak.

The team has set up a site with the evocative name of ASGARD (Artifical Soil Gassing and Response Detection), where CO₂ is injected into the soil to determine its effect on various plant species.

Another part of the research is looking at whether elevated CO₂ levels in the Earth cause changes in the colour of the plants growing above the leak. At present, said Snape, there is no way to detect a leak; if there is a colour change, then the plants themselves could become a remote sensing system, with satellite imaging allowing leaks to be spotted early.

This technique could also be used to police carbon trading agreements, Snape said. While sequestration will form a credit for carbon trading, as it represents a reduction in emissions, the ASGARD research could help ensure that countries claiming to store CO₂ are effectively preventing it from leaking into the atmosphere.

Another intriguing possibility is light harvesting, a technique that regards the CO₂ not as a waste product to be locked away but as a resource in its own right. The concept, Snape explained, is to mimic photosynthesis and ‘close the CO₂circle,’ converting the gas back into fuel compound, using power from the sun.

‘What we need is to make the reactions go quickly,’ he said, ‘and that’s a matter of developing photocatalysts.’ Much current research is focused around developing compounds based on titanium dioxide, the pigment used in most white paints and optical brighteners in the paper industry.

The clock is ticking on these technologies, stressed Snape. ‘The EU is looking for 10-12 technologies to go into a demonstration phase by 2015, with commercialisation to follow soon afterwards. It’s very much an accelerated timescale, and we urgently need the right fiscal climate to develop these technologies.’

In the UK, at least, there have been some moves to put this sort of investment climate in place, with last year’s launch of the national Energy Technologies Institute. Aimed at funding technologies entering their demonstration phase, the institute has secured involvement from many of the largest players in the energy field, including Shell, BP, E.On, EDF, Rolls-Royce and Caterpillar.

The DTI and Defra are looking at bids to house the ETI. ‘Nottingham and the ETRI are hoping to play a significant part in the Energy Technologies Institute,’ said Snape. ‘Our strengths map directly onto the ETI themes.’