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2008
26 November 2008
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Gone to ground
Returning used carbon to subterranean reservoirs looks a good idea on paper. But it’s time to stop talking and start acting, the experts tell
Justin Cunningham
As long as there are fossil fuels, somebody is going to burn them, said Jeff Chapman, chief executive of the Carbon Capture and Storage Association, at a conference on the subject at Birdcage Walk. “Anything we try to do in the meantime in terms of renewables and nuclear will only delay the onset of climate change, it won’t stop it.”
Carbon Capture and Storage (CCS) is the concept of capturing the CO2 released when fossil fuel is burnt and putting it back in the ground. The technology will allow carbon dioxide emitted from large sources, such as coal or gas-fired power stations, to be transported and stored in naturally occurring geological formations, such as oil reservoirs that have been depleted.
The Intergovernmental Panel on Climate Change (IPCC) has projected that CCS could deliver as much as 55% of the total carbon mitigation effort by the end of the century and could reduce atmospheric CO2 emissions from coal-fired power stations by 90%.
The UK has the advantage of vast storage potential in the depleted North Sea oil and gas reservoirs. The captured carbon dioxide would be delivered through pipework out to sea before being injected into the ground where it would be permanently contained.
“The myth that the CO2 may leak is contrary to all the evidence we have,” says Jonathan Periselneris, a clean coal development project engineer at E.On. “As long as the site is selected on a good geological basis, we believe that CO2 storage is permanent. The mechanisms are well understood. But we need to promote a more rigid monitoring and verification programme to ensure that the CO2 is permanently stored.”
There are still a lot of unknowns. Although advocates may argue that natural gas has been held stably in geological formations for millions of years, it was a slow process lasting millennia. Extracting the gas, which reduces pressure inside the reservoirs leading to a tendency for the surrounding structure to sag in on itself, and reinjecting CO2 for CCS, which should again help support the weight of the internal structure of the reservoir, is a significantly shorter process.
However, a report published by the IPCC suggests this will not be a problem. It said: “Observations from engineered and natural analogues as well as models suggest that the fraction [of CCS CO2] retained in appropriately selected and managed geological reservoirs is very likely to exceed 99% over 100 years and 99% over 1,000 years."
Carbon Capture and Storage in the UK is being driven by the closure of a number of coal-fired and nuclear power stations, which will result in a shortfall of national capacity by around 2015. The dilemma faced by the industry when it comes to new-build options is the trade-off between carbon, cost, and security of supply.
Although most energy experts agree that nuclear and renewables should be pursued, there are really only two fuels that can realistically fill the shortfall – coal and gas.
There is likely to be a mix of the two for new power stations in the near future; the question is in what proportions? Coal-fired power stations are highly controversial and unpopular with environmentalists. And they have been dealt another blow with the introduction of emission performance standards.
“The idea is to limit new-build power stations to a certain amount of emissions,” says Chapman. “The proposal in Europe is 500g/kWh. That would mean you’d have to apply CCS to a coal-fired power plant but be able to build a combined-cycle gas turbine power plant without one. That would probably drive people towards gas and that is fraught with unintended consequences.”
Although gas is a sensible contender – it is cleaner than coal, producing around 350g/kWh, and the technology is well established – delve a little deeper and problems begin to appear. It would lead to a reliance on foreign imports and prices have been extremely volatile in the last few years. Cost and security of supply begin to point to coal, with its relatively stable price, to play a bigger part in the mix.
Very little has been done to address the shortfall in capacity or developing the concept of CCS. “We have to get on with it pretty damn quick because every moment we waste releases CO2 in the atmosphere,” says Chapman. “We are doing a lot of talking and it is time the talking stopped and we started putting some hardware down.”
There are three main technologies for CCS; pre-combustion, post-combustion and oxyfuel. RWE npower has begun demonstrating post-combustion capture technology at its Didcot site. The small 100kW pilot plant, which is operational, has the ability to capture about one tonne of carbon dioxide a day.
It is part of a three-phase strategy to get the technology on to a larger demonstration facility. It is hoped the project will help the company gain an understanding of the operational aspects behind making CCS successful as well as provide a more accurate assessment of the costs of building and operating such a facility.
“It gives us the ability to learn,” says Gerry Riley, a fuels and combustion engineer at RWE npower. “One of the things we have to do as engineers is understand the process. We have to run it day in, day out and we hope it will provide the data to take us up to a larger scale.”
The government has launched a competition to build a prototype power station by 2014 to demonstrate the full chain of CCS that successfully captures, transports and stores CO2. The rules also require a 300MW demonstration unit on a
supercritical coal-fired power station by 2019. Four bids made the shortlist although BP recently pulled out of the contest to focus its CCS efforts in California and Abu Dhabi. The winning bid is likely to be announced in the middle of next year.
Periselneris says: “E.On’s main focus is to look at a 300MW demonstration unit at Kingsnorth, which would capture approximately two million tonnes of CO2 a year and sequester it in the North Sea.”
There is a consensus of a two-track approach towards reducing CO2 emissions from coal. The first is to cut the amount of carbon by making plants as efficient as possible and, critically, making them carbon capture-ready (CCR). This would mean power stations would have to have space to implement a CCS system and a feasible CO2 pipeline route to a suitable storage area.
This is important in the context of new-build power stations, which are needed on a much larger and faster scale than CCS is feasibly able to deliver. Once CCS has been successfully commercialised – possibly by 2020 – all capture-ready plants could be retrofitted with the technology. As well as implementing the 350g/kWh limit, much of the industry would also like to see CCR become mandatory for new builds.
It is clear that advocates of the technology face a long uphill battle to win over environmental concerns and attract the massive amounts of investment needed for a technological concept that is, at present, largely untried and tested on the scales needed.
In the long run the cost of producing carbon under the European Union’s Emission Trading Scheme is likely to rise to a sufficient level to make CCS on power plants cost-effective. But in the short term it is the big chunks of capital, estimated to be some £1 billion per project, that is raising more than a few eyebrows. However bitter the pill, the fact remains: the UK needs to produce more energy and less CO2.
© PE Publishing, 26 November 2008
