23 June 2008

Dig deep - Carbon storage will be expensive at best. At worst, it may not work

The Economist print edition - Jun 19th 2008
Original URL

EVEN in the most alternative-friendly future imaginable, coal is unlikely to go away. It is cheap, abundant and often local. So what can be done to make coal’s use more acceptable?

One much-discussed possibility is carbon capture and storage, or CCS, which involves burying the carbon dioxide deep underground. The generating companies have high hopes of it (see chart 3). There are just two problems. No one knows if it will work (in other words, if the CO2 will stay buried). And everyone knows that, whether it works or not, it will be expensive—so much so that the alternatives start to look rather attractive. The one serious attempt to investigate its use in an actual power station, the FutureGen project, based in Illinois, was cancelled in January because the expected cost had risen from $830m to $1.8 billion.

The “capture” part is not that hard. Carbon dioxide reacts with a group of chemicals called amines. At low temperatures CO2 and amines combine. At higher temperatures they separate. Power-station exhaust can thus be purged of its CO2 by running it through an amine bath before it is vented, and the amine can be warmed to release the gas where it will do no harm. Better still, the coal can be reacted with water to produce a mixture of CO2 and hydrogen in which the carbon dioxide is much more concentrated than in normal flue gas, so it is easier to scrub out. What is then burned is pure hydrogen.

All this processing is expensive, but there is no reason why it should not work. An experimental plant in Denmark that uses monoethanolamine as the captor has been running for two years. Alstom, a French firm, has almost finished building one in Wisconsin that uses ammonia.

It is what comes next that is the problem. The disposal of carbon dioxide needs to be permanent, so a lot of conditions have to be met. To be a successful burial site, a body of rock needs to be more than 1km underground. That depth provides enough pressure to turn CO2 into what is known as a supercritical fluid, a form in which the stuff is more likely to stay put. The rock in question also has to have enough pores and cracks in it to accommodate the CO2. Lastly, it needs to be covered with a layer of non-porous, non-cracked rock to provide a leakproof cap.

So far, only three successful CCS projects are under way. The Weyburn-Midale CO2 project is burying carbon dioxide from a coal gasification plant in North Dakota in a depleted oil field in Saskatchewan. The Salah gasfield project in Algeria, run by BP, strips CO2 from local natural gas and injects it back into the ground. And Statoil, a large Norwegian oil and gas company, performs a similar trick at two places in the North Sea. None of these projects is actually linked to generating electricity. Still, a few years ago they were touted proudly. But the touting has become more nervous, and no new projects have come on stream.

The scale of the problem is awesome. The three showcase projects each dump about a million tonnes of CO2 a year. But America’s electricity industry alone produces 1.5 billion tonnes, which would mean finding 1,500 appropriate sites, and nobody knows whether the country’s geology can oblige. Even transporting that amount of gas would be a huge task.

As to the cost, a report published last year by MIT reckons on $25 a tonne to capture CO2 and pressurise it into a superfluid, and $5 a tonne to transport it to its burial site. It therefore suggests that power stations which dump CO2 into the atmosphere should be charged $30 a tonne, a figure conveniently near both the middle of the IPCC’s suggested carbon price and the actual price in Europe. Another report, by a consultancy called Synapse Energy Economics, notes that American power companies are already starting to employ carbon prices in their internal accounting, using a range of $3-61 a tonne. Again, the middle of that range is about $30.

Such a charge, whether a tax or a system of tradable permits to pollute, would change energy economics radically. But even the most optimistic proponents of carbon capture and storage doubt it will be a serious alternative much before 2020. And by then both the physical and the political climate may look rather different.

Copyright © The Economist Newspaper Limited 2008

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