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28 July, 2004

Buried in the sand

I'm not sure I understand the central premise behind this BBC article: scientists wish to develop ways to store (sequester) carbon dioxide underground to allow exploitation of 'abundant' UK coal deposits.

Sequestration involves trapping CO2 as it is emitted, and storing it in huge reservoirs underground or beneath the sea. It is already being used in Norway, where the carbon helps to force oil out of partly-exploited fields.

Okay, but that's petroleum: liquid and gas. I don't understand how gas injection could assist the removal of solid coal. Am I missing something? Is the journalist?

I thought the intention was to use CO2 to pressurise and drive out coal gas from unmineable coal deposits; indeed, that impression was confirmed by a quick Google search for 'carbon sequestration geological'. The US Dept. of Energy says:

Coal beds typically contain large amounts of methane-rich gas that is adsorbed onto the surface of the coal. The current practice for recovering coal bed methane is to depressurize the bed, usually by pumping water out of the reservoir. An alternative approach is to inject carbon dioxide gas into the bed. Tests have shown that CO2 is roughly twice as adsorbing on coal as methane, giving it the potential to efficiently displace methane and remain sequestered in the bed. CO2 recovery of coal bed methane has been demonstrated in limited field tests, but much more work is necessary to understand and optimize the process.

Great; good idea. Yet the graphic accompanying the BBC article indicates that purified CO2 will be forced into water-filled permeable rock (e.g. sandstone) beneath impermeable strata preventing the gas from escaping; not into coal at all, and with no indication that anything would be extracted. Why?

[Independent energy consultant Dr. David White] said there was enough space beneath the North Sea to store Europe's carbon emissions for a century.

Is that it? Mere storage? Surely not! A subheading in the article also says:
Burning coal underground

Though no other hint of that possibility is even mentioned in the text itself.

On another matter, the article reports pessimism about the prospects for renewable energy policy in the UK:

They say the other priority [after CO2 sequestration] should be to build a new generation of nuclear power plants to meet demand for power.

The scientists, speaking at the Royal Institution in London, said plans for renewable energy use were unrealistic.

Speaking at a briefing on the future of energy at the RI's Science Media Centre, Professor Ian Fells [chairman of the New and Renewable Energy Centre, Blyth, Northumberland] said he thought it would be 'hellishly difficult' to persuade people to invest in nuclear power, but he did not know how the UK would manage without it.
"I can't believe the UK will ever get far beyond generating 10% or so of its energy renewably - and that would be a heroic effort."
Professor Fells said the UK was now emitting as much CO2 as in 1997, and he put the chances of reaching the government's target of cutting emissions by 20% by 2010 as "slender, to say the least".
He thought the UK should aim for an energy mix where coal, gas and nuclear power each provided 30%, and renewables 10%.


The idea is that the coal is mined and burned producing CO2. The CO2 is then buried in the ground thus making a zero nett contribution of CO2 to the atmosphere. Of course some of the energy derived from the coal burning will be used in the sequestration process.
The CO2 burial site does not need to be in the same location as the coal deposit, nor even the same country. This is the idea behind CO2 trading.
You burn some coal, I'll plant a tree. Will it work? Probably not.

Posted by Alan Ogden at July 28, 2004 03:11 PM

Sorry, mate, but your first paragraph doesn't make sense, and the second is a different issue!

The true situation is as the US DoE described: carbon dioxide is pumped in, displacing methane, which is burned to drive turbines. The coal itself isn't extracted - the whole point is that it is unmineable.

Posted by NRT at July 28, 2004 06:43 PM
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