August 02, 2006
|Will Carbon Sequestration Save Us?||Energy Environment Peak Oil|
Oil's about to peak, but we've still got lots of coal, and coal, unfortunately, will become the path of least resistance. All that coal means lots more carbon in the atmosphere. Unless we can bury the CO2, permanently — so-called carbon sequestration.
For every tonne of anthracite [coal] burned, 3.7 tonnes of CO2 is generated. If this voluminous waste could be pumped back into the ground below the power station it would not matter as much, but the rocks that produce coal are not often useful for storing CO2, which means that the gas much be transported. In the case of Australia's Hunter Valley coal mines, for example, it needs to be conveyed over Australia's Great Dividing Range and hundreds of kilometres to the west.
Once the CO2 arrives at its destination it must be compressed into a liquid so it can be injected into the ground — a step that typically consumes 20 per cent of the energy yielded by burning coal in the first place. Then a kilometre-deep hole must be drilled and the CO2 injected. From that day on, the geological formation must be closely monitored; should the gas ever escape, it has the potential to kill.
The largest recent disaster caused by CO2 occurred in 1986, in Cameroon, central Africa. A volcanic crater-lake known as Nyos belched bubbles of CO2 into the still night air and the gas settled around the lake's shore, where it killed 1800 people and countless thousands of animals.
Earth's crust is not a purpose-built vessel for holding CO2, and the storage must last thousands of years so the risk of leak must be taken seriously.
Even the volume of CO2 generated by a sparsely populated country such as Australia beggars belief. Imagine a pile of 200-litre drums, ten kilometres long and five across, stacked ten drums high. Even when compressed to liquid form, that daily output would take up a cubic kilometre, and Australia accounts for less than 2 per cent of global emissions! Imagine injecting 50 cubic kilometre of liquid CO2 into the Earth's crust every day of the year for the next century or two.
If geosequestration were to be practised on the scale needed to offset all the emissions from coal, the world would very quickly run out of A-grade reservoirs near power stations and, especially if the power companies are not liable for damages resulting from leaks, pressure would be on to utilise B, C, D and E grade reservoirs.
As always when it comes to world energy usage, the fundamental issue is a question of scale. 50 cubic kilometers a day, every day, 'til the coal runs out. And it's got to stay buried. What are the chances?