Tuesday, November 4, 2008

Adding lime to seawater

Shell Oil is funding a project that is studying the potential of adding lime to seawater to store carbon dioxide (CO2) in the sea.

Due to increased CO2 levels, the oceans have become more acid. Adding lime (calcium hydroxide) to seawater will increase the alkalinity of the water, making the water absorb more CO2 and reducing the release of CO2 from the water into the atmosphere.

Tim Kruger, a management consultant at London-based Corven, believes that this can be done most economically where there's plenty of limestone, and plenty of energy that is too remote to exploit for conventional commercial purposes.

"There are many such places — for example, Australia's Nullarbor Plain would be a prime location for this process, as it has 10,000km3 of limestone and soaks up roughly 20MJ/m2 of solar irradiation every day," said Kruger.

Although the process generates CO2 emissions, on paper it sequesters twice as much of the warming gas than it produces. Kruger says the process is therefore 'carbon negative'.

'This process has the potential to reverse the accumulation of CO2 in the atmosphere. It would be possible to reduce CO2 to pre-industrial levels,' he explained.

"We think it's a promising idea," says Shell's Gilles Bertherin, a coordinator on the project, which is being developed in an "open source" manner. "There are potentially huge environmental benefits from addressing climate change — and adding calcium hydroxide to seawater will also mitigate the effects of ocean acidification, so it should have a positive impact on the marine environment."

Sources and Links:

Shell Oil funds "open source" geoengineering project to fight global warming, at:
Mongabay.com

'Turning back the clock on climate change' - A technology to reverse climate change? To reduce ocean acidification? And that also promises to increase food production? Cath O’Driscoll investigates, at:
Chemistry & Industry Magazine

Adding lime to seawater feasibility study, funded by Shell, at: www.cquestrate.com

1 comment:

Sam Carana said...

The post says that adding lime to seawater will generate CO2 emissions, but that it on paper will sequester twice as much of the warming gas than it produces. Tim Kruger says the process is therefore 'carbon negative'.

Kruger says that "Australia's Nullarbor Plain soaks up roughly 20MJ/m2 of solar irradiation every day". So, when using solar energy, one assumes that very little CO2 will be released.

Nevertheless, I feel more comfortable with CO2 capture from ambient air, using wind energy.

Here are the arguments:

1. Dumping huge amounts of lime into the oceans can have negative side-effects and it's hard to undo. Since air-capture machines can recycle the lime, they each require only a small amount of lime and save the lime for other usage later, such as making concrete. If needed, the lime can always be dumped into the sea at some later stage, but for now it makes more sense to proceed carefully with that.

2. Secondly, air capture can be powered by wind energy. At night - when there's plenty of wind - there's little demand for electricity. So, a wind turbine in, say, New York could feed electricity into the grid at times of peak usage, while powering air capture at off-peak times.

Since energy constitutes the biggest cost of air capture, it makes sense to use surplus power from wind turbines, which might otherwise remain unused. In other words, the cost of wind turbines can be shared in this way.

3. Thirdly, it makes sense to use captured CO2 for commercial purposes, such as in greenhouses, to make agrichar, fuel, building materials, carbon fiber, etc. This commercial use could open a second line of sharing the cost of air capture. Furthermore, these products could replace polluting products.

4. The above two points benefit from the fact that air capture machines can be located anywhere. This may also help with raising the necessary funding in another way. Companies that are willing to contribute funding, in efforts to offset their CO2 emissions, may be more likely to do so when they can choose the location of such machines (as opposed to contributing to a large dumping project in the Australian desert). Similarly, it seems politically more viable to raise public funding - say in the UK - for locally manufactured air-capture machines, as opposed to making financial contributions to a project in Australia.

Much of the above was discussed at:
Removing Carbon from the Air