Limestone captures carbon dioxide

Scientists at New Zealand based Industrial Research Ltd (IRL) are developing a new process that uses limestone to capture carbon-dioxide emissions from coal-fired power stations and other industries that emit significant amounts of the greenhouse gas.

IRL has been awarded NZ$350,000 (£159,000) over three years by the Foundation for Research Science and Technology to develop its technology further.

In the IRL process, limestone is first heated to around 900^oC to become lime, which is a very effective material for absorbing carbon dioxide. When post-combustion flue gas is passed through the lime in a fluidised bed, the CO₂ is captured. The process is then reversed to transform the lime back into limestone, which is then used again to capture more CO₂.

The CO₂ can then be compressed to about three per cent of its original volume and stored efficiently or used in another industrial process.

This process has been known for many years, but until now it has not been efficient enough to be considered commercially applicable.

'Every time the lime is reused, its ability to absorb the gas declines. This is the result of the pores on the lime surface closing over. Lime absorption slows so much on successive cycles that this technique is not commercially viable,' said IRL scientist Robert Holt.

But the IRL team found that exposing the lime to steam reopens its pore structure and enables it to absorb CO₂ efficiently again.

'Our big breakthrough was the discovery of a way of thermally treating the lime, after it had been hydrated, so that we could also maintain its activity and structural integrity. This is key in an industrial context because it means the lime can be used 100 times before it breaks down significantly,' added Holt.

The IRL team has patented its novel reactivation process and hopes the practical implementation of the technology will be less than two years away.

'We have estimated that our technique will reduce CO₂ capture costs by up to 70 per cent. We are currently seeking a commercialisation partner to take this technology and apply it in an industrial context,' said Holt.