THE CASE FOR CARBON CAPTURE AND STORAGE
dioxide is going to be distributed through a large body of porous rock , it ’ s not sitting in a big tank ,” Green says .
In essence , CCS involves separating carbon dioxide from the mixture of gases emitted from a tail pipe or a power station ’ s chimney . Once the CO2 has been captured , it can be pressurised and transformed into a liquid-like state for transport through pipelines and , ultimately , burial inside porous geological formations deep underground .
In the UK , most of the practical prospective stores are offshore — anywhere between one and four kilometres beneath the seabed . An impermeable layer of so-called ‘ cap rock ’ will rest over the top of an ideal CCS formation . Once underground , there are a number of natural mechanisms which will ensure that carbon dioxide doesn ’ t escape : Firstly , the buoyant CO2 will slowly move upwards through the porous rock until it is trapped by the cap rock . Along the way it gets caught in the microscopic channels in the porous rock like water in a sponge . Over time , the carbon dioxide will dissolve into the saltwater already present in the formation and , over hundreds or thousands of years , harden into solid carbonate .
“ If you choose the right geology you end up with a very secure long term store for the CO2 ,” Green says .
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