Ammonium Nitrate Chemistry

Clean Coal on the Ropes

power plant emissions

Clean coal is a seductive proposition for arresting climate change.  It means we could continue to burn coal for power as usual and use carbon capture and storage (CCS) to remove carbon dioxide from the flue gas and bury it underground.  Carbon capture is actually a mature technology, widely used in natural gas processing, where gas is bubbled through a liquid amine mixture which chemically binds to carbon dioxide, letting the desired gas pass through.  The amine solvent is then heated to liberate relatively pure carbon dioxide.

Companies and governments invested in coal have devoted massive resources to try and adapt carbon capture technology for coal fired power, with the typical approach being to bolt on a conventional amine solvent plant to an existing power station.  This approach has, however, failed to succeed.  The Boundary Dam project, a flagship effort aiming to demonstrate that CCS is feasible on an industrial scale, was plagued by budget overruns during construction, and its future remains unclear.  The plant has also seen operating costs blow out, with it now revealed that the amine solvent is to blame.  Although this process can be made to work when removing trace contaminants from natural gas, it appears that the complex flue gas and punishing operating conditions make it incompatible with coal fired power generation.  The solvent degrades too quickly, requiring it to be replaced and creating a large toxic amine waste stream.

The amine waste issue serves as a reminder that CCS is not "clean coal".  Amine solvents, for instance, also create significant new air pollutants.  Sequestered carbon dioxide is a legacy waste that must continue to be monitored.  Coal mining pollutes the land and water.  The transport and processing of coal is responsible for particulate matter emissions.  There are many reasons for us to finally abandon coal, and few compelling arguments for why we should use CCS to keep burning it.