Published August 2003
To achieve the reductions in greenhouse gases targeted by many governments will take more than just using energy efficiently. And the much vaunted hydrogen economy is far from reality, certainly today and perhaps forever.
Therefore policy makers are considering seriously the idea of capturing CO2, an inevitable byproduct of fossil fuel combustion, and removing it from the atmosphere. Sequestration schemes would inject captured CO2 underground (in disused or underused wells) and in the ocean. Except in science fiction, such schemes would have been laughable 15 years ago. But, as 2003 notches up yet another record high temperature, nobody is laughing anymore; sequestration research and development is moving rapidly. One of the most obvious sources of carbon dioxide for sequestration is power generation. It accounts for about one-third of global CO2 emissions, and generating plants are highly central emission sources, thus easier and more economical to capture than, say, decentralised transport, which accounts for about one-fifth of global emissions. So, out of almost nowhere, lower-carbon power generation is suddenly of great interest. Research and development are focused on four technologies
- Post-combustion carbon capture - essentially amine scrubbing of flue gases
- Lower carbon fuels - switching to gas and biofuels
- Pre-combustion carbon concentration (oxyfuel) - running power plants on pure oxygen rather than air, so that the flue gas has a much higher concentration of carbon dioxide
- Decarbonization - this means reforming or gasification to concentrate CO2 in the flue gas. Hydrogen from the reformer or gasifier is then used as a fuel.
This review surveys the state-of-play with these technologies, summarizing 32 current projects or studies using lower-carbon technology. Unfortunately, none of them appear to offer a magic bullet for CO2 removal. The proven technologies are expensive to operate, and the unproven ones will be expensive to develop. For process developers, this is not a bad thing. It will justify massive public subsidies to spur development so much of the commercial risk will be put on the public. And for whomever does find the magic bullet, the market potential is enormous.