Carbon Capture

Carbon Capture involves the production of a pure stream of CO₂ from a combustion process. There are two main ways in which this can be done, pre-combustion and post-combustion capture. In pre-combustion a series of reactions is used to produce H₂ and a pure stream of CO₂ from a hydrocarbon fuel. The H₂ can then be burned in (for example) a specially modified gas turbine, or a fuel cell. Post combustion capture can be done in a number of ways: Solvent Capture (including MEA or amine scrubbing), uses some form of solvent to reversibly react with CO₂ from the flue gas (i.e. after the fuel has been burned, a post-combustion technology), with heat being applied to remove the CO₂ and produce a pure stream of CO₂. In Oxyfuel combustion, the fuel is burned in pure O₂ (thereby forming a pure stream of CO₂) and some of the CO₂ from the exhaust is recycled back to the combustor to moderate the flame temperature. Integrated Gasification Combined Cycle (IGCC, a pre-combustion technology) involves the gasification of the fuel by burning it in a small amount (far less than required to burn it completely) of O₂, to produce a gas which is rich in CO and H₂. Further treatment produces separate streams of CO₂ (for sequestration) and H₂ (which can be burned without any climate change effects). The Calcium looping cycle (post-combustion) uses the ability of CaO from natural limestone (CaCO₃) to reversibly react with CO₂ in the flue gas, again to produce a pure stream of CO₂. The ZECA process has aspects of the calcium looping cycle associated with it. Using a complicated series of reactions, described below, the ZECA process (joint research with Cambridge University) produces hydrogen which is used in a fuel cell to generate electricity with an extremely high thermodynamic efficiency (60 – 70 %) from a standard fuel. Chemical looping combustion is effected by the use of a metal oxide to carry oxygen from air to a fuel (either gaseous, or otherwise), meaning that the combustion of the fuel produces a pure stream of CO₂. Direct carbon fuel cells and artificial leafs (removing CO₂ from the air) are also under investigation.