Synthetic CaO-based Sorbent for CO<inf>2</inf> Capture

The capture and purification of carbon dioxide (CO2) from flue or fuel gas underlies the cost efficiency of carbon capture and storage (CCS) applications in the power and industrial sectors and there is considerable scope for cost reduction with the development of novel capture technologies. High-temperature sorbents are seen as a "next-generation" technology and a promising candidate is calcium oxide (CaO) derived from natural limestone, which is used in a process known as carbonate looping. This process exploits the reversible reaction between CaO and CO2 to form calcium carbonate (CaCO3). Unfortunately, sorbent derived from natural limestone loses its capacity to capture CO2 through long-term cycling, and a large amount of fresh limestone is required to maintain an acceptable CO2 capture efficiency. This work describes the development and characterisation of synthetic CaO-based sorbents, such as those incorporating a mixed calcium-aluminium oxide binder in this case produced by precipitation in a slurry bubble column. Reactivity tests using a thermogravimetric analyser (TGA) demonstrate the improved long-term CO2 uptake of the synthetic sorbent. The highest CO2 uptake observed after 30 cycles was achieved with 85 wt.% CaO and binder, which was three times higher than the observed capacity of a natural limestone (Havelock). However, contrary to TGA results, experimental results for reactivity tests conducted using a bench-scale fluidised bed reactor (FBR) showed the highest uptake for the precipitated sorbent with no binder. A decrease in uptake was observed corresponding an increase in binder loading from 0-25 wt.%, which was coupled with an increase in mass loss owing to elutriation, attributed to decrepitation during cycling. © 2011 Published by Elsevier Ltd