Carbonation performance of lime for cyclic CO2 capture following limestone calcination in steam/CO2 atmosphere

Steam can be used to lower calcination temperatures or to provide the process heat for calcination in a Ca-looping cycle because it can be removed from the CO2 stream by simple condensation. Here, the performance of limestone for CO2 removal from flue gases, calcined in the presence of steam, has been investigated. Three steam concentrations (28%, 48% and 78%) were used to investigate the effect of high-temperature steam in the calciner. For comparison, the effects of steam were compared to similar levels of N2 as the primary diluent. Subsequent to calcination at elevated steam levels, the performance of the calcined sorbent was tested during carbonation with two levels of steam (6% and 20%) typical for flue gases from fossil fuel power plants. This allowed the effects of steam in carbonation to be investigated as well. As this study focused on CO2 capture from flue gases produced by existing power plants (using Ca-looping as a post-combustion process), the corresponding industrial conditions were simulated for the carbonation atmosphere. Steam addition in the calciner was found to be more effective in improving capture than steam addition in the carbonator, with CO2 capture capacity being increased with increasing steam levels in the calciner.