Effect of pressure and gas concentration on CO2 and SO2 capture performance of limestones

Two Greek limestones with different properties were tested to determine their CO2 and SO2 capture performance. The reversibility of the sorbents for CO2 capture was investigated by performing looping cycles in atmospheric and pressurized thermogravimetric reactors, with synthetic gas mixtures containing different partial pressures of CO2 and SO2 to simulate flue gases. The morphological and porosity characteristics of the original and spent sorbent were examined by Scanning Electron Microscopy and Pore Sized Distribution analyses. Increasing pressure from atmospheric to 10 bar led to deterioration in CO2 capture performance. Further pressure increment had negligible effect on the CO2 capture performance. SO2 retention, however, improved with increasing pressure. For calcium looping with repeated cycles, sorbents sulphated via the unreacted-core mode converted more available calcium, but this adversely affected the reversibility of cyclic CO2 capture. The reversibility strongly deteriorated when higher total pressure was combined with increased SO2 partial pressure. The CO2 uptake of an unreacted-core sulphated sorbent, previously used for SO2 retention, was mainly affected, apart from pore blockage or sintering, by the occupation of calcium. Sulphation during simultaneous capture resulted in higher CO2 removal efficiency for uniformly and network sulphated particles compared to the sulphur capture via direct sulphation. (C) 2014 Elsevier Ltd. All rights reserved.