Production of high-concentration CO2 from electrified limestone calcination for carbon capture applications

Operating electrically heated kilns under high-CO2 atmospheres can increase CO2 capture efficiency but creates reducing conditions that drive CO formation. In this work, CO generation during limestone calcination in a 280 kW electrically heated rotary kiln at 75 vol-% CO2 and low O2 concentration is investigated. Equilibrium calculations indicate that sulphide and sulphite phases in limestone decompose, releasing SO2 and promoting CO formation. Complementary packed-bed experiments confirm that sulphur species are a major CO promoter and reveal a synergistic interaction between sulphur compounds and elevated CO2 levels. Using low-sulphur limestone could suppress CO emissions. Where low-sulphur feedstocks are unavailable, targeted electrolytic O2 or air injection coupled with indirect limestone preheating is proposed to strip sulphur and preserve the high-purity CO2 stream which will improve the efficiency of electrified kilns integrated with a carbon capture process.