Reductive calcination of calcium carbonate in hydrogen and methane: A thermodynamic analysis on different reaction routes and evaluation of carbon dioxide mitigation potential

Abstract

Calcium carbonate (CaCO3) minerals represent a valuable resource, but its exploitation is based on the decarboxylation reaction at high temperatures, which inevitably release carbon dioxide (CO2) into the atmosphere. Here, a reductive calcination of CaCO3 in the hydrogen (H2) and methane (CH4) atmospheres was proposed, thermodynamic analysis and process simulation were carried out. In CH4 atmosphere, lower CaCO3 decomposition temperature and higher CO2 conversion can be achieved, while undesirable solid carbon deposition was produced as well. Optimized H2:CH4 ratio in feeding can effectively avoid carbon deposition and achieve the complete decomposition of CaCO3 at 738 °C which reaching CO2 conversion of 69.69 %. In addition, this work established the traditional route as a reference process to compare the energy efficiency and carbon footprint of the different CaCO3 calcination processes. CaCO3 calcination in H2:CH4 atmosphere with 1:1 ratio achieved an energy efficiency of 67.01 % and a GWP value of 0.954 kgCO2/kgCaCO3. With sustainable energy (bio-power, bio-H2, and bio-CH4) substitution, even lower GWP value of −0.640 kgCO2/kgCaCO3 can be achieved. This work performed that direct reduction of CaCO3 to syngas and CaO under H2 or CH4 atmosphere, which not only reduces the reaction temperature but also alleviates the CO2 emission, which offers a promising option for carbon emission reduction in the carbonate industry.