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

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.