Reaction mechanisms for H₂O-enhanced dolomite calcination at high pressure

Despite extensive research, our understanding of the dolomite calcination mechanism remains unclear, especially concerning how dolomite calcination is influenced by a change in H₂O and CO₂ partial pressure under high-pressure conditions. In this study, dolomite calcination behaviors and mechanisms at different H₂O and CO₂ partial pressures were investigated using thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy. Under dry thermal conditions, CO₂ has a delaying effect on dolomite calcination; however, this effect is independent of CO₂ partial pressure, indicating that the calcination could be controlled by the CO₂ adsorption capacity on dolomite active sites. In an H₂O atmosphere, calcination might begin at a low temperature due to the adsorption of H₂O on active sites and then be controlled by the dissociation of HCO₃⁻. A delaying effect of H₂O was also observed, with the H₂O partial pressure being lower than the CO₂ partial pressure in an H₂O and CO₂ mixture. This could be attributed to the formation of CO₃²⁻ via 2OH⁻ + CO₂ = CO₃²⁻ + H₂O. A model was developed to predict the dolomite conversion time under isothermal conditions. A process window considering the effect of operating variables on the conversion time at 550–1000 °C and H₂O partial pressures of 1–20 bar is presented.