Understanding the enhancement effect of high-temperature steam on the carbonation reaction of CaO with CO2

The steam-enhanced carbonation reaction of CaO with CO2 is a widely observed phenomenon, but its mechanism is unclear. This study proposed that OH− formation caused by the dissociation of H2O molecules may explain enhanced carbonation. The relationship of oxygen vacancies with OH− at different temperatures and steam fractions was established and integrated into a new carbonation model. This new model included a simplified rate equation model to describe product island formation and a multi-ion diffusion model that describes product layer growth. Experiments on carbonation and sorption-enhanced water gas shift reactions in a laboratory-scale fluidized bed reactor were conducted to validate the idea of OH− formation. The new developed models were validated by thermogravimetric analysis.