Abstract:A modified shrinking unreacted-core model, based on thermogravimetric analysis, was developed to investigate CaSO₄ decomposition in oxy-fuel combustion, especially under isothermal condition which is difficult to achieve in actual experiments due to high-temperature corrosion. A method was proposed to calculate the reaction rate constant for CaSO₄ decomposition. Meanwhile, the diffusion of SO₂ and O₂, and the sintering of CaO were fully considered during the development of model. The results indicate that the model can precisely predict the decomposition of CaSO₄ under high SO₂ concentration (>1100×10^-6). Concentrations of SO₂ and O₂ on the unreacted-core surface were found to increase first and then decrease with increasing temperature, and the average specific surface area and porosity of each CaO sintering layer decreased with increasing time. The increase of SO₂ and/or O₂ concentration inhibited CaSO₄ decomposition. Moreover, the kinetics of CaSO₄ decomposition had obvious dependence on temperature and the decomposition rate can be dramatically accelerated with increasing temperature.

Key words: oxy-fuel combustion; shrinking unreacted-core model; CaSO₄; decomposition; CaO sintering