Modified shrinking unreacted-core model for the reaction between sulfur dioxide and coal fly ash/CaO/CaSO4 sorbent

The kinetics for non-catalytic solid gas reaction between SO2 and sorbent prepared from coal fly ash, CaO and CaSO4 in a fixed-bed reactor at low temperature were modeled and simulated. A modified shrinking unreacted-core model (SCM) with chemical reaction coupled with diffusion as the rate limiting step were developed to predict the breakthrough curves of the desulfurization reaction. The kinetic parameters of the mathematical model were obtained from a series of experimental desulfurization reactions conducted under isothermal conditions at various operating parameters; SO2 initial concentration (500 ppm ≤ CSO ≤ 2000 ppm), NO initial concentration (250 ppm ≤ CNO ≤ 750 ppm), reaction temperature (60 °C ≤ T ≤ 90 °C) and relative humidity (50% ≤ RH ≤ 80%). MATLAB software was used to solve the partial differential equations using finite difference method. The SCM model was found to give a good description of the experimental data with error less than 5%. The validated model was then used to simulate the desulfurization reaction under a wide range of operating conditions. It was found that higher initial concentration of SO2 reduces the desulfurization activity. In contrast, the presence of higher concentration of NO, reaction temperature and relative humidity in the system enhanced the desulfurization activity of the sorbent.