Kinetic studies on the removal of hydrogen chloride from flue gas by hydrated lime powders in a bench scale fixed bed reactor

The kinetics of the removal of hydrogen chloride gas by hydrated lime powders was determined in a fixed bed bench scale reactor at conditions representative of low temperature dry sorbent injection process.

The kinetic tests showed that relative humidity of the gas was the most important parameter in determining both the rate and extent of conversion. Other operating parameters such as temperature, gas concentration, surface area of the hydrated lime also affected the conversion at different degrees depending on the relative humidity of the test condition. Hygroscopic property of the reaction product i.e. calcium chloride, significantly affected the conversion at relative humidities of 25% and higher. Diffusional resistance in the solid product layer, was determined to be the primary reason for incomplete conversion of the hydrated lime in test conditions <25% relative humidity.

The shrinking unreacted core model based on diffusion of hydrogen chloride through the product layer as the limiting mechanism, was found to be unsuitable for the tests exhibiting incomplete conversion. An empirical model, developed based on empirical correlations from the experimental data of this study, was found to predict reasonably well the reported conversions in other studies.