Removal of HCl in Flue Gases by Calcined Limestone at High Temperatures

Experimental study of dry HCl removal from simulated combustion flue gases using calcined limestone (CaO) is reported. The study was conducted in a unique fixed-bed reactor coupled with an online Fourier transform infrared (FTIR) spectrometer to investigate the effects of the presence of SO2, CO2 and O-2 on the chlorination reactivity of calcined limestone. The dechlorination efficiency, defined by the effluent HCl concentration, would be used to describe the HCl absorption history to gain a better understanding of the chlorination behavior. The experimental results indicated that the HCl uptake capacity remains less affected under various gas atmospheres at 650 degrees C although the chlorination is found to be faster when CO2 is present. At temperatures of 750 or 850 degrees C, the presence of SO2 or O-2 significantly decreases the reactivity of the calcined limestone toward HCl. The concurrent sulfation of chlorides, such as CaCl2 center dot H2O and/or CaClOH, causes the subsequent rerelease of HCl to the gas phase, thus reducing the attainable extent of the chlorination reaction. The presence of O-2 impedes the conversion of calcined limestone to chlorides, presumably through some type of reaction involving the dechlorination of the sorbent particles.