Simultaneous HCl/SO2 Capture by Calcined Limestone from Hot Gases

Some confusion still exists in the literature regarding the simultaneous absorption of SO2 and HCl by calcined limestone in hot flue gases. Therefore, further efforts to understand and clarify the absorption behaviors of SO2 and HCl are presented in this study. Experiments were carried out under conditions that simulated combustion in a fixed-bed reactor coupled with an online Fourier transform infrared spectrometer. The fixed-bed reactor used was specially designed to be capable of handling high-temperature operations involving gas-solid reactions. This paper described and explained the phenomena of variations in the concentration profiles of SO2 and HCl during, the simultaneous absorption process. This work suggested possible heterogeneous and homogeneous reactions that may occur under the conditions being studied. Particular emphasis is placed on elucidating why concurrent sulfation enhancement and chlorination suppression occurs; experimental evidence confirmed that these processes were caused because of the behavior of the sulfation process of chloride. In the present study, to continuously monitor SO2 and HCl discharged during reaction processes plays a crucial role in observing particular phenomena, providing important information regarding absorption characteristics. From the experimental results, it was observed that, upon increasing the temperature from 650 to 700 degrees C, chlorination was considerably suppressed because chloride started to vigorously react with SO2, leading to the indirect enhancement of sulfation and the re-release of HCl into the gas phase. It was also surprising to find that, at or above 700 degrees C, the overall uptake efficiency remained nearly unchanged despite the difference in reactivity of SO2 and HCI. Besides, the importance and impact of the gas atmosphere on the uptake efficiency was also analyzed and compared.