Optimization of Ca-Based Sorbents for Acidic Gases Removal Produced by Municipal Solid Waste Combustion

Acidic gases (mainly hydrochloric acid, HCl; and sulphur dioxide, SO2) are the common pollutants released from the incineration of municipal solid waste (MSW). To meet the stiffening emission limits on incineration process, the dry scrubbing process is now widely accepted as one of the preferred methods for treating acidic gases. This work focuses on the optimization of a Ca-based sorbent (Ca(OH)2) for acidic gases. The effects of the pellet size, the concentration of acidic gases as well as the addition of fly ash were studied. Sorbents before and after reaction were characterized by using the X-ray diffraction (XRD) to identify the solid species. Together with different particle sizes (100 up to 425 mm), it was found that only internal kinetic phenomena are of importance. External transport processes can be considered as infinitely fast. It was observed that the behavior of HCl and SO2 is completely different. While SO2 removal can really be described by a shrinking core model, the reaction of HCl is much more complex, and influences the diffusivity of the SO2. This was observed by adapting the HCl/SO2 ratios. Furthermore, fly ash was investigated as sorbent or additive for acidic gases removal. Fly ash itself showed very low activity for HCl and SO2 removal. However, when it was added as additive to Ca(OH)2, the removal efficiencies of Ca(OH)2 for HCl and SO2 were enhanced dramatically. More experiments will be carried out to further investigate this improvement. The systematic experimental study in this work helps us to better understand the reaction network between the Ca(OH)2 sorbent and the acid gases in flue gas cleaning process. A mathematical model for the combined removal is under development, both for the industrial entrained flow reactor as for the lab packed bed set up.