Studies of Cd, Pb and Cr distribution characteristics in bottom ash following agglomeration/defluidization in a fluidized bed boiler incinerating artificial waste

This study focused on the effects of agglomeration/defluidization on the Cd, Pb and Cr distribution in bottom ash particles of different sizes. In this study we have incinerated artificial waste, which was a mixture of sawdust, polypropylene, selected metal solutions, and polyethylene. The experimental parameters included Na concentration, addition of Ca and Mg and operating temperature. The results indicated that particle size decreased by attrition and thermal impact in the absence of added Na. When Na was added to the system, this metal reacted with silica sand to form eutectics, which increased particle size. Further addition of Ca and Mg was found to prolong the operating time, with greater amounts of liquid eutectic accumulating, leading to increase particle size.The heavy metal concentrations in coarse and fine particles were greater than those present in particles of intermediate sizes over a range of experimental conditions. As the particle size decreased below 0.59 mm or increased above 0.84 mm, the heavy metal concentrations increased. As Ca and Mg were added, the heavy metal concentrations in particles of all sizes increased relative to those present in identical particles when no metals or only Na were added. Additionally, the ratio of Cd sorption to silica sand decreased with increasing Na concentration, but Cr sorption had the opposite tendency. Therefore, while the addition of Na tended to increase agglomeration, it also increased the tendency for heavy metals to remain in the sand bed of fluidized bed incinerators. Addition of Ca and Mg not only inhibited the agglomeration/defluidization process, resulting in increased operating time, but also enhanced the removal of heavy metals by silica sand, decreasing the concentration of heavy metals in reactor exhaust.