Development of CCSEM for the Characterization of Chemical Species in PM_(10) Emitted from Combustion of Sewage Sludge

摘要

Computer Controlled Scanning Electronic Microscopy (CCSEM) was developed to characterize the chemical species in PM_(10) emitted from combustion of dried sewage sludges in laboratory-scaled drop tube furnace (DTF). Compared to the traditional CCSEM analysis method, the collected PM_(10) was first size-segregated by low-pressure-impactor, and each size was then subjected to CCSEM analysis to avoid the bias of the larger particles against the smaller ones. More than 1000 particulates were analyzed in each size. After analysis, the original results were processed by the newly developed categories to quantify both the species in each size and the mode of occurrence of elements of interest. The elemental/oxide composition, analyzed by CCSEM, was compared with that analyzed by XRF, while the chemical species was also characterized by XRD to prove the preciseness of CCSEM analysis. The comparison of PM oxide composition indicates that, the developed CCSEM analysis has a rather incredible preciseness. The species in PM larger than 2.5 μm are dominated by aluminosilicates and their mixture with phosphates consisting of the refractory elements. These particles were formed by two routes: direct transferring of the inherent minerals and agglomeration of smaller particles. As a result, PM around 2.5 μm was formed having the irregular shape. With PM size down to around 0.1 μm, the species within it was found to be dominated by the phosphates, sulfates and chlorides as well. They were formed by the re-condensation of vaporized elements including alkali and zinc. In addition, both the sludge type and the oxygen content in the gas atmosphere affect the species in PM considerably