Morphology and composition of the fly ash particles produced in incineration of municipal solid waste

This paper describes the results of experiments using a pilot-scale, 140,000 Btu/h, solid fuel continuous feed laboratory incinerator. A synthetic fuel representative of the municipal solid waste in the United States was formulated and used in this research. The fuel contained Fe and SiO2,, and was doped with trace amounts of Al, Ni, Cr, Hg, and PbO. Experiments were performed with varying fuel-air ratio, and both gaseous and condensed products were collected and analyzed. This work focuses on the characterization of composition and morphology of fly ash particles captured in a fabric filter. Particle size distributions were obtained using optical microscopy and sieving. Atomic absorption (AA) was used to determine bulk compositions of the size-classified ash fractions. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to study the morphology and surface compositions of the ash particles. It was observed that the fly ash particles have bimodal size distribution and, most interestingly, that the ash particles of different sizes have different elemental and phase compositions. Concentrations of Cr, Ni, and Fe were greater in the coarse particles (up to I-mm diameter), whereas concentrations of Al and Si were higher in the finer particles (less than 75 mum). Maximum concentrations of Pb and Hg occurred in the 150-300-mum particles. It is suggested that if a correlation between the composition and size of the ash particles similar to that observed in this research exists in the products of industrial combustors, a technique of ash processing based on the particle size classification could be developed. Applying such a technique could result in the efficient and inexpensive removal of the lead- and mercury-rich particulates from the produced ash. The processed, environmentally benign ash portions will therefore be useful for a variety of the recycling-based manufacturing, and metal recovery processes. (C) 2002 Elsevier Science B.V. All rights reserved.