Parametric study of heavy metal partitioning in a pilot scale incinerator burning simulated municipal solid waste

Incineration is a combustion process used to convert toxic waste to benign gases and residue in presence of excess air. The products of the incineration process are bottom ash, fly ash and the flue gas. Most of the metal-based phases formed in incineration are toxic and their emissions need to be strictly controlled. Therefore, behavior of metal species during incineration must be well understood. Such understanding is possible based on the experimental identification of the metal phases formed in the waste combustion and determination of their concentration in various incineration products. A pilot-scale incinerator of 140,000 Btu/hr capacity was constructed, characterized and operated at NJIT. A synthetic fuel representative of the municipal solid waste in the United States was formulated and produced in 600 lb batches. The synthetic fuel was in the form of solid pellets and was characterized by standard ASTM tests. The solid fuel contained Fe and SiO2, and was doped with trace amounts of Al, Ni, Cr, Hg and Pb. Several experiments were performed on the incinerator with varying fuel-air equivalence ratio and both gaseous and condensed products were sampled.Atomic absorption spectroscopy was used to identify metal concentrations in the ashes and the flue gas. X-ray diffraction was used to identify metal phases in the bottom ash and the fly ash. Scanning electron microscope was used to study the morphology of the ash particles and energy dispersive X-ray spectroscopy was used to identify the spatial composition of the ash particles. Size distributions of the fly ash particles were obtained using sieves and optical microscopy. It has been observed that the fly ash particles have bimodal size distribution and that the particles of different sizes have different elemental and phase compositions. Thermodynamic equilibrium computations for the incineration process were conducted to obtain the adiabatic flame temperature and identify the metal phases produced at equilibrium conditions