The Fate of Trace Elements during the Co-Combustion of Wood-Bark with Waste

Abstract

An experimental study has been made into the behavior of trace elements during the combustion of spruce wood-bark with three auxiliary fuels, agricultural waste, pulp sludge, and plastic waste, under simulated fluidized bed combustion conditions. A novel suspension-firing reactor has been used to achieve these conditions, with operation at 800 and at 900 °C, with an air/fuel ratio of 1.2:1 throughout. Experimental results have been interpreted using a thermodynamic equilibrium model. The behavior of seven trace elements (Cd, Cr, Mn, Ni, Pb, Se, Zn) has been studied using inductively coupled plasma ionization-mass spectrometry. In addition, an atomic absorption-based technique has been used to study the behavior of Hg. The experimental data indicate significant emissions of all the elements except Ni and Se, which was present in the fuels at low concentration below the lower limit of quantification. Whereas the majority of fuel Hg is likely to be emitted from the combustor, irrespective of fuel blend employed, the level of emissions of Cd, Cr, and Mn may be affected significantly by the addition of auxiliary fuel. The use of wood-bark as a base fuel for boilers is pertinent to paper mills and timber producers where large quantities of bark are generated as a byproduct.