Analysis of Industrial Waste in Wood Pellets and Co-combustion Products

The present work aims to explore the blending of inorganic industrial residues and wood in the pelletization and evaluate the effects in the combustion products. This procedure can provide an alternative route for residues disposal with the added benefit of energy recovery. However, as this study shows, some problems can arise. The pellets were produced from a mix of sawdust and six different residues: plastics, polymeric mould wastes, tire fluff, polishing dust, textile and shoemaking residues; in quantities ranging from 5 to 10 %. The chemical composition and physical characteristics, of both the raw residue materials and the different types of pellets produced, were evaluated. Afterwards, the combustion of the pellets was studied, and gas emissions and ashes were analyzed. The pellet production process presents some problems. The structure of some residues such as plastics, textiles and fluff, can decrease the mechanical strength and increase pellet fines. The co-combustion gas emissions of pellets with 10 % of shoemaking residues, 5 % of textiles and 10 % of plastics do not meet the legal concentration limits for CO. Moreover, the total concentration of heavy metals proved to be problematic in pellets with incorporation of 5 % of fluff. The pellets with incorporation of 10 % of plastics and 10 % of polishing dust presented some problems related to the formation of ash in the domestic boiler used. Indexes of slagging and fouling prediction indicate a high tendency for ash problems occurrence given the total alkalis present in all the pellets, and the silica/aluminum complex in the pellets with 10 % plastics.