Investigation on ash slag from combustion of medium-density fiberboard production residues

Abstract

Medium-Density Fiberboard (MDF) is made by breaking down of wood as conifer wood thinnings and wood processing industry residues including sawdust, which is glued and pressed together, and is widely used as a building material. Woody residues from production of MDF (MDFres) is a large and available amount and can be combusted for heat and energy production. In this study, MDFres fuel properties and ash melting behavior were investigated. The ash slag from combustion of MDFres in a residential combustion appliance was collected and analyzed with scanning electron microscopy–energy-dispersive X-ray spectrometry (SEM–EDX). The results show that MDFres ash contains considerably high content of calcium, silicon, potassium and sodium. The ash has a very low fusion temperature, of about 878 °C in oxidizing atmosphere. The ash slag collected from combustion of the MDFres has dense and intact structure and glass-like morphology, indicating that the ash experienced intensive melting. EDX spot analyses on the chemical composition of the slag reveal that Ca, Si, Al, Mg, K and Na are the main elements contained in the slag. Together with the spot analysis, EDX mapping analyses results indicate strong correlations between the elements Ca, Si and K and indicates formation of alkali silicates that have low melting temperatures during combustion of MDFres. Formation and presence of these low temperature melting compounds are the main reason for ash sintering and slagging at a sufficiently high combustion temperature.