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Release of Alkalis and Chlorine from Combustion of Waste Pinewood in a Fixed Bed

Combustion of biomass in a boiler releases alkali metals and chlorine which, together with silicon and sulfur, are responsible for slagging, fouling, corrosion, and particulate emissions. This research investigated the effects of the primary (under-fire) air flow rate, ṁair, and its preheating temperature on the ignition and burning rates of pinewood chips in a laboratory fixed bed furnace and on the release of alkali metals and alkali earth metals (potassium (K), sodium (Na), calcium (Ca), magnesium (Mg)) and chlorine. The air flow rate, ṁair, through the bed was varied in the range of 0.085–0.237 kg/(m2 s), resulting in an overall excess primary air coefficient λ varying from 0.56 to 1.1. Air was also preheated in the range of 20–135 °C. Results showed that increasing either ṁair or the air preheat temperature increased the flame propagation rate (ignition rate) and the mass burning rate of the fuel. Moreover, the release of Cl was nearly complete (>99%) in all examined cases, whereas the release of alk...