Distribution of Inorganics and Trace Elements during Waste Gasification in a Bench-Scale Fluidized Bed

The gasification of refuse-derived fuel (RDF) in a fluidized bed gasifier followed by a high-temperature filter was investigated in a bench-scale plant. The tests were performed at a fixed reactor (bed and freeboard) temperature of 850 °C and filter temperatures of 450 and 550 °C using air-N2 and air-steam mixtures as gasification agents with equivalence ratios (ER) in the range of 0.24-0.32 and sand and sand/dolomite mixtures as bed material. The influence of these parameters on the gasification performance was studied with the primary objective of understanding the fate of fuel-N, fuel-S, fuel-Cl, and the distribution of fuel-trace elements into the gas and ash streams (both filter and bottom ashes). It was found that steam addition, besides increasing the yield of H2, promoted the yields of NH3, H2S, and tars. The catalytic effect of dolomite on decreasing tar production was not observed in our experiments. Fuel-N and fuel-S were mainly converted into ammonia (≥40%) and H2S (≥20%). Most of fuel-Cl was measured in the filter ash, whereas only a minor fraction of the fuel-S was detected in this solid fraction, especially at low temperature. The distribution of trace elements into the filter and bottom ashes was consistent with their inherent volatile behavior, although precise quantification was difficult due to the heterogeneity of the fuel. Preliminary assessment of utilization/disposal options of the filter and bottom ashes generated was made by studying the enrichment factor.