Release characteristics of potassium and sodium during pellet combustion of typical MSW fractions using the FES method

Abstract

The temporal release characteristics of sodium and potassium (Na and K) during the pellet combustion of municipal solid waste (MSW) were comparatively studied using calibrated flame emission spectroscopy (FES). A lab-scale setup with a Hencken burner was used to create a stable high-temperature environment for pellet ignition and combustion. The results revealed a three-stage combustion process (devolatilization, char, and ash stages) for most waste fractions, whereas a one-peak release distribution was observed for plastics. In contrast, biomass-based products and kitchen waste were characterized by dual-maxima release shapes. In general, the release concentrations of both Na and K were the highest in the char and ash stages because of the higher pellet surface temperature than that in the devolatilization stage. Although the variation in pellet mass changed significantly during devolatilization, less than 10% of alkali contents were released. Compared to the combustion characteristics, the waste compositions were considered a critical factor. The peak release concentrations increased almost linearly with the initial alkali concentrations during char oxidation. In addition, paper and wood waste were found to be the potential sources for the release of Na and K, respectively, second only to kitchen waste. Finally, the possible transformation processes of alkalis during waste combustion were discussed.