2015

Bajamundi, Cyril

Waste-to-Energy (WtE) facilities have the potential to treat large volumes of waste generated by constantly growing communities. Due to the heterogeneous and dynamic nature of the composition of these wastes, several issues arise that work against the realization of this potential. This thesis seeks to address production of polychlorinated dibenzo-p-dioxins/ dibenzofuran (PCDD/F) and alkali chloride production in a 140 MWth bubbling fluidized boiler fired with fuel mixtures with advanced energy-share (50 to 70%) solid recovered fuel. Combustion of 50% solid recovered fuel (SRF) - 44% bark - 6% sludge results to an in-boiler PCDD/F production level of 0.7 ng/Nm³; with the addition of Spellets the production level is reduced to 0.3 ng/Nm³; while co-combustion with peat increases production to 1.3 ng/Nm3. Aerosol data from the backpass, thermodynamic modeling and x-ray absorption analysis of electrostatic precipitator (ESP) fly ash reveals that adding sulfur pellet could induce sulfation of Cu, a key catalyst in the de novo formation of PCDD/F. During peat cocombustion, high amounts of Cu (mostly coming from the SRF) poorly volatilized, have remained in the ash and could have easily aided the heterogeneous formation of PCDD/F in the post combustion zones on the boiler. The ESP on the other hand can reduce the concentration of PCDD/F in the flue gas path however phase redistribution of PCDD/F from solid to gas can occur. In the search for a robust anti-corrosion procedure, sulfate injection is found to be superior in ensuring that the superheater (SH) deposits have minimal Clcontent even during firing of 70% SRF - 24% bark - 6% sludge mixture. Sulfate injection can be introduced in a strategic location in the boiler to ensure inflight sulfation of corrosive alkali chlorides. Other strategies tested to minimize Clcontent in the deposits are peat co-combustion and sulfur-pellet addition. Peat co-combustion can lower the Cl-content both in the aerosol and superheater deposits, but its performance is highly dependent on the quality of the SRF; sulfur-pellet addition meanwhile can lower the concentration of Cl in the aerosol and SH deposit though to a lesser extent compared to sulfate injection. Through the use of sulfur based additive, PCDD/F and alkali chlorides production can be addressed, thus contributing to the realization of the potential of WtE facilities.