In this study, the co-combustion of black liquor and oil sludge is investigated. The properties of the fuels are analyzed, and the co-combustion characteristics are explored by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TG-FTIR). The synergistic effect, activation energy as well as gas yield are also studied from TG-FTIR results. The results show that the addition of oil sludge can promote the reaction in the early stage, as indicated by the combustion characteristic index and the flammability index. The TG-FTIR also shows that the swelling behavior of black liquor appears to block the release of volatile matter. The weaker SO2 emission and XRF analysis for the black liquor indicate that most of the sulfur remained in the ash. A positive synergy effect existed in the early stage, and the activation energy decreased with the addition of oil sludge. Distinct stages could be observed in the single pellet combustion experiments. Adding oil sludge to the black liquor promoted surface bubbles and ash melting. Surface bubbles indicate more volatile breaks through the plastic state layer formed on the black liquor and increase the reaction. However, adding oil sludge should be controlled to reduce the hindrance to the reaction due to ash melting.
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