Thermogravimetric analysis of (co-)combustion of oily sludge and litchi peels: combustion characterization, interactions and kinetics

Highlights: • (Co-)combustion of oily sludge and litchi peels was quantified. • Kinetic parameters were estimated using Kissinger-Akahira-Sunose method. • Blend E_a increased with devolatilization and decreased with char oxidation. • E_a reached its minimum with 15%–20% litchi peels added. • D3, R2 and A3 were the potential reaction models for oily sludge and their blends. - Abstract: The thermal characteristics and kinetics of oily sludge, litchi peels and their blends were comprehensively evaluated using thermogravimetric experiments under air atmosphere. Results showed that devolatilization, ignition and burnout indices of litchi peels were higher than those of oily sludge, with better combustion characteristics. However, co-combustion performance decreased with increased litchi peels fraction. Such interactions as inhibition effect on devolatilization and promotion effect on char oxidation of oily sludge occurred. Average activation energy was estimated at 118.1 kJ/mol for oily sludge and 215.2 kJ/mol for litchi peels using the Kissinger-Akahira-Sunose integral method and reached its minimum value with the addition of 15%–20% litchi peels. Trend of activation energy was consistent with the interaction analysis during co-combustion process. Kinetic triplets were also estimated using the integral master-plots method, while the most suitable reaction model for three stages of oily sludge and their blends was proposed.