Fast pyrolysis of pulp and paper mill sludge in a bubbling fluidized bed: Unlocking energy potential through insights into tar formation and combustion characteristics

The fast pyrolysis of pulp and paper mill sludge (PPMS) in a bubbling fluidized bed (BFB) is a promising solution for converting PPMS into liquid fuels or chemicals for waste utilization but lacks sufficient understanding. This study comprehensively explored the effects of bed temperature, fluidization number, and particle size on the fast pyrolysis of deinking sludge (PPMS-DS) and sewage sludge (PPMS-SS) from a wastepaper pulp and paper mill, unveiling for the first time the combustion behavior of PPMS tar, gas release patterns, and reaction kinetics. Results revealed that bed temperature was the most critical factor influencing tar yield, followed by the fluidization number. Under optimal conditions, the tar yields were 61.49 wt% for PPMS-DS and 66.13 wt% (dry ash-free basis) for PPMS-SS. PPMS-DS tar exhibited better fuel properties, with a higher heating value (38.41 MJ/kg) and lower oxygen content (7.08 wt%). The combustion of PPMS tar involved three steps: low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature oxidation (HTO). The kinetic differences among the reaction steps were clear, with LTO and FD having the respective lowest and highest apparent activation energies. This research supports the development of efficient and sustainable PPMS-to-energy technologies, with significant potential for large-scale industrial applications.