Thermal degradation of Miscanthus pellets: kinetics and aerosols characterization

Interest in the cultivation of plants specifically for energetic use has grown tremendously in recent years. Among the numerous tested energetic plants, Miscanthus seems to be an especially, promising 'energy crop'. The presented data may have a contribution in developing Miscanthus pellets as a feedstock for energy recovery systems. Combustion and pyrolysis are efficient methods for controlling energy efficiency from Miscanthus. Thermogravimetric analyses were performed at heating rates of 5, 10, 15, and 20 degrees C min(-1) under nitrogen and air atmospheres with analysis of gaseous (CO, CO2 and VOC) pollutants and aerosols. Reactivity and kinetics measurements of Miscanthus pellets were also performed. Thermal degradation of Miscanthus pellets under inert atmosphere is similar to those found for other lignocellulosic materials. Under nitrogen, the main study was the determination of kinetic constants. These constants for main devolatilization step are not affected by variation of the heating rate with activation energy of 90 kJ mol(-1) and a first reaction order. Thermal degradation of Miscanthus pellets under air occurs in main two steps: rapid decomposition and residual degradation. The amounts of CO2, CO and VOC emitted were 17.4, 3.7 and 1.0 mmol g(-1), respectively. Pellets degradation produces 1.0 x 10(12) particles (PM10) per gram of sample. 99% are particles with a diameter below 1 mu m (57% are nanoparticles inferior to 0.1 mu m). Nucleation mode dominates during the first step (190-253 degrees C) centred at 0.04 mu m whereas during the second step (253-310 degrees C) a coagulation mode is observed centred at 0.5 mu m.