Thermal degradation of olive solid waste: Influence of particle size and oxygen concentration

Abstract

The aim of this work is to study the effect of the particle size and the oxygen content on the thermal degradation of olive solid waste (OSW). Thermogravimetric analyses of different particles sizes (0.5–2.8 mm in diameter) were performed. Three different atmospheres were used: on the one hand, an inert atmosphere (N 2) in order to study the pyrolysis of the olive solid waste and on the other hand two oxidative atmosphere (10% O 2/N 2; 20% O 2/N 2). Pyrolysis under oxidative conditions (10% O 2/N 2; 20% O 2/N 2) takes place according to three stages: drying, volatiles emission and char oxidation whereas in the case of pyrolysis under inert conditions only the two first stages occur. Loss of humidity and volatiles are independent of the oxygen concentration. However, the initial temperature of char oxidation is decreasing with the increase of oxygen concentration. Weight loss profiles as well as CO and CO 2 emission rates during the oxidative pyrolysis are depending on the particle size of OSW. In fact, thermal degradation and emission rates of carbon oxides emissions proceed at lower temperatures for the smallest particle size. The temperature ranges of volatilization and char oxidation as well as the amount of remaining ash are also depending on the particle size. Reaction kinetic parameters are obtained under inert and oxidative conditions using global independent reactions model and compared with other biomass. Activation energy and preexponential factor of the devolatilization step increase with oxygen concentration. However, the reaction order was not affected by the variation of the oxygen concentration and the particle size with a value between 0.6 and 0.8.