Pyrolysis and Char Burnout Characteristics of Cassava Peelings as Potential Energy Source

Abstract

The pyrolysis behaviour, kinetics and char burnout of cassava peelings as a potential source of energy has been investigated using TGA. Four heating rates: 5, 10, 15 and 20oC/min were used to evaluate the kinetic parameters of the thermal decomposition process using iso-conversional non-isothermal method. An isothermal method was used to evaluate the burnout behaviour of char produced at 20oC/min by adopting the Arrhenius equation. During the pyrolysis process, it was observed that two distinct peaks were identified during hemicellulose decomposition which could be due to component complexity of agricultural waste products. The activation energy at 20% conversion was found to be 164 KJ/mol which is higher than what was observed between 30-50% conversions (151-154 KJ/mol). However, as the conversion increased from 60-90% the activation energy also increased from 162-290KJ/mol which suggests that the pyrolysis reaction progressed through multi step kinetic process. It was observed that the burnout of the chars was found to decrease with increase in heating rate up to the char produced at 15oC/min. However, further increase in the heating rate to 20oC/min during the pyrolysis process produced char with faster burnout profile. This may be due to higher porosity of the chars formed at that heating rate. It was also observed that as the heating rate increased from 5-15oC/min during pyrolysis, the activation energy of the resultant chars reduced. Again, higher activation energy was observed for the char produced at 20oC/min implying that highly porous char structure can diminish mass transfer limitations during char combustion. The pyrolysis and char combustion kinetics will be useful for modelling and the design of thermo-chemical cassava peelings conversion systems

Keywords: Biomass pyrolysis, heating rates, char burnout, kinetics