Combustion characteristics and kinetics of torrefied olive pomace

• A two step process based on torrefaction and combustion is proposed for OP recovery.
• Torrefaction improves strongly the OP combustion properties.
• The global reactivity of TOP decreases with increasing the torrefaction temperature.
• Kinetic model based on OP pseudo-components simulates correctly the TOP combustion.
• Model allows extracting the TOP composition (HC, C, L) and the kinetic parameters.

This investigation aims to examine the OP (olive pomace) recovery as a fuel in heat production systems. A two-steps process is proposed to adapt OP for such application. Firstly, the OP torrefaction is performed for various temperatures in order to improve the combustion properties. It is seen that, in addition to the hydrophobic character, the higher heating value of the samples increased with the torrefaction severity. Secondly, the reactivity in air of TOP (torrefied olive pomace) using thermogravimetric analyses is examined. The results show a decrease in the TOP reactivity with the increase of the torrefaction temperature. This behaviour is attributed to the degraded proportion of the three macro-components: Hemicellulose (HC), Cellulose (C), Lignin (L). A kinetic model based on the HC, C and L thermal degradation is applied to simulate the combustion of OP and TOP samples. The activation energies of the macro-components degradation and char combustion reactions are determined. In addition, the proportions of HC, C and L left in the TOP samples after the torrefaction step are extracted. This modelling part brings understanding keys on both torrefaction and combustion steps. It also provides kinetic parameters concerning OP and TOP combustion, which are necessary for combustor sizing.