Kinetic analysis of co-pyrolysis of biomass/sorbent mixtures at different ratios

Abstract

Biomass is one of the most promising sources of renewable energy. Gasification of carbonaceous and lignocellulosic biomasses produces gases, which can be upgraded as a clean feedstock for power plants. However, control and optimization of industrial gasification is still a challenging task due to a lack of understanding in solid state reaction mechanisms. This work attempts to improve kinetic modelling of a gasification process through analyses of four locally available biomasses, namely, oil palm trunk, fronds, empty fruit bunches, and coconut fibre. The biomasses were mixed with sorbents to enhance the pyrolysis and gasification reaction in a thermogravimetric analyser. In addition to common sorbents such as oxides of magnesium and calcium, two other sorbents, namely, rice husk and eggshell (a source of calcium carbonate) were blended at different ratios of biomasses to investigate their behaviour under pyrolytic decomposition conditions. Activation energies of the mixtures were obtained with the Reaction Rate Constant Model (RRCM). It was found that the mixtures had higher activation energies as compared to pure biomasses. For example, oil palm trunk without sorbent and with 50 wt% calcium oxide had activation energies of 26.87 and 46.83 kJ/mol, respectively. Majority of the sorbents also increased the thermal stability of the biomasses by increasing the mixtures’ resistance to weight loss under high temperature. However, rice husk reduced the mixtures’ thermal stability when compared with pure biomasses as evident in the oil palm trunk case when the mixture became 6.2% less thermally stable.