Isothermal kinetic study of CO_2 gasification of torrefied oil palm biomass

摘要

Torrefaction is an attractive pre-treatment route to enhance the fuel properties of oil palm biomass before their utilisation in thermochemical process. This work evaluates the effect of torrefaction on the gasification behaviours and kinetics of three oil palm biomass, i.e., EFB, MF, and PKS. Three well-known kinetics models, i.e., modified volume reaction model (MVRM), random pore model (RPM), and modified random pore model (MRPM) were used to correlate the conversion rate, dX/dt versus the extent of conversion, X data. The gasification reactivity generally increases in the order of PKS, MF, and EFB, which correlates with their inorganic minerals content. Torrefied oil palm biomass showed reduced gasification reactivity relative to their non-torrefied analogues due to the removal of volatile matters from biomass after torrefaction. Amongst the three kinetic models, MRPM best represents the gasification reactivity profile for all the three torrefied and non-torrefied oil palm biomass. The resultant apparent activation energies reveal: (ⅰ) Higher activation energies for the torrefied EFB and MF compared to their non-torrefied analogues, which is consistent with the lower reactivity for the former caused by the higher residual carbon content in the torrefied samples; (ⅱ) Higher activation energy for non-torrefied PKS relative to that for torrefied PKS, which can be attributed to the formation of pores and cavities in the latter; and (ⅲ) Lower activation energies values for the three oil palm biomass relative to the literature values, which is likely caused by the presence of potassium and calcium in these oil palm biomass.