Kinetic studies and mathematical modelling of Imperata cylindrica flash pyrolysis

Abstract

Biomass pyrolysis product offers great potentials in facilitating energy and environmental challenges. This is, however, yet to be realized due to some technological barriers that limit its economic potential. In this thesis, a flash pyrolysis of Imperata cylindrica in a transported bed reactor is investigated, aiming at improving its overall performances from both operation and design perspectives using a mathematical modelling approach. A macroscopic model of the process was used in estimating the kinetic parameters of I. cylindrica and in determining the optimal operating conditions of the reactor. A microscopic model using Computational Fluid Dynamics (CFD) was applied to study the reactor’s hydrodynamics and to determine optimal values for key design parameters, i.e., solid inlet positions, gas inlet position and height-width ratio. To facilitate more detailed analyses, a new algorithm was developed for determining cellulose, hemicellulose and lignin compositions from biomass devolatilization kinetic study. The results obtained confirmed that I. cylindrica has good fuel properties and decomposes easily in the presence of heat, thus making it a suitable feedstock for biofuel production in thermochemical processes. However, the laboratory scaled transported bed reactor was found inefficient and requires very high operating temperature in maximizing biooil yield. Based on the CFD study, the efficiency can be improved if the biomass and hot-sand inlets were positioned closer to the reactor wall and at opposite end. The results also indicated that a good hydrogen gas yield could be obtained from steam reforming of I. cylindrica biooil. In conclusion, the mathematical modelling approach carried out in this study has highlighted the potential of the proposed process and the use of I. cylindrica as a good biomass source for energy.