Kinetics of Biomass and Waste During Pyrolysis and Steam Gasification

Abstract

High temperature pyrolysis and steam gasification of paper and yellow pine woodchips have been investigated in a batch type flow reactor at defined temperatures in the range of 700°C to 900°C and known molar ratio of steam to feedstock. The initial weight loss of the material during both pyrolysis and gasification was found to be similar thus revealing that material initially undergoes pyrolysis. The weight loss increased with increase in gasification temperature and retention time during both pyrolysis and gasification. The char yield decreased with increase in reaction time due to thermal decomposition of the material and the progress in char reactions during the gasification process. The yield of char decreased with increase in the reaction temperature from low temperature of 700°C to high temperature of 900°C at any residence time in the reactor. The weight remaining from the gasification of paper was lower than that from woodchips initially but at longer residence times the paper showed higher weight remaining than woodchips because of higher mineral matter and fixed carbon in paper than woodchips. The presence of higher volatile matters in paper was easily released from structure when compared with the volatile matters of woodchips at low temperatures. The Arrhenius’s plots obtained from the weight loss data of the sample during gasification at different temperatures was used to obtain the activation energy. The activation energy for steam gasification of woodchips and paper were found to be 117.2 and 69.6 kJ/mol, respectively while the pre-frequency factor for woodchips and paper were found to be 10,029 and 3.2 s−1, respectively. The specific rate for steam gasification of woodchips and paper was compared by the Arrhenius plot. The results showed higher specific steam gasification rate of woodchips than paper at all the temperatures examined. It is conjectured that higher porosity of wood chips favors faster reaction rate because of the increased surface area for devolatilization and reaction. The biomass and wastes are good source of renewable fuels to produce hydrogen or liquid fuels using controlled steam gasification for minimum char and residue by utilizing the most desirable conditions favorable for gasification. The kinetics data assists in the modeling and simulation to provide aid in the development design tools for practical implementation.