Comparative behaviour of agricultural biomass residues during thermochemical processing.

Abstract

A study of the pyrolysis and gasification of biomass residues such as oil palm shells and fibers, coffee shells, sugarcane bagasse and beech wood is presented. All of them are abundant agroindustrial biomass residues in Latin American countries. The characterization of the raw materials and products includes proximate analysis (water, ash and volatile matter contents) and ultimate analysis. Pyrolysis and gasification experiments are carried out in a thermobalance and in a pilot scale rotary kiln reactor. Both facilities are equipped with evolved gas analysis. Pyrolysis experiments were carried out using nitrogen as carrier gas by heating up to a temperature of 950 °C. Gasification is performed using water vapour as reaction agent in a concentration of 70 % H2O in nitrogen. The gasification temperature is set to 850 °C. All wastes show similar behavior during pyrolysis in the thermobalance with the main mass loss at temperatures below 550 °C. The solid fraction varied from 18 % for sugarcane bagasse to 27 % for oil palm shells and the gas fraction from 18 % for oil palm shells to 22 % for sugarcane bagasse. The main evolved gases are CO2 (9 – 12%), CO (3.5 – 7.5 %) and CH4 (1.6 – 3 %). H2 was also found but in a very small fraction (0.5 – 0.7 %) (all fractions are referred to the initial dry mass). The heating value of the pyrolysis products from the experiments in the thermobalance of the different wastes presented small variations with a mean value of 6.5 MJ kg -1 for the evolved gas, 20 MJ kg -1 for the tar and 19 MJ kg -1 for the solid residual. The presence of secondary reactions in the rotary kiln affects considerably the amount of gas and tar in the products. The higher heating value of the evolved gases varies between 17 and19 MJ kg -1 . The obtained results allow a possible further technological use of these materials as a cheap renewable energy source in countries where these materials can be found.