Energy conversion of agricultural biomass char: Steam gasification kinetics

The present study investigates steam gasification kinetics of chars from six agro-industrial biomass residues (citrus pomace, grape pomace, reed, olive pomace, reed lignin and straw lignin). Experiments were performed in a TGA in steam/N2 mixtures at different temperatures and steam partial pressures. Kinetic parameters are determined by fitting computed char conversions to experimental char conversions. The conversions curves are computed using recently suggested models which are selected based on the K/(Si + P) ratio. The objective of the study is threefold: (1) to determine kinetic parameters for agricultural biomass chars, (2) to validate the models and (3) to test whether a unified activation energy can be used to predict the char gasification times. The activation energies varied between 135 and 165 kJ/mol, and the reaction orders with respect to steam varied between 0.4 and 1.0 for the investigated chars. By using a unified activation energy of 150 kJ/mol for all of the chars, computed char gasification times were in good agreement to experimental measurements. The results support recommendations that the choice of kinetic models should be based on the K/(Si + P) ratio of the chars. The introduction of an Avrami-Erofeev model allowed predicting the conversion behavior of the chars that showed sigmoidal conversion.