Predicting biomass gasification histories with CBK/G. Part 1. Kinetic parameter assignments

Abstract

With coal chars, CBK/G is a reaction mechanism that accurately predicts gasification histories across the commercial domain of temperature, pressure, gas composition, size, and coal quality, given data to tune-in a single kinetic parameter for each char sample. This study develops a CBK/G parameter estimation protocol for biochars from diverse biomass forms. Kinetic parameters are specified to accurately match gasification histories for 17 biochars from 700 to 1000 °C at steam and CO2 pressures to 0.1 MPa. With biochars, calibration data must specify both a frequency factor and activation energy for the desorption of a surface carbon oxide. Half the biochars in the database required different activation energies than the 180 kJ/mol baseline value, which spread the assigned energies from 130 to 220 kJ/mol. Woods in raw, torrefied, and pelleted forms tend to have the fastest reactivities, along with a few biochars of agricultural residues (AgRes). The biochars of grasses and AgRes have reactivities only one-third of woods’, although the reactivities of diverse AgRes biochars spans a very broad range. Steam gasification is faster than CO2 gasification, but the differences in rates are much smaller than with coal chars. The cross relations in CBK/G that relate channels for steam and CO2 gasification remain to be validated with tests under both steam and CO2 and their mixtures for diverse biochars.