Characterisation of coal and biomass based on kinetic parameter distributions for pyrolysis

Abstract

We performed pyrolysis analyses of various biomasses and biomass-derived materials using a thermogravimetry device and a wire-mesh reactor. Kinetic parameters, which were a frequency factor and an activation energy, were derived based on a distributed activation energy model. We validated the prediction of thermogravimetric curves calculated using the kinetic parameters in the case of rapid pyrolysis of biomass having the least interaction between particles and volatiles. Unlike coal, the kinetic parameters of the samples changed markedly with progression of pyrolysis. We estimated that the low activation energy in the initial step was caused by hydration and the volatilisation of lighter components. Some biomass samples showed a decrease in both the frequency factor and activation energy during pyrolysis. Changes in the chemical structures of xylan and cellulose from cyclic aliphatic units to aromatic units, accompanying amorphism, softening, or melting of part of the solid phase in some cases, caused a decrease in kinetic parameters during pyrolysis. Both the frequency factor and activation energy of all biomass samples increased in the final stages, which was considered to be the result of char forming by carbonisation. Analysing in detail the changes in kinetic parameters provided information on the behaviour of the volatilisation, the change in solid state, and the extent of char structural development.