A new modelling approach for the pyrolysis step in biomass gasification

Abstract

The main goal of this work was to develop an improved pyrolysis model that can be used for gasification simulation. The improvement consisted in introducing additional mass and energy balance equations to two highly cited models, as well as introducing a set of tar model compounds, which are important for modelling the subsequent gasification stages. These changes led to novel results such as: the new model does not give negative concentrations and yields of the products (the already reported ones do), yields of tar model molecules can be predicted in a more accurate fashion that previous models, empirical correlations with extremely low fitting used in reported models are no longer needed. After applying several selection criteria, an improved empirical model for the pyrolysis step in biomass gasification was developed. This improved model allowed obtaining all the parameters that are needed for the further simulation of the gasification process: yield of main pyrolytic fractions, concentrations of gas molecules, element composition of char, element composition of tar and concentrations of molecules present in tar. Reported models have not covered this last issue and it is crucial for the modelling of the gasification reactions. The selected model has element mass balance deviations lower than 6 % and low deviations from the experimental results reported for several biomass samples. The minimum of a sum of squares method, used to solve the equation systems, allowed imposing the positive-value condition for yields and concentrations, leading to physically sound results.