Modeling of biomass pyrolysis kinetics

Over the next decade there will be a renewed emphasis on the use of biomass as a fuel and the cofiring of coal and biomass materials. In view of the tremendous diversity of biomass feedstocks, a great need exists for a robust, comprehensive model that could be utilized to predict the composition and properties of pyrolysis products as a function of feedstock characteristics and process conditions. The objective of this work was to adapt an existing coal pyrolysis model, the Functional Group-Depolymerization, Vaporization Crosslinking (FG-DVC) model, and make it suitable for the pyrolysis of biomass. The soundness of this approach is based on numerous similarities between biomass and coal. However, there are important differences, which preclude direct application of the coal model. This work involved: (1) selection of a set of materials representing the main types of biomass, (2) development of a classification scheme, (3) development of a modeling approach based on an extension of a coal pyrolysis model, (4) calibration of the model for a set of standard materials against pyrolysis data taken over a range of heating rates, and (5) validation of the model against pyrolysis data taken under higher heating rate conditions. A streamlined version of the FG-DVC coal pyrolysis model was successfully developed for whole biomass samples and demonstrated to have predictive capability when extrapolated to high heating rate conditions (103 °C/sec). Improvements will be needed in the model to properly account for mineral effects and secondary reactions, and the model has not yet been tested under the very high heating rates that may exist in some combustion devices (104–105 °C/sec).