A dynamic model for predicting tar content in gases from a stratified downdraft gasifier: Part i -model development

This paper describes the development and the predictions of a dynamic model for a stratified downdraft wood gasifier. The numerical model, which incorporates a two-step pyrolysis mechanism, uses mass and energy balances, together with information about rates of chemical reactions and physical transport processes, to describe the complex physical and chemical processes taking place in the gasifier. The model is capable of predicting the gas composition, primary and secondary tar contents, and gas and solid surface temperature profiles along the axis of the gasifier. The model predicts an outlet gas tar content of between 20 and 200 mg/Nm3 for the range of input parameters used in the model simulation, assuming that prior to ignition the section of the gasifier below the ignition ports contains charcoal rather than wood. The stability of the reaction zones was also investigated and for stable operation it was found that the mass flux of supplied air needed to be in the range 0.158-0.167 kg/m2s. © 2012 Nova Science Publishers, Inc. All rights reserved.