A dynamic model for predicting tar content in gases from a stratified downdraft gasifier: Part III-experimental validation

A pilot-scale downdraft gasifier was designed, fabricated and tested. The experimental data obtained from it were compared with the predictions of a dynamic model the development and analysis of which are described in previous papers [1 & 2]. River red gum (Eucalyptus camaldulensis) wood blocks of two different sizes were used as gasifier feedstock. The gasifier was operated at inlet airflow rates of 7.5 to 27.6 kg/hr, with corresponding energy outputs ranging from 54 to 168 MJ/hr. An average cold gas efficiency of 70% was obtained. Two modes of operation were used. In the first mode, the section of the gasifier below the ignition port was filled with charcoal prior to start up and the remainder of the gasifier filled with wood; in the second mode, no initial charge of charcoal was used. Operating the reactor with wood fuel alone produced an outlet gas with a final tar content that was around 20 times higher than the average tar content values in gas produced when using an initial charge of charcoal. Transient temperature profiles, outlet gas compositions, and outlet tar contents predicted by the model were in generally good agreement with experimental values. However, the model predicted a more rapid increase in concentrations of H and CO along the gasifier axis than was observed experimentally. There was good agreement between the predicted and experimentally observed rates and directions of reaction zone movement within the gasifier over the range of inlet airflow rates studied. © 2012 Nova Science Publishers, Inc. All rights reserved. 2