Kinetics of woodchips char gasification with steam and carbon dioxide

Abstract

Kinetics of woodchips char gasification has been examined. Steam and CO 2 were used as the gasifying agents. Differences and similarities between kinetics of steam gasification and CO 2 gasification have been discussed. Comparison was conducted in terms of gasification duration, evolution of reaction rate with time and/or conversion, and effect of partial pressure on reaction rate. Reactor temperature was maintained at 900 °C. Partial pressure of gasifying agents varied from 1.5 bars to 0.6 bars in intervals of 0.3 bars. Steam and CO 2 flow rates were chosen so that both gasifying agents had equal amount of oxygen content. CO 2 gasification lasted for about 60 min while steam gasification lasted for about 22 min. The average reaction rate for steam gasification was almost twice that of CO 2. Both reaction rate curves showed a peak value at certain degree of conversion. For steam gasification, the reaction rate peak was found to be at a degree of conversion of about 0.3. However, for CO 2 gasification the reaction rate peak was found to be at a conversion degree of about 0.1. Reaction rates have been fitted using the random pore model (RPM). Average structural parameter, ψ for steam gasification and CO 2 gasification was determined to be 9 and 2.1, respectively . Average rate constant at 900 °C was 0.065 min −1 for steam gasification and 0.031 min −1 for CO 2 gasification. Change in partial pressure of gasifying agents did not affect the reaction rate for both steam and CO 2 gasification.