PREDICTION OF MICROPORE GROWTH DURING GASIFICATION REACTIONS

ABSTRACT

The concept of changing pore geometry during the course of a reaction allows the microscopic solid-gas reaction models to have the potential to describe the porosity change during the reaction. However, only the bulk porous properties can be predicted due to the pore size range chosen for most of these models. The two population systems, micropore and macropore, chosen by the model of Zygourakls et al. [1] provides a method for predicting micropore property changes. However, this model over-predicts micropore property changes because it assumes that the average micropore radius is enlarged. By examining several sets of published carbon gasification data, it is shown that the average micropore radii are not enlarged by gasification. The commonly-used concept that reaction will enlarge all the pore radii is the major reason for the prediction error. A new concept is proposed in which the reaction will not enlarge the size of the micropores and will maintain a constant micropore length by reacting at both ends of micropores at equal rates. Based upon this concept, the model of Zygourakls et al. [1] has been modified. Both the original and the modified models can predict the gasification rate well by utilizing data from the carbon activation study of Yanai [2]. The model of Zygourakls et al. [1] gives a micropore surface area change close to the measured value, but the reaction enlarged micropores result in predicting high of values of micropore volume changes and average micropore sizes. The steady-state micropore concept used in the improved model predicts more realistic micropore property changes.