A new active site/intermediate kinetic model for K2CO3-catalyzed steam gasification of ash-free coal char

Experimental results showed that the K2CO3-catalyzed steam gasification of ash-free char had two distinct characteristics of gas evolution. One was a broad maximum of gasification rate versus carbon conversion at a higher carbon conversion as a result of the sustained catalytic activity. Another was the variations of gas composition with carbon conversion arising from the complex reaction pathways. No model was reported to describe both characteristics in the literature. In this work, a new kinetic model was formulated in terms of an active site/intermediate mechanism with an assumption of the variations of effective carbon concentration with carbon conversion. The mechanism involved three potassium species and four reaction pathways for the catalyst cycle and gas release. The model was associated with five parameters including four rate constants and a catalysis factor, and it manifested a capability of predicting accurately the profiles of both gasification rate and gas composition over the entire range of carbon conversion. All four rate constants estimated from the modeling followed the Arrhenius equations with the reasonable activation energies. Moreover, the model could predict the formation, growth and decline of three potassium species during the gasification. The modeling result would deepen the understanding of the chemical processes of K2CO3-catalyzed steam gasification of char.