Thermodynamics and Kinetics of Gasification

Abstract

This chapter deals with the basic thermodynamics and chemical kinetics pertaining to the various physicochemical phenomena that are collectively termed as the phenomenon of gasification. Although the phenomena associated with the gasification of various feedstocks differ from each other in detail, the underlying thermodynamics is more or less common and is attempted to be captured here. The technology of gasification also has a wide variety, and this results in different phenomena having varying grades of importance in each. Thermodynamics of a phenomenon is described in terms of conservation equation for mass and the first law, often discussed under the headings of stoichiometry and energetics of a phenomenon, and in terms of the second law, which determines the equilibrium state at the end of the phenomenon, and thus defines the product compositions in gasification when the reactor is maintained at a given pressure and temperature. The variety of phenomena involved in gasification, namely drying of feedstock, its pyrolysis, homogeneous and heterogeneous reactions which form part of the gasification in the form of oxidation and reduction reactions, proceed at different rates in a given system, and also vary widely between different types of gasification systems. Hence, it is important to study the kinetics of these phenomena, in addition to the study of thermodynamic equilibrium states pertaining to these phenomena. Owing to the fact that each of these phenomena is extremely complex, in mathematical modelling of these phenomena, often apparent mechanism and their thermodynamics and kinetics are studied. This leads to a variety of models and thermodynamic and kinetic data in the literature, often in apparent conflict with each other. This chapter also attempts to identify some of these conflicts through the experience of the authors in modelling gasification phenomena.