In recent years considerable advances have been made in our understanding of gas-solid reaction systems. These advances are due in part to the development of more sophisticated mathematical models in which account is taken of such structural effects as pore size, grain size, and pore diffusion. Another important contributory factor has been the use of more sophisticated experimental techniques such as electron microscopy, X-ray diffraction, and porosimetry, which together with pore diffusion measurements provide information on the key structural parameters and make possible the critical assessment of this new generation of models.
These new developments were motivated to a great extent by the societal and economic importance of gas-solid reaction systems due to their relevance for a broad range of processing operations, including iron oxide reduction, the combustion of solid fuels, the desulfurization of the fuel gases, and the incineration of solid wastes.
The purpose of this monograph is to present in an integrated form a description of gas-solid reaction systems, where full account is taken of these new developments and where structural models of single particle systems, experimental techniques, the interpretation of measurements, the design of gas-solids contacting systems, and practical applications are treated in a unified manner.
The actual approach to be developed here is based on methodology similar to that employed in chemical reaction engineering in the interpretation of rate data and the design of process systems in heterogeneous catalysis. More specifically, through the use of this methodology, the individual components of the overall reaction sequence are studied and examined in isolation and the description of the system is then synthesized from these components. This approach provides greatly improved insight and at the same time allows a much broader generalization of the results than is possible through the use of empirical models.
While there is a close parallel between heterogeneous catalytic reaction systems and gas-solid reactions, the latter systems are rather more complicated because of the direct participation of the solid in the overall reaction. As the solid is consumed or undergoes chemical change, its structure changes continuously, making the system inherently transient. It follows that the analysis of gas-solid reactions involves an additional dimension, that of time, which is not necessarily needed in the study of heterogeneous gas-solid reactions. The inherently unsteady nature of gas-solid reaction systems introduces a number of complicating factors which render the tackling of these problems a definitely nonroutine task requiring originality.
It is noted here that while the discussion in this text is devoted to gas-solid reactions, with little modification the treatment developed here should be applicable to liquid-solid reaction systems.
The material presented here could form part of a one-semester graduate level course to be given to students either in metallurgy (materials engineering) or in chemical engineering. It is hoped, moreover, that the book will appeal to the growing number of practicing engineers engaged in process research, development, and design in the many fields where gas-solid reactions are of importance.