Absorption Towers [antikvár]

PREFACE The absorption and desorption of gases are important processes on many chemical plants. This book is concerned essentially with packed towers in which these processes are most frequently carried out; other types of apparatus are only briefly described. The aim of the book is to provide the engineer with the methods and data needed to enable him to design full-scale towers which are both technically and economically satisfactory. For this reason, the book difFers in character from a standard text-book on absorption, such as " Absorption and Extraction " by Sherwood and Pigford. Because of the emphasis on design, the fundamental theories of diffusion, and analogies between fluid friction, heat transfer and mass transfer have been omitted. On the other hand, greater stress has been placed, for example, on the design of liquid distribution systems and on economic factors than would be in order in a text-book. The methods described here are based largely on the results of work carried out by Impérial Chemical Industries Limited, much of which has hitherto remained unpublished. Where possible, however, refer-ences to published work have been given. These methods have been widely used within the Company and are believed to be an improve-ment on those generally available. Absorption towers are difficult to test, and published test data for full-scale towers are scanty. For this reason, the methods described here must be used with caution, and factors of safety may still be required. It is hoped that this book may encourage engineers to carry out tests on full-scale towers and to make their results generally available. Two design methods are presented, the first making use of absorption coefficients and the second of transfer units. The method in which absorption coefficients are used is the more fundamental of the two, but the transfer-unit method, in a simplified form, can be used with advantage under certain conditions and has been included for that reason. Both methods should lead to the same conclusion in any particular design problem if full allowance is made for ail the factors involved. The scheme used in this book is to- consider first certain simple types of laboratory absorption equipment and then to discuss packed towers since these are considerably more complicated. In so doing, it is shown how the laboratory towers can be used to provide standards with which the performance of packed towers can be compared. In both cases, the results are expressed in terms of the two-film theory. This is simple and generally suitable for design purposes as long as the