Chemical engineering

Summary

This book is a revision and extension of Fast Breeder Reactors: An Engineering Introduction, published in 1981. I have rewritten much of it in the light of developments in fast reactor technology that have taken place in the subsequent three decades, and to take account of the new applications for fast reactors that have been suggested.

It is intended for the newcomer to the study of fast reactors, either as a student or at a later stage of his or her career. It will probably be most useful to someone who already has some knowledge of nuclear reactors. There are many excellent introductory texts for the beginner in nuclear engineering but they all concentrate on thermal reactors. The purpose of this book is to provide an up-to-date account of fast reactors for those who want to take the next step.

Fast reactor technology has become a wide field, so wide that it is not possible to cover all of it in depth in a single book of reasonable length. What I have attempted is to cover the whole in sufficient detail to allow the reader to understand the important features, and to provide suitable references for further study. I have gone into detail on the neutron physics because any fast reactor engineer, whether he or she is a designer, an operator or a researcher, needs to understand how the machinery works at a basic level. I have also attempted to include the results of experience, often hard-won, of operating a fast reactor power station.

An invaluable resource for both graduate-level engineering students and practising nuclear engineers who want to expand their knowledge of fast nuclear reactors, the reactors of the future. This book is a concise yet comprehensive introduction to all aspects of fast reactor engineering. It covers topics including neutron physics; neutron flux spectra; flux distribution; Doppler and coolant temperature coefficients; the performance of ceramic and metal fuels under irradiation, structural changes, and fission-product migration; the effects of irradiation and corrosion on structural materials, irradiation swelling; heat transfer in the reactor core and its effect on core design; coolants including sodium and lead-bismuth alloy; coolant circuits; pumps; heat exchangers and steam generators; and plant control. The book includes new discussions on lead-alloy and gas coolants, metal fuel, the use of reactors to consume radioactive waste, and accelerator-driven subcritical systems.

Summary

Separations for preparative or analytical purposes are often carried out batchwise in a closed vessel. On the other hand, industrial-scale separations are commonly achieved in a continuous manner with open vessels into which feed streams enter and from which product streams leave. In this chapter, we consider the available methods of describing separation in such open separators. The quantities, fluxes and mass balances necessary for such descriptions are presented first in Section 2.1. Section 2.2 describes the available indices of separation and their interrelationships for binary separation with a single feed stream entering the separator. In Section 2.3, we briefly introduce indices for binary separation with two feed streams entering a separator. The complications encountered in describing multicomponent separations with a single-entry or double-entry separator are presented in Section 2.4. This section provides also an introduction to the description of systems of continuous chemical mixtures and size-distributed population of particles. Separation by any of the separators considered in these sections presupposes that the output streams have different compositions. There are separation processes, e.g. chromatography, in which the separator has only one output stream, but that has a time-varying composition. The description of separation in such a separator with the help of various indices has been considered in Section 2.5. Triple-entry separators etc. have not been dealt with here. Further, except for Section 2.5, steady state operation is assumed throughout.

Summary

This is an introductory textbook for studying separation. Primarily, this book covers the separation of mixtures of molecules; in addition, it provides a significant treatment of particle separation methods. Separation of macromolecules has also received some attention. The treatment and coverage of topics are suitable for chemical engineering students at undergraduate and graduate levels. There is enough material here to cover a variety of introductory courses on separation processes at different levels.

This book is focused on developing a basic understanding of how separation takes place, and of how the resulting separation phenomenon is utilized in a separation device. The role of various forces driving molecules or particles from a feed mixture into separate phases/fractions/regions is basic to such an approach to studying separation. The separation achieved is then amplified in an open separator via different patterns of bulk-phase velocities vis-à-vis the direction(s) of the force(s). The forces are generated by chemical potential gradient, electrical field, rotational motion, gravity, magnetic field, etc. The resulting separation is studied under three broad categories of separation processes.

Summary

The preceding chapters introduced first the notion of separation and then a variety of indices to describe separation. These indices were used to characterize quantitatively the amount of separation achieved in a closed or an open separation vessel. The quantitative description included systems at steady or unsteady state involving chemical or particulate systems. Systems studied were either binary or multicomponent or a continuous mixture. Not considered in these two chapters was the fundamental physicochemical basis for these separations; appropriately, this is the focus of our attention in this chapter.

In Section 3.1, we distinguish between bulk and relative displacements and describe the external and internal forces that cause separation-inducing displacements. This section then identifies species migration velocities and the resulting fluxes as a function of various potential gradients. Section 3.2 is devoted to a quantitative analysis of separation phenomena and multicomponent separation ability in a closed vessel as influenced by two basic types of forces. The criteria for equilibrium separation in a closed separator vessel and individual species equilibrium between immiscible phases are covered in Section 3.3. Section 3.4 treats flux expressions containing mass-transfer coefficients in multiphase systems. Flux expressions for transport through membranes are also introduced here.

Summary

Chapter 4 described the extent of separation that can be achieved in a closed vessel under three basic categories of separation: phase equilibrium based separations; external force based separations; membrane based separations. Beginning with Chapter 6, we focus on separation achieved in an open vessel: fluid streams and/or solid streams may flow into and/or out of the vessel. Thus, we have bulk flow/s in and/or out of this device. A broad variety of bulk flow patterns can exist in a separation vessel. We will, however, mostly study separations under three general categories of bulk flow configurations defined with respect to the direction of the force which is the source of the basic separation phenomenon. The three general categories of bulk flow–force combinations are:

Summary

Energy is needed to separate a mixture into pure compounds. Some separation operations are highly energy consuming; others are less so. But all separations require a minimum amount of energy. Section 10.1 introduces the concept of minimum energy required for separation, independent of the process employed. This section then illustrates the minimum energy required in various separation processes such as membrane gas permeation, distillation, extraction and adsorption. How to reduce the amount of energy needed for a given separation by particular separation processes is the general topic of Section 10.2. The specific separation processes and topics covered in this section include: evaporation of water for desalination by multiple-effect evaporation, multistage flash evaporation, vapor-compression evaporation; distillation based separation of mixtures by multieffect and heat pump configuration. The role of free energy of mixing in influencing the energy requirement for separation is briefly considered here. Finally, the special considerations needed for processing dilute solutions of solutes of interest are discussed in the context of reducing the total energy required.

Summary

Separations in which the feed phase or feed-containing phase has a bulk motion parallel to the direction of the force causing separation have been studied in Chapter 6. In many separation techniques/processes/operations, the feed phase or feed-containing phase has a bulk motion perpendicular to the direction of the driving force. In a number of situations, the feed is introduced in small amounts in a carrier fluid whose bulk motion is perpendicular to the force direction. Such separations will be studied in this chapter.

For separations based on distribution of species between two phases in equilibrium, we study in Section 7.1 primarily those two-phase systems where the second phase (e.g. adsorbent particles in a packed adsorbent bed) is stationary; the first phase, which is more often the feed solution/mixture, moves perpendicular to the direction of chemical potential driving force between the two immiscible phases (Figure 7.0.1(a)). This first phase (the mobile phase) bulk motion is generally in one direction. The benefits of such bulk motion in terms of extreme purification achievable in two-component systems and multicomponent separation capability will be illustrated. In the cyclic processes studied next, the direction of motion of the mobile phase is periodically reversed; the direction of force is also reversed, except it remains perpendicular to the bulk-phase flow direction (Figures 7.0.1(b) and (c)). The mobile phase is sometimes generated by the separation operation, as in the case of the blowdown phase of pressure swing adsorption (PSA). The elution chromatographic process considered next involves injection of a sample to be separated into a carrier fluid flowing perpendicular to the direction of the force between the fluid and the stationary adsorbent phase (Figure 7.0.1(d)); this and other related chromatographic processes are also studied in Section 7.1.5. The imposition of an electrical force parallel to the direction of flow in a packed chromatographic column is studied in Section 7.1.6 in what is called counteracting chromatographic processes.

Summary

We have studied in Section 8.1 how a number of double-entry separation stages can be connected together in a countercurrent fashion. We have also learnt that such an arrangement achieves a far greater extent of separation in separation processes such as distillation, extraction, absorption and adsorption compared to what can be achieved in a single stage. Such multistage configurations are generally identified as “cascades,” and in the case of configurations of an overall countercurrent flow as “countercurrent cascades.” Such countercurrent cascades can have significant variations, for example ideal cascades, squared off cascades, tapered cascades, etc. Further, there can be novel countercurrent cascades with single-entry separation stages. In addition, there can be other types of connections between a number of single stages, resulting in, for example, crosscurrent cascades, two-dimensional cascades, etc.

We will briefly focus in Section 9.1 of this chapter on many such configurations of cascades, beginning with countercurrent cascades. Special attention will be paid to single-entry separation stages in, for example, the configuration of an ideal cascade. These cascades are generally employed to enhance substantially the separation achieved in a single stage for a binary mixture. Such cascades can also reduce the amount of energy or mass-separating agent needed for the separation of a binary mixture. In the separation of a multicomponent mixture by distillation, a number of such cascades may be joined together in particular ways – Section 9.2 will provide a brief introduction to this topic. Section 9.3 briefly considers cascades for multicomponent mixture separation involving other separation processes.

Summary

The area of separations is extremely broad. Most separation processes/techniques have an extensive literature. Each process has its own universe. Yet there are a few common principles and characteristics that are shared by many separation techniques/processes. This book has provided an elementary introduction to such principles and characteristics, even as it provides some details of many of the most commonly used separation processes. It is hoped that this book will help the reader to be prepared to undertake more extensive studies of individual processes/techniques or of a certain class of techniques or certain sequences of separation processes/techniques.

An important goal of this book is to develop an appreciation that separation processes/techniques may be understood on the basis of a few key features/concepts: the nature of the force causing the selective movement of molecules, macromolecules and particles; the nature of the various regions/phases in the separation system; the four types of bulk flow pattern of the regions/phases vis-à-vis the direction(s) of the forces causing selective movement of species/particles to be separated; the method of feed introduction. Further, for relatively simple systems, one could develop the governing equations that describe the separation achievable from the set of basic governing equations provided in Section 6.2 for most systems described in the book. In addition, a useful introduction to the role played by chemical reactions of certain types for a variety of separations has been provided.

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APPENDIX A - Tables of Properties and Universal Constants

APPENDIX H - Monte Carlo Method for Carrier Transport

APPENDIX C - Derivation of Minimum Phonon Conductivity Relations

APPENDIX D - Derivation of Phonon Boundary Resistance

Nomenclature

Preface

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An Introduction to the Engineering of Fast Nuclear Reactors

2 - Description of separation in open separators

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Preface

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Frontmatter

3 - Physicochemical basis for separation

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6 - Open separators: bulk flow parallel to force and continuous stirred tank separators

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List of notation

10 - Energy required for separation

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7 - Separation in bulk flow of feed-containing phase perpendicular to the direction of the force

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Index

Appendix C - Various quantities expressed in different units

9 - Cascades

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Postface

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Appendix A - Units, various constants and equivalent values of various quantities in different units

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An Introduction to the Engineering of Fast Nuclear Reactors

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