A. C. Hoffmann L. E. Stein

Gas Cyclones and Swirl Tubes

Springer-Verlag Berlin Heidelberg GmbH

ON LI NE LIBRARY

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Alex C. Hoffmann Louis E. Stein

Gas Cyclones and Swirl Tubes Principles, Design and Operation

i Springer

Prof. Dr. Alex C. Hoffmann Programme for Process Technology Department of Physics University of Bergen Allegaten 55 5007 Bergen Norway email: Alex.Hoffmann@fi. uib.no

Dr. Louis E. Stein Process Engineering Consulant Mechanical Separations 5818 Autumn Forest Drive Houston, TX 77092 USA email: lestein@swbell.net

ISBN 978-3-662-07379-7

Die Deutsche Bibliothek- CIP-Einheitsaufnahme

Hoffmann, Alex C. :

Gas cyclones and swirl tubes : principles, design and operation I Alex C. Hoffmann ; Louis E. Stein. (Engineering online library)

ISBN 978-3-662-07379-7 ISBN 978-3-662-07377-3 (eBook) DOI 10.1007/978-3-662-07377-3

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Preface

This book has been conceived to provide guidance on the theory and design of cyclone systems. Forthose new to the topic, a cyclone is, in its most basic form, a stationary mechanical device that utilizes centrifugal force to separate solid or liquid particles from a carrier gas. Gas enters near the top via a tangential or vaned inlet, which gives rise to an axially descending spiral of gas and a centrifugal force field that causes the incoming particles to concentrate along, and spiral down, the inner walls of the separator. The thus-segregated particulate phase is allowed to exit out an underflow pipe while the gas phase constricts, and - in most separators - reverses its axial direction of flow and exits out a separate overflow pipe.

Cyclones are applied in both heavy and light industrial applications and may be designed as either classifiers or separators. Their applications are as plentiful as they are varied. Examples include their use in the separation or classification of powder coatings, plastic fines, sawdust, wood chips, sand, sintered/powdered meta!, plastic and meta! pellets, rock and mineral cmshings, carbon fines, grain products, pulverized coal, chalk, coal and coal ash, catalyst and petroleum coke fines, mist entrained off of various processing units and liquid components from scmbbing and drilling operations. They have even been applied to separate foam into its component gas and liquid phases in recent years.

This book strives to provide a long overdue overview of the state of the art in this specialized, albeit, important area of separation technology. Theory and design methods are presented covering the important classical topics, including particle cut size, grade-efficiency, overall efficiency and pressure drop. In addition, many special topics are covered on basis ofthe authors' experiences and interests. These include discussions and sections on a very wide variety of topics that, in one way or the other, relate to cyclone technology:

- particle characterization, motion, size distribution, sampling swirl flow and flow pattems

- important cyclone separation and pressure drop models - static and dynamic pressure - computational fluid dynamics - vapour-liquid (demisting) and foam-breaking cyclones - swirl-tube type cyclones - wall roughness and solids loading effects - model predictions and comparison with experiments - dimensional analysis and scaling mies - sampling and performance measurement

VI

- in-leakage (up-flow) effects and hopper crossflow - dipleg 'backup' - hopper venting - forces acting on a flapper valve - erosion and erosion protection methods - particle settling in conveying lines - high vacuum operation

estimating feed drop sizes distribution - non-uniform inlet flow distribution - inlet, overflow and underflow geometries and configurations including inlet

vane design cyclone length and the 'natural' vortex length

- parallel and series arrangements and multiclones

A number of cyclone models of varying degree of complexity are given. The modeling approach instigated by W alter Barth, and further developed by Edgar Muschelknautz and co-workers to account for solids loading and wall roughness effects is given special treatment due to its overall practical usefulness.

Many drawings and photographs are included to help illustrate key concepts or interesting aspects. A number of worked example problems are included to help firm-up ideas presented in the textual discussions.

Even with today's modern tools, the complexity of cyclone behaviour is such that experimental studies are necessary if one is to truly understand the phenomena governing their behaviour. Thus, laboratory-scale studies are discussed on basis of the writers' understanding and experiences in this central area.

For the researcher in gas cleaning and cyclone technology, the basic concepts underlying the working of centrifugal Separators are set out, with references to Iiterature where the topics are treated in more detail. Understanding the peculiari­ties of swirling flows and the basic description of fluid dynamics in rotation­symmetic coordinate systems is very much the key to appreciating the topic at band. Other essential topics are elements of particle characterization and fluid­particle interaction. Although it is not possible to give the derivations of all the model equations in full, the basic reasoning behind each is discussed, and refer­ences are given to the original articles with full accounts of the derivations. Di­mensional analysis is another key topic for understanding cyclone technology and the basis for cyclone modeling and scaling. Computational fluid dynamics (CFD) simulations of the fluid and particle flows in cyclones has become a 'hot topic', and it has clear advantages for understanding the details of the flow in cyclones, but also limitations in terms of modelling cyclone separation performance accu­rately.

Obviously, the design of cyclone systems requires some expertise in many di­verse areas of the physical sciences and engineering disciplines. For the benefit of the reader who works in either a manufacturing plant, a contractor or engineering­design firm, an engineering division of a company, or as an independent consult-

VII

ant, the book tries to go beyond the 'research' or 'mathematical' aspects of cyclone behaviour and to provide examples of how one designs, sizes and evaluates com­mercial-scale equipment. Those who have the responsibility to design, operate, evaluate, troubleshoot or modify cyclone systems must not only understand the theory and principles underlying their performance, but must also leam how to apply this understanding in a practical, cost- and time-effective manner. Because so many variables or factors govem the performance of cyclones, one must under­stand them weil enough to know which variables are important and which are not, in any given situation. One must be able to see the 'whole picture' and not be content, for example, with having developed a mathematical or computer model of cyclone behaviour.

The cyclone separator is one of the most efficient and most robust dust and mist collectors available for the cost. Its robustness is largely the result of its Iack of moving parts and ability to withstand harsh operating environments. Cyclones can be fabricated from a wide variety of materials of construction including carbon steel, stainless steel and exotic alloys, or they may be made from castings. Where conditions require they may be equipped with refractory, rubber, fluorocarbon, or specially hardened meta! Iiners or electro- polished surfaces. Furthermore, cy­clones are particularly weil suited for high pressure applications and severe solids and liquid loadings, where filter media is sensitive to abrasion, sparks, oil, humid­ity, temperature, et cetera, and in applications wherein the separator must operate unattended for extended periods of time - up to several years in some refinery processing units. Nevertheless, things can and will 'go wrong'. When they do, it tends to happen at the discipline or equipment interfaces. We are referring here to the fact that design, fabrication and installation work is often performed by iso­lated groups or by individuals and, unless all aspects or components of the system are examined from the standpoint of their impact on all other aspects or compo­nents, the system may fail to perform up to expectations. This applies to both the 'process' and the 'mechanical' aspects of their design. A simply spray nozzle, for example, can shut down a huge commercial operation if it fails to atomize the water, and a jet of water impacts an 800 oc cyclone nearby. Because such things will happen, good communication and an appreciation of how the various compo­nents ofthe entire ' system' interact will prevent mostsuch problems.

Experience teaches that the more one understands and leams about cyclones, and the more performance and equipment experience one obtains, the more suc­cessful and confident one becomes in applying his or her knowledge in a Iabara­tory or operating plant environment. And, with this understanding, some of the mystery surrounding these deceptively 'simple looking' devices will vanish.

We recognize that the International System of Units (SI) has become the fun­damental basis of scientific measurement worldwide and is used for everyday commerce in virtually every country except the United States. As painful as it may be for those ofus who have leamed and practiced the 'British' or 'US Customary' system of units, we feel that it is time to put aside the units of the industrial revolu­tion and adopt the SI system of measurement in all aspects of modern engineering

VIII

and science. Forthis reason, SI units have been adopted as the primary system of units throughout this book. However, it is recognized that US customary or British units are still widely used in the United States and some use of them is provided herein for the benefit of those who still relate closely to them. Dimensional con­stants specific to the British system, such as gc, have been left out ofthe formulae.

In this book, we have tried to capture not only the state of the art pertaining to cyclone technology but to also capture and convey as much of our 45 cumulative years of experience as possible and, in some few cases, permissible. Still, there are areas where further research and analysis is required to fill the gaps in the check­erboard of our understanding. W e hope this book will be a stepping-stone and an aid to all those who work with cyclones and who find them as useful and fascinat­ing as we do.

Houston and Bergen, April 2002 Louis E. Stein Alex C. Hoffmann

Foreword

The cyclone is one of the most elegant pieces of engineering equipment - a tri­umph, one might say, of the particle technologist's art. Here is a device with no moving parts and virtually no maintenance which enables particles of micrometres in size to be separated from a gas moving at 15 m/s or so, and without excessive pressure-drop. It gets better: the harder you drive it (up to a point), the better the efficiency; the heavier the particle loading, the less the pressure drop. There can be few examples of engineering equipment that are so forgiving. It is for this reason that cyclones have become ubiquitous in processes. In catalytic cracking they are the main reason why the catalyst stays in the process. In power generation and innumerable manufacturing plants, they are the first line of defence of the envi­

ronment. In air intakes to turbines on trains and helicopters 1 they are essential components. Even in the home they now enable vacuum cleaning without frequent bag cleaning.

Where did the principle come from and why do we design them as we do? The first design is probably lost in the mists of time. There are reports that the first Renault car factory, in late 191h century France, was equipped with an extraction system incorporating cyclones, but the idea must go back much further than that -probably to the flour milling industry. Their subsequent development is an interest­ing story of design evolution, with largely empirical optimisation studies being carried out simultaneously and apparently independently in the USA (Lapple, Leith and others), the UK (chiefly Stairmand), Japan (linoya and others) and the Eastem bloc countries. Seidom could it have been more clearly demonstrated that good engineering will converge on the same range of designs, wherever it is per­formed. Despite many attempts to improve on those basic general-purpose designs, they still represent the bulk ofthe industrial units installed today.

A full understanding of how the cyclone works and how individual particles be­have within it has been slow in following these pioneering industrial develop­ments. Little could be done until the invention of the measuring equipment neces­sary to measure fluid velocities within the cyclone (particularly Iaser Doppler anemometry - LDA), the assembly of theoretical models (largely in Germany, by Barth, Muschelknautz, Löffler and others), and ultimately the development of computational fluid dynamics (CFD) codes (pioneered by Swithenbank) which could accurately model swirling flows. Arrned with these devices and techniques, it became clear that cyclones are in fact far from simple, and there is still much to

1 As discovered on President Carter's ill-fated rescue mission ofthe Iranian hostages in 1980.

X

know. At the same time, new uses have been found and new designs developed. Despite ( or because of) its simplicity, the cyclone is not about to disappear.

It seems odd that there has not been before now an attempt to put together what is known empirically and theoretically about this most essential of separation devices. This book is both necessary and fascinating - a useful guide, complete with worked examples, for those attempting to design and use cyclones, and the first authoritative assembly of what is known both experimentally and theoretically for the benefit of those skilled in the art.

Jonathan Seville University of Birmingham

Gas Cyclones and Swirl Tubes-Principles, Design and Operation is a valuable and necessary work in the field of gas cyclones. lt will become a dassie in this field because of the comprehensive manner in which it covers the study and usage of cyclones. In addition, this work provides unbiased presentations of the many theories used to describe and calculate the performance of cyclones, empirical methods of cyclone design, and the practical aspects of using cyclones.

Cyclones have the ability to provide for fine particle collection while arguably also providing for the most robust methods of construction and simplicity of de­sign. If one is faced with a particle/gas separation application a cyclone should be the first technology examined. Low capital cost, low operating cost, and reliability are the reasons for this placement within the hierarchy of technologies that may be selected. Cyclones have been successfully used in industrial applications from the most common to the most severe, including highly erosive applications - a topic that this book discusses in some detail. Cyclones are routinely used in applications where the operating temperatures exceed 1000° C and in applications where the pressures may exceed 100 bar. Cyclones may be safely designed to handle highly explosive powders or pyrophoric materials. They can be used to recover pharma­ceuticals without the loss of expensive product due to contamination.

This then raises the question, why not use a cyclone for all particle-gas separa­tion applications. The two cases where a cyclone may not be the correct choice are:

- The engineering and data collection required to design a cyclone to meet the requirements of the application are too high, and The cost of the cyclones required to meet the particulate collection requirements exceeds that of other technologies.

Although it is relatively simple to fabricate a cyclone for severe duty, it is not so simple to select the geometry and subsequently accurately predict the performance of a cyclone. As shown herein, predicting the particle collection performance of a cyclone also requires accurate particle size and loading data at the inlet of the proposed cyclone. While this may be worthwhile and feasible for a severe duty

XI

industrial application, it may not be for the operator of a small wood shop whose neighbors are complaining about the dust.

Cyclones may be designed to effectively remove virtually any size particulate from a gas stream. Several worked examples of this are presented herein. The barriers to cyclone usage for small particle collection are largely those of econom­ics. Small cyclones are routinely used for particulate as small as .5 micron with 90% removal efficiency. Unfortunately, these small cyclones are not an attractive economical choice for many industrial applications. Conversely though, cyclones are now able to satisfy environmental and process requirements on particulate that is much finer than is commonly believed. With the advances in cyclone design that have begun in the late 20th century cyclones are commonly used for emission con­trol and product recovery on particulates with average particle sizes below 10 m1crons.

Gas Cyclones and Swirl Tubes-Principles, Design and Operation provides a valuable tool in the advancement of the design and usage of cyclones. The authors, a scientist and an industrialist, bring varied backgrounds and strengths to this work. The result is the most comprehensive work in the field of cyclones to date. Although it would be impossible to provide a complete treatise of all of the sub­jects covered, this work covers a wide array of the most critical, to a depth that allows the reader to understand the concepts and applications that are appropriate for designing or using a cyclone.

William L. Heumann, President and CEO, Fisher-Klosterman Inc.

Acknowledgments

We wish to separately thank and acknowledge those who have inspired and helped us write this book:

I, Alex C. Hoffmann, wish to thank Professor John G. Yates ofUniversity Col­lege London, for introducing me to powder technology, and for many years of productive and very enjoyable collaboration, and Professor Ray W.K. Allen of Sheffield University and Professor Roland Clift of the University of Surrey for introducing me to cyclones and gas cleaning.

I, Louis E. Stein, wish to affectionately thank Professors Frank L. Worley, Jr. and Frank M. Tiller of the Chemical Engineering Department of the University of Houston, and engineering consultant, Dr. Moye Wicks, III, for teaching me through their own example the value of dedication to a cause and personal integ­rity. Perhaps unsuspecting on their part, they have been my most honored role models and inspiration these past 25 to 35 years.

Together we wish to also thank our friend and professional associate, Ir. Huub W. A. Dries of Shell Global Solutions International of the Royal Dutch/Shell Group for years of collaboration in the cyclone field, and for his expert review and suggestions on the draft copy of this book. Likewise, we wish to acknowledge and thank Mr. William L. Heumann, president and owner of Fisher-Kiosterman, lnc. and Professor Jonathan P. K. Seville of the University of Birmingham, Editor-in­Chief of Powder Technology, for their kind and insightful views expressed in the two Forewords they wrote for this book. Valuable contributions were received from Dr. Hugh Blackburn of CSIRO Building Construction & Engineering, from Professors Steve Obermair and Gernot Staudinger of the Institute of Chemical Apparatus Design, Particle Technology and Combustion of the Technical Univer­sity of Graz, and from Professor Emeritus Frederick A. Zenz, now of PEMM­Corp, New York.

Finally, we wish to express our appreciation and to dedicate this book to our dear wives and children: Doris, Travis, Courtney and Jennifer on Louis' side; Gloria, Erik and Andrea on Alex's, who relinquished an untold number of hours with us to make this book possible.

All things were rnade by hirn; and without hirn was not any thing rnade that was rnade. (lohn 1:3)

Alex C. Hoffmann Louis E. Stein

About the Authors

Alex C. Hoffmann is of Danish nationality. He graduated with a Ph.D. from Uni­versity College London in 1983 in high pressure fluidization. During his studies he worked one year for UOP oil products in Chicago. He worked for three years as a post-doctoral research fellow at Surrey University, stationed at Separation Proc­esses Services at Harwell, acting as Research Engineer and Industrial Consultant in cyclone technology and gas cleaning. In 1987 he moved to the University of Gron­ingen, as a Lecturer and, Iater, Senior Lecturer. In 2001 he started as Professor at the Programme for Process Technology at the Department of Physics at the Uni­versity of Bergen.

Professor Hoffmann has carried out a number of research projects in collabora­tion with processing industry, mainly the oil and gas industry, specializing in parti­cle and multiphase technology. He is the author of more than 70 scientific articles and has one patent to bis name. He is married to Gloria and has two children.

Louis E. Stein graduated with a Ph.D. in Chemical Engineering from the Univer­sity of Houston in 1974. After graduating he worked as a post-doctoral research fellow at the University of Utah, as a NASA Engineering Aide, and as a process engineer at the Sindair Refinery, Pasadena Texas. During the period 1970-74, he held the post of Chemical Engineering Instructor at the University of Houston. After an interval as Research Engineer at Envirotech, Salt Lake City, he joined Shell in 1975 and, after several promotions, and numerous company awards, re­tired in 1999 as a Senior Staff Process Engineer. He remains active as a Separa­tions and Fluid Flow Consultant to industry and as Fluid Mechanics Lead Instruc­tor for Shell.

Dr Stein has four patents to bis name, he has held the Presidency of the South Texas Chapter of the International Filtration Society. He is married to Doris and has 3 children and 2 grandchildren.

Contents

1 lntroduction 0000000000 00 000 00 00000000 00000000000000 00 0000 000000 000000 0000 oooo oooooooooo o .. .. oo 0000000000000 00 000 0 1 1.1 Removal ofPartides from Gases .......... .... ...... .. ............ .... .... .......... ...... o1

l olol Filtration .......... .. o .... ...... .............. o .. o .... .. .... .................. o ................ o2 10102 W et Scrubbers 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 10103 Centrifugal/Cydonic Devices .................................. ........ .. .. ........ o 5 101.4 Knock-out Vesse1s and Setding Chambers ...................... .. .......... 0 6

1.2 A C1oser Look at Centrifugal Gas C1eaning Devices ...... ........ .............. o6 1.2.1 App1ications of Centrifuga1 Separators ................ .. .. ...... .. .... ........ 0 8 1.202 Classification of Centrifugal Separators ........ ...... ...... .. .... .... ...... 011 10203 Two Main Classes - Cydones and Swirl Tubes .............. .... .. .. .. o 13

2 Basic ldeas .............................. .... .............. 0 .... 0 .. .. 0 ...... .............. 0 .... 0 .... .. 0 ........ o 15 201 Gas Flowooooooooooooooooooooo ooo oooooooooooooooooooooooooooooo0ooooooooooooooooooooooooo ooooooooooooool5

20101 Swirling Flow ........ .. .......................... ...... .................................. 015 201 02 Static and Dynamic Pressure .. .. ........ ...... .................................. .. 17

202 Partide Motion 0 ...... o .............. 0 ...... 0 .... .. o .. .. .. ................ 0 ........................ 19 203 Partide SizeO OOO oooooo oo OooOOOOOOOOOOOOOo ooo ooooooooooOo oooooooooo ooooooooooooooo oooooooo oooo oo ...... 24

20301 Definitions ofPartide Size .. .................. .. .................................. 024 20302 Partide Size Distribution .............. o .. .. .... .. .... o .......... o .... .. o ............ 25

2.4 Partide Density ........ o .......... o .............. o .... .... ........ o ........................ o ...... 29 Appendix 2A Ideal Vortex Laws from the Navier-Stokes Equations .......... 0 30 Appendix 2B Common Models Functions for Particle Size Distribution .... o33

2Bol The Normal Distribution .................................................... .. .. .. .. o34 2Bo2 The Log-Normal Distribution ...... .. .... .. .. ........ ...... ........ .. ........ .... 034 2Bo3 The Rosin-Rammler Distributiono .......... o .... o ............ o .... o ...... o ...... 35

3 How Cyclones Work .......... .. .......... .. .............. .. .. .... ...................... ................ 037 3 01 Flow in Cydones 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 7

30101 Gas F1ow Pattern ............................ ........ .................................... 37 30102 Partide F1owo .... o .... .. .. o .................. .. ............................................ 40

3 02 Separation Efficiency ...... .. ........ o .... o ............ .. ................ 0 .... o ................ 0 41 302.1 Overall Separation Efficiency ...................................... o .. .... ........ 41 30202 Grade-Efficiency ooooooo oooooooooOoOoOOoooooooooo oooooooooooooo oooo ooo oooooooooooo oooo ooo42 30203 Converting Between Overall Efficiency and Cut Size ............ .. .. 44

303 Pressure Drop .......... o .. ...... o .... o ........ .. o .... o ...... .. o .. ...... .. o ...... o .. o .. ...... o .... .. 45 Appendix 3A Worked Examp1e: Calcu1ating a Grade-Efficiency Curve .... .46

Solution oooo oooo oooooooooo ooO oo ooooooooooooooooooooo oooooooooooooo oooooooooooooo ooOOOOO OOooOoOO OOoo000000046

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4 Cyclone Flow Pattern and Pressure Drop .... ............ .. .... ... ................. .. ... .. . .49 4.1 Discussion ........ .... .... .... ... ... ..... .. ... .. .. ....... ... ... .... ......... ............... ... ..... ... 49

4.1.1 Flow Pattem ....... ..... ... .. .. ..... .. ... ... ...... ... ... ..... .... .... .......... ........... .. 49 4.1 .2 Pressure Drop ... ...... .. ........ ......... .. ...... .. ...... .. ... .... ...... ..... ........... .. 51

4.2 Models for the Flow Pattern .. ............. ..... .... ... .... ..... .... ........... ....... ...... 53 4.2.1 n-Type Model .. ... ........... .... ........ ... .... ... .. ..... .... .. .................. .... ... . 55 4.2.2 Barth ..... ....... ..... ...... ..... ...... ... ... ... .... .... .... .......... .......... .... ........... . 56

4.3 Models for the Pressure Drop .. .... ... .... ..... ......... .......... ...... .. .. ........ ... ... . 59 4.3 .1 Models Based on Estimating the Dissipative Loss ... ....... .. .... ..... 59 4.3.3 Core Model ..... .... ......... .... ..... ...... ......... .. .. ... ...... .. ... .. ............. .. ... . 61 4.3.3 Purely Empirical Models ............. ...... ....... .. ... ....... .. .. ......... .... ..... 66

4.4 Model Assumptions in Light ofCFD and Experiment ...... ...... ... ......... 67 4.5 Overview .. ... ... .. .... ....... .... ...... ........... .. ..... .. .... .. ..... ........ .... .......... ......... 71 Appendix 4A Worked Example for Calculating Cyclone Pressure Drop ..... 72

Solution .. ...... .. .. .... ...... .. ...... .... ...... ... .... ... .... .. .. .... ..... ......... .. ......... .... .. ... .. 72 Appendix 4B The Meissner and Löffler Model ... .. ...... ... ....... .. .. .... ... .... ....... 74

5 Cyclone Separation Efficiency ................. ...... .... ... ... ..... .... ............ ...... ..... .... 77 5.1 Discussion ... ..... .. ........... ..... .. ... ......... ... .... .. ... .... ..... .... .. ... .. .... ..... ........... 77 5.2 Models .... .. ..... ........... ................ ............ ... .... ....... .. .... .... .... .... .. ....... .. .... 78

5.2.1 Equilibrium-orbit Models: the Model ofBarth .. .... ........ ...... ....... 78 5.2.2 Time-of-Flight Models ..... .. ........ ....... .. ... .. ... ........ ... ..... .... .... ...... . 81 5.2.3 Hybrid Models: the Models ofDietz and ofMothes and Löffler83 5.2.4 Comparing the Models ....... ....... .. .... ... ... .... .... .......... .... ... ..... .... ... 84

5.3 Comparison ofModel Predictions with Experiment... ...... .... ............. .. 85 5.3 .1 Agreement with Experiment in General... .. .................. .... ......... .. 85 5.3.2 A Case Study: the Effect ofCyclone Length ......... .... .... ..... ...... .. 86

5.4 Overview .. ... .. ....... .... ..... .. .. ..... ..... ...... ......... ..... ...... .... ........ ......... ......... 89 Appendix 5A Worked Example for the Prediction ofCyclone Separation Performance .......... ... ... .. ..... ... ... ... .. ....... ...... .. ..... .. ......... ......... ... .... ........ .. .... .. 90

Solution ...... ..... .. ... ........ ... .. .... .......... ... ..... .. ... ....... ... .. ... .. .. .... ... ........... .. 90 Appendix 5B The Cyclone Efficiency Models ofDietz and ofMothes and Löffler ...... ........... .. .............. ........ ...... ... .... .... ................ ........ ... .... ... .. .......... .. 93

6 The Muschelknautz Method of Modefing .... .. ..... ........... .. .. .. ... .............. ... .. . 97 6.1 Basis of the Model. .. ............... ... ........ ..... .. ...... .. ... .... ... ..... .... ......... .. .... . 98 6.2 Computation ofthe Cut-Point of the Inner Vortex, x50 ... . .... . ... . . . ..... .. 103 6.3 Computation of Efficiency at Low Solids Loadings ......... .... ... ...... ... . 1 05 6.4 Determining ifthe Mass Loading Effect will Occur. .... .. ... ... .... ......... l07 6.5 Overall Separation Efficiency when C0 > CoL .. . . . . . . . . .. . . . . . ... . .. . .. . . ..... ... . I 07 6.6 Computation of Pressure Drop ........ .... .......... .... ..... .... ... ..... .............. . 1 08 Appendix 6A Example Problems .. .... ...... .. ..... ..... ..... ... ..... .... ... ... ... ... ... ... ... . 11 0

6A.l Simulation of Data from Hoffmann et al. (200 I) .. .... ......... .. ..... 110 6A.2 Simulation of the Data from Übermair and Staudinger (200 1). 113 6A.3 Simulation of the Data from Greif (1997) .. ..... ... .. ..... .. .. ..... .... ... 115

XIX

Appendix 6B Incorporation ofthe 'Inner Feed' ... .. .. .. ... ...... ..... .... ..... .. ... .... 117

7 Computational Fluid Dynamics .. ...... ........ .......................... .... .................. . 123 7.1 Simulating the Gas Flow Pattern ................ ...... .. .. .. .... .................... .. . 124

7 .1.1 Setting up the Finite Difference Equations .......... .... .. .. .. ........ .. . 124 7.1.2 Turbulence Models ................ .. .... .................... .... .. ...... .. ........... 126 7 .1.3 Simulations ............................... .. .... ........ .. .... .. ..... .... ... .. ........... . 127

7.2 Simulating the Partide Flow .... .. ........ .. .............. .. .......... .... ................ 131 7.2 .1 Eulerian Modeling .......................... ...... .... .......... .. ............ ........ 131 7.2.2 Lagrangian Partide Tracking .... ................ .. .................. .. ........ . 132 7 .2.3 Simulations .. ......... ...... .. ... ..................... ..... ........... ...... ... .... .... ... 132

Appendix 7 A: Transport Equations ........ .. .... .. ........ .... .. .. .... .. .... .. .. .... .. ........ 134

8 Dimensional Analysis and Scaling Rules ............ .. .. .. .............. .. .... .. .. .. .. .. .. . 13 7 8.1 Classical Dimensional Analysis .... .... ... .. .. .. ............ .... .. .. .. .. ...... .. ........ 138

8.1.1 Separation Efficiency .. .. .. .... .. .... .... ...... .. ........ .... .. .. .. .... .. .. ........ .. 138 8.1 .2 Pressure Drop .. .. .. .. ................ .. .. .. .......... .. ................... .. .... .. .. .... 141

8.2 Scaling Cydones in Practice .... .. ........ ...... .. .. .. .......... .... .. ...... .... .... .. .... l42 8.2.1 Approximately Constant Stk50 over a Wide Range of Re .. .. ...... 142 8.2.2 Eu only Weakly Dependent on Re ................ ...... .. .. .... .... .. ........ 144 8.2.3 Some other Considerations .. .... .. .. .............. .. ........................ ..... 145 8.2.4 Stk-Eu Relationships ............. .. .. ... .. .. .... ...... .. ......... .. .......... ........ 145

Appendix 8A. Inspecting the Equations ofMotion .......... .. .................... .. .. 147 8A.1 Equation ofMotion for the Gas .......................................... .. .... 147 8A.2 Equation ofMotion for a Partide .. ........................................... 148

Appendix 8B. Sampie Cydone Scaling Calculations ................................. 148 8B .1 Calculating the Inlet Velocity in a Scale Model Required for Re Similarity ...... ... ....... ... .................... .... .. ... .. .. ... ... ........... .... .. ... .. ...... .. ... 148 8B.2 Predicting Full-Scale Cydone Performance using a Sca1e Model ... .... .. ............... ... ...... ...... .... ....... .... ...... ........ ......... ... .... ...... ..... ... ...... ... 149

9 Other Factors lnfluencing Performance .................. .......................... ....... 155 9.1 The Effect ofSolids Loading ...................... .. .... ............ .. .... ............... 155

9 .1 .1 Effect on Separation Efficiency of Cydones .... .......... .. ............ 15 5 9.1.2 Models for the Effect on Separation Efficiency of Cyclones .. .. l56 9 .1.3 Effect on the Separation Efficiency of Swirl Tubes .. .. .......... .. .. 162 9 .1.4 Effect on the Pressure Drop of Cydones .................. .. .............. 163 9.1.5 Effect on the Pressure Drop Across Swirl Tubes ...... ...... .. .. .. .... 164 9 .1. 6 Computing the Performance of a Cyclone with High Loading . 164

9.2 The Effect ofthe Natural Vortex Length .... .. ........................ .... ...... ... l65 9 .2.1 The Nature of the Vortex End ........ .. ........ .......... ...................... 166 9.2.1 The Significance ofthe Vortex End .......... .. ........ .. ............ .... .. . 168 9.2.2 Models for the Natural Vortex Length ...... .. ........ .. .......... .. .... .... l69

Appendix 9A Predicting the Effect ofSolids Loading on Cyclone Efficiency .. ......... ........................ ... .. ........... ................ ..... ....... ... ....... ................. ... 170

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Appendix 9B Predicting the Effect ofLoading on Cyclone Pressure Drop 173

10 Measurement Techniques .... ................................. .......................... .. ..... ..... l75 10.1 Gas Flow Pattern ...................................................................... ........ . 176 10.2 Pressure Drop .............................................. .. .................................... 179 10.3 Partide F1ow ................. ............................ .... .. .. ................................ . 180 10.4 Overall Separation Efficiency ............................................. .. ............. 180

1 0.4.1 On-line Sampling of Solids ........ ..... ............................ ............ 182 10.5 Grade-Efficiency .... ............................. ...... .... .. .................. ................ 184

10.5 .1 On-Line vs. Off-Line Size Analysis .. .. .. .. .................. .. ............ 184 10.5.2 Sampie Capture and Preparation .... .. ............. .. .... ...... .. ... .. ...... 185 10.5.3 Methods for Size Analysis ............. .. ....................................... 186

Appendix 1 OA Estimate of Errors ................... ... ....................... .. ..... .... ...... 190

11 Underflow Configurations and Considerations ........ .............. ........ ........ .. 193 11 .1 Underflow Configurations .... ............ .... .................... ... ..... .. ............. .. 193 11.2 Importance of a Good Underflow Seal.. ... ..... .. .. .......... .. .... ........ ... .. ... 197

11.2.1 Inleakage Example ........................ .. .............................. .. ..... .. 199 11.3 Upsets Caused by 'too Good' an Underflow Seal ............... .. ...... ... ... 200 11.4 Second-Stage Dipleg Solids 'Backup' .... .. ............................. .... ........ 203 11.5 Hopper 'Crossflow' .............................. ....... ........................... .. ... ...... 205 11.6 Hopper Venting Options .................................. .................................. 207 Appendix 11A Dipleg Calculation ......................... .................................... 210

Solution ............... .. .. ... ..... ........ ... ........ ... .... .................... ........ ....... ..... 210 Appendix 11 B Moment Balance on Flapper Valve Plate ........................... 210

llB.l Example .................... .............................................................. 213

12 Some Special Topics .. ......... .. ... .. .... .. .................. .. .................... .. .... ............. . 215 12.1 Cyclone Erosion .............. .. ................................................................ 215

12.1.1 Inlet 'TargetZone' .. ..... .............. ... .. ... .. ...................... .. ...... .. ... 215 12.1.2 Lower Cone Section ............... .. ... ... .... ................ ...... .. .. .. ........ 217 12 .1.3 Erosion Protection ....................... ............................... ............ 221

12.2 Critical Deposition Velocity .................................................. ............ 232 12.3 High VacuumCase ........................................................ ....... .. .. ......... 233

12.3.1 Application to Cyclone or Swirl Tube Simulation .... .... ... ....... 234 Appendix l2A Worked Example for Calculation ofthe Critical Deposition Velocity .......... .................... .............. .... ....... ... ......... .......... ....... .... ... .... ....... 235

Solution ......................... .................. ....... ...... ............ ....... ..... .......... ... 235 Appendix l2B Worked Example Taking Into Account Slip in Calculation of the Cut Size ........................ .......................... .. ............................. .......... ..... 236

Solution ......................... ...... ... ........ ........ .... .... ...... .. .................. ......... 236

13 Demisting Cyclones .. ................. ..... .... ... .. ................ .......................... .. ........ 239 13.1 Liquid Creep and 'Layer Loss' .......................................................... 240 13.2 Demisting Cyclone Design Considerations ....... ................ .... ........ ..... 241

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13.3 Some Vapor-Liquid Cyclone DesignGeometriesand Features ......... 243 13.4 Estimating Inlet Drop Size for Two-Phase Mist-Annular Flow ......... 248

13.4.1 Estimating Drop Size Distribution ............. ......... ..... ... ...... ...... 251 13.5 Modeling the Performance ofVapor-Liquid Cyclones ... ........ ..... .... .. 252

13.5.1 Computation ofCut Size ............. ....................... ............. ... .... 252 13.5.2 Computation ofEfficiency at Low Inlet Loadings .................. 253 13.5.3 Criteria for Determining if 'Mass loading' ('Saltation') Occurs ..... ......................... ...................................... ... .. ....... ........ ... .... .... ..... ... 253 13.5 .4 Overall Separation Efficiency when c0 > CoL ............ .. ............ 254

Appendix 13A Example Calculations ofDroplet Sizes in Pipe Flow ......... 255 13A.1 Finding the Mean Droplet Size .............. ...... ...... .. .. .. .... .. .. .. .. ... 255 13A.2 Finding the Droplet Size Distribution .................... ........ ........ . 256

Appendix 13B Flow Distribution in Parallel Demisting Cyclones ............. 256 13B.1 Calculation ofFlow Distribution ..... .. ............................ .. ........ 261 13B.2 Calculation ofthe Liquid Level Difference between the Front and Back Cyclones ............ .... ................... ..... ... ............ ..... ............ ........... 261

14 Foam-Break.ing Cyclones ... .... ... ......................... .. ... ...................... ............. 263 14.1 Introduction ........ ...... ... ............................ ...... ..................... ...... ......... 263 14.2 Some Design Considerations and Factars Influencing Behavior ....... 265 14.3 Applications .............. ............................... .............................. ... ..... .... 268 14.3 Estimating Submergence Required to Prevent Gas 'Blow Out' ....... .. 272 Appendix 14A Example Computation of Submergence Required to Prevent Underflow Gas 'Blow Out' ........ ............................................. .. ........ .. .. .. ... 274

Solution .................... .................. .... ... ......... .... ....................... ............ 274

15 Design Aspects ... ... ........ .... ...... ............ ..................... ...................... ....... ....... 277 15.1 Cylinder-on-Cone Cyclones with Tangential Inlet... .......................... 277

15.1.1 Some Standard Cyclone Designs .... ...... .. ............................ .... 277 15.1.2 Design ofthe Inlet .. .. ........ .... ........ .. .. .... .... ...... .. .... .. .. .. .. .... .. .... 278 15.1.3 Design ofthe Cone Section ............................................ ........ 282 15.1.4 Solids Outlet Configurations .......... .... .................... .. .............. 284 15.1.5 Vortex Finder Geometries ............ .. ....................... ......... ........ 286 15.1.6 Cyclone Length .. .. ...................... .. .. .. .. .... ................... .... ........ .. 290 15.1.7 Cyclone Operating Conditions .... .... ...... ...... .. .. .. .... ........ .. ... ..... 291

15.2 Design ofSwirl Tubes with Swirl Vanes .............................. .. ........... 292 15.2.1 Design ofthe Inlet Vanes .. ........ .. .. .. ... .. ........ ...... .......... .. ........ 292 15.2.2 Calculation oflnlet 'Throat' Area Fora Vane-Type Inlet Device ................. ................. ......................... ......................... ........ ..... .... ...... 293 15.2.3 Length ofthe Swirl Tube Body and the Solids Exit .. .... .. ....... 295

Appendix 15A Example Calculation ofthe Throat Area .................... ...... .... 296 Solution ........ ............ ............ ........... .............. ...................... .............. 296

16 Multicyclone Arrangements ............ ........... ........ ............ .......... .................. 299 16. 1 Cyclones in Series ...... ...... .. .................................................. .... .... ..... 299

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16.2 Cyclones in Parallel .. ...... ... ........................ .......... .............. .......... .. .. .. 300 Appendix 16A Example Calculation for Multicyclone Arrangements ....... 308

Solution .. ........ ........... ...... ......... .. ...... ................... .. ............... ............. 309

List of Symbols ................................... ... ............... ..................... .... .. ..... .... ......... 313 Greek and Other: ................... ................................... ...................... ........... .. 315 Subscripts: ................................................ .. .......................... ............. ......... . 316 Superscripts ................ ............ .... .................. ....................... ............ ............ 318

List of Tradenames ................ ..... .. ....................... ........ .................... .................. 319 References .... ......................................................... ..................... .... ................... 321 Index ...... ..... ................................ ..................... ..... ........ .................... ................... 325