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Transport Phenomena at Elevated Temperatures

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Transport Phenomena at Elevated Temperatures TRANSPORT PHENOMENA AT ELEVATED TEMPERATURES - STUDIES RELATED TO DIRECT POLYMETALLIC SMELTING by ROBERT KEITH HANNA A thesis submitted to the Faculty of Engineering of the University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Chemical Engineering, University of Birmingham, P.O. Box 363, Birmingham, B152TT England. February 1990 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ABSTRACT The modelling of two key areas of transport phenomena in a new polymetallic smelter has been achieved by using both mathematical and physical models to investigate optimum operating conditions. A study of oxygen mass transfer caused by multiple top-blown, subsonic gas jets contacting water flowing in a full-scale channel model of the smelter converting hearth has been carried out. A liquid phase solute mass transfer model that incorporates a flowing liquid phase has been developed. It has been used to compare mass transfer for both open-packed and close-packed multiple lance arrays of 2.26 mm, 4.95 mm, 10.95 mm and 24.40 mm nozzles delivering the same quantity of gas. It was found that for fewer lances of the larger nozzle diameters, up to a 75% reduction in liquid phase mass transfer occurred especially for the close-packed configurations. This restriction of mass transfer will result in reduced metal losses in the analogous smelter situation.Over a wide range of channel flowrates the mass transfer coefficient was found to be independent of water velocity. A computer model that predicts the amount of fog formation in the zinc vacuum condenser of the smelter for binary vapour/gas mixtures has identified operating conditions most susceptible to vapour fogging and subsequent metal losses. A fog problem is most likely to occur in condensable mixtures with high vapour concentrations and low initial quantities of superheat, and at low cooling wall temperatures as well as at high total pressures. Any lead in a Pb/Zn/N2 condensable mixture will fog heterogeneously at least 400°C before zinc droplets form and act as condensation nuclei for the zinc vapour. An engineering approach to estimating quantities of homogeneous fog formation has been developed and is used to analyse the performance of the Imperial Smelting Furnace zinc condenser and the Port Pirie Vacuum Dezincing Unit. ACKNOWLEDGEMENTS The author wishes to extend his gratitude to Professor N.A. Warner for his supervision and guidance during the course of this project. Thanks are due to Mr. P. Hinton and the Minerals Engineering Workshop for their help in constructing the experimental rigs. The author is grateful to Mr. S. Clabon for the fabrication of the glass models and lances used in the testwork. The photographs by Dr. J. Anderson, the advice from Mr. G. Titmus and the typing by Miss C. Green are all very much appreciated. The assistance of Mr. A. Roberts during the development of the computer program is also gratefully recognized. The author is indebted to Mr. P. Partington of Broken Hill Associated Smelters, Port Pirie, South Australia, Mr. R. Knight of Britannia Refined Metals, Northfleet, Kent and Mr. M. Gammon of Commonwealth Smelting Limited, Avonmouth for access to samples from their zinc condensers and their ready provision of technical information. The criticism of this work and the technical comments offered by the following people are all very much appreciated: Dr. T. Jones, British Steel's Teesside Research Laboratories, Grangetown, Middlesbrough. Dr. E.R. Buckle, Department of Metallurgy, University of Sheffield, and Mr. D.E. Steinmeyer, Monsanto Company, St. Louis, Missouri, U.S.A. The Department of Education for Northern Ireland is acknowledged for providing financial support during the term of this venture. To Betty and Kenneth "Some men see things as they are and ask 'Why?' I dream of things that never were and ask 'Why not?' " JOHN F. KENNEDY CONTENTS CHAPTER 1 INTRODUCTION 1 1.1 PYROMETALLURGY: ITS RELATIONSHIP TO CHEMICAL ENGINEERING 1 1.2 SCOPE AND AIMS OF THIS INVESTIGATION 4 1.3 MATHEMATICAL AND PHYSICAL MODELLING IN PYROMETALLURGY 6 1.4 DIRECT POLYMETALLIC SMELTING 11 CHAPTER 2: LITERATURE SURVEY AND THEORETICAL BACKGROUND 1 9 2.1 TOP-BLOWING THEORY 19 2.1.1 The Scope of Published High and Low Temperature Investigations 19 2.1.1.1 High Temperature Top-Blowing Experiments 2.1.1.2 Top-Blowing Physical Modelling Studies 21 2.1.2 Structure and Properties of a Turbulent Gas Jet 24 2.1.2.1 Velocity of the Gas Jet 26 2.1.3 The Interaction of a Top-Blown Gas Jet With Liquid Surfaces in Stationary Baths 32 2.1.3.1 Deformation of the Liquid Surface 32 2.1.3.2 Depth, Diameter and Profile of the Liquid Depression 34 2.1.3.3 Critical Depth of Depression and the Onset of Splashing 38 2.1.4 Induced Liquid Circulation Patterns During Top-Blowing 41 2.1.4.1 Single Lance Fluid Flow Pheno­ mena in Stationary Baths 41 2.1.4.2 Multiple Lance Fluid Flow Phenomena With Superimposed Channel Flow 44 2.1.5 Multiple Jet Flow Phenomena 49 2.1.5.1 Interference Between Jets in a Multiple Jet Array 49 2.1.5.2 The Effect of Containing Vessel Walls on Jet Flow 55 2.1.6 Interfacial Phenomena Associated With Impinging Gas Jets 58 2.1.7 Impinging Gas Jet Transport Phenomena 62 2.1.7.1 Simultaneous Heat and Mass Transfer 62 II Page 2.1.7.2 Development of a Theoretical Model for Multiple Gas Jet Liquid Phase Mass Transfer During Channel Flow Including Governing Equations 63 2.1.8 Similarity Criteria For High and Low Temperature Top-Blowing Systems: Dimensionless Correlations 74 2.2 CONDENSATION AND FOG FORMATION THEORY 77 2.2.1 Condensation Under Normal Atmospheric Pressure 77 2.2.1.1 Pure Saturated Vapours 77 2.2.1.2 Vapour/Inert Gas Mixtures 78 2.2.1.2.1 High Vapour Con­ centrations 84 2.2.1.2.2 Metallic Vapours and the Effect of Interfacial Thermal Resistance 86 2.2.1.3 Multiple Vapour/Inert Gas Mixtures 88 2.2.1.4 The Imperial Smelting Furnace Zinc Condenser 91 2.2.2 Condensation Under Vacuum 95 2.2.2.1 Low Temperature Vapour/Inert Gas Studies 96 2.2.2.2 High Temperature Metallic Vapour/Inert Gas Studies 98 2.2.2.2.1 Laboratory and Nuclear Distillation 98 2.2.2.2.2 Industrial Vacuum Dezincing Processes 98 2.2.3 Fogging in a Vapour/Gas Mixture 108 2.2.3.1 Introduction and Definitions 108 2.2.3.2 Detrimental Effects of Fog and Mist Formation 118 2.2.3.3 Formation and Growth of Liquid Droplets in a Vapour/Gas Mixture 119 2.2.3.4 Homogeneous Fog Formation 123 2.2.3.4.1 Kinetics of Homogen­ eous Fog Nucleation 123 2.2.3.4.2 Critical Vapour Super- saturation Criterion For Homogeneous Nucleation 126 2.2.3.5 Heterogeneous Fog Formation 129 Page 2.2.3.6 Coalescence of Fog Droplets 133 2.2.3.7 Fog Deposition and Settling 137 2.2.3.8 Fog and Mist Preventative Measures Offered in the Published Literature 138 2.2.3.9 Forced Convection Fog Formation 142 CHAPTER 3: TOP-BLOWING EXPERIMENTAL WORK 153 3.1 APPARATUS 1 53 3.1.1 Analogue Model of the Smelter Converting Hearth 1 53 3.1.2 Gas Delivery to the Lances 1 58 3.1.3 Multiple Lance Assemblies 159 3.1.4 Measuring Oxygen Concentration 164 3.2 CALCULATION OF JETTING PARAMETERS 170 3.2.1 Comparison of Calculated and Measured Jet Momentum Fluxes and Mass Flow- rates 170 3.2.2 Variation in Radius and Area of the Jet Impact Region With Lance Height 173 3.3 EXPERIMENTAL PROCEDURE 175 3.4 TYPICAL TOP-BLOW RUN CALCULATION 178 CHAPTER 4: TOP-BLOWING RESULTS AND DISCUSSION 183 4.1 INTRODUCTION 183 4.2 ACCURACY AND EXPERIMENTAL REPROD- UCIBILITY 186 4.3 THE EFFECT OF CHANNEL FLOWRATE ON LIQUID PHASE MASS TRANSFER FOR CLOSE-PACKED TRIANGULAR AND SQUARE PITCH ARRAYS OF 2.26 mm NOZZLES 188 4.4 THE EFFECT OF LANCE HEIGHT ON LIQUID PHASE MASS TRANSFER FOR CLOSE- PACKED ARRAYS OF 2.26 mm NOZZLES 193 4.5 THE EFFECT OF NOZZLE DIAMETER AND MULTIPLE LANCE PACKING ON LIQUID PHASE MASS TRANSFER 198 4.6 NITROGEN JET OXYGEN DESORPTION EXPERIMENTS 206 4.7 THE CHANGE IN MOMENTUM FLUX OF A JET DUE TO PACKING OF NEIGHBOURING JETS IN AN ARRAY AND CHANNEL WALLS 211 4.8 TOP-BLOW UNIT DESIGN FOR THE PILOT- SCALE SMELTER 216 IV Page CHAPTER 5: FOG FORMATION DURING VACUUM CON­ DENSATION 219 5.1 DEVELOPMENT OF A COMPUTER PROGRAM FOR HIGH TEMPERATURE CONDENSABLE MIXTURES 219 5.1.1 Consideration of Cooling Curves For Vapour/Gas Mixtures 219 5.1.2 Numerical Solution of First Order Differential Equations 220 5.1.3 Solution of the Cooling Curves by a Computer Program 222 5.2 TYPICAL COMPUTER PROGRAM PRINTOUT AND SUBSEQUENT ANALYSIS 233 5.3 ASSESSMENT OF THE EFFECT OF STEP LENGTH ON THE PROGRAM ACCURACY 237 5.4 LOW TEMPERATURE PHYSICAL MODEL OF THE WARNER VACUUM CONDENSER 239 CHAPTER 6: ZINC CONDENSER COMPUTER PROGRAM FOG PREDICTIONS AND DISCUSSION 245 6.1 INTRODUCTION 245 6.2 CONSIDERATION OF ZINC VAPOUR HETEROGENEOUS FOG FORMATION IN ZINC/NITROGEN MIXTURES 246 6.2.1 The Effect of Inlet Vapour Concentration on Fog Formation 246 6.2.2 The Effect of Condensate Interfacial Temperature on Vapour Fog Formation 255 6.3 CONSIDERATION OF LEAD VAPOUR HETEROGENEOUS FOG FORMATION IN ZINC/LEAD/NITROGEN MIXTURES 259 6.4 ESTIMATING HOMOGENEOUS FOG FORMATION
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