Contents 1 Introduction 2 Basic Ideas 3 How Cyclones Work

Transcription

1 Contents 1 Introduction Removal of Particles from Gases Filtration Wet Scrubbers Centrifugal/Cyclonic Devices Knock-out Vessels and Settling Chambers A Closer Look at Centrifugal Gas Cleaning Devices Applications of Centrifugal Separators Classification of Centrifugal Separators Two Main Classes - Cyclones and Swirl Tubes 13 2 Basic Ideas Gas Flow Swirling Flow Static and Dynamic Pressure Particle Motion Particle Size Definitions of Particle Size Particle Size Distribution Particle Density 29 Appendix 2A Ideal Vortex Laws from the Navier-Stokes Equations 30 Appendix 2B Common Models Functions for Particle Size Distribution 33 2B.1 The Normal Distribution 34 2B.2 The Log-Normal Distribution 34 2B.3 The Rosin-Rammler Distribution 35 3 How Cyclones Work Flow in Cyclones Gas Flow Pattern Particle Flow Separation Efficiency Overall Separation Efficiency Grade-Efficiency Converting Between Overall Efficiency and Cut Size Pressure Drop 45 Appendix 3A Worked Example: Calculating a Grade-Efficiency Curve 46 Solution 46

2 XVIII Cyclone Flow Pattern and Pressure Drop Discussion Flow Pattern Pressure Drop Models for the Flow Pattern n-type Model Barth Models for the Pressure Drop Models Based on Estimating the Dissipative Loss Core Model Purely Empirical Models Model Assumptions in Light of CFD and Experiment Overview 71 Appendix 4A Worked Example for Calculating Cyclone Pressure Drop 72 Solution 72 Appendix 4B The Meissner and Loftier Model 74 Cyclone Separation Efficiency Discussion Models Equilibrium-orbit Models: the Model of Barth Time-of-Flight Models Hybrid Models: the Models of Dietz and of Mothes and L6ffler Comparing the Models Comparison of Model Predictions with Experiment Agreement with Experiment in General A Case Study: the Effect of Cyclone Length Overview 89 Appendix 5 A Worked Example for the Prediction of Cyclone Separation Performance 90 Solution 90 Appendix 5B The Cyclone Efficiency Models of Dietz and of Mothes and Ldffler 93 The Muschelknautz Method of Modeling Basis of the Model Computation of the Cut-Point of the Inner Vortex, x so Computation of Efficiency at Low Solids Loadings Determining if the Mass Loading Effect will Occur Overall Separation Efficiency when c o > C O L Computation of Pressure Drop 108 Appendix 6A Example Problems 110 6A.1 Simulation of Data from Hoffmann et al. (2001) 110 6A.2 Simulation of the Data from Obermair and Staudinger (2001) A.3 Simulation of the Data from Greif (1997) 115

3 XIX Appendix 6B Incorporation of the 'Inner Feed' Computational Fluid Dynamics Simulating the Gas Flow Pattern Setting up the Finite Difference Equations Turbulence Models Simulations Simulating the Particle Flow....' Eulerian Modeling Lagrangian Particle Tracking Simulations 132 Appendix 7A: Transport Equations Dimensional Analysis and Scaling Rules Classical Dimensional Analysis Separation Efficiency Pressure Drop Scaling Cyclones in Practice Approximately Constant Stkso over a Wide Range of Re Eu only Weakly Dependent on Re Some other Considerations Stk-Eu Relationships 145 Appendix 8A. Inspecting the Equations of Motion 147 8A.1 Equation of Motion for the Gas 147 8A.2 Equation of Motion for a Particle 148 Appendix 8B. Sample Cyclone Scaling Calculations 148 8B.1 Calculating the Inlet Velocity in a Scale Model Required for Re Similarity 148 8B.2 Predicting Full-Scale Cyclone Performance using a Scale Model Other Factors Influencing Performance The Effect of Solids Loading Effect on Separation Efficiency of Cyclones Models for the Effect on Separation Efficiency of Cyclones Effect on the Separation Efficiency of Swirl Tubes Effect on the Pressure Drop of Cyclones Effect on the Pressure Drop Across Swirl Tubes Computing the Performance of a Cyclone with High Loading The Effect of the Natural Vortex Length The Nature of the Vortex End The Significance of the Vortex End Models for the Natural Vortex Length 169 Appendix 9 A Predicting the Effect of Solids Loading on Cyclone Efficiency.. 170

4 XX Appendix 9B Predicting the Effect of Loading on Cyclone Pressure Drop Measurement Techniques Gas Flow Pattern Pressure Drop Particle Flow Overall Separation Efficiency On-line Sampling of Solids ' Grade-Efficiency On-Line vs. Off-Line Size Analysis Sample Capture and Preparation Methods for Size Analysis 186 Appendix 10A Estimate of Errors Underflow Configurations and Considerations Underflow Configurations Importance of a Good Underflow Seal Inleakage Example Upsets Caused by 'too Good' an Underflow Seal Second-Stage Dipleg Solids 'Backup' Hopper 'Crossflow' Hopper Venting Options 207 Appendix 11A Dipleg Calculation 210 Solution 210 Appendix 1 IB Moment Balance on Flapper Valve Plate B.1 Example Some Special Topics Cyclone Erosion Inlet'Target Zone* Lower Cone Section Erosion Protection Critical Deposition Velocity High Vacuum Case Application to Cyclone or Swirl Tube Simulation 234 Appendix 12A Worked Example for Calculation of the Critical Deposition Velocity 235 Solution 235 Appendix 12B Worked Example Taking Into Account Slip in Calculation of the Cut Size 236 Solution Demisting Cyclones Liquid Creep and 'Layer Loss' Demisting Cyclone Design Considerations 241

5 XXI 13.3 Some Vapor-Liquid Cyclone Design Geometries and Features Estimating Inlet Drop Size for Two-Phase Mist-Annular Flow Estimating Drop Size Distribution Modeling the Performance of Vapor-Liquid Cyclones Computation of Cut Size Computation of Efficiency at Low Inlet Loadings Criteria for Determining if'mass loading' ('Saltation') Occurs Overall Separation Efficiency when c o > c ol 254 Appendix 13A Example Calculations of Droplet Sizes in Pipe Flow A.1 Finding the Mean Droplet Size A.2 Finding the Droplet Size Distribution 256 Appendix 13B Flow Distribution in Parallel Demisting Cyclones B.1 Calculation of Flow Distribution B.2 Calculation of the Liquid Level Difference between the Front and Back Cyclones Foam-Breaking Cyclones Introduction Some Design Considerations and Factors Influencing Behavior Applications Estimating Submergence Required to Prevent Gas 'Blow Out' 272 Appendix 14A Example Computation of Submergence Required to Prevent Underflow Gas 'Blow Out' 274 Solution Design Aspects Cylinder-on-Cone Cyclones with Tangential Inlet Some Standard Cyclone Designs Design of the Inlet Design of the Cone Section Solids Outlet Configurations Vortex Finder Geometries Cyclone Length Cyclone Operating Conditions Design of Swirl Tubes with Swirl Vanes Design of the Inlet Vanes Calculation of Inlet 'Throat' Area For a Vane-Type Inlet Device Length of the Swirl Tube Body and the Solids Exit 295 Appendix 15A Example Calculation of the Throat Area 296 Solution Multicyclone Arrangements Cyclones in Series 299

6 XXII 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 ListofTradenames 319 References 321 Index 325

7 PPN: Titel: Gas cyclones and swirl tubes : principles, design and operation / Alex C. Hoffmann; Louis E. Stein. - Berlin : Springer, 2002 ISBN: Bibliographischer Datensatz im SWB-Verbund