Pneumatic conveying of bulk

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  • University of WollongongResearch Online

    University of Wollongong Thesis Collection University of Wollongong Thesis Collections

    1989

    Pneumatic conveying of bulk solidsP. W. WypychUniversity of Wollongong

    Research Online is the open access institutional repository for theUniversity of Wollongong. For further information contact ManagerRepository Services: [email protected]

    Recommended CitationWypych, P. W., Pneumatic conveying of bulk solids, Doctor of Philosophy thesis, Department of Mechanical Engineering, Universityof Wollongong, 1989. http://ro.uow.edu.au/theses/1590

  • PNEUMATIC CONVEYING OF BULK SOLIDS

    A thesis submitted in fulfilment of the

    requirements for the award of the degree of

    DOCTOR OF PHILOSOPHY

    from , UNIVERSITY OF llum

    'WOLLONGONG LIBRARY

    THE UNIVERSITY OF WOLLONGONG

    by

    P. W. WYPYCH, BE, MIEAust.

    Department of Mechanical Engineering

    1989

  • This is to certify that this work has not been submitted for a degree to any other university or institution

    Peter W. Wypych

  • Dedicated to my wife, Linda, and my children, David, Emma and Amanda

    for their love, support and patience.

  • i

    SUMMARY

    The pneumatic conveying of bulk solids through pipelines has been used in industry for several decades. With the introduction in recent years of new techniques and more efficient hardware, there has been a considerable increase in the use of this method of transport (e.g. dense-phase, low-velocity and long-distance conveying). Unfortunately, the technology available to assess the relative merits of the large number of commercial systems that now compete for a particular application is lacking sadly, especially when efficient and reliable dense-phase or long-distance transportation is required. The main objective of this thesis is to provide industry with some of this technology in relation to fine powders (e.g. pulverised coal, fly ash, P V C powder, fly ash/cement mix) and some coarser products (e.g. screened coke, crushed bath, granulated aluminate). A convenient method for presenting the variation of major steady-state conveying parameters is needed for efficient design, system evaluation and optimisation. One technique based on other work and extended to include saltation and minimum transport behaviour is established. A standardised-test procedure comprising three different types of pneumatic conveying experiment also is developed to generate efficiently the data required for this purpose. The method of scaling up test rig data to full-scale installations, previously used quite extensively in the design of pneumatic conveying systems, is investigated and found to be inadequate in particular applications. T w o popular forms of definition and three existing empirical correlations for the solids pressure drop are modified to demonstrate the possible extent of this inadequacy. Steady-state pipeline conveying characteristics of three products are used in the development of an improved scale-up procedure. Methods to predict the air-only pressure drop for both single- and stepped-diameter pipelines and to generalise the conveying characteristics of a particular material (applicable to other combinations of length and diameter) also are formulated and verified. Pulverised coal conveyed over 25 m and fly ash over 943 and 293 m (utilising three different configurations of blow tank) are used to investigate the effect of blow tank air injection on the performance of a pneumatic conveying system. The addition of supplementary conveying-air to a blow tank incorporating a top-air supply and transporting a good dense-phase material (pulverised coal) is shown to achieve higher values of mass flow ratio and/or conveying rate and also provide smoother and more consistent transportation. The installation of a fluidising discharge cone to the outlet of a blow tank conveying a cohesive fly ash is found to improve the discharge characteristics of the blow tank, as well as decrease pressure and flow rate fluctuations. The method of air injection also is found to have a significant impact on the plug-phase mode of conveying. Experiments on three different products are carried out to demonstrate the advantages of this method of transport (i.e. to handle conventionally difficult dense-phase materials, such as crushed bath) but also its sensitivity to changes in material property (viz. particle size). However, it is shown further that this may be compensated to some extent by selecting a different method of air injection.

  • ii

    T w o powder classification techniques based on physical properties are evaluated and found useful in explaining and indicating the minimum transport (dense-phase) behaviour for a wide range of materials. The steady-state pipeline conveying characteristics (dilute- and dense-phase) and the fluidisation behaviour of ten products are compared for this purpose. Various mathematical models utilising numerical integration and analytical approximations are formulated to predict blow tank performance characteristics. Despite the lack of good accurate data for the experimental verification of these models (i.e. due to certain difficulties in measurement technique), preliminary results still are obtained and presented in graphical format. Five existing pipeline theories also are investigated and reviewed. One particular model is found useful in predicting the dense-phase conveying parameters of fine powders, and a worked example is presented. The applicability of generalised solids friction factor correlations to the design of pneumatic conveying systems is reviewed. The resulting degree of uncertainty is considered too great for applications involving relatively high operating pressures (e.g. long-distance and/or large-throughput conveying). Test rig data obtained from pulverised coal, a fly ash/cement mix and various fly ash samples are used to identify certain areas of improvement. Based on this work, a test-design procedure is developed to determine an accurate solids friction factor correlation (i.e. for a given material and a wide range of diameters). Results from recent investigations into the long-distance pneumatic conveying of pulverised coal are used to demonstrate the good accuracy and reliability of this improved approach.

  • iii

    A C K N O W L E D G E M E N T S

    The author gratefully acknowledges the guidance, continuous support and encouragement of his supervisor Professor P. C. Arnold throughout the course of this work. The support provided by the following colleagues during the various stages of this work also are acknowledged sincerely by the author.

    Mr O. C. Kennedy for his assistance with the laboratory test work and the processing of some of the experimental results and figures.

    Mr D. M. Cook for his patience and assistance with the pneumatic conveying test work, construction and installation of the experimental apparatus.

    The author particularly acknowledges the assistance provided by the staff of the Maintenance Workshop for the construction and installation of the various test rigs and equipment. The financial support provided by the National Energy Research Development and Demonstration Council, the Australian Electrical Research Board and The University of Wollongong is acknowledged gratefully by the author. The contributions made by Ramsey Engineering and Keystone Valve (A/Asia) Pty. Ltd. for the donation/supply of Clarkson knife-gate and butterfly valves respectively for the various test rigs also are acknowledged.

  • iv

    TABLE OF CONTENTS

    SUMMARY ACKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES NOMENCLATURE

    P a g e i

    iii iv vii xiii xvii

    CHAPTER 1 INTRODUCTION

    CHAPTER 2 PNEUMATIC CONVEYING TEST RIGS

    2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8

    TEST RIG A

    TEST RIG B

    TEST RIG C TEST RIG D

    TEST RIG E TEST RIG F

    AIR SUPPLY AND FLOW RATE MEASUREMENT DATA ACQUISITION

    6 7 14 15 18 21 24 26

    CHAPTER 3 PNEUMATIC CONVEYING CHARACTERISTICS 27

    3.1 PULVERISED COAL 3.2 DEFINITION OF DENSE-PHASE 3.3 FLY ASH 3.3.1 Introduction 3.3.2 Test Rig Description 3.3.3 Test Results 3.4 STANDARDISED-TEST PROCEDURE 3.4.1 Experiments 3.4.1.1 Test 1 - Standard Batch Cycle 3.4.1.2 Test 2 - Increase of Apt for Approximately Constant mf 3.4.1.3 Test 3 - Decrease of mf at Steady-State Conditions 3.4.2 Results 3.4.3 Minimum Transport Behaviour 3.4.4 Test Procedure Applications and Limitations

    31 35 36 36 37 39 45 46 46 48

    48 48 53 55

  • CHAPTER 4 BLOW TANK CONFIGURATION & AIR INJECTION 60

    4.1 4.2 4.2.1 4.2.2 4.3 4.3.1 4.3.2 4.3.3 4.3.4

    PULVERISED COAL FLY ASH Introduction Test Results PLUG-PHASE CONVEYING

    62 66 66 68 72

    Screened & Unscreened Granulated Aluminate (SGA & UGA) 72 Bone Char 77 Crushed Bath 80 Summary 82

    CHAPTER 5 POWDER CHARACTERISATION 86

    5.1 INTRODUCTION 5.2 PHYSICAL PROPERTIES 5.2.1 Definitions of Particle Size 5.3 FLUIDISATION 5.3.1 Experimental Apparatus 5.4 PIPELINE CONVEYING CHARACTERISTICS 5.5 POWDER CLASSIFICATION TECHNIQUES 5.5.1 Fluidisation 5.5.2 Slugging 5.5.2.1 Slugging Diagram Modifications 5.5.2.2 Results

    87 87 87 90 90 95 95 97 100 100 102

    CHAPTER 6 SCALE-UP CONVEYING CHARACTERISTICS 109

    6.1 INTRODUCTION 6.2 SCALING RELATIONSHIPS 6.2.1 Definitions for Aps 6.2.2 Empirical Relationships 6.3 EXPERIMENTAL INVESTIGATIONS 6.3.1 Fly Ash / Cement Mix 6.3.2 Screened Coke 6.3.3 PVC Powder 6.4 SCALE-UP OF Apt 6.5 SUMMARY

    110 113 113 115 117 117 120 122 126 1

  • VI

    6.6 GENERALISED PIPELINE CONV. CHARACTERISTICS 130

    CHAPTER 7 THEORETICAL INVESTIGATIONS 133

    7.1 INTRODUCTION

    7.2 BLOW TANK DISCH

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