University of WollongongResearch Online

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1989

Pneumatic conveying of bulk solidsP. W. WypychUniversity of Wollongong

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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 DISCHARGE CHARACTERISTICS 7.2.1 Approximate Analytical Solution 7.2.1.1 Results 7.2.1.2 Discussion 7.2.2 Numerical Analysis 7.2.2.1 Results

7.3 DENSE-PHASE PIPELINE CONV. CHARACTERISTICS 7.3.1 Pressure Loss Predictions by Muschelknautz &

Krambrock [59] 7.3.1.1 Theory 7.3.1.2 Calculation Procedure 7.3.1.3 Worked Example 7.4 CORRELATION ANALYSIS AND STEPPED-DIAMETER

PIPELINES

7.4.1 Generalised Correlation for Solids Friction Factor 7.4.2 Design of Stepped-Diameter Pipelines 7.4.2.1 Stepping Pipe Criteria 7.4.3 Test-Design Procedure

134 134 136 137 138 139 142 144

144 145 146 149

151 152 159 160 162

CHAPTER 8 CONCLUSIONS 174

8.1 FURTHER WORK 177

CHAPTER 9 REFERENCES 179

APPENDIX A

APPENDIX B

APPENDIX C

APPENDIX D

Compilation of Particle Size Data (Samples 1 to 11, Table 5.1) 186 Modified Slugging Diagram based on Dixon [23,39] and Cliftefa/. [41] 191 Compilation of Operating Conditions for Correlation Analysis (Samples 1 to 11, 12 and 13, Table 7.2) 197 Summary of Solids Friction Factor Calculations for Pulverised Brown Coal (Test-Design Procedure, Section 7.4.3) 203

Vll

LIST O F FIGURES

Chapter 2 Page

Figure 2.1 Configuration of the original 0.425 m3 blow tank (Test Rig A). 6 Figure 2.2 General arrangement of the original pneumatic conveying

Test Rig A. 8 Figure 2.3 Configuration of the final 0.425 m 3 blow tank (Test Rig B). 9 Figure 2.4 Exploded view of a typical pipeline air pressure tapping

location. 11 Figure 2.5 Full-sectional view of a 50 m m N.B. 90 blinded-tee bend. 12 Figure 2.6 General arrangement of Test Rig B. 13 Figure 2.7 Configuration of the original 0.9 m 3 blow tank (Test Rig C). 14 Figure 2.8 General arrangement of Test Rig C. 16 Figure 2.9 Configuration of the original tandem 0.9 m 3 blow tank feeding

system (Test Rig D). 17 Figure 2.10 Configuration of the final tandem 0.9 m 3 blow tank feeding

system (Test Rig E). 19 Figure 2.11 General arrangement of Test Rig E1 (refer to Figure 2.8 for

arrangement of pipe loops). 20 Figure 2.12 Configuration of the 0.113 m 3 plug-phase blow tank. 22 Figure 2.13 General arrangement of Test Rig F. 23 Figure 2.14 General arrangement of compressed air supply. 25 Figure 2.15 HP-85B plot of a typical uncalibrated pipeline air pressure

transducer response. 26

Chapter 3

Figure 3.1 General form of steady-state pneumatic conveying characteristics for a given material and pipeline configuration. 29

Figure 3.2 Alternative form of pneumatic conveying characteristics. 29 Figure 3.3 The Rizk [7] two-phase flow diagram for pneumatic conveying

in horizontal pipes. 30 Figure 3.4 Pneumatic conveying characteristics of pulverised coal for

Test Rig A1 (L = 25 m & D = 52 m m ) , displaying lines of constant Apj. 31

VIII

Figure 3.5 Pneumatic conveying characteristics of pulverised coal for Test Rig A1 (L = 25 m & D = 52 m m ) , displaying lines of constant ms. 32

Figure 3.6 Pneumatic conveying characteristics of pulverised coal for Test Rig A1 (L = 25 m & D = 52 m m ) displaying lines of constant, steady-state m s (Apj ordinate). 33

Figure 3.7 Pneumatic conveying characteristics of pulverised coal for Test Rig A1 (L = 25 m & D = 52 m m ) , displaying lines of constant, steady-state m s (Apt ordinate). 34

Figure 3.8 Schematic layout of the pneumatic conveying Test Rig B1 used during the fly ash test program. 38

Figure 3.9 Pipeline conveying characteristics of Eraring fly ash for L = 71 m & D = 52 m m (Test RigB1). 41

Figure 3.10 Pipeline conveying characteristics of Eraring fly ash for L = 71 m & D = 52 m m (Test Rig B1). 42

Figure 3.11 Pipeline conveying characteristics of Tallawarra fly ash for L = 71 m & D = 52 m m (Test Rig B1). 42

Figure 3.12 Pipeline conveying characteristics of Munmorah fly ash for L = 71 m & D = 52 m m (Test Rig B1). 43

Figure 3.13 Pipeline conveying characteristics of Vales Point fly ash for L = 71 m & D = 52 m m (Test Rig B1). 43

Figure 3.14 Pipeline conveying characteristics of Gladstone fly ash for L = 71 m & D = 52 m m (Test Rig B1). 44

Figure 3.15 Pipeline conveying characteristics of Wallerawang fly ash for L = 71 m & D = 52 m m (Test Rig B1). 44

Figure 3.16 Pipeline conveying characteristics of Liddell fly ash for L = 71 m & D = 52 m m (Test Rig B1). 45

Figure 3.17 Transient plots of major conveying parameters for Eraring fly ash demonstrating Test 1 (Test Rig B1, Exp. No. 236). 47

Figure 3.18 Transient plots of major conveying parameters for Eraring fly ash demonstrating Test 2 (Test Rig B1, Exp. No. 240). 49

Figure 3.19 Transient plots of major conveying parameters for Eraring fly ash demonstrating Test 3 (Test Rig B1, Exp. No. 249). 50

Figure 3.20 Pipeline air pressure drop (Test Rig B1, Exp. No. 236). 51 Figure 3.21 Pipeline conveying characteristics of Eraring fly ash for L = 71

m & D = 52 m m (Test Rig B1) demonstrating Tests 1, 2 and 3. 53

IX

Figure 3.22 Transient plots of major conveying parameters for Eraring fly ash demonstrating blockage condition using Test 3 (Test Rig B1, Exp. No. 232). 54

Figure 3.23 Pipeline conveying characteristics of P V C powder [21] for L = 71 m & D = 52 m m (Test Rig B1). 56

Figure 3.24 Transient plots of major conveying parameters for P V C powder demonstrating plugging condition using Test 2 (Test Rig B1, Exp. No. 387). 57

Figure 3.25 Transient plots of major conveying parameters for P V C powder demonstrating plugging condition using Test 3 (Test Rig B1, Exp. No. 414). 58

Chapter 4

Figure 4.1 0.425 m3 Sturtevant blow tank and air supply arrangement. 62 Figure 4.2 Transient plots of major conveying parameters from Exp. Nos.

21, 23 and 35 for pulverised coal conveyed over 25 m (Test RigA1). 63

Figure 4.3 Transient plots of major conveying parameters from Exp. Nos. 61 and 62 for pulverised coal conveyed over 25 m (Test Rig A1). 65

Figure 4.4 Configuration of bottom-discharge blow tank demonstrating incomplete discharge of material due to rat-holing. 67

Figure 4.5 Configuration of top-discharge blow tank demonstrating incomplete discharge of material due bad channelling and rat-holing. 68

Figure 4.6 Blow tank comparison using fly ash and Test Rig D2 (L = 940 m & D = 60/69/81/105 m m ) . 70

Figure 4.7 Blow tank comparison using transient plots of major conveying parameters for fly ash conveyed over 293 m (Test Rig D1). 71

Figure 4.8 Transient plots of major conveying parameters for S G A (Exp. No. 1274, Test Rig F2). 74

Figure 4.9 Particle size distributions of S G A and UGA. 75 Figure 4.10 Transient plots of major conveying parameters for U G A (Exp.

No. 1356, Test Rig F2). 76 Figure 4.11 Transient plots of blow tank and pipeline air pressure for bone

char (Exp. Nos. 1227 & 1235, Test Rig F2). 79

x

Figure 4.12 Transient plots of blow tank and pipeline air pressure for bone char (Exp. Nos. 1237 & 1245, Test Rig F2). 81

Figure 4.13 Transient plots of major conveying parameters for crushed bath (Exp. No. 108-12, orifice-air only, Test Rig F3). 83

Figure 4.14 Transient plots of major conveying parameters for crushed bath (Exp. No. 108-16, orifice-, ring- and supplementary-air, Test Rig F3). 84

Chapter 5

Figure 5.1 Schematic layout of the fluidisation test facility. 92 Figure 5.2 Comparison of fluidisation curves for pulverised coal (Sample

1) and fly ash (Samples 2 to 8). 93 Figure 5.3 Fluidisation curves of P V C powder (Sample 9) and screened

coke (Sample 10). 94 Figure 5.4 Comparison of pipeline conveying characteristics for fly ash

(Samples 2 to 8, Test Rig B1). 96 Figure 5.5 The Geldart [24] fluidisation diagram. 97 Figure 5.6 The Geldart [24] fluidisation diagram showing the location of

Samples 1 to 11. 99 Figure 5.7 The Dixon [23] slugging diagram for a 50 m m pipe diameter

system. 101 Figure 5.8 The Dixon [23] slugging diagram for a 100 m m pipe diameter

system. 101 Figure 5.9 The modified Dixon [23] slugging diagram for a 50 m m pipe

diameter system showing the classification of Samples 1 to 11 listed in Table 5.1. 103

Figure 5.10 Transient plots of major conveying parameters demonstrating flow irregularities for Sample 6 (Exp. No. 662, Test Rig B1). 104

Figure 5.11 Pipeline conveying characteristics of screened coke [14,16,26] for L = 25 m & D = 52 m m (Test Rig A1). 106

Chapter 6

Figure 6.1 Pipeline conveying characteristics of fly/ash cement mix for L| = 162 m & Di = 0.060 m (Test Rig C1). 118

Figure 6.2 Pipeline conveying characteristics of fly/ash cement mix for L| = 1 6 2 m & D i =0.105 m (Test Rig C3). 118

xi

Figure 6.3 Scale-up conveying characteristics of fly/ash cement mix for L2 = 162 m & D2 = 0.105 m based Figure 6.1 and Equation (6.6). 119

Figure 6.4 Scale-up conveying characteristics of fly/ash cement mix for L2 = 162 m & D2 = 0.105 m based on Figure 6.1 and Equation (6.28) with rj = 2.8. 120

Figure 6.5 Scale-up conveying characteristics of screened coke for L2 = 71 m & D2 = 0.052 m (based on Figure 5.11 and Equations (6.5) to (6.7)) with four experimental data points from Test Rig A 2 (L-i = 71 m & Di = 0.052 m ) . 121

Figure 6.6 Pipeline conveying characteristics of P V C powder for Li = 162 m & Di = 0.105 m (Test Rig C3). 122

Figure 6.7 Scale-up conveying characteristics of P V C powder for L2 = 162 m & D2 = 0.105 m, based on Figure 3.23 and Equation (6.29). 123

Figure 6.8 Scale-up conveying characteristics of P V C powder for L2 = 162 m & D2 = 0.105 m, based on Figure 3.23 and Equation (6.30). 124

Figure 6.9 Variation of Apt according to Equation (6.37) with experimental data points obtained from six different pipeline configurations. 127

Figure 6.10 Generalised pipeline conveying characteristics of fly ash/cement mix based on Test Rig C1 results (L|' = 162 m & Di= 0.060 m). 131

Figure 6.11 Generalised pipeline conveying characteristics of fly ash/cement mix based on Test Rig C3 results (L-|' = 162 m & Di= 0.105 m). 131

Chapter 7

Figure 7.1 The Enstad [62] element of a converging flow channel. 135 Figure 7.2 Example of blow tank model results (approximate analytical

solution). 140 Figure 7.3 Example of blow tank model results (numerical solution). 143 Figure 7.4 Full-bore plug transport system. 145 Figure 7.5 Variation of velocity ratio [59]. 147 Figure 7.6 Variation of particle free settling velocity based on the Clift et

al. [41] drag correlations. 148 Figure 7.7 Correlation of pipe friction coefficient due to solids according

to Stegmaier [68]. 153

xii

Figure 7.8 Comparison between experimental data and the Stegmaier [68] correlation. 1 5 5

Figure 7.9 Improved correlation of pipe friction coefficient due to solids. 157 Figure 7.10 Examples of air pressure drop for the Dj = 0.060 m section of

pipe, showing the location of the three 1 m radius x 90 bends. 164

Figure 7.11 Relationship between Xs and Frm showing actual values of m*. 166

Figure 7.12 Relationship between Xs and X = Frm p f m 0 2 showing experimental values of m* and predicted curves, based on Equation (7.48). 168

Figure 7.13 Relationship between Y and X, where Y = Xs (m*)0-5 and X = Frmpfm0-2. 169

Figure 7.14 Comparison between actual and predicted values of Xs, based on Equation (7.48). 170

Figure 7.15 Pipeline conveying characteristics of pulverised coal for L = 947 m and D = .060/.069/.081/.105 m (Test Rig E1), showing experimental data points and predicted curves, based on Equation (7.48). 171

Appendix B

Figure B.1 The modified Dixon [39] slugging diagram for a 52 mm pipe diameter system. 192

Figure B.2 T h e modified Dixon [39] slugging diagram for a 7 8 m m pipe diameter system. 193

Figure B.3 T h e modified Dixon [39] slugging diagram for a 102 m m pipe diameter system. 1 9 4

Figure B.4 T h e modified Dixon [39] slugging diagram for a 154 m m pipe diameter system. 195

Figure B.5 T h e modified Dixon [39] slugging diagram for a 2 0 3 m m pipe diameter system. 196

xiii

LIST O F T A B L E S

Chapter 2 Page

Table 2.1 Pipeline details for Test Rigs A1 & A2. Table 2.2 Pipeline details for Test Rig B1. Table 2.3 Pipeline details for Test Rigs C1, C2, C3 & C4. Table 2.4 Pipeline details for Test Rigs D1 & D2. Table 2.5 Pipeline details for Test Rigs E1. Table 2.6 Pipeline details for Test Rigs F1. Table 2.7 Orifice plate details.

7 10 15 18 19 21 24

Chapter 3

Table 3.1 List of power station fly ash samples. 36 Table 3.2 Chronology of the fly ash test program. 39 Table 3.3 Summary of experiments and data points for Eraring fly ash. 52 Table 3.4 Steady-state operating conditions obtained from Exp. Nos.

236, 240 and 249. 52

Chapter 4

Table 4.1 Physical properties of test materials. 61 Table 4.2 Set-up conditions for the blow tank air injection experiments. 64 Table 4.3 Conveying parameters of fly ash for L = 293 m & D = 69 m m

(Test Rig D1). 69 Table 4.4 Cumulative % mass passing through sieve size (for orifice-

and ring-air). 78 Table 4.5 Cumulative % mass passing through sieve size (for orifice-,

ring- and supplementary-air). 80 Table 4.6 Summary of plug-phase conveying parameters for crushed

bath (Test Rig F3, L = 160 m & D = 105 mm). 82

Chapter 5

Table 5.1 List of samples and physical properties. 90

Chapter 6

Table 6.1 Physical properties of test materials. 117 Table 6.2 Comparison of predicted and actual values of ms for mf > 0.3

kg s'1 (i.e. based on Figures 6.2 and 6.3). 119 Table 6.3 Summary of screened coke results for Test Rig A2 (Li = 71 m

& D 2 = 0.052 m). 121 Table 6.4 Empirical expressions for Apt. 128 Table 6.5 Long-distance pneumatic conveying pipeline (Test Rig D2). 129 Table 6.6 Comparison of experimental and theoretical values of Apt for

the long-distance pneumatic conveying stepped diameter pipeline (Test Rig D2). 129

Chapter 7

Table 7.1 Summary of results obtained from Steps 4, 5, 6 and 7. Table 7.2 Summary of products and experimental data for correlation

analyses. Table 7.3 Pipeline configuration for Test Rig E1. Table 7.4 Steady-state operating conditions for the 947 m Test Rig E1

pipeline. Table 7.5 Predicted values of pressure drop for the test rig pipeline,

based on Equation (7.48). Table 7.6 Comparison between experiment and predicted values of Apt. Table 7.7 Suggested pipeline configurations and predicted operating

conditions for pulverised brown coal conveyed at 241 rr1 over L = 1800 m.

150

154 163

164

170 171

172

Appendix A

Table A.1 Mass percentage frequency distribution for Tallawarra pulverised coal (Sample 1), using the Coulter Counter. 187

Table A.2 Mass percentage frequency distribution for Tallawarra fly ash (Sample 2), using the Coulter Counter. 187

Table A.3 Mass percentage frequency distribution for Eraring fly ash (Sample 3), using the Coulter Counter. 187

Table A.4 Mass percentage frequency distribution for Munmorah fly ash, (Sample 4), using the Coulter Counter. 188

XV

Table A.5

Table A.6

Table A.7

Table A.8

Table A.9

Table A. 10

Table A. 11

Mass percentage frequency distribution for Vales Point fly ash (Sample 5), using the Coulter Counter. 188 Mass percentage frequency distribution for Gladstone fly ash (Sample 6), using the Coulter Counter. 188 Mass percentage frequency distribution for Wallerawang fly ash (Sample 7), using the Coulter Counter. 189 Mass percentage frequency distribution for Liddell fly ash (Sample 8), using the Coulter Counter. 189 Mass percentage frequency distribution for PVC powder (Sample 9), using the sieve test. 189 Mass percentage frequency distribution for screened coke (Sample 10), using the sieve test. 1 go Mass percentage frequency distribution for coarse fly ash (Sample 11), using the Malvern analyser. 190

Appendix C

Table C.1 Steady-state operating conditions of pulverised coal (Sample 1) for Test Rigs A1 (L = 25 m & D = .052 m) and A3 (L = 96 m & D = .052m). 198

Table C.2 Steady-state operating conditions of Tallawarra fly ash (Sample 2) for Test Rig B1 (L = 71 m & D = .052 m). 198

Table C.3 Steady-state operating conditions of Eraring fly ash (Sample 3) for Test Rig B1 (L = 71 m & D = .052 m). 199

Table C.4 Steady-state operating conditions of Munmorah fly ash (Sample 4) for Test Rig B1 (L = 71 m & D = .052 m). 199

Table C.5 Steady-state operating conditions of Vales Point fly ash (Sample 5) for Test Rig B1 (L = 71 m & D = .052 m). 200

Table C.6 Steady-state operating conditions of Gladstone fly ash (Sample 6) for Test Rigs B1 (L = 71 m & D = .052 m) and C3 (L = 162 m & D = .105 m). 200

Table C.7 Steady-state operating conditions of Wallerawang fly ash (Sample 7) for Test Rig B1 (L = 71 m & D = .052 m). 201

Table C.8 Steady-state operating conditions of Liddell fly ash (Sample 8) for Test Rig B1 (L = 71 m & D = .052 m). 201

xvi

Table C.9 Steady-state operating conditions of fly ash/cement mix (Sample 12) for Test Rigs C1 (L = 162 m & D = .060 m) and C3 (L = 162 m & D = .105 m). 202

Table C.10 Steady-state operating conditions of fly ash [59] (Sample 13) for L = 1200 m & D = .200 m. 202

Appendix D

Table D.1 Solids friction factor calculations for pipe section No. 1 (Di = 0.105 m & ALi = 150.0 m). 204

Table D.2 Solids friction factor calculations for pipe section No. 2 (D2 = 0.081 m & AL2 = 261.0 m). 204

Table D.3 Solids friction factor calculations for pipe section No. 3 (D3 = 0.069 m & AL3 = 390.0 m). 205

Table D.4 Solids friction factor calculations for pipe section No. 4 (D4 = 0.060 m & AL4 = 146.0 m). 205

NOMENCLATURE

a A A1.A2.A3 As b c

Co Cp

CV c

d

50 dp

dp50 dpm dpwm dsv

dsvm dv dV50 dvm dvwm dpg/dL D Dj DP Do DT e

E EkEv f Fr

Exponent in permeability Equation (7.10) Cross-sectional area of pipe, A = 0.25 TC D'2

Variables in velocity Equation (7.7) Surface area of Enstad [62] element Exponent in compressibility Equations (7.9) and (7.18) Permeability coefficient of bulk solid, Equation (7.4) Value of c when 01 = a-|0 Value of c when 01 = oip Volumetric concentration of solids, Equation (6.13) Constant relating o 0 with dynamic head at outlet, Equation (7.13) Drag coefficient, Equation (7.26) Particle diameter Median particle diameter Arithmetic mean of adjacent sieve sizes Value of dso based on a sieve size distribution Mean particle size from a standard sieve analysis, Equation (5.1) Weighted mean diameter based on a sieve analysis, Equation (5.2) Diameter of a sphere with the same surface area to volume ratio as the particle Mean surface volume diameter, Equation (5.3) Diameter of a sphere with the same volume as the particle Value of dso based on a volume diameter distribution Mean equivalent volume diameter, Equation (5.4) Volume weighted mean diameter, Equation (5.5) Pipeline air pressure gradient due to solids Internal diameter of pipe Value of D for pipe section No. i Differential pressure Outlet diameter of blow tank Diameter of blow tank at transition Exponent used in the equation X = Frm (pfm)e, Section 7.4.3 Constant in Equation (7.39) Variables used in the Ergun [64] Equation (7.17) Exponent used in the equation Y = kg (m*)f, Section 7.4.3 Froude No., Equation (7.24)

xviii

Fr-i, Fr2 Value of Fr at upstream and downstream end of test or pipe section Fr m M e a n value of Fr based on Equation (7.38) Frmin Minimum reliable value of Fr Frs Particle Froude No., Equation (7.25) g Acceleration due to gravity, g 9.81 m s_1

Gi Constant used in Equations (7.11) and (7.12) and to define A2 h D Height of bed of material in a fluidisation test chamber i Numbering system used to designate different sections of pipe or

different ranges of particle size k Constant in Equation (6.26) K Ratio of vertical to horizontal pipeline air pressure gradient,

Equation (6.33) K1 Constant in Equation (7.45), K-| = 10 -

xix

PG1 Pipeline air pressure gauge (transducer location G1, Test Rig B1, 15.7 m from blow tank outlet, Figure 3.8)

PG2 Pipeline air pressure gauge (transducer location G 2 , Test Rig B1, = 17.8 m from blow tank outlet, Figure 3.8)

Po Value of p at blow tank outlet P T Value of p at blow tank transition P Absolute air pressure inside blow tank, P= p + P a t m Patm Atmospheric air pressure, Patm 1010 hPa or 101 kPa abs Pfi Initial (or upstream) absolute air pressure of a pipeline section Pf2 Final (or downstream) absolute air pressure of a pipeline section Pfm Mean absolute air pressure of test or pipe section Qf Volumetric flow rate of air r Radial distance from vertex of flow channel r0 Value of r to blow tank outlet rr Value of r to blow tank transition r' Radius of Enstad [62] element, Figure 7.1 R Gas constant for air, R = 287.1 N m kg-1 K*1

Re s Particle Reynolds No. defined by Equation (7.27) t Cycle time tc Conveying cycle time T Absolute air temperature "h, T2, T3, T4 Variables used to define A-(, A 2 and A 3 u Interstitial air velocity inside blow tank vs Solids velocity vso Value of vs at blow tank outlet vsj Value of vs at blow tank transition vTO Terminal velocity or free settling velocity of particle Vf Superficial air velocity Vfi, Vf2 Value of Vf at upstream and downstream end of test or pipe section Vfm Mean value of Vf based on pfm, Vf m = 4 mf (% ptm D2)"1

VfS Value of Vf that almost produces saltation of a material under load conditions

VfS0 Value of Vf that almost produces saltation of a single particle Vf.min Minimum superficial conveying air velocity (at minimum or reliable

transport limit) V p Velocity of a full-bore plug, Figure 7.4

XX

W i Variable used to define A-j x Constant in Equation (6.9) X Abscissa variable used in correlation analysis, X = Frm (pfm)e

Xi Variable used in Enstad [62] theory and to define Ai, A2 and A3 y Exponent in Equation (6.9) Y Ordinate variable used in correlation analysis, Y = Xs (m*)f Yi, YY1 Variables used in Enstad [62] theory and to define A 3 and G1 Z-| Variable used to define A 2 and A 3 a Half angle of converging flow channel p Angle between major principal stress and normal to hopper wall for

flow conditions y Material coefficient, Equation (7.21) 8 Effective angle of internal friction of a bulk solid e Power index for air density ratio in Equation (6.20) Power index for pipeline length ratio in Equation (6.20) H Power index for pipe diameter ratio in Equations (6.20) and (6.28) 0 Exponent in Equation (6.31) X\ Overall friction factor for test section No. i, X\ = Xi\ + m* Xs\ Xf Air-only friction factor Xu Value of Xf for test section No. i Xs Pipe friction coefficient due to solids Xs\ Value of ^ s for test section No. i Lif Absolute or dynamic air viscosity Variable defined by Equation (7.23) Pb Bulk density of bulk solid Pbc Value of pb when 01 = aic Pbi Loose-poured bulk density of bulk solid pb0 Value of pb when 01 = 010 Pt Air density pf.atm Value of pf at atmospheric conditions pf.max Value of pf at maximum operating pressure pfm Mean value of air density based on Equation (7.37) ps Solids density p* Density ratio defined by Equation (7.22) a Mean consolidation stress o 0 Value of o at blow tank outlet

XXI

a-| Major consolidation stress o-jc Reference value of 01 to define pb, Equation (7.9) 010 Value of 01 at blow tank outlet aip Reference value of G-\ to define c, Equation (7.10) oj Value of o at blow tank transition x , v Exponents in Equation (7.39) Kinematic angle of friction between a bulk solid and a hopper wall X , co Exponents in Equation (7.45) \|r Particle sphericity, Equation (5.6) r Porosity or voidage of a bulk solid, r = 1 - (pb ps"1) AdPi Size range No. i for sieve size distribution AdVj Size range No. i for volume diameter distribution AL Length of test section ALj Value of AL for test section No. i A M Mass percent of material contained in a given size range AMj Value of A M for size range No. i Ap Air pressure drop for test section of length AL Api Value of Ap for Dj and ALj (i.e. test section No. i) Apb Air pressure drop across bed of material in a fluidisation chamber Apbt Air pressure drop across material in a blow tank Apt Air-only pipeline pressure drop Ap s Pipeline air pressure drop due to solids Aps* Value of A p s modified according to Equation (6.34) ApF Air pressure drop across receiving hopper filter Apt Total pipeline air pressure drop, Apt = Apt + A p s Apu Value of Apt for Dj and ALj (i.e. for pipe section No. i) A p j Total system pressure loss (including feeder)

Subscripts

1 Experimental data pertaining to a test rig 2 Scale-up data pertaining to an actual or proposed system f Fluid or air h Horizontal i Pipe or test section number s Solids or particles v Vertical

1

CHAPTER 1

2

1. INTRODUCTION

The pneumatic transportation of bulk solids is continuing to gain popularity for a wide range of applications, especially as more efficient hardware and techniques are introduced onto the market (e.g. long-distance [1] and low-velocity [2] conveying). Subsequently, there has been a substantial increase in the number of commercial systems available to industry. The main features that make this method of transport attractive to the designer of materials handling plants are listed below. The relative ease of routing the conveying pipeline (e.g. verticals, bends,

inclines) adds flexibility to the design or upgrading of a plant.

The physical size of a pneumatic conveying pipeline is small compared to an equivalent conveyor-belt/bucket-elevator system (especially for the dense-phase mode of transport which requires usually relatively small sizes of pipe).

Atmospheric contamination is avoided due to the completely enclosed nature of the transport system (e.g. dusty, hygroscopic and even toxic products are able to be conveyed safely and hygienically).

New technology allows friable products to be transported at low-velocity and with either extremely low or undetectable levels of product degradation or damage [3]. As a consequence, air consumption and hence running costs are reduced significantly. Also, erosion of the system (e.g. bends, conveying pipeline) is minimised.

The use of a pipeline can offer increased security as opposed to an open-belt conveyor system (e.g. for diamond recovery plants).

With improved hardware (e.g. blow tanks) and techniques (e.g. solids metering [1], air injection [4], stepped-diameter pipelines [5,6]), several materials such as pulverised coal, cement and fly ash are able to be transported efficiently at large conveying rates (e.g. 100 to 200 t Ir1) and/or over long distances (e.g. 1 to 3 km).

Unfortunately, the technology available to assess for a given application the relative merits of the competing systems is lacking sadly, particularly when dense-phase [7] or long-distance conveying is considered. Although Flain [4] and more recently Klintworth and Marcus [2] have provided a general overview of several of the more c o m m o n types of commercial system and also have indicated their fields of application, the potential user of such equipment usually is faced still with the difficult problem of selecting the most appropriate configuration (i.e. in terms of cost and, more importantly, operational efficiency and reliability). Furthermore, when attempting to design or optimise a pneumatic conveying system, the following additional difficulties need to be overcome.

3

(a) Establishing a standardised-test procedure to determine sufficient information on the material (e.g. from a test rig) and also deciding on what data are relevant for a particular requirement (e.g. plant specification). Also, it is necessary to present this information in an efficient and workable form.

(b) Scaling-up the test rig data to the full-scale system.

(c) Determining minimum transport behaviour to optimise the operating conditions (e.g. for the dilute- [7] or dense-phase mode of conveying).

(d) Choosing between dilute-, dense-, pulse-phase [8] or low-velocity conveying as the most suitable method of transport for a given material and specification. Also, the most efficient feeder (e.g. blow tank, rotary valve, screw feeder) and method of air injection [4] need to be selected in terms of reliability, running costs, product conditioning requirements and maintaining a constant and reliable feed rate of product into the pipeline.

(e) Determining an optimal size of pipe for a proposed pipeline route (over short and long distances) and also predicting operating conditions (e.g. pressure drop for a given air flow and product conveying rate). Also, a stepped-diameter pipeline [5] m a y need to be considered for long-distance conveying applications.

(f) Predicting operating conditions for existing or working installations (e.g. for the requirements of troubleshooting or uprating system capacity).

(g) Establishing the feasibility of transporting a certain material in the dense-phase mode or over long distances (e.g. up to 3 km).

(h) Minimising hardware problems and improving the reliability of system instrumentation and control (e.g. level indicators, discharge and vent valves, bend/pipe erosion).

The main aim of this thesis is to provide industry with some of the technology that is needed in relation to Items (a) to (g) above. Particular research objectives include determining and presenting pneumatic conveying characteristics for

the purposes of system comparison, optimisation of operating conditions and general design,

investigating the effect of blow tank configuration and method of air injection on pneumatic conveying performance,

assessing the influence of material properties on conveying characteristics and minimum transport behaviour,

evaluating existing and developing improved techniques to scale-up test rig data to a full scale installation,

improving/developing mathematical models and computer software to predict system design parameters (viz. for the blow tank and pipeline) and verifying these predictions by experiment.

4

This thesis investigates many aspects of pneumatic conveying and does result in significant improvements to the procedures for designing and/or selecting pneumatic transport systems. Note that due to the wide ranging nature of this thesis, the literature appropriate to each chapter is reviewed in the relevant section(s) of work. A total of fourteen different test rigs comprising six configurations of blow tank were employed throughout the test work program and are described in the following sections (i.e. Chapter 2). Note that the majority of the experimental work and investigations undertaken in this thesis were limited mainly to bottom-discharge blow tank feeders, which were available in the

Bulk Solids Handling Laboratory at The University of Wollongong,

fine powders (e.g. pulverised coal, fly ash, fly ash/cement mix, PVC powder) and some coarser products (e.g. crushed bath, bone char, screened coke).

Chapter 3 is concerned with the development of a technique to represent test rig data efficiently for the purpose of general design. Referred to as pipeline conveying characteristics, this representation of data includes the dilute- and dense-phase regimes, minimum transport boundaries and the air-only component of pressure drop. Investigations into the effect of blow tank air injection on the performance of pneumatic conveying systems are considered in Chapter 4. This is followed by an evaluation of powder classification techniques in Chapter 5 to determine for a given material the suitability of dense-phase transportation (i.e. based on bench-type experiments). Chapter 6 is concerned with the scale-up of test rig data and the development of an improved technique based on experimental data. The generalisation of pipeline conveying characteristics also is included as an alternative method.

The problem of estimating blow tank discharge characteristics and pipeline operating conditions is considered in Chapter 7. Also, the development of a new technique (based on correlation analysis) to predict total pipeline air pressure drop (for single- or stepped-diameter pipelines, as well as short- or long-distance conveying) is included. Finally, concluding remarks and suggestions for further work based on the investigations and results presented in this thesis are contained in Chapter 8.

5

CHAPTER 2

6

2. PNEUMATIC CONVEYING TEST RIGS

A total of ten test rigs incorporating six different configurations of blow tank and/or method of air injection were used to obtain all the data necessary for the various aspects of this thesis project. The test rigs were developed at different stages over a period of approximately six years. A general description of the overall test facility and five case studies to emphasise the need for large-scale product testing prior to design, have been presented recently by Wypych and Arnold [10]. The main purpose of this section is to provide a description of each test rig configuration and, where necessary, a brief explanation, as appropriate, of some of the more important features, modifications and/or improvements. Note that a system of letters and numbers is employed to label each test rig configuration. A letter is used to refer to a particular blow tank feeding system (including its method of air injection) and numbers are used to designate different pipeline layouts fed by the same blow tank. For example, Test Rigs A1 and A2 refer to different conveying pipelines (viz. L = 25 and 96 m, respectively) fed by the same blow tank. 2.1 Test Rig A In 1980, the Electricity Commission of N.S.W. provided funds to the University of Wollongong for the purchase of a Sturtevant Pulse-Phase Powder Conveyor. This original test rig was installed as part of an undergraduate thesis project during 1980 and consisted of the following major components.

Material Inlet

Top Air Vent Filter

Fluidising Ring Air

Original S Discharge Valve

Figure 2.1 Configuration of the original 0.425 m 3 blow tank (Test Rig A).

7

A 0.425 m 3 capacity blow tank with a maximum safe working pressure (S.W.P.) of 350 kPag (see Figure 2.1) and fitted with a 50 m m N.B. discharge valve (viz. a stainless steel ball valve). An electro-pneumatic control cabinet housing all the necessary control equipment for conveyor operation (e.g. pressure regulators). A 0.5 m 3 receiving hopper supported by tension load cells to monitor the delivered mass of solids. A D C E Model U M A 70V venting dust control unit mounted on top of the 0.5 m 3 receiving hopper and fitted with polypropylene filter bags. Four horizontal loops of mild steel pipeline with change-over sections to provide effective [9] conveying distances of 25, 48, 71 or 96 m. A general arrangement of the original test rig and the 25 m pipe loop is presented in Figure 2.2. Only three different configurations of pipeline were used in this thesis project and are summarised in Table 2.1. Test Rig

A1

A2

A3

L (m)

25

71

96

D (m)

.052

.052

.052

Lv(m)

3.6

3.6

3.6

Lh (m)

21.4

67.4

92.4

No. & Type of Bends

5 x 1 m radius 90 bends

13 x 1 m radius 90 bends

17 x 1 m radius 90 bends

Table 2.1 Pipeline details for Test Rigs A1 & A2.

2.2 Test Rig B

Operating principles of the original Sturtevant blow tank (i.e. as shown in Figure 2.1) were based on the pulse-phase concept [8] and were found to have considerable limitations. Several modifications to the blow tank and its operating sequence were necessary to allow sufficient versatility for testing purposes (e.g. extending the range of air flow) and to fulfil the requirements of the thesis project in general (e.g. investigating different methods of air injection, determining pipeline conveying characteristics of various products). The following list summarises the major modifications and improvements that were carried out to Test Rig A. The vent filter, which is shown in Figure 2.1 and is used to remove the

displaced air during the filling cycle of the blow tank, was found to be ineffective for fine powders such as pulverised coal and was replaced by a 25 m m N.B. ball valve and pipe connected directly to the 0.5 m 3 receiving hopper. The blow tank outlet was modified to provide additional air for transportation (viz. conveying-air). Also, the existing discharge valve, which proved unsuitable for fly ash (e.g. the stainless steel ball valve seized frequently), was replaced by a Figure 990 Keystone butterfly valve and positioner. Note that this valve was bolted directly to the outlet flange of the blow tank. Refer to Figure 2.3 for the final configuration of the 0.425 m 3 blow tank.

8

25m of 52mm I.D. Mild Steel Pipeline

Ring Air

Original Discharge-Valve

\ Knife Air

Figure 2.2 General arrangement of the original pneumatic conveying Test Rig A.

Material Inlet

Vent Air

Top Air

Fluidising Ring Air

Discharge Valve

Conveying Air

Figure 2.3 Configuration of the final 0.425 m 3 blow tank (Test Rig B).

10

Shear-beam-type load cells were installed on the blow tank to monitor the supplied mass of solids. An accurate weighing-scale system was introduced to calibrate the load cells mounted on both the receiving hopper and blow tank. Three orifice plate assemblies with D and D/2 pressure tappings and designed according to B.S. 1042: Part 1:1964 were installed to measure the amount of air being used in various sections of the test rig (viz. conveying-air, blow tank top- and ring-air). Numerous pressure tappings were installed along the pipeline, so that air pressure gradients could be recorded. Refer to Figure 2.4 for an exploded view of a typical pressure tapping location. An efficient pipeline unblocking technique (using an in-line back-pressure valve) was installed at the end of the pipeline to minimise the amount of stoppage time due to blockages. This valve was used also to pressurise the pipeline and blow tank, so that all pressure transducers could be calibrated accurately at selected pressures. The two 1 m radius 90 bends, which were connected to the vertical pipe in Test Rig A, were replaced by two 90 blinded-tee bends (see Figure 2.5) and connecting spool pieces. This was carried out for the main purpose of increasing the actual length of vertical pipe to provide more accurate measurements of the vertical pipeline air pressure gradient. Note that despite these modifications, the effective conveying distances of Test Rig A essentially remained unchanged. Figure 2.6 presents a general arrangement of Test Rig B showing the four horizontal pipe loops, which provided a total effective conveying distance of 96 m. Table 2.2 provides details on the 71 m pipeline, which was the only configuration used in this thesis project. Test Rig

B1

L(m)

71

D (m)

.052

Lv (m)

3.6

Lh (m)

67.4

No. & Type of Bends

11 x 1 m radius 90 bends and

2 x 90 blinded-tee bends

Table 2.2 Pipeline details for Test Rig B1.

The air knife (see Figure 2.1) was removed from the pipeline (mainly due to its ineffectiveness on materials such as pulverised coal, see Section 4.1). All other components used on Test Rig A (e.g. the control cabinet, receiving hopper and venting dust control unit) essentially remained unchanged for Test Rig B. However, during the test program on fly ash, which is discussed later in Section 3.3, the polypropylene filter bags of the dust control unit were replaced with epitropic Goretex bags (due to an excessive build up of material, see Section 3.3.3).

11

Pressure Transducer"

j^L

Retaining Screw

Porex Disc

Quick-Connect Coupling

1/4" BSPT Thread

TM O-Ring

1/4" BSP Socket

52mm I.D. Pipeline

Figure 2.4 Exploded view of a typical pipeline air pressure tapping location.

12

"TT

L. ^

/ / / /

-. / / / /

////// 77-7 A

50mm N.B. Table E Flanges

V /////////. >; ;/;;//;///;;//;;// r-ry

52mm I.D. Mild Steel Pipeline ~

3

Direction of

Flow

Figure 2.5 Full-sectional view of a 50 m m N.B. 90 blinded-tee bend.

13

Wl CT

CD LT) CD

O CD ac

t -D i (0 i O OJ

CQ g> DC w CD h-

14

2.3 Test Rig C

In 1982, NEI John Thompson (Aust) formed a consortium with Kloeckner-Becorit Industrietechnik-KBI G m b H and then negotiated with the University of Wollongong to install a pneumatic conveying test rig in the Bulk Solids Handling Laboratory. A blow tank fitted with a cone dosing valve, which is a solids metering device designed primarily for long distance transportation, was imported from West Germany and installed initially with 162 m of 65 m m N.B. Schedule 80 (i.e. 60 m m I.D.) mild steel pipe. However, after preliminary test work, the length and size of the pipeline was found to be inadequate (i.e. for the needs of Australian industry) and additional pipework was installed. The following list summarises the major components of the test rig, which was used in this thesis project. A 0.9 m3 capacity blow tank with a maximum S.W.P. of 700 kPag and

fitted with a cone dosing valve and a 100 m m N.B. discharge Argus ball valve (see Figure 2.7). Also, the blow tank is supported by shear-beam-type load cells. A pneumatic PI controller with an adjustable set point (i.e. maximum operating pressure) is used to control the stroke and oscillation frequency of the cone dosing valve. The measured air pressure signal is taken upstream of the blow tank discharge valve. However, during the major part of the test program for this thesis project, the cone dosing valve was .not used and was either removed physically or raised in a position not to interfere with the normal operation of the blow tank. Note, the cone dosing valve was required only for recent investigations into the long-distance pneumatic conveying of pulverised brown coal (refer to Section 7.4.3).

Conveying Air

Vent ' Line

Pipeline

Figure 2.7 Configuration of the original 0.9 m 3 blow tank (Test Rig C).

15

A 5 m 3 receiving silo supported by two load blocks to monitor the delivered mass of solids. However, due to possible eccentric loading effects, the conveying rate during an experiment is determined from the response of the blow tank load cells. A D C E Model D L M V8/7B reverse jet insertable vent filter mounted on top of the 5 m 3 receiving silo and fitted with polypropylene filter bags. An NEI John Thompson (Aust) standard mini-pot [3] to transfer conveyed material to the blow tank (see Figure 2.8). Horizontal loops of mild steel pipeline with change-over sections to provide effective [9] conveying distances from 42 to 940 m. Figure 2.8 presents a general arrangement of Test Rig C and the 940 m pipeline (containing 60, 69, 81 and 105 m m I.D. sections of pipe). However, only four different pipeline configurations were used in this thesis project and these are summarised in Table 2.3.

Test Rig

C1

C2

C3

C4

L(m)

162

59

162

553

D (m)

.060

.105

.105

.069

Lv(m)

4.4

4.5

4.5

4.4

Lh (m)

157.6

54.5

157.5

548.6

No. & Type of Bends

5 x 1 m radius 90 bends

5 x 1 m radius 90 bends

5 x 1 m radius 90 bends

17 x 1 m radius 90 bends

Table 2.3 Pipeline details for Test Rigs C1, C2, C 3 & C4.

2.4 Test Rig D

During investigations into long-distance pneumatic transportation on Test Rig C, the capacity of the 0.9 m 3 blow tank (i.e. refer to Figure 2.7) was found to be insufficient for the establishment of steady-state flow conditions (i.e. during the conveying cycle). To overcome this deficiency and other problems (e.g. overpressurisation of the 5 m 3 silo due to material build up on the polypropylene filter bags - similar to the problem described in Section 2.2), the following improvements and modifications were carried out to Test Rig C. A second 0.9 m3 blow tank with a max. S.W.P. of 700 kPag was

manufactured by NEI John Thompson (Aust) and installed alongside the original KBI G m b H blow tank (see Figure 2.9). Due to occasional feeding problems from the original blow tank (e.g. rat-holing which is discussed later in Section 4.2), the new blow tank was fitted with a fluidising discharge cone. Also, an improved cone dosing valve and actuator was installed.

16

o

c 03

O D) . ir i_ 9-

o -

co

Sg CD V 2 a) h a. CO Q. _ CD

2 2E 00 CD

N 0) 3 O

17

Material Inlet

Material Inlet

Aeration Air

Fluidising Discharge Cone

Conveying Air

Figure 2.9 Configuration of the original tandem 0.9 m 3 blow tank feeding system (Test Rig D).

The 0.7 m long polypropylene bags of the D L M V8/7B insertable vent filter were replaced by 1.5 m long epitropic Goretex bags. This effectively converted the filter unit to a Model D L M V8/15B. Apart from the above-mentioned modifications to the filter, the rest of the 5 m 3 silo, as described previously for Test Rig C, remained unchanged.

The pipeline installations for Test Rig C were not modified. Throughout the thesis project, only two pipeline configurations were fed by the blow tank system shown in Figure 2.9, and these are summarised in Table 2.4. Note that Test Rig D 2 employs a stepped-diameter pipeline, which is used primarily to minimise pressure drop and conveying velocity (i.e. mainly for long-distance pneumatic conveying applications [4,5]).

18

Test Rig

D1

D2

L(m)

293

146 940 390

261 143

D (m)

.069

.060

.069

.081

.105

Lv (m)

4.4

4.5

Lh (m)

288.6

146.0 390.0 261.0 138.5

No. & Type of Bends

9 x 1 m radius 90 bends

3 x 1 m radius 90 bends 13 x 1 m radius 90 bends 8 x 1 m radius 90 bends 5 x 1 m radius 90 bends

Table 2.4 Pipeline details for Test Rigs D1 & D2.

2.5 Test Rig E

After carrying out several experiments on Test Rig D and also analysing the transient plots of major conveying parameters, the following disadvantages were realised.

(a) The method of air injection used on Blow Tank No. 1 (see Figure 2.9) was inferior to the one used on Blow Tank No. 2 (e.g. refer to Section 4.2 for some typical results on fly ash). This prevented proper tandem operation of the blow tanks (i.e. discharging one blow tank after another and achieving the same steady-state flow conditions).

(b) Despite the problems referred to in (a), the duration of discharge of the two 0.9 m 3 blow tanks, during the high-pressure (i.e. large conveying rate) experiments, was insufficient to maintain steady-state operating conditions.

(c) The mini-pot [3] filling system for the blow tanks was slow and tedious and allowed only a limited number of experiments to be carried out during one day of testing.

As a result of these deficiencies, the following modifications and improvements were carried out to Test Rig D.

Blow Tank No. 1 was replaced with one of similar design to Blow Tank No. 2 (Le. see Figure 2.10).

A 3 m3 receiving silo was designed, manufactured and installed on top of the tandem blow tank system to provide gravity discharge and also enable continuous transportation (viz. in conjunction with a Programable Logic Controller, which was contained inside the original control panel of Test Rig C). Refer to Figure 2.11 for a general arrangement of Test Rig E and the pipe loops providing a total possible conveying distance of 947 m (see Table 2.5). Note that a D C E Model D L M V12/7B reverse jet insertable vent filter (complete with epitropic Goretex filter bags, anti-static provisions, horizontal upstand, polypropylene explosion panels and a pressure relief flap valve) was mounted on top of the receiving silo.

19

The pipeline configurations of Test Rig D were extended slightly to connect the existing pipework to the new 3 m 3 silo. However, during this thesis project, only one configuration of pipeline was used (i.e. refer to Table 2.5).

Test Rig

E1

L(m)

146 947 390

261 150

D (m)

.060

.069

.081

.105

Lv (m)

7.0

Lh (m)

146.0 390.0 261.0 143.0

No. & Type of Bends

3 x 1 m radius 90 bends 13 x 1 m radius 90 bends 8 x 1 m radius 90 bends 5 x 1 m radius 90 bends

Table 2.5 Pipeline details for Test Rigs E1.

Material Inlet

Vent

Conveying Air .

Figure 2.10 Configuration of the final tandem 0.9 m 3 blow tank feeding system (Test Rig E).

20

r-

o z _*: r to H * o CO 1

1-m

CM

O

z -V CD

> >-< O) c CD ->

r n O

> < O

cii > m > r C) Cfl

h *-

o

z .* r CO H 5 o m

,_

> O

CD > 5 > .

CO

5 ^ CVJ s_ o fi z. 3 ^ -o c J2 10 H J"

5 1-o CD

CM > Q

i

t_

21

2.6 Test Rig F

Some coarse materials such as crushed coal and petroleum coke can be conveyed more efficiently in the plug-phase mode (i.e. where a limited amount of material, usually in the form of a plug, is conveyed through the pipeline per cycle). Note this method of transport is similar to the pulse-phase mode [8], except that instead of conveying numerous plugs or slugs of material through the pipeline, only one plug of material is transferred during each cycle. Also, note that a discharge valve is not required usually for a plug-phase blow tank. NEI John Thompson (Aust), as a part of their development program to design and market a plug-phase conveying system, supplied to the University of Wollongong a 0.113 m 3 blow tank, which was connected to the existing 105 m m I.D. pipeline of Test Rig C. Additional change-over sections were installed to provide intermediate conveying distances of 41, 58, 80 and 100 m. This test rig consisted of the following major components. A 0.113 m3 capacity plug-phase blow tank with a maximum S.W.P. of 700

kPag (see Figure 2.12). A 5 m3 receiving silo supported by two load blocks to monitor the

delivered mass of solids. However, due to possible eccentric loading effects (see Section 2.3), the batch conveying rate during an experiment is determined by dividing the actual mass of conveyed solids (removed from the silo and weighed on a load platform) by the conveying time (i.e. m s = M S V 1 ) - The overall conveying rate is determined by allowing for transient effects such as blow tank fill time, tf, and total valve switching time ,tv (i.e. overall m s = M s (tc + tf + tv)"1). Note that this 5 m 3 silo and its vent filter are identical to those described for Test Rig D (i.e. in Section 2.4).

Of the five different possible configurations of pipeline, only three were used for this thesis project. Table 2.6 provides a summary of the relevant details. Also, refer to Figure 2.13 for a general arrangement of Test Rig F.

Test Rig

F1

F2

F3

L(m)

41

58

161

D (m)

.105

.105

.105

Lv (m)

4.5

4.5

4.5

Lh (m)

36.5

53.5

156.5

No. & Type of Bends

5 x 1 m radius 90 bends

5 x 1 m radius 90 bends

5 x 1 m radius 90 bends

Table 2.6 Pipeline details for Test Rigs F1.

22

Material Inlet

Orifice Air

Figure 2.12 Configuration of the 0.113 m 3 plug-phase blow tank.

23

Figure 2.13 General arrangement of Test Rig F.

24

2.7 Air Supply and Flow Rate Measurement

Air at a maximum pressure head of 800 kPag is supplied from any combination of the three following rotary screw compressors.

Atlas Copco electric-powered Model GA-308, 3.1 m3 min-1 free air delivery.

Ingersoll Rand diesel-powered Model P375-WP, 10.6 m3 min"1 free air delivery.

Ingersoll Rand diesel-powered Model P850-WGM, 24.1 m3 min-1 free air delivery.

The compressors are connected to an aftercooler, two refrigerated air dryers and two air receivers (1.75 and 6.0 m 3 capacity). Various filters and separators are installed in series with these compressors to ensure a dry and oil-free air supply. Figure 2.14 provides a general arrangement of the air supply system.

Depending on the test rig and desired rangeability of flow rate, one of the five orifice plates listed in Table 2.7 (with D and D/2 pressure tappings and designed according to B.S. 1042 : Part 1 : 1964 ) is selected to monitor the conveying air usage.

Orifice Plate

+ ++

No.

1 2 4 5 6

Orifice Dia. (mm)

14.73 9.98 20.65 33.08 44.55

Pipe Dia. (mm)

26.64 25.30 78.10 78.10 78.10

Min. mf+ (kg s-1)

.027

.012

.050

.130

.250

Based on a DP of = 381 m m H2O @ 600 kPag & 20 C. Based an a DP of - 3810 mm H2O @ 600 kPag & 20 C.

Max. mf+ +

(kg s-1)

.085

.037

.155

.410

.775

Test Rig

A&B A&B CtoF CtoF CtoF

Table 2.7 Orifice plate details.

-{04-P850-WGM 24.1 m '/min

Ingersoll Rand Compressors

To Test Rig

Pressure Regulator

Filters'

Aflercooler 4>-V-4> o

Atlas Copco Compressor

Dryer

HXr-B) -

D and 0/2 tapping*

t/iiiiMYSir>/i'/V. Z%4m

OHfle. plol..

uzzzzzzzzzzzzzzzi

>?>>>>i//rrm

V. fr T7ZZZZZZZZZZZZZ2ZZZZ

* ORIFICE PLATE DETAIL

Figure 2.14 General arrangement of compressed air supply.

26

2.8 Data Acquisition

During the early stages of this thesis project, priority was given to developing the necessary software to capture the voltages of up to 20 analogue channels using a portable Hewlett-Packard 3054A Data Acquisition System. Major components of the system included a HP-85B desk-top computer, a HP-3497A scanning control unit and a transducer signal-conditioning unit. Typical transducer channels, which were recorded with respect to cycle time, included : blow tank top-air pressure; pipeline air pressure; upstream pipeline and differential air pressures for the orifice plate assemblies; the mass of material entering the receiving hopper and/or leaving the blow tank. After storing these responses on either the HP-85B computer or a Tektronix 4923 digital tape recorder, the data are then transferred to the University's Univac mainframe computer for final processing and graphical output. On-site graphics also were developed on the HP-85B computer, so that plots of raw data also could be achieved easily after the completion of any experiment. An example of a typical pipeline air pressure response copied from the HP-85B C R T screen is presented in Figure 2.15. Throughout the course of this project, the software of all major programs was updated and improved continually as required. For example, memory capacity and scanning speed were increased recently to accommodate a maximum number of 64 channels for the investigations into long-distance pneumatic conveying.

10

>

c o Q. VI

m

A

Plot of C h.

\

14

CD

27

CHAPTER 3

28

3. PNEUMATIC CONVEYING CHARACTERISTICS

If a pneumatic conveying system is to be designed or upgraded to ensure satisfactory and efficient operation, it is suggested that as much information as possible be obtained on the bulk solid to be handled (e.g. physical properties, conveying performance). Also, any possible operational problems should be investigated (e.g. material cohesion causing incomplete discharge of a blow tank, or unusual physical properties producing unforeseen blockage phenomena). It is important for efficient and reliable design, that any conveying performance data be summarised in a convenient and workable form. Several methods were investigated and the technique [11] that was selected finally is shown in Figure 3.1, which displays the variation of steady-state m s (the solids mass flow rate, kg s_1) with respect to mt (the supplied air mass flow rate, kgs-1) and Apt (the total pipeline air pressure drop, kPa). An alternative form is presented in Figure 3.2, on which straight lines of constant mass flow ratio (m* = m s mf 1) are superimposed easily. Note that m* is adopted frequently by researchers to define the dense-phase mode of transport and compare the efficiencies of commercial systems. However, there are certain inadequacies with this form of definition and these are discussed further in Section 3.2. These two methods of data presentation were selected for the following reasons. (a) The data represent steady-state operating conditions and are accurate

for the selected configuration of pipeline. Hence, they usually are referred to as steady-state pipeline conveying characteristics of a given product. This information also can be applied to other pipelines of similar configuration and with different types of feeder (e.g. blow tanks, rotary valves, screw feeders) as long as the feed rate is consistent and steady-state.

(b) The use of air velocity instead of mf to represent operating conditions can be confusing and often leads to calculation error due to

the frequent lack of proper definition to distinguish between pick-up, average and exit velocity, as well as actual and superficial air velocity,

the functional dependency of air velocity on pressure and hence, pipeline length.

(c) Under steady-state conditions, mt is constant at any point along the pipeline (for both positive and negative pressure systems). Hence, the superficial velocity Vf may be calculated easily using the continuity equation Vf = mf (pf A)*1.

(d) the use of pressure gradient instead of actual pipeline air pressure drop can be misleading and often tempts the user to apply the data to vastly extrapolated lengths of pipeline. It is Important to be aware of the particular pipeline configuration that actually was used to generate the data.

APt (kPa)

\

1

1

1

I

I

1

1

^ > ^

mf (kgs~:)

Figure 3.1 General form of steady-state pneumatic conveying characteristics for a given material and pipeline configuration.

m<

(kgs-1)

mf (kgs-1)

Figure 3.2 Alternative form of pneumatic conveying characteristics.

Logarithmic scales often are used on the abscissa and ordinate axes to represent the variation in conveying rate. However, the generation or utilisation of such graphs is far more tedious than the simpler linear scale representations, as shown in Figures 3.1 and 3.2. Also, note that the main reason for selecting log scales is to linearise the m s curves with respect to say velocity and pressure gradient, as shown in Figure 3.3. Unfortunately, such simplifications do not always occur especially for materials of wide particle size range and realistic pipelines containing bends and vertical sections.

dense phase dilute phase

1

<

i

S

pressurized flow vacuum and pressurized flow steady stale unsteady statel steady state

; plug-dune | layer-disperse

Vmin lag (average air velocity)

State Diagram for Horizontal Conveying

Product

Particle size Density Pipe diameter Pipe material

Styropor -3 dp = 2,385mm pp =1050 kg/m3 d =52,6mm stainless steel

Average pipe watt roughness R ~ 6 r 10 \im

Figure 3.3 The Rizk [7] two-phase flow diagram for pneumatic conveying in horizontal pipes.

31

3.1 Pulverised Coal

During the first two years of this thesis project, pulverised coal (obtained through the Electricity Commission of N.S.W. from the Tallawarra Power Station) was used as the test material. The first attempt to determine the pneumatic conveying characteristics of this material resulted in a series of experiments being carried out on the original test rig (i.e. Test Rig A1) with the following specification. 0.425 m3 blow tank with top-air only (refer to Figure 2.1).

25 m of 52 m m I.D. pipeline (refer to Figure 2.2). Five 1 m radius, 90 bends. 270, 240, 200, 165 and 135 kPag initial blow tank air pressures.

From the conveying parameters recorded for each experiment, values of mf, ms and A p j (total system pressure loss) were extracted at selected increments of the conveying cycle and plotted on a graph similar to that shown in Figure 3.2 (except for the use of Apj instead of Apt). Lines of constant Apjwere then drawn through the data to provide a family of curves at intervals of 10 kPa, as shown in Figure 3.4. With mf representing the abscissa axis and m s the ordinate axis, straight lines of material to air mass flow rate ratio, m*, also were drawn on Figure 3.4. The alternative method of presenting this information is shown in Figure 3.5 (adopting the form given in Figure 3.1). These methods of data presentation are similar to those presented by Mason etal. [11].

.004 .006 .008 .010 .012 .014 mf (kgs-1)

Figure 3.4 Pneumatic conveying characteristics of pulverised coal for Test Rig A1 (L = 25 m & D = 52 m m ) , displaying lines of constant Apj.

140

120 -ApT (kPa)

100 -

80

60 .004 .006 .012

32

.014 .008 .010

mf (kgs-1) Figure 3.5 Pneumatic conveying characteristics of pulverised coal for Test Rig A1 (L = 25 m & D = 52 m m ) , displaying lines of constant ms.

It must be emphasised that such information is relevant only to the

conveyed material (viz. pulverised coal), blow tank (Sturtevant, 0.425 m 3 capacity), pipeline/bend configuration (L = 25 m, D = 52 m m , five 1 m radius 90 bends), method of air injection (viz. top-air)

that were used for this particular set of experiments. However, if one of these conditions were to be varied with respect to the other three, then the technique would provide a very useful design tool. For example, the relative conveyability of different materials, the effects of pipeline length on conveying performance and a comparison of the various conveying modes may be summarised and evaluated easily on such plots. Note that the above values of mf, ms and Apr were extracted at certain increments of the conveying cycle and, hence, actually represented instantaneous values. Furthermore, note that

where

and

Apj = Apbt + Apt + ApF (3.1)

Apj is the total system pressure loss (kPa), Apbt is the pressure drop across the blow tank (kPa), Apt is the total pipeline air pressure drop (kPa), ApF is the pressure drop across the receiving hopper filter unit (kPa).

33

Assuming that A p F - 0 and noting that the final pressure of the system essentially is atmospheric, the value of A p T was taken to be numerically equal to the air pressure on top of the material in the blow tank. That is,

APT = (Pbt + Patm) - Patm = Pbt (3.2)

where pbt is the blow tank top-air pressure (usually transducer location A1), Patm is atmospheric pressure (usually = 101000 Pa abs).

During later work on fly ash (and especially in relation to the development of the standardised-test procedure, described in Section 3.4), it was decided to consider only steady-state conveying parameters and plot Apt instead of ApT. The reasons were : some doubt existed over the accuracy of the instantaneous curves drawn in Figures 3.4 and 3.5 (due to the pipeline creating a time-delay in the system); a graph displaying lines of constant Apt would be more applicable to other pipelines (of similar configuration) fed by different types of feeder (e.g. rotary valve) and blow tank configuration (e.g. top-discharge). To explore these matters further, steady-state values of mt, m s, Apt and A p j were obtained from the original conveying parameter plots and the resulting family of m s curves were plotted, as shown in Figures 3.6 and 3.7 (the former representing Apj and the latter Apt). After comparing the trends displayed in Figures 3.5, 3.6 and 3.7, it can be seen that, although some similarities do exist, the m s contour lines displayed in Figures 3.6 and 3.7 are significantly flatter. W h e n these discrepancies were realised during the latter stages of the thesis (viz. during the fly ash test program), it was intended to apply the standardised-test procedure (described in Section 3.4) to the same pulverised coal sample (i.e. to determine more accurate conveying characteristics).

140

120

(kPa) 100

80

60 .004 .006 .008 .010 .012 .014

mf (kgs-1)

Figure 3.6 Pneumatic conveying characteristics of pulverised coal for Test Rig A1 (L = 25 m & D = 52 mm) displaying lines of constant, steady-state ms (Apj ordinate).

140

120 -Apt (kPa)

100 -

80 _

60 .004 .006 .008 .010

mf (kgs-1) .012 .014

Figure 3.7 Pneumatic conveying characteristics of pulverised coal for Test Rig A1 (L = 25 m & D = 52 m m ) , displaying lines of constant, steady-state m s (Apt ordinate).

Unfortunately, due to the following reasons, this work was not able to be completed during the normal course of this project. The original four 200 litre drum samples were no longer available.

The d e m a n d s of the fly ash test program (including powder characterisation, long-distance conveying) reduced the emphasis on the investigations involving pulverised coal. During the initial experiments on fly ash, significant sparking was observed along a perspex sight tube installed at the end of the pipeline (i.e. on the original Test Rig A1). This was considered as a possible problem for pulverised coal, and the acquisition and testing of further material had to be postponed.

In fact, the latter prompted further investigations into possible sources of ignition (i.e. in all test rigs) and methods of explosion prevention and relief. The most applicable was found to be sparking caused by electrostatic charging of the conveying pipeline (due to inadequate earthing) and the filter bag surfaces (i.e. inside the venting dust control unit). Earthing of the perspex surface was attempted, but the tube was replaced eventually by a section of mild steel pipe to provide improved earthing of the pipeline and hence, eliminate any possibility of sparking. Electrostatic charging of the filter bag surfaces was still considered to be a problem and an extensive investigation resulted in the request to purchase (via University funds) a reverse-jet air filter comprising epitropic Goretex filter bags earthed to the filter housing,

a horizontal upstand fitted with an explosion relief panel, an exhaust fan to provide additional vacuum in the receiving hopper and the filter housing, and

35

a discharge duct to provide venting of any explosion directly to atmosphere.

The funding for this equipment was forthcoming and a DCE Model DLM V7/7F1 was purchased in April, 1985. The installation was postponed until July/August, 1985 due to the priority of completing the fly ash testing program. Note that the polypropylene filter bags which were used in the original D C E Model U M A 70V venting dust control unit were replaced with Goretex bags in August, 1984 to eliminate the dust emission problems that were being experienced with Vales Point fly ash. This aspect is discussed further in Section 3.3.3. Although accurate conveying characteristics were not able to be determined for the pulverised coal, the results that were obtained from the initial test work still were considered sufficient for the other requirements of this thesis (viz. blow tank air injection, powder characterisation and mathematical model verification). One other important aspect which stemmed from this initial work on pulverised coal was the need to clarify the definition for dense-phase. 3.2 Definition of Dense-Phase

Several researchers have adopted material to air mass flow rate ratio (viz. m*) as the basis of definition for dense-phase. For example, Mason et al. [12] have suggested that dense-phase conveyors operate normally with m* > 40; Duckworth [13] has indicated that for dense-phase suspensions, m* typically is greater than 100. However, as reported by Wypych and Arnold [14], this form of definition seems to be inadequate. The main reasons are m* is dependent on pipeline length for a given condition of flow, as

indicated by the scale-up criteria used by Mills et al. [15], and a material may display dense-phase pneumatic conveying characteristics at relatively low values of mass flow ratio (or dilute-phase performance at relatively high values of m*).

Such aspects particularly are important if long-distance transport is considered or if a theoretical prediction of pressure drop is required. S o m e researchers, for example, have compared discrete experimental pressure drop data with dilute-phase mathematical model predictions without verifying whether dilute- or dense-phase conditions actually are prevalent. It would be more convenient to use a definition based on actual flow characteristics, and it is suggested that dense-phase should refer generally to the condition of non-suspension flow, whether it occurs in the form of unstable dunes [16], discrete full-bore plugs [17], sliding beds [18] or as an extruded condition [19]. Saltation is defined therefore, as the transition from dilute- to dense-phase (or suspension to non-suspension) pneumatic transport in horizontal pipes. Rizk [7] has provided a similar form of definition by using a phase diagram for horizontal pneumatic conveying. This diagram, which is similar to the Zenz [20] two-phase flow diagram, was presented earlier in Figure 3.3. Note the similarity with the pneumatic conveying characteristics given in Figure 3.1. A comparison between Figure 3.3 and Figure 3.7, indicate that the pulverised coal was transported in the dense-phase mode (i.e. for the range of mf values considered). Furthermore, this is supported by the relatively large values of m*. which were obtained from these experiments (e.g. 260< m* < 420).

36

3.3 Fly Ash

3.3.1 Introduction

During the first two years of this project, considerable interest was expressed by industry to extend the research work to investigate the pneumatic conveying of power station fly ash. Preliminary investigations on Vales Point fly ash in 1982, demonstrated that the handling problems significantly were greater than those associated with pulverised coal and emphasised the importance of continuing work in this area. Therefore, fly ash was included in the scope of work of this thesis and resulted in priorities being placed on comparing the conveyability of fly ash samples collected from six power stations (viz. Tallawarra, Eraring, Munmorah, Vales Point, Wallerawang and Liddell. Details of each sample and the type of boiler used are provided in Table 3.1.

Power Station Fly Ash Sample

Tallawarra

Eraring

Munmorah

Vales Point

Wallerawang

Liddell

Unit No.

6

1

2&3

5

8

4

Unit Load Op./Max. (MW)

90/100

400/660

190/350 (U2) 290/350 (U3) 630/660

460/500

390/500

Type of Boller+

A

B

C

D

D

D

Method of Dust Collection (Location)

Fabric Filter (Pozzolanic Tank)

Fabric Filter (Cell 23)

Electrostatic Precipitator (Zone 2)

Electrostatic Precipitator (Zone 3)

Electrostatic Precipitator (Zone 3)

Electrostatic Precipitator (Zone 2)

+ Type of Boiler: A Tangentially-fired B Opposed-wall-fired conventional type conventional type

C Tangentially-fired D Tangentially-fired down-flow type tower type

Table 3.1 List of power station fly ash samples

Note that all the above samples were collected and supplied by the Electricity Commission of N.S.W. Particular objectives of the fly ash work included the determination of complete pneumatic conveying characteristics displaying minimum

transport behaviour (i.e. dense-phase performance), relevant physical properties (e.g. particle diameter, solids density, loose-

poured bulk density), and fluidisation performance.

37

This information was intended to provide a data base, from which the pneumatic conveying performance of a given fly ash sample could be estimated qualitatively (i.e. after ascertaining the physical properties and fluidisation behaviour of the sample, as described later in Section 5.1). As indicated in Section 3.1, in order to compare the conveyability of different materials, it was found necessary to employ the same blow tank, pipeline/bend configuration and operating modes. A detailed description of the test rig that was used in these investigations is given in the following section. Section 3.3.3 presents the pipeline conveying characteristics that were obtained for each fly ash sample. 3.3.2 Test Rig Description

A schematic layout of the test rig that was used extensively during the fly ash test program is presented in Figure 3.8, which includes the location of all recorded transducers. The following list provides a description of the major components of the test rig (i.e. Test Rig B1) and the relevant operating modes. 0.425 m3 Sturtevant blow tank with a maximum safe working pressure

of 350 kPag (refer to Figure 2.3). Blow tank top-air, fluidising ring-air and conveying-air (originally referred to as supplementary-air) all were used in various amounts throughout the test program. 71 m total effective length of 50 m m Schedule 40 (52 m m I.D.) conveying pipeline. 3.6 m vertical lift (located 5.4 m from the blow tank outlet). Eleven 1 m radius, 90 bends. T w o blinded-tee bends connected to the vertical pipe (refer to Figure 2.5). A D C E Model U M A 70V venting dust control unit mounted on top of the receiving hopper.

Note that the effective length [9] of a 1 m radius 90 bend is 2.0 m, whereas the actual length is 1.57 m. Therefore, the total actual length of the pipeline is "71 m -11 x (2.0 - 1.57) 66 m". However, for the purpose of scale-up (discussed later in Chapter 5), it was decided to use effective length (instead of actual length) to represent the total length of pipelines. The air supply consists of the Atlas Copco Model GA308 rotary screw compressor (see Section 2.7), an S M C Model LDP-150S refrigerated air dryer and two air receivers totalling 7.8 m 3 volumetric capacity. The capacity of the compressor is 3.1 Nm3min-1 (free air delivery) with a maximum pressure head of 800 kPag. Orifice Plate No. 1 (see Table 2.7) with D and D/2 pressure tappings and designed according to B.S.1042 : Part 1 : 1964 is selected to record the amount of air used during the conveying cycle. All the important conveying parameters such as blow tank top-air pressure, pipeline air pressure (refer to Figure 2.4 for details of a typical pressure tapping location), supplied/delivered mass of solids and supplied air mass flow rate are recorded with respect to cycle time using the portable HP3054A Data Acquisition System (described earlier in Section 2.8). A chart recorder is used in conjunction with the Data Acquisition System to ensure that steady-state conditions occur during the conveying cycle (a requirement for the standardised-test procedure described in Section 3.4).

38

O)

cu c

39

3.3.3 Test Results

The procedure for determining the pneumatic conveying characteristics of each fly ash sample consisted of the following six major steps. 1. Apply the standardised-test procedure (refer to Section 3.4).

2. Obtain steady-state values of mf, ms and Apt from the transient plots of the major conveying parameters recorded for each experiment.

3. Present this information in tabular form.

4. Plot values of ms against mf (abscissa axis) and Apt (ordinate axis), as depicted by the generalised form given in Figure 3.1. Note that Apt is the preferred primary variable since it is a limitation on the plant by the compressor used.

5. Using interpolation, draw lines of constant ms through the data at appropriate intervals.

6. Delineate any regions of unreliable transport displayed by the transient plots of both the pipeline air pressure and the delivered mass of solids. This supplementary information will determine the limits of reliable transport and the suitability of conveying the material in the dense-phase mode. The two main types of flow irregularity, which predominated during the fly ash test program, were unstable duning and blockage conditions. Examples are presented in Section 3.4.3, which also includes results from P V C powder, which was found to display unstable plugging or blockage conditions in the conventional dense-phase (or non-suspension) mode of transport.

The chronological order in which the fly ash samples were tested is given in Table 3.2, which also includes a summary of the experiments carried out for each sample.

Fly Ash Sample

Tallawarra Eraring

Munmorah Vales Point Gladstone Wallerawang

Liddell

Duration of Test Work

25-10-83 to 31-01-84 03-02-84 to 15-02-84 13-03-84 to 02-04-84 09-08-84 to 19-09-84 03