PREMIXED FLAME ACCELERATION IN STRAIGHT AND BEND CLOSED PIPE MISS HASIMAWATY BINTI MAT KIAH A thesis submitted in fulfilment of the requirements for the award of the degree of Master of Engineering (Gas) Faculty of Petroleum and Renewable Energy Engineering Universiti Teknologi Malaysia SEPTEMBER 2013
24
Embed
PREMIXED FLAME ACCELERATION IN STRAIGHT …umpir.ump.edu.my/9465/1/CD8264.pdfPREMIXED FLAME ACCELERATION IN STRAIGHT AND BEND CLOSED PIPE MISS HASIMAWATY BINTI MAT KIAH A thesis submitted
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
PREMIXED FLAME ACCELERATION IN STRAIGHT AND BEND CLOSED PIPE
MISS HASIMAWATY BINTI MAT KIAH
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Master of Engineering (Gas)
Faculty of Petroleum and Renewable Energy Engineering
Universiti Teknologi Malaysia
SEPTEMBER 2013
v
ABSTRACT
There were many studies on premixed flame propagation in tubes, including open tubes and enclosures. Yet, no sufficient data obtained for explosion properties in medium scale piping system to assist engineers or practitioners in determining the potential hazard posed due to explosion. In this work, an experimental study had been carried out to investigate the explosion properties in a pipeline using two pipe configurations, i.e. straight and 90 degree bend. A horizontal steel pipe, with 2 m long(L) and 0.1 m diameter (D), giving L/D ratio of 20 was used in the range of equivalence ratios (Ф) from 0.5 to 1.8. The 90 degree bend pipe had a bend radius of 0.1 m withadded a further 1 m to the length of the pipe (based on the centerline length of the segment). Natural gas/pure oxygen mixture was prepared using partial pressure method and a homogeneous composition was achieved by circulating the mixture using a solid ball which was placed in the mixing cell. It was shown that stoichiometric mixtures gave the highest flame speed measurement, both on straight and bend pipes. Stoichiometric concentration (Ф = 1.0) gave significant maximum overpressure of 5.5 bars for bend pipe, compared to 2.0 bars on straight pipe explosion test; approximately 3 times higher. This was due to bending part that acted like obstacles. This mechanism could induce and created more turbulence, initiated the combustion of unburned pocket at the corner region, causing high mass burning rate and hence, increased the flame speed. It was also shown that the flame speed was enhanced by factor of 3 for explosion in bend pipe compared to straight pipe. It can be concluded that the bend can create greater turbulence effect compared to straight pipe configuration and applying appropriate safety devices before the area of the bends is recommended as one of the effective methods to prevent the explosion from happen.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF EQUATIONS xiii
LIST OF SYMBOLS xiv
LIST OF APPENDICES xvii
1 INTRODUCTION
1.1 Motivation/Introduction 1
1.2 Problem Statement 3
1.3 Objective of Research 5
1.4 Scope of Research 5
2 LITERATURE REVIEW
2.1 Research Background 6
2.2 Gas Explosion 7
2.3 Explosion Properties 10
viii
2.3.1 Flame Speed, Burning Velocity and Unburned
Gas Velocity10
2.3.1.1 Calculation of the Unburned Gas
Velocity, Sg12
2.3.1.2 Laminar or Turbulent Flame Speed
and Burning Velocity13
2.3.2 Overpressure and Rate of Pressure Rise 19
2.4 Factors Influence the Explosion Properties 25
2.4.1 Mixture Ratios and Stoichiometric
Concentration25
2.4.2 Ignition Position 28
2.4.3 Flammability Limit and Fuel Type 29
2.4.4 Pipe Configuration, Size and Shape 34
3 METHODOLOGY
3.1 Initial Preparation of Equipment and Fuel/Air
Mixture38
3.2 Method of Calculations for the Pressure of Fuel/Air
Mixture45
3.3 Detail of Research Methodology 50
3.4 Calculations of Flame Speed 54
3.5 Data Collection and Analysis 55
4 RESULTS AND DISCUSSION
4.1 Explosion in Straight Pipe 57
4.1.1 Pressure Time/Histories on Straight Pipe 57
4.1.2 Effect of Equivalent Ratio on Explosion
Pressure in Straight Pipe59
4.1.3 Rate of Pressure Rise (dP/dt) on Straight Pipe 61
4.1.4 Flame Speeds on Straight Pipe 62
4.2 Explosion in 90 Degree Bend Pipe 65
ix
4.2.1 Pressure Development/Profile on 90 Degree
Bend Pipe65
4.2.2 Effect of Equivalent Ratio on Explosion
Pressure in 90 Degree Bend Pipe66
4.2.3 Rate of Pressure Rise (dP/dt) on 90 Degree
Bend Pipe69
4.2.4 Flame Speeds on 90 Degree Bend Pipe 71
4.3 Unburnt Gas Velocity, Sg 73
4.3.1 Unburnt Gas Velocity, Sg for Straight and 90
Degree Bend Pipe73
4.4 Comparison with the Previous Published Data 75
4.4.1 Explosion Pressure on Straight Pipe 75
4.4.2 Flame Speed Comparison on Straight Pipe 77
5 CONCLUSION
5.1 Conclusion 79
5.2 Recommendation and Future Research 81
LIST OF PUBLICATIONS AND CONFERENCES 82
REFERENCES 83
Appendices A - D 89 - 101
x
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Laminar flame speed for stoichiometric composition 15
2.2Fuel-air mixtures concentration at stoichiometric
composition27
2.3Collected pressure and volume ratio for stoichiometric
mixtures at standard test conditions32
2.4Data summary of flame speed and overpressure for methane
explosions36
3.1Calculated gauge pressures (Pa and Pb) at different
concentration of fuel/air mixture for straight pipe48
3.2Calculated gauge pressures (Pa and Pb) at different
concentration of fuel/air mixture for 90 degree bends pipe49
3.3 Special procedure during the test 53
4.1Turbulent enhancement factor for various mixture
concentrations68
4.2Severity factor or deflagration index, KG at lean,
stoichiometric and rich mixture concentrations71
4.3Pressure and flame speed of methane explosion at
stoichiometric75
xi
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Steps for explosion mechanism 9
2.2 Transmission of flame in cylindrical vessel 11
2.3 Flow path diagram for element in laminar and turbulent form 14
2.4 Growth of turbulent boundary layer in tube 18
2.5 Pressure versus time for various mixture concentrations 20
2.6Pressure versus time at different methane-air mixture
concentrations21
2.7Maximum rate of pressure rise against methane-air
concentrations for various ignition positions22
2.8 Lower flammability and upper flammability limit 30
2.9Flammability limits of fuel-air mixtures at standard
atmospheric condition32
2.10Maximum pressure collected for various fuel-air mixtures at
stoichiometric concentration of the gases mixture33
2.11Flame speed profile and development for methane-air
explosions in various pipe configurations35
3.1 Mixer and straight pipe configuration 39
3.2 Mixer and 90 degree bend pipe configuration 40
3.3 Mixing cell configuration 41
3.4 Data logger configuration 42
3.5 Configuration of explosion piping system (main testing pipe) 43
3.6 Tanks (natural gas, oxygen and nitrogen) 44
xii
3.7 Vacuum pump configuration 45
3.8 Flow Chart of the research study 54
3.9 Recorded image by LabView Signal Express 56
4.1Pressure against time at lean, stoichiometric and rich
concentration58
4.2Pressure profile along the pipe for different mixture
concentrations60
4.3 Rate of pressure rise against distance from ignition, x 62
4.4Flame speed profile against L/D at various mixture
concentrations64
4.5 Pressure developments against time 66
4.6 Pressure rise versus L/D at different mixture concentrations 67
4.7Turbulent enhancement factors at various mixture
concentrations69
4.8Rate of pressure rise at lean, stoichiometric and rich
concentration70
4.9 Flame speed on 90 degree bend pipe 72
4.10Unburnt gas velocity, Sg for straight and bending at various
Ф74
4.11Explosion pressure for present and previous studies at
stoichiometric condition for different L/Ds76
4.12 Flame speed comparison at stoichiometric condition 78
xiii
LIST OF EQUATIONS
EQUATION TITLE PAGE
2.1 Flame speed, S or Sf (relation with U or Su and u or Sg) 10