Ignitability and Explosibility of Gases and Vapors

230 Pages·2015·6.344 MB·English

by  Tingguang Ma (auth.)

Tingguang Ma
Ignitability and
Explosibility
of Gases and
Vapors
Ignitability and Explosibility of Gases
and Vapors
Tingguang Ma
Ignitability and Explosibility
of Gases and Vapors
123
Tingguang Ma
Fire Protection andSafety Technology
Oklahoma State University
Stillwater, OK
USA
ISBN978-1-4939-2664-0 ISBN978-1-4939-2665-7 (eBook)
DOI 10.1007/978-1-4939-2665-7
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Preface
Before starting your journey reading this monograph, I want to explain three
concepts from etymology perspective (using only etymology dictionary at http://
etymonline.com/).
The first concept is “inflame,” from which flammability is derived. It first
appeared in the mid-fourteenth century, “make (someone) ardent; set (the spirit,
etc.)onfire”withapassionorreligiousvirtue,afigurativesense,fromOldFrench
enflamer, from Latin inflammare “to set on fire, kindle,” figuratively “to rouse,
excite,”fromin-“in”+flammare“toflame,”fromflamma“aflame.”Literalsense
of “to cause to burn” first recorded in English in the late fourteenth century.
Meaning“toheat,makehot,causeinflammation”isfromthe1520s.Inordertoget
a flame, you need fuel/air combination, which is difficult to characterize, since air
itself is a mixture of oxygen/nitrogen. The tertiary nature of the mixture makes a
universal consistent flammability theory difficult to establish.
The second concept to appear is “explode,” “to reject with scorn,” from Latin
explodere“driveoutoroffbyclapping,hissoff,hootoff,”originallytheatrical,“to
drive an actor off the stage by making noise,” hence “drive out, reject, destroy the
repute of” (a sense surviving in an exploded theory), from ex- “out” (see ex-) +
plaudere “to clap the hands, applaud,” which is of uncertain origin. Athenian
audiences were highly demonstrative: clapping and shouting approval, stamping,
hissing, and hooting for disapproval. The Romans seem to have done likewise. So
theactof“explode”hasnothingtodowithafuel,simplyrelatedtothecapabilityof
air to support noise (acoustic wave) or flame (combustion wave). In this mono-
graph, the latter is used for combustion safety, not explosion safety.
Finally, “Ignite” appeared in the 1660s, from Latin ignitus, past participle of
ignire“setonfire,”fromignis“fire.”IgneousisderivedfromLatinigneus“offire,
fiery,” from ignis “fire,” or Sanskrit agnih “fire, sacrificial fire.” So the latest word
hasamuchremoteorigin.Perhaps,itistheextremeweatherinthe1660sthatmade
the fire initiation process difficult, so an ancient word was revived to describe the
difficultiesinsettingafire.However,thereisnoairinvolvedintheignitionprocess,
assuming air is always sufficient.
v
vi Preface
Based on the original meanings, the explosibility of air and the ignitability of
fuelareredefinedtodescribe theflammabilityoffuel/air mixture.Similar concepts
havealreadybeenutilizedinindustry.Theexplosibilityofairiscalled“In-Service
Oxygen Concentration (ISOC),” while the ignitability of fuel is called “Out-of-
Service Fuel Concentration (OSFC).” By isolating the concepts of ignitability and
explosibilityfromtheconceptofflammability,andcorrelatingthemwiththesimple
oxygen calorimetry, a new flammability theory is born. It shows mass transfer is
more important than heat transfer, though radiative loss is only important in
determiningtheflammability.Inordertounderstandcriticalbehaviorsforgasesand
vapors,weneedtounderstandfirstprinciplesinheatandmasstransfer.Thisisthe
starting point of this monograph. Hope you can have a comfortable journey with
these concepts.
Inaddition,IwouldliketotakethisopportunitytothankProf.StevenSpivakfor
accepting me into the ENFP program at the University of Maryland to study fire.
Withouthisinterestsinmycareergoal,itwouldhavebeendifficultformetopursue
fire studies 16 years ago. My second thanksgiving should be to Prof. Jose Torero,
whoseteachingonadvancedfiresuppressiontechnologiesinthespringof2001lent
me the foundation to build this flammability theory. I am also indebted to Prof.
Arnaud Trouvé, from whose numerical training I developed an interest in theo-
retical development. I would also like to thank my colleagues, Drs. Michael
Larrañaga and Qingsheng Wang, whose kind help supported my teaching work at
OSU. Special thanks should be extended to my former students, Caleb Scheve,
Nash McMurtrey, and Kevin Stamper for supporting my writing. They are the
targetedaudienceofthismonographandwerewillingtohelpmetogetthisproject
through. I am proud of them.
Stillwater, USA Tingguang Ma
Contents
1 A Historical Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Dawn of Combustion Science for Safety. . . . . . . . . . . . . . . . . . 1
1.1.1 Fire Chemistry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Flammability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.3 Suppressibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.4 Detection by Upper Limits . . . . . . . . . . . . . . . . . . . . . . 3
1.1.5 Minimum Ignition Energy. . . . . . . . . . . . . . . . . . . . . . . 3
1.1.6 Combustion Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Continued Efforts After Davy . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 Three Types of Flammability. . . . . . . . . . . . . . . . . . . . . 4
1.2.2 Experimental Efforts. . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Who Still Cares About Flammability?. . . . . . . . . . . . . . . . . . . . 11
1.4 How This Methodology Is Developed?. . . . . . . . . . . . . . . . . . . 12
2 Classical Flammability Theories . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 Empirical Rules on Flammability . . . . . . . . . . . . . . . . . . . . . . . 16
2.1.1 Milestone Events on Flammability Theory . . . . . . . . . . . 16
2.1.2 Energy Dependence. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1.3 Temperature Dependence . . . . . . . . . . . . . . . . . . . . . . . 18
2.1.4 Chemistry Dependence. . . . . . . . . . . . . . . . . . . . . . . . . 20
2.1.5 Fuel Dependence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.1.6 Pressure Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2 Correlations for Flammability. . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3 ISO10156 Method for Predicting Mixture Flammability . . . . . . . 25
2.4 Flammability Diagrams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.4.1 Standard Flammability Diagram. . . . . . . . . . . . . . . . . . . 28
2.4.2 Diluted Flammability Diagram. . . . . . . . . . . . . . . . . . . . 28
2.4.3 Explosive Triangle Diagram . . . . . . . . . . . . . . . . . . . . . 29
2.4.4 Ternary Flammability Diagram . . . . . . . . . . . . . . . . . . . 30
vii
viii Contents
2.5 Problems and Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.5.1 ISO10156 Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.5.2 Operations in a Ternary Diagram. . . . . . . . . . . . . . . . . . 32
2.5.3 Reading a Ternary Diagram . . . . . . . . . . . . . . . . . . . . . 33
2.5.4 Safe Dilution of a Flammable Gas Mixture. . . . . . . . . . . 35
2.5.5 Methane Dilution by Air. . . . . . . . . . . . . . . . . . . . . . . . 36
3 Combustion Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.1 Thermochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.1.1 Chemical Reactions and Stoichiometry. . . . . . . . . . . . . . 37
3.1.2 Equivalence Ratio and Non-stoichiometric Equations . . . . 38
3.1.3 Heat of Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1.4 Heat of Combustion. . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.1.5 Oxygen Calorimetry. . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2 Adiabatic Flame Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2.1 Method of Interpolated Enthalpy . . . . . . . . . . . . . . . . . . 43
3.2.2 Method of Lump-Sum Specific Heat . . . . . . . . . . . . . . . 44
3.2.3 Method of Accumulative Quenching Potentials . . . . . . . . 44
3.3 Evaporation Process (Isothermal) . . . . . . . . . . . . . . . . . . . . . . . 46
3.3.1 Vapor Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.3.2 Raoult’s Law. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.3.3 The Vaporization of Liquid. . . . . . . . . . . . . . . . . . . . . . 48
3.3.4 Flashpoint. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.3.5 Estimation of Flashpoints . . . . . . . . . . . . . . . . . . . . . . . 52
3.3.6 Classification of Liquid Fuels . . . . . . . . . . . . . . . . . . . . 53
3.4 Problems and Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.4.1 Balance of Stoichiometric Equations. . . . . . . . . . . . . . . . 54
3.4.2 Non-stoichiometric Equations . . . . . . . . . . . . . . . . . . . . 55
3.4.3 Heat of Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.4.4 Heat of Combustion. . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.4.5 Flame Temperature by Interpolation of Enthalpy . . . . . . . 59
3.4.6 Flame Temperature by Lump-Sum Specific Heat. . . . . . . 60
3.4.7 Flame Temperature by Quenching Potentials. . . . . . . . . . 63
3.4.8 Suppression Modeling by Flame Temperature . . . . . . . . . 65
3.4.9 Flashpoint by Integrated Clasius-Claperon Equation. . . . . 66
3.4.10 Vapor Pressure of a Mixture. . . . . . . . . . . . . . . . . . . . . 68
3.4.11 Flashpoint of a Binary Mixture . . . . . . . . . . . . . . . . . . . 69
3.4.12 Evaporation Profiles on Liquid Surface. . . . . . . . . . . . . . 70
3.4.13 Ambient Conditions for Liquid Evaporation . . . . . . . . . . 71
4 Thermal Balance Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.1 Thermal Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.2 Correlations for Flammability Limits. . . . . . . . . . . . . . . . . . . . . 76
Contents ix
4.3 The Flammability Limits of a Mixture . . . . . . . . . . . . . . . . . . . 78
4.3.1 Le Chatelier’s Rule (LCR) . . . . . . . . . . . . . . . . . . . . . . 78
4.3.2 Thermal Balance Method (TBM). . . . . . . . . . . . . . . . . . 78
4.3.3 Beyler’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.3.4 Estimation Using Correlations. . . . . . . . . . . . . . . . . . . . 80
4.3.5 Non-conventional Estimations . . . . . . . . . . . . . . . . . . . . 80
4.4 Temperature Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.5 Reconstruction of Flammability Diagrams. . . . . . . . . . . . . . . . . 83
4.5.1 Standard Flammability Diagrams. . . . . . . . . . . . . . . . . . 83
4.5.2 Diluted Flammability Diagrams. . . . . . . . . . . . . . . . . . . 86
4.6 Problems and Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.6.1 Temperature Dependence . . . . . . . . . . . . . . . . . . . . . . . 90
4.6.2 Flammable State with Multiple Fuels . . . . . . . . . . . . . . . 91
4.6.3 Flammable State with Multiple Diluents. . . . . . . . . . . . . 93
4.6.4 Flammable State of a Coal-Mine-Gas Mixture. . . . . . . . . 94
5 Ignitability, Flammability and Explosibility. . . . . . . . . . . . . . . . . . 99
5.1 Two Types of Flammability Problems. . . . . . . . . . . . . . . . . . . . 99
5.1.1 Type I Problem (Variable Oxygen
in Background Air) . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
5.1.2 Type II Problem (Variable Diluents in a Stream). . . . . . . 103
5.2 Critical Points in a Flammability Diagram. . . . . . . . . . . . . . . . . 105
5.3 Critical Parameters for a Flammability Diagram. . . . . . . . . . . . . 109
5.4 Two Modes of Suppression. . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.5 Problems and Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.5.1 Tank Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.5.2 Mixture Flammability. . . . . . . . . . . . . . . . . . . . . . . . . . 113
6 Operations Within Flammability Diagrams . . . . . . . . . . . . . . . . . . 117
6.1 Flammable States in Diagrams. . . . . . . . . . . . . . . . . . . . . . . . . 117
6.2 A Thermal Explanation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
6.3 Purge in Flammability Diagrams . . . . . . . . . . . . . . . . . . . . . . . 123
6.3.1 Different Levels of Safety. . . . . . . . . . . . . . . . . . . . . . . 123
6.3.2 Purging Operation in the Standard
Flammability Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 125
6.3.3 Purging Operations in the Diluted
Flammability Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 127
6.3.4 Purging Operations in the Explosive
Triangle Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
6.3.5 Purging Operations in the Ternary
Flammability Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 130
x Contents
6.4 Dilution in Flammability Diagrams. . . . . . . . . . . . . . . . . . . . . . 131
6.4.1 Diluting Operations in a Standard
Flammability Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 132
6.4.2 Diluting Operations in a Diluted
Flammability Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 133
6.4.3 Diluting Operations in an Explosive
Triangle Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
6.4.4 Diluting Operations in a Ternary
Flammability Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 136
6.5 Summary on Purge and Dilution in Diagrams . . . . . . . . . . . . . . 137
6.6 Application on Tank Operations. . . . . . . . . . . . . . . . . . . . . . . . 138
6.6.1 Safe Operations Before Filling a Liquid Tank
(Type I Problem). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
6.6.2 Safe Operations Before Emptying a Liquid Tank
(Type II Problem) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
6.7 Problems and Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
6.7.1 Flammable State in a Ternary Diagram. . . . . . . . . . . . . . 142
6.7.2 Dilution and Purge for Gasoline Safety. . . . . . . . . . . . . . 143
6.7.3 Filling and Emptying a Fuel Tank . . . . . . . . . . . . . . . . . 151
7 Applications on Fuel Streams (Type II Problem) . . . . . . . . . . . . . . 153
7.1 Clean Combustion Technologies. . . . . . . . . . . . . . . . . . . . . . . . 153
7.1.1 Role of Diluent on Flammability . . . . . . . . . . . . . . . . . . 154
7.1.2 Role of Oxygen on Flammability (Oxy-combustion). . . . . 156
7.1.3 Role of Hydrogen Doping on Flammability
(Hydrogen-Doping Combustion) . . . . . . . . . . . . . . . . . . 157
7.1.4 Role of Temperature on Flammability
(High Temperature Combustion) . . . . . . . . . . . . . . . . . . 159
7.1.5 Discussion on Fuel Properties . . . . . . . . . . . . . . . . . . . . 160
7.2 Critical Flammability Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
7.3 Problems and Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
8 Applications in Compartment Fires (Type I Problem) . . . . . . . . . . 171
8.1 Underground Mine Fires. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
8.1.1 Oxygen-Modified Flammability Diagram . . . . . . . . . . . . 173
8.1.2 A Global Progress Variable. . . . . . . . . . . . . . . . . . . . . . 178
8.1.3 Fire Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
8.2 Critical Behaviors in a Compartment Fire . . . . . . . . . . . . . . . . . 183
8.2.1 Introduction to Backdraft . . . . . . . . . . . . . . . . . . . . . . . 183
8.2.2 Blow-Torch Effect. . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
8.2.3 Critical Conditions for Backdrafts
and Blow-Torch Effects . . . . . . . . . . . . . . . . . . . . . . . . 187
8.2.4 Controlling Strategies. . . . . . . . . . . . . . . . . . . . . . . . . . 188
8.3 Problems and Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190