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Explosive Nature of Explosive Nature of Hydrogen in a Partial Hydrogen in a Partial
Pressure VacuumPressure Vacuum
Trevor JonesTrevor JonesProject EngineerProject Engineer
Solar Atmospheres Inc.Solar Atmospheres Inc.Souderton, PASouderton, PA
www.solaratm.com & www.solarmfg.comwww.solaratm.com & www.solarmfg.com
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Hydrogen Consumption:Hydrogen Consumption:
•• Hydrogen is the most abundant element in Hydrogen is the most abundant element in the universethe universe
•• Worldwide consumption of hydrogen is Worldwide consumption of hydrogen is around 103 million kg per day (44 billion around 103 million kg per day (44 billion scfd)scfd)
•• United states consumes 20% of worldwide United states consumes 20% of worldwide supplysupply
•• More hydrogen gas is consumed than More hydrogen gas is consumed than natural gas by the commercial sectornatural gas by the commercial sector
(ref. 1)
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History on Hydrogen History on Hydrogen Applications:Applications:
•• Fuel Cells Fuel Cells •• FooFood d •• Chemical processiChemical processingng•• PharmaceuticalPharmaceuticals s •• AerospacAerospacee
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History on Hydrogen History on Hydrogen Applications Applications (continued)(continued)
•• Electronics Electronics •• Petroleum Recovery and RefinePetroleum Recovery and Refineryry•• Power Generation Power Generation •• Metal productioMetal production and n and fabricatiofabricationn•• Heat TreatingHeat Treating
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Vacuum FurnacesVacuum Furnaces
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HydrogenHydrogen’’s Role in a Vacuum Furnaces Role in a Vacuum Furnace
•• Partial Pressure:Partial Pressure:•• Hydride / DeHydride / De--Hydride of tantalum, Hydride of tantalum,
titanium, and other metalstitanium, and other metals•• Dilutant in Vacuum CarburizingDilutant in Vacuum Carburizing•• Reducing gas for oxide reductionReducing gas for oxide reduction•• Formed from dissociated ammonia gas in Formed from dissociated ammonia gas in
the gas nitriding processthe gas nitriding process
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Characteristics of HydrogenCharacteristics of Hydrogen
(ref. 1 & 2)
141.90 Mj/kgHigher Heating Value
11.89 Mj/m³
119.90Mj/kgLower Heating Value
10.505 Mj/m³
Stoichiometric Mixture in Air 29.53 (vol.%)
LEL % by Volume 4
UEL % by Volume 74.2
Ft.³ Air Required to Burn 1 Ft.³ of Gas 2.5
Minimum Self-ignition Temperature of Stoichiometric Mixture 1085°F
Adiabatic Flame Temperature in Air 3712.73°F
Minimum Ignition Energy of Stoichiometric Mixture (mj) 0.02
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(ref. 2)
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•• Understand the explosive nature of hydrogen gas Understand the explosive nature of hydrogen gas at atmospheric pressure and in near vacuum at atmospheric pressure and in near vacuum conditionsconditions
ProjectProject GoalsGoals
•• Determine minimal levels of energy to ignite Determine minimal levels of energy to ignite hydrogen / air mixtureshydrogen / air mixtures
•• Determine if Nitrogen or Argon gas will act as a Determine if Nitrogen or Argon gas will act as a dilutant for hydrogen / air reactionsdilutant for hydrogen / air reactions
•• Develop recommendations for the safe use of Develop recommendations for the safe use of hydrogen in vacuum systemshydrogen in vacuum systems
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SolarSolar’’s Hydrogen / Air Reaction Chambers Hydrogen / Air Reaction Chamber
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Energy SourcesEnergy SourcesAtmosphereAtmosphere VacuumVacuum
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Procedure for Conducting Tests:Procedure for Conducting Tests:
1.1. Pump down vessel to 0.1 TorrPump down vessel to 0.1 Torr
2.2. Backfill vessel with air to desired pressureBackfill vessel with air to desired pressure
3.3. Backfill vessel with HBackfill vessel with H22 to obtain finalto obtain finaltest pressure and gas ratiotest pressure and gas ratio
4.4. Ignite mixture with either spark or heater elementIgnite mixture with either spark or heater element
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Experimental Results:Experimental Results:Minimum Ignition PointsMinimum Ignition Points5000 Voltage Spark 1/16" Gap
050
100150200250300350400450500550600650700750
0 10 20 30 40 50 60 70% Hydrogen in air
Pres
sure
(tor
r)
ExperimentalTheoretical
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Experimental Results:Experimental Results:Minimum Ignition PointsMinimum Ignition Points5000 Voltage Spark 1/4" Gap
050
100150200250300350400450500550600650700750
0 10 20 30 40 50 60 70 80 90% Hydrogen in Air
Pres
sure
(tor
r)
Experimental
Theoretical
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Experimental Results:Experimental Results:Minimum Ignition PointsMinimum Ignition Points
Heated Element Wire
050
100150200250300350400450500550600650700750
0 10 20 30 40 50 60 70
% Hydrogen in air
Pres
sure
(tor
r)
ExperimentalTheoretical
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Temperature vs. H2 Concentration Temperature vs. H2 Concentration Ignition PointsIgnition Points
850
900
950
1000
1050
1100
1150
0 10 20 30 40 50 60 70% Hydrogen in Air
Tem
pera
ture
(F°)
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050
100150200250300350400450500550600650700750
0 10 20 30 40 50 60 70 80 90% Hydrogen in Air
Pres
sure
(tor
r)
1/4" High Voltage SparkHeated Wire1/16" Gap Spark
Experimental Results:Experimental Results:Minimum Ignition Points Minimum Ignition Points -- Comparing All Three TestsComparing All Three Tests
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Visuals of Explosions at Visuals of Explosions at Different PressuresDifferent Pressures
AtmosphericAtmospheric SubSub--AtmosphericAtmospheric
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Minimum Ignition Energy vs. % Hydrogen in Air
0.01
0.1
1
10
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
Hydrogen in air, percent by volume
Min
imum
Igni
tion
ener
gy, m
Joul
es
Pressure 0.2 atmPressure 0.33 atmPressure 0.5 atmPressure 1.0 atm
(ref. 3)
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Quenching Distance vs. % Hydrogen in Air at Various Pressures
0.01
0.1
1
0 10 20 30 40 50 60 70
Hydrogen in air, percent by volume
Dis
tanc
e (b
etw
een
para
llel p
late
s) c
m
Pressure 0.2 atmPressure 0.33 atmPressure 0.5 atmPressure 1.0 atm
(ref. 3)
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Contained ReactionsContained ReactionsIgnitions under 150 torrIgnitions under 150 torr
0
50
100
150
200
250
300
0 0.5 1 1.5 2 2.5Time (sec)
Pres
sure
(tor
r)
∆P
Initial PressureInitial Pressure Final PressureFinal Pressure
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Inert Gas as a Dilutant for Inert Gas as a Dilutant for Hydrogen / Air BurningHydrogen / Air Burning
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Experimental ResultsExperimental ResultsInert Gas as a Dilutant for Hydrogen / Air BurningInert Gas as a Dilutant for Hydrogen / Air Burning
•• Hydrogen alone will easily burn if vented out of a pipe into opHydrogen alone will easily burn if vented out of a pipe into open air en air and ignited with an energy sourceand ignited with an energy source
•• Extremely lean hydrogen mixtures (<5%) will not burn in open aiExtremely lean hydrogen mixtures (<5%) will not burn in open air r if diluted with inert gasif diluted with inert gas
•• Lean HLean H22 mixtures (5mixtures (5--25%) mixed with inert gas will burn, however 25%) mixed with inert gas will burn, however will not support a flame once energy source is taken away will not support a flame once energy source is taken away (Forming Gas)(Forming Gas)
•• 2525--100% hydrogen in inert gas will burn and sustain a flame once 100% hydrogen in inert gas will burn and sustain a flame once energy source is taken awayenergy source is taken away
•• Argon showed slightly better flammable suppression compared to Argon showed slightly better flammable suppression compared to nitrogennitrogen
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ConclusionsConclusions
••The use of inert gas as a dilutant does lower the flammability The use of inert gas as a dilutant does lower the flammability limit of hydrogen however only slightlylimit of hydrogen however only slightly
••As the pressure of the hydrogen & air mixture decreases, the As the pressure of the hydrogen & air mixture decreases, the amount of energy required to ignite the mixture increases more amount of energy required to ignite the mixture increases more than an order of magnitude than an order of magnitude (ref. 3)(ref. 3)
••Lower pressures than 0.2 atm (150 torr) can be ignited with a Lower pressures than 0.2 atm (150 torr) can be ignited with a larger diameter vessel and increased energy source larger diameter vessel and increased energy source (ref. 3)(ref. 3)
••0.02 mJ is all the energy required to ignite a stoichiometric 0.02 mJ is all the energy required to ignite a stoichiometric mixture of hydrogen & air at atmospheric pressure mixture of hydrogen & air at atmospheric pressure (ref. 3)(ref. 3)
••Larger spark gaps result in wider flammability limitsLarger spark gaps result in wider flammability limits
••As hydrogen is increased in concentration, a higher temperature As hydrogen is increased in concentration, a higher temperature is required to ignite the mixturesis required to ignite the mixtures
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Safety PrecautionsSafety Precautions•• Stay below 1/2 the LEL of hydrogen (2% or 15 torr)Stay below 1/2 the LEL of hydrogen (2% or 15 torr)
•• Pump down to 0.1 torr, then backfill with inert gas to atmosphePump down to 0.1 torr, then backfill with inert gas to atmospheric ric pressure prior to exposure to airpressure prior to exposure to air
•• Perform a leak test on the vacuum chamber and be sure the leak Perform a leak test on the vacuum chamber and be sure the leak up up rate is less than 0.015 torr per hourrate is less than 0.015 torr per hour
•• Design intrinsically safe & redundant safety controls when usinDesign intrinsically safe & redundant safety controls when using g hydrogenhydrogen
•• Oxygen probe to detect an air leak in the vacuum system. If oxOxygen probe to detect an air leak in the vacuum system. If oxygen ygen is present then perform 5 volume change purge with argonis present then perform 5 volume change purge with argon
•• Use an inert diluting gas to lower the flammability limitUse an inert diluting gas to lower the flammability limit
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Future ExperimentsFuture Experiments
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References:References:
••Ref. 1 Ref. 1 -- Bose Tapan; Hay, Rober; and Ohi Jim: Sourcebook for Hydrogen Bose Tapan; Hay, Rober; and Ohi Jim: Sourcebook for Hydrogen Applications. Hydrogen Research Institute and National RenewablApplications. Hydrogen Research Institute and National Renewable Energy e Energy Laboratory., 1998 Laboratory., 1998
••Ref. 2 Ref. 2 -- Barbir, Frano: Safety Issues of Hydrogen Vehicles. Energy partBarbir, Frano: Safety Issues of Hydrogen Vehicles. Energy partners., ners., 2001; http://iahe.org/hydrogen2001; http://iahe.org/hydrogen
••Ref. 3 Ref. 3 -- Drell Isadore; Belles Frank: Report 1383 Survey of Hydrogen Drell Isadore; Belles Frank: Report 1383 Survey of Hydrogen Combustion Properties. Lewis Flight Propulsion Laboratory, NatiCombustion Properties. Lewis Flight Propulsion Laboratory, National Advisory onal Advisory Committee for Aeronautics., Cleveland, Ohio: April 1957Committee for Aeronautics., Cleveland, Ohio: April 1957