Determination of Clearance Distances for Venting Determination of Clearance Distances for Venting of Hydrogen Storage of Hydrogen Storage
Andrei Tchouvelev, Pierre Benard, Vlad Agranat and Zhong ChengAndrei Tchouvelev, Pierre Benard, Vlad Agranat and Zhong Cheng
AcknowledgementsAcknowledgements
• Work partially supported by– Natural Resources Canada (NRCan) CTFCA
Clearance Distance Project– Natural Sciences and Engineering Research
Council of Canada (NSERC) Industrial Research Fellowship
IntroductionIntroduction
• Part of Hydrogen Clearance Distances Project under Canadian Transportation Fuel Cell Alliance (CTFCA)
• R&D study with practical application: contribute to development of model codes and engineering guidelines for design of vent stacks for hydrogen venting under conditions of a hydrogen energy station
• Innovative approach:– Clearance distances related to venting of hydrogen storage were
differentiated between distances to people and equipment (at 1.8 m above ground) and distances to air intakes and ignition sources (located above the top of a vent stack)
– Recommended clearance distances are based on extents of 100% LFL hydrogen concentration envelopes plus 25% safety factor
• Obtained tables and graphs were based on CFD modeling of hydrogen releases and dispersion, implemented through the PHOENICS software package and on thermal effects analysis using TNO “Yellow Book” recommendations
International Fire Code, Section 2209International Fire Code, Section 2209
Flux (kW/m2) Damage to Equipment
Damage to human beings
37.8 Damage to process equipment
1% mortality in 10 sec
25.0 Minimum energy required to ignite wood at indefinitely
long exposure
Significant injury in 10 sec
12.6 Plastic tubing melts 1st degree burns in 10 sec
9.5 Immediate skin reactions
4.7 (1,500 BTU/ft2) Pain threshold
1.6 (500 BTU/ft2) Safe level
Thermal Level Standards for Thermal Level Standards for Hazard AssessmentHazard Assessment
API Recommended Practice 521API Recommended Practice 521
• “Flame length varies with emission velocity and heat release. Information on the subject is limited and is usually based on VISUAL observations in connection with emergency discharges from flares. Figures 8 and 9 were developed from some PLANT-SCALE experimental work on flame lengths covering relatively high release rates of various mixtures of hydrogen and hydrocarbons”.
API Recommended Practice 521API Recommended Practice 521
Hydrogen Release from Vent Stack:Hydrogen Release from Vent Stack:2000 CFM, 30 ft/s (9.14 m/s) wind2000 CFM, 30 ft/s (9.14 m/s) wind
Flow rate 0.949 m3/sec / 2000 SCFM
Stack height 3.658 m / 12 ft
IFC Distance 1D 7.92 m – 10.97 m / 26 – 36 ft
Lot line 1.25D 9.9 m – 13.7 m / 32.5 ft – 45 ft
Leak type Choked Subsonic
Stack diameter 25 mm / 1” 50 mm / 2”
CFD 2% vol. extent 5.5 m / 18.0 ft 9.7 m / 31.8 ft
4% vol. extent 2.0 m / 6.6 ft 4.0 m / 13.1 ft
Hydrogen Release from Vent Stack:Hydrogen Release from Vent Stack:2000 CFM, 30 ft/s (9.14 m/s) wind2000 CFM, 30 ft/s (9.14 m/s) wind
Flow rate 0.949 m3/sec / 2000 SCFM
Stack height 3.658 m / 12 ft
IFC Distance 1D 7.92 m – 10.97 m / 26 – 36 ft
Lot line 1.25D 9.9 m – 13.7 m / 32.5 ft – 45 ft
Leak type Choked Subsonic
Stack diameter 25 mm / 1” 50 mm / 2”
CFD 2% vol. extent 5.5 m / 18.0 ft 9.7 m / 31.8 ft
4% vol. extent 2.0 m / 6.6 ft 4.0 m / 13.1 ft
Flame Net length 3.17 m 3.32 m
Max diameter 1.01 m 1.30 m
At 1.8 m level
Max radiation 4.22 kW/m2 6.93 kW/m2
Dis. to max flux 2.31 m 2.18 m
Distance to 1.6 kW/m2 7.81 m 9.69 m
Distance to 4.7 kW/m2 -- 4.78 m
Pain Threshed Calculations Max radiation flux at ground level: 4.7 kW/m2
Pain Stack height 3.46 m 4.46 m
Distance to max flux 2.18 m 2.58 m
Distance to 1.6 kW/m2 7.94 m 9.33 m
Clearance Distances Based on Concentration Clearance Distances Based on Concentration EnvelopesEnvelopes
Flow, CFM 500 1000 2000 5000 10000 20000
Flow, m3/s 0.25 0.5 1 2.5 4.75 9.5
2% extent (sonic), m 2.6 4 5.5 9.2 14.4 19.5
2% extent (subsonic), m 5.5 7 9.7 13.5 16 21.5
4% extent (sonic), m 0.8 1.2 2 3.4 5.9 8.9
4% extent (subsonic), m 2.5 3 4 6.2 7.1 9.7
Vent Diameter, mm 25 25 25-50 25-75 50-75 75
Extents of 2% and 4% vol. concentration envelopes for sonic and sub-sonic flows
R2 = 0.9963
R2 = 0.9978
R2 = 0.9927R2 = 0.9975
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10
Hydrogen flow rate, m3/s at NTP
Ho
rizo
nta
l ex
ten
t, m
0
5
10
15
20
25
2% extent (subsonic), m 4% extent (sonic), m
4% extent (subsonic), m 2% extent (sonic), m
Pow er (2% extent (subsonic), m) Pow er (4% extent (sonic), m)
Pow er (4% extent (subsonic), m) Pow er (2% extent (sonic), m)
Recommended Clearance Distances For Ignition Recommended Clearance Distances For Ignition Sources Above Vent Stack TopSources Above Vent Stack Top
Approach: Applying Subsonic Data Reasonably Conservative (Metric Units)
Flow, CFM 500 1000 2000 5000 10000 20000
Flow, m3/s 0.25 0.5 1 2.5 4.75 9.5
2% LFL extent (subsonic), m 5.5 7 9.7 13.5 16 21.5
4% LFL extent (subsonic), m 2.5 3 4 6.2 7.1 9.7
Clearance Distance, m 3.1 3.8 5.0 7.3 9.0 12.0
Vent Diameter, mm 25 25 25-50 25-75 50-75 75
Clearance Distances for Air Intakes and Ignition Sources Located Above the Top of Hydrogen Vent Stacks
3.13.85.0
7.39.0
12.0
R2 = 0.997
0123456789
10111213
0 1 2 3 4 5 6 7 8 9 10
Hydrogen Flow Rates, m3/s at NTP
Cle
ara
nc
e D
ista
nc
e, m
Clearance Distances Based on Thermal EffectsClearance Distances Based on Thermal Effects
Sonic + Subsonic Flow - Imperial Units
H2 Flow Rate 2,000 CFM 5,000 CFM 10,000
CFM 20,000
CFM
Vent Diameter, in 1 2 2 1 1 3 3 2 3 3
Height, ft 11.4 12 14.6 17 18.2 17 17.8 19 20.9 22.3
Distance to 1,500 BTU/ft2 , ft 7.2 15.7 8.5 16.7 11.1 18.3 13.2 16 16.2 22.3
Sonic flows correspond to lowest stack diameter in each flow rate range. It is interesting that the best sonic (coloured green) and subsonic (coloured yellow) results in terms of distances to 1,500 BTU/ft2 for each flow rate range are quite close to each other. This indicates that if an appropriate height of the vent stack is selected, the stack orifice will not materially affect the clearance distance.
Recommended Clearance Distances Based on Recommended Clearance Distances Based on Thermal EffectsThermal Effects
Approach: Averaging Sonic and Subsonic Data, Reasonably Conservative (Imperial Units)
Flow, CFM 500 1000 2000 5000 10000 20000
H, ft 11 13 15 18 21 24
D, ft 6 8 10 14 18 23
Vent Dia, in 1 1 1 - 2 1 - 3 2 - 3 3
Minimum Vent Stack Height and Separation Distance vs Hydrogen Flow RateImperial Units
1113
15
18
24
68
10
14
18
2321
y = 3.0166x0.2101
R2 = 0.9992y = 0.6457x0.3611
R2 = 0.9994
0
5
10
15
20
25
30
0 5000 10000 15000 20000
Hydrogen Flow Rate, CFM at NTP
Ven
t S
tack
Hei
gh
t (H
) o
r S
epar
atio
n
Dis
tan
ce (
D),
ft
H, ft D, ft Pow er (H, ft) Pow er (D, ft)
SummarySummary
• Clearance distances related to venting of hydrogen storage were derived using both thermal effects and concentration envelope approaches
• Obtained tables and graphs were based on thermal effects analysis using TNO “Yellow Book” recommendations and CFD modeling of hydrogen releases and dispersion, implemented through the PHOENICS software package
• Obtained results provide comprehensive guidance to both design engineers and regulatory authorities to design and provide regulatory approvals for placement of hydrogen storage systems vent stacks