ISO 9001:2000 www.hsl.gov.uk an agency of the Health & Safety Executive

VAPOUR CLOUD EXPLOSIONS FROM THE IGNITION OF METHANE/HYDROGEN/AIR MIXTURES IN A

CONGESTED REGION

Mark Royle(1) Les Shirvill(2) and Terry Roberts(1)(1) Health and Safety Laboratory (2) Shell Global Solutions

PRESENTED by Geoff Chamberlain2

INTRODUCTION

NATURALHY – potential for hydrogen distribution within existing natural gas pipeline networks

• This work funded by Shell Hydrogen B.V.

• Hydrogen mixed with methane

• Change in explosive properties

AIM

• Measure over-pressures produced by premixed clouds in a repeated pipe congestion array

• Determine the amount of hydrogen which can be added to methane without a large increase in explosion overpressure

EXPERIMENTAL PROGRAMME

• Perform experiments igniting mixtures of methane, hydrogen and air in a repeated pipe congestion rig.

• Measure the overpressures produced by the different mixtures.

EXPERIMENTAL PROGRAMME

• Mixtures chosen– 100% hydrogen– 25% methane 75% hydrogen– 50% methane 50% hydrogen– 75% methane 25% hydrogen– 100% methane

• Nominal equivalence ratio – 1.1 for methane mixtures. 1.2 for 100% hydrogen.

CONGESTION RIG

• 3 m x 3 m x 2 m metal framework structured to consist of 18 one cubic metre units

• Bottom units fitted with 9 layers of vertical bars

• Top units fitted with 7 layers of criss-crossed horizontal bars

• Rig wrapped in plastic film to hold in gas

TEST FACILITY

INSTRUMENTCABIN

AIRCOMPRESSOR

FOR PNEUMATICCONTROL

PNEUMATICCONTROL SYSTEMBUNKER

FUEL CYLINDERS

CO2 CYLINDERS

AIR CYLINDERSCONFINEMENT

WALL

VIDEO

GAS SUPPLY DUCTING

INSTRUMENT CABLE DUCTING

PROTECTIVEWALL

CONGESTION RIG

Measurements within congestion rig

• Temperature

• Humidity

• IR methane analyser

• Paramagnetic oxygen analyser

• 8 x electro-chemical oxygen sensors

PRESSURE SENSORS

H16(hy16)

H15(hy15)

0.60 m

0.70 m1.77 m10.93 m16 m

K8(hy5)

K9(hy6)

K10(hy7) 0.32 m

0.46 m

K1(hy3)

K2(hy2)

K3(hy1)

K4(hy4)

0.35 m

0.75 mK5(hy10

) 1.84 mK6

(hy8)

K7(hy9)

3.55 m

2.60 mKW12 (hy12)KW13 (hy13)KW14 (hy14)

3.20 m 0.30 m

Gas mixtures

• Certified gas mixtures used (hydrogen / methane) made to order by BOC.

• Gas mixture injected into rig via air amplifiers to entrain air

• Oxygen and methane concentration monitored until required equivalence ratio obtained

TRIAL EQUIVALENCE RATIOS

Test name Certified proportion of hydrogen in mixture

(%)

Nominal equivalence

ratio

Actual* equivalence

ratio

NATHY_01 100 1.2 1.28

NATHY_02 0 1.1 1.06

NATHY_03 50.9 1.1 1.06

NATHY_04 25.5 1.1 1.09

NATHY_05 75 1.1 1.1

* Calculated from mean depleted oxygen concentration

PHOTOGRAPHS 2nd frame after ignition

100% hydrogen

100% methane 51% hydrogen25% hydrogen

75% hydrogen

PRESSURE DATA AT 16 METRES

Pressureat16m.xls

-15

-10

-5

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350 400

Time (ms)

Pres

sure

at 1

6 m

(kPa

)

0% hydrogen25% hydrogen51% hydrogen75% hydrogen100% hydrogen

DETONATION OF HYDROGEN

• For 100% hydrogen– Pressure 3.03 bar just inside and

4.58 bar just outside rig– Plastic shredded into narrow

strips (20.5 + 6.7 mm)

• Groethe et al. (2002) found: – 21 mm for a 20% hydrogen no-

obstacle detonation test• explosive charge initiation

– 13 mm for a 30% hydrogen with obstacle test

• spark initiation with 10.9% volume repeated pipe blockage (c.f. 4.4%)

– 8 mm for a 30% hydrogen no-obstacle detonation test

• explosive charge initiation

MAXIMUM PRESSURESInside and near rig (parallel to wall)

MethaneHydrogen_comparison.xls

0

50

100

150

200

250

300

350

400

450

500

0 1 2 3 4 5 6 7 8

Distance from spark parallel to wall (m)

Max

imum

pre

ssur

e (k

Pa)

0% Hydrogen (NatHy_02)25% Hydrogen (NatHy_04)51% Hydrogen (NatHy_03)75% hydrogen (NatHy_05)100% Hydrogen (NatHy_01)

PARALLELTO WALL

MAXIMUM PRESSURESFar field (away from wall)

MethaneHydrogen_comparison.xls

0

20

40

60

80

100

120

140

0 4 8 12 16 20 24 28 32

Distance from spark away from wall (m)

Max

imum

pre

ssur

e (k

Pa)

0% Hydrogen (NatHy_02)25% Hydrogen (NatHy_04)51% Hydrogen (NatHy_03)75% hydrogen (NatHy_05)100% Hydrogen (NatHy_01)

AWAY FROMWALL

CONCLUSIONS

• For 100% hydrogen transition to detonation occurred at the corners of the rig

• Only 0.02 bar difference between 0% & 25% H2 – 0.12 bar ca. 0.14 bar

• 50% hydrogen gives ca. 3.5 times the pressure given by methane– 0.44 bar inside rig

CONCLUSIONS (2)

• Explosion effects from the mixtures correlate reasonably with mass of hydrogen in the mixture.

• Results suggest maximum overpressures generated in large scale trials by methane hydrogen mixtures containing up to 25% (volume) hydrogen may not be much more than those generated by methane alone.