1 JRC – IE Pisa on 8.9.2004

CFD modelling of accidental hydrogen release from pipelines.

H. Wilkening - D. Baraldi

Int. Conf. on Hydrogen Safety

Pisa Sept. 8-10, 2005

1. Motivation2. 2-D Simulations for methane and hydrogen3. 3-D Simulation for methane and hydrogen4. Conclusion

2 JRC – IE Pisa on 8.9.2004

Pipeline disaster in Belgium in 2004

Left picture is a view of the industrial area destroyed by the explosion and the subsequent fire. The right picture shows the fire caused by the natural gas released from the pipeline after being ignited by the explosion.

3 JRC – IE Pisa on 8.9.2004

Modelling of light methane dispersion (1/2)

Streamlines of high-pressure release from the pipeline and wind at 10 m/s from left to right.

Molar methane concentrations the same case

4 JRC – IE Pisa on 8.9.2004

Modelling of methane gas dispersion (2/2)

Molar methane concentrations, no wind.

Molar methane concentrations, 10 m/s wind from left to right.

5 JRC – IE Pisa on 8.9.2004

Comparison to hydrogen

Molar hydrogen concentrations, 10 m/s wind from left to right.

Molar hydrogen concentrations, no wind.

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Comparison of thermal energy released between methane and hydrogen

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12

Time [s]

Th

erm

al E

ner

gy

[GJ/

m]

CH4 10 m/s wind

CH4 no wind

H2 10 m/s wind

H2 no wind

The thermal energy released is very similar for methane and hydrogen until the first gas is leaving the computational domain, the wind keeps the gas within the computational domain longer.

7 JRC – IE Pisa on 8.9.2004

Methane molar concentrations for wind (top) and no-wind (bottom) case both 7.5 s after the high-pressure release starts. Shown are only those concentrations within the flammability limit. These are the values between 5.3 % and 15 % all other concentrations are set to 0 %.

Flammability limits in methane gas dispersion

8 JRC – IE Pisa on 8.9.2004

Flammability limits in hydrogen gas dispersion

Hydrogen molar concentrations for wind (top) and no-wind (bottom) case. Shown are only those concentrations within the flammability limit. These are the values between 4 % and 74 % all other concentrations are set to 0 %.

9 JRC – IE Pisa on 8.9.2004

Comparison of thermal energy released within the flammability limits

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12

Time [s]

Rel

ease

d T

her

mal

En

erg

y [G

J/m

]

CH4 flammable 10 m/s wind

CH4 flammable no wind

H2 flammable 10 m/s wind

H2 flammable no wind

The thermal energy of the released flammable gases is very different for methane and hydrogen due to the wider flammability limits of hydrogen (4 – 74% vol. conc.) compare to methane (5.3 – 15%).

10 JRC – IE Pisa on 8.9.2004

Numerical Setup 3-D Simulation

Grid discritisation and domain decomposition for parallel computingTotal grid with 3.5 mio. cells run on 16 CPU’s or 8 CPU’s

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3-D methane release and dispersion simulation

121 kg/s methane release rate corresponds to 6 GW thermal power

4 % molar conc. Isosurface10 m/s wind

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Flammability limits of methane within the release

About 10% to 30% of the released methane within the flammability limits

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3-D hydrogen release and dispersion simulation

4 % molar conc. Isosurface10 m/s wind

42.2 kg/s hydrogen release rate corresponds to 5 GW thermal power

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Flammability limits of hydrogen within the release

About 70% of the released hydrogen within the flammability limits

15 JRC – IE Pisa on 8.9.2004

Comparison of thermal energy released between methane and hydrogen for 3-D

0.E+00

1.E+07

2.E+07

3.E+07

4.E+07

5.E+07

6.E+07

0 1 2 3 4 5 6 7 8 9

Time [s]

En

erg

y [K

J]

H2 total released 10 m/s wind

H2 flammable 10 m/s wind

CH4 total released 10 m/s wind

CH4 flammable 10 m/s wind

The thermal energy of the released gases is similar for methane and hydrogen also in 3-D but again differs quite a lot for the gases within the flammability limits.

16 JRC – IE Pisa on 8.9.2004

Conclusions

1. Accidental releases from a methane and hydrogen pipeline have been modelled and compared for a scenario with and without wind.

2. Although the amount of total released energy is similar for methane and hydrogen, the amount of flammable hydrogen is larger than methane in all cases due to the wider flammability limits of hydrogen.

3. Due to the larger density of methane, methane might be more easily accumulated close to the ground under certain conditions (wind and geometric configuration) than hydrogen.

17 JRC – IE Pisa on 8.9.2004

18 JRC – IE Pisa on 8.9.2004

Governing Equations for Fluid Flow

0 = U)+)

(( t

Mass

B + τ)( + - = UU)+U) pt

((Momentum

Species iiii YYt

+J = )U+) ((

Energy hSt

phh

t

d

d(( + Uτ +q = )U+)

19 JRC – IE Pisa on 8.9.2004

Gas Dispersion in HyJet Jx7

Iso surface of 15% Vol. He colored with turbulent intensity at 200 s

The HyJet experiments will be used to validate a CFD-Code for dispersion modelling. The experiments were performed in the Battelle-Model-Containment. Within the experiments Helium is release through a nozzle in one of the lower so called banana rooms. After the release a Helium stratified atmosphere is developed in the upper part of the containment.In HyJet Jx7 Helium is released through a 9.5 cm nozzle at a speed of 42 m/s for 200 s.

20 JRC – IE Pisa on 8.9.2004

HyJet Jx7 comparison with experiment

Axial profile through jet axis 190 s after the beginning of injection

21 JRC – IE Pisa on 8.9.2004

New High Performance Computing Hardware

The CURIE High Performance Computing Cluster is installed with a total of 50 CPU’s. The System has a performance of 128 GFLOPS (billion floating point operations per second) being by fare the most powerful computing system in the JRC.

The system is used for hydrogen safety studies, for safety studies of new innovative nuclear reactors and for modelling of material failure on very small scale (crystal modelling) and other applications demanding high performance computing power.

22 JRC – IE Pisa on 8.9.2004

HPC load on CURIE last month (2/2)

Performance of the cluster via web interface (individual compute nodes)

23 JRC – IE Pisa on 8.9.2004

HPC load on CURIE last month (1/2)

Performance of the cluster via web interface