1

Workshop

Putting Science into Standards: Power-to-Hydrogen and HCNG

Session 3: use of HCNG for re-powering, mobility, heat

Standardization: Benno Weinberger R&D Manager Unit Safe and Clean

Energy and Processes

2

Safe use of hydrogen

Hydrogen is used in large quantity by the petrochemical industry with a good safety record up to now.

But challenges need to be addressed :

• Integration of H2 applications P2G in existing infrastructure

• Various concepts in decentralized infrastructures

• Irregular frequencies of use related to intermittent energy carrier

• Contact of untrained people to these hydrogen services

Public acceptance of new H2 applications : only possible if all risks are identified and correctly assessed

3

Basic properties of Hydrogen

Hydrogen properties are quite different from hydrocarbons and have to be addressed in standardization

Hydrogen-air Methane-air

Explosion limits 4% à 75 % 5 à 15 %

Mini. ignition energy 20 µJ 200 µJ

Burn rate 3,3 m/s 0,5 m/s

Quenching limit (tube

burner)

3,9 µg/s 40 µg/s

“Density” ~14 times less dense

than air

~2 times less dense

than air (CH4)

Heat conductivity 0,186 W(m*K) 0,0341 W(m*K)

4

Risk: Fire

• Hydrogen fires: The hydrogen flame is nearly invisible at daytime

• …while it is clearly visible at night

Fuel Leak Simulation Dr. Michael R. Swain University of Miami Coral Cables, FL 33124

Elmore et al., « Hydrogen emergency response training for first responders », International Conference on Hydrogen Safety, San Sebastian (Spain), 2009

5

Risk: Ignition energy

• Ignition energy as a function of gas concentration:

The low ignition energy of hydrogen over a large range of concentration makes its inflammation very likely in the case of a leak in confined space

6

Risk: Embrittlement

Hydrogen is non-corrosive but can weaken materials by its entrance into metals and alloys ("H2 embrittlement"). This embrittlement depends on many factors: temperature, pressure, purity, concentration, exposure time, mechanical properties, microstructure, surface ...

•

Particular attention should be paid to the selection of materials

e.g. Hydrogen blistering e.g. Hydrogen “attack”

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What has to be done in H2 standardization? (1)

• A critical issue is the probable leak size for H2 installations

• The leak size permits to determine • the ATEX zone according to European regulation

• the necessary dimension of ventilation

• This issue is addressed in: • Standard EN 60079-10-1 Explosive atmospheres gives an example of a leak

surface of 1 mm2

• EIGA IGC Document 134/05/E makes reference to a leak diameter for hydrogen of 0,1 mm.

An international standard concerning the probable leak size for hydrogen applications would be the first step to harmonize safety distances and ventilation

8

What has to be done in H2 standardization? (2)

• Vented deflagrations in containers and in enclosures for hydrogen energy applications is an important issue to prevent unacceptable consequences in terms of disruption of confinements, missiles, pressure waves

• Vent sizing for hydrogen is addressed in the standard EN 14994 Gas explosion venting protective systems but related to the reactivity of Hydrogen not applicable

Further pre-normative research is necessary to standardize explosion venting protective systems for hydrogen

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Risks related to accidental HCNG releases

• Looking to the transport of HCNG two scenarios are predictable:

- The transport of HCNG by the existing natural gas pipes

- The development of an adapted gas distribution system

In both cases the accidental situation with gas release will be different from natural gas

• Modeling of accident scenarios involves determining the basic data of natural gas / hydrogen mixtures like:

Flame length

Flame temperature

Thermal radiation of the flame

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Example of pre-normative research: Flame length of HCNG

=> The flame length mainly depends on the pressure and the diameter of the orifice and marginally on the composition of the gas.

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30 35 40 45

Pression de rejet (bar)

Lo

ng

ue

ur

de

fla

mm

e (

m)

100% H2

80% H2

50% H2

20% H2

100% CH4

Flame length as a function of discharge pressure for 10mm orifice*

*Results of the project HYDROMEL supported by French Research National Agency

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=> The temperature of the flame increases with the hydrogen content, but remains modest in the field of HCNG (20% H2)

Example of pre-normative research: Flame temperature of HCNG

1200

1250

1300

1350

1400

1450

1500

1550

1600

0 20 40 60 80 100 120

Concentration en H2 (% v/v)

Te

mp

éra

ture

ma

xim

ale

(°C

)

4 mm

7 mm

10 mm

Maximum flame temperature as a function of the hydrogen concentration for three leak diameters*

Result: Highest temperatures are

obtained for pure hydrogen

Smaller flow rates correspond to the highest temperatures

*Results of the project HYDROMEL supported by French Research National Agency

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Example of pre-normative research: Radiation of CHNG

The influence of the gas composition to the thermal flux radiated by the flame is very modest while the influence of the diameter of the orifice appears to be real.

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

0 10 20 30 40 50 60 70 80 90 100

Concentration H2 (%v/v)

Flu

x r

ay

on

né

(W

/m2

)

4 mm

7 mm

10 mm

Trend: the radiated flux increases with the flame length (and thus the leak diameter)

Average values of the heat flux radiated by the flame depending on the composition of the mixture and the size of the flame*

*Results of the project HYDROMEL supported by French Research National Agency

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What has to be done for HCNG standardization?

End user installations have to be certified for HCNG e.g. regarding the compatibility to flame stability and hydrogen embrittlement

Gas detection devices have to be standardized for HCNG

All kinds of mitigating safety measures (TPRD, Explosion Protection Systems, etc.) have to be certified for HCNG

Re-assessment of the ATEX Zoning should be standardized for HCNG

The probable leak size for HCNG installations has to be standardized

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Conclusions

The specific properties of Hydrogen are well known in petrochemical industry but not to end-users of HCNG

Current standardization related to hydrogen work mainly focused on transport applications, not on P2G addressing similar but not the same problems

To ensure the safety of P2G and the management of risks, new standards are necessary taking in account its irregular use related to intermittent energy carrier

Acceptance by the general public is key for success, this is only possible if all risks are identified and correctly assessed

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Perspectives

All relevant basic safety data of natural gas / hydrogen should be determined - e.g. mitigating safety measures design like explosion venting - and formalized to a safety standard

In addition there is a need of a generic risk analysis of the different HCNG systems

Results should be condensed into a new standard for such systems

This could serve as reference to the logic of the “New approach” legislation