Gas Build-up in a Domestic Property Following Releases of Methane/Hydrogen Mixtures

Preparing for the Hydrogen Economy by Using the Existing Natural Gas System as a Catalyst // Project Contract No.: SES6/CT/2004/502661

NATURALHY is an Integrated Project funded by the European Commission’s Sixth Framework Programme (2002-2006) for research, technological development and demonstration (RTD)

Gas Build-up in a Domestic Gas Build-up in a Domestic Property Following Releases Property Following Releases

of Methane/Hydrogen of Methane/Hydrogen MixturesMixtures

Barbara Lowesmith, Geoff Hankinson, Catalina Spataru and Michael Stobbart

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Naturalhy ProjectNaturalhy Project

Aim is to assess the possibility of using the existing natural gas pipeline network for conveying natural gas/hydrogen mixtures Provides ‘greener’ fuel if burned directly H2 can be separated out for use in fuel cells

Provides a means of introducing and developing the Hydrogen economy at an earlier stage

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Naturalhy ProjectNaturalhy Project

Naturalhy Project studying the impact of introducing Hydrogen into Natural Gas pipelines Effect on durability and integrity of pipeline

network Effect on safety of the public Separating the Hydrogen from the mixture Using the mixture in existing appliances Socio-economic aspects

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To assess the change in risk to the public caused by adding hydrogen to the gas network

Objective of Safety WorkObjective of Safety Work

In particular, for Domestic customers – does the risk in the home increase?

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Domestic CustomersDomestic Customers

To answer this question we are: Assessing gas accumulation behaviour by

performing large scale experiments and developing mathematical models

Determining minimum ignition energies and ignition probabilities by laboratory experiments

Assessing explosion severity by models and experiments

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Gas Build Up Experiments Gas Build Up Experiments

‘Room’ - 3m x 3m x 2.3m

Door in front wall

Release in centre of back wall

Vent openings in two opposing walls – upward crossflow ventilation by wind

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Gas Build-up ExperimentsGas Build-up Experiments

Methane, or methane:hydrogen mixtures (80:20 and 50:50)

At 20-30mbar from 5 or 10mm diameter hole close to floor or 1.1m above floor

Measured gas concentration throughout enclosure with time using oxygen cells

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Typical Results – Release at Typical Results – Release at 1.1m above floor1.1m above floor

0

4

8

12

16

20

24

0 1000 2000 3000 4000 5000Time (s)

Ga

s C

on

ce

ntr

ati

on

(%

)

1.6m and above

1.4m

1.3m

1.2m

1.1m and below

Gas OnGas Off

Height (m)

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Typical Results – Layer Typical Results – Layer FormationFormation

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25Gas Concentration (%)

He

igh

t (m

)

250s500s750s1000sS State

Time from onset of gas

Release at 1.1m above floor

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Mathematical Model - Mathematical Model - ObjectivesObjectives

To predict with time the position of the interface and the concentration in the upper layer

To validate against experimental data

To apply model to study effect of different release conditions

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Mathematical ModelMathematical Model

inQ

pQ

outQ

1H

sQ

hs

hlower vent

opening

interface

H

upper buoyant layer

lower layer

upper ventopening

air entrained

into jet

jet

wind

horizontal cross-sectional area, S

Qj

Qin

Qout

Hl

Qs

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Mathematical ModelMathematical Model

Equations describing: Volume of layer formed and

concentration within it Air flow as a combination of wind and

buoyancy induced flow Buoyancy induced flow as a function

density (and hence concentration) of layer

Air entrained into jet of gas released

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Equations: Layer Equations: Layer

Volume of Layer:

)(1sinjoutj QQQQQ

dt

dV

Concentration within Layer:

js cQQdt

dcV 1

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Equations: VentilationEquations: Ventilation

Combination of wind driven and buoyancy induced:

Wind driven:

Buoyancy Induced:

where:

22WBin QQQ

Wvd

W UAC

Q2

122

HgAC

Q vdB

ggair

air

1

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Equations: JetEquations: Jet

Air entrainment proportional to local mean jet velocity

Entrainment constant of 0.05 used

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Validation of Model- Transient Validation of Model- Transient PredictionPrediction

0

5

10

15

20

25

30

35

0 1000 2000 3000 4000

Time (s)

Ga

s C

on

ce

ntr

ati

on

(%

)

Experiment

Numerics

Test 6

Test 8

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Steady State ComparisonSteady State Comparison

1

10

100

1 10 100

Predicted Steady State Concentration (%)

Ex

pe

rim

en

tal

Ste

ad

y S

tate

C

on

ce

ntr

ati

on

(%

)

10mm dia, 50:5010mm dia, 20:8010mm dia, 10:9010mm dia, CH45mm dia, 50:505mm dia, CH4

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Application of Model-Effect of Application of Model-Effect of H2 ContentH2 Content

20

21

22

23

24

25

26

27

28

0 10 20 30 40 50 60 70

Percentage Hydrogen in the Released Gas (%)

Ste

ad

y S

tate

Ga

s C

on

ce

ntr

ati

on

(%

)

1.23

1.25

1.27

1.29

1.31

He

igh

t o

f In

terf

ac

e (

m)

Release Diameter = 10 mmRelease Pressure = 30 mbar

Release Height = 1.1 mVent Height = 20 mm

Wind=4 m/s

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ConclusionsConclusions

Adding H2 to Natural Gas results in increased volume flow when a leak occurs

This leads to increased gas concentration in an accumulation formed

However, the buoyancy forces are greater for the lighter gas resulting in increased ventilation

This mitigates the gas concentrations to some extent

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ConclusionsConclusions

However, the concentrations are higher and the flammability limits are wider

This means that a flammable inventory persists for longer

Hence the risk to the domestic customer may increase

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Further WorkFurther Work

Extend capabilities of model

Quantify the ignitability of accumulations following methane/hydrogen releases

Assess the change in risk to the public in the home environment as a result of introducing a given level of hydrogen to the natural gas

Gas Build-up in a Domestic Property Following Releases of Methane/Hydrogen Mixtures

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