Risk Assessment of Small Scale LNG Terminals

A Design Approach to Risk ReductionLNG vapour dispersion – CFD simulations

Ingrid Lunde, Safety Engineer

Jan Dahlsveen, Sen. Safety Eng.

Safetec Nordic

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Background/relevance

● There is an increasing number of small LNG terminals in close proximity to the public.

• Need efficient ways to reduce the size of necessary safety-zones around terminals.

• Need for tools which can accurately model risks and consequencesof LNG related accidents (3rd party risks).

● The use of Computational Fluid Dynamics (CFD) makes it possible to include the terminal’s geometry into risk- and consequence modelling.

● Can the design of the LNG terminal help reduce the size of safety zones?

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Safety zone

● For fires due to accidental LNG release EN 13645 defines maximum acceptable thermal radiation fluxes for all areas adjacent to concerned boundary.

• 13 kW/m2 for isolated areas

• 5 kW/m2 for intermediate areas

• 1.5 kW/m2 for critical areas

● In investigating potential risks connected to accidental LNG spills, the extension of the Lower Flammability Limit (LFL) of the gas cloudformed may be used as a measure.

● The maximum extension of the flammable cloud is closely connected to the maximum reach of radiation levels given ignition of the cloud.

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LNG vapour dispersion – release geometry

● Instantaneous release (703 kg)

Into bund Wall (2.5 m)

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LNG vapour dispersion – release geometry

● The maximum distance to 50% of LFL - 5 release geometries

0

20

40

60

80

100

120

140

0 20 40 60 80 100

Time (s)

Max.

dis

tan

ce t

o 5

0%

of

LF

L (

m)

Land - duration 5 s

Land - duration 1 s

Bund - duration 5 s

Wall - duration 5 s

Hill - duration 5 sec

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LNG vapour dispersion – release geometry

Into bund On ground

Rough groundWall (2.5m)

Hill side (10 deg.)

Bund and wall

● The release geometry and topography highly influence the LNG vapour dispersion and consequently the 3rd party risk

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Variation of design of Small Scale LNG terminal

LNG tank

Vaporiser

Bunding(1m)

Control room

● Base Case (left)

● Case with collection tub for spilt LNG divided from the rest of the terminal by 1.5 metre high wall

● Case with 3 metre high surrounding grated fence.

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Effects of different terminal design (1)

● Transient release: 1000kg

Terminal base case Terminal with collection tub

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Effects of different terminal design (2)

● Transient release: 1000kg

Terminal base case Terminal with surrounding fence (3m)

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Effects of different terminal design - Summary

Reach of gas cloud

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200 250

time [s]

dis

tan

ce f

rom

cen

tre o

f te

rmin

al

[m]

Basecase LFL

Basecase 50% of LFL

Tub LFL

Tub 50% of LFL

Fence LFL

Fence 50% LFL

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Potential Radiation from flammable gas clouds

Radiation leves from LNG fire on terminal

-140

-120

-100

-80

-60

-40

-20

0

20

40

60

80

100

120

140

-14

0

-12

0

-10

0

-80 -60 -40 -20 0 20 40 60 80 100 120 140

Heat Flux

5 kW/ m2

13 kW/ m2

50 kW/ m2

Flame Drag

Flame

All Distances in metres (m)

Horizontal Plane at 1 metres

Down W ind

6 (m/ s)

Material : Methane

Confined spill

on Land

Radiation leves from LNG fire on terminal

-250

-200

-150

-100

-50

0

50

100

150

200

250

-250 -200 -150 -100 -50 0 50 100 150 200 250

Heat Flux

5 kW/ m2

13 kW/ m2

50 kW/ m2

Flame Drag

Flame

All Distances in metres (m)

Horizontal Plane at 1 metres

Down W ind

6 (m/ s)

Material : Methane

Confined spill

on Land

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Conclusion

● Simple changes applied to Small Scale LNG terminal design can reduce the necessary size of safety zones significantly(in the test cases shown, up to 40% for intermediate areas).

● By doing studies as the ones presented here in the design phase of a project, significant cost benefits to the project can be achieved.● Limiting the size of safety zones could in some cases even make

or break a project.

● In determining efficient site-specific design varations experience and accurate modelling tools are key factors. ● In our experience, the use of CFD modelling is highly beneficial.

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