Madhat Abdel Jawad, GexCon: Using dedicated CFD-tool FLACS for floating LNG liquefaction plants

Optimal design of

FLNG installations:

limiting the potential

consequences of

accidental

explosions Dr. Madhat Abdel-jawad MD GexCon Australia Indonesia and the Middle East

GexCon – 2008 2

GexCon in short

More than 800 man years of

explosion experience

~ 400 fire and explosion

projects per year

Main office in Bergen, Norway

Other offices in Perth(AUS),

Jakarta (Indonesia), others.

Agents in Qatar, UAE,

Malaysia and elsewwhere.

GexCon spun off CMR which started Large

research programs in the 70s, 80s and 90s

within gas explosion and dust explosion safety

GexCon – 2008 3

GexCon’s Core Business

Consequence Explosion Analysis Worst case Analysis

Targeted Analysis

Probabilistic Analysis

Fire and Smoke Analysis FEA and CFD

Toxic Dispersion Analysis

Causes

Examples of Past accident investigations include:

TWA 800 (NTSB)

P36 (Petrobras)

Piper Alpha (Investigation led by Lord Cullen)

Buncefield (Total)

Prevention

Protection

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Acceleration

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I could have left at 5pm

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Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012 6

Explosion generated turbulence

• Positive feedback

mechanism of explosion

generated flow and

combustion

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Experiments – 45 m long array of cross

flow obstructions; no confinement

Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012

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Experiments – obstructed vs. non-

obstructed

Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012

Experiments in congested area – DDT and

detonation

Experiments – DDT and detonation

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Experiments in 3-D corner

P = 0.025 bar

P > 4.0 bar

GexCon – 2008 12

Analysis Process Overview

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Geometry import

FLACS Import + Adjustments

Vapour Cloud Explosion Consequence Modelling

Structural Response

Leak Dispersion

Gas Explosions Hazards on Offshore Facilities, Kuala Lumpur, 19-20 October 2010 12

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FLNG: probabilistic study; step 1

geometry: Anticipated congestion

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FLNG: Heavy gas, spill & aerosols Heavy or non-buoyant gas:

Refrigerant medium

NGL extracted offshore

Flashing releases may generate large

dense clouds

Non-buoyant clouds

Greater probability of drifting into

adjacent modules

Larger cloud sizes and higher ignition

probability

Stronger explosions

Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012

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FLNG: LNG spills Implications for explosion analysis:

FLACS geometry – bunds

Bunding: significant impact on pool/cloud size

Leak locations: relative to edge of vessel, drainage points, drip

trays, leaks relative to larger objects

Wind speed will be important for mixing

Wind: 1m/s

Wind: 5m/s

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FLNG example: summarized

In spite of lower leak frequency, release of

non-buoyant gas is the major contributor to

explosion risk:

For the same release rate, clouds becomes

bigger (stay on the ground and don’t

disappear upward)

For the same cloud size, heavier (non-

buoyant) HC give stronger explosions

Non-buoyant gases stay along the ground

and have higher likelihood of being ignited

Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012

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FLNG: probabilistic study

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Port side vs. Starboard side modules

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FLNG: choice of dispersion

scenarios

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FLNG: generation of large clouds

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FLNG: explosion simulations

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Exceedance curves

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Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012 23

Safety gaps • FLNG layout: module based with safety gaps:

1. Reduce likelihood of clouds spanning several modules

2. Reduce pressure if clouds span several modules

3. Reduce pressure load from one module to the other

Implications for Design Accidental Loads (DAL)

• Explosion where clouds span a gap:

Flame propagation in:

1. Congested areas -> flame acceleration & pressure

2. Open gap -> flame deceleration & reduced pressure

3. Flame re-enters congested area -> flame acceleration & pressure

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Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012 24

Safety gaps

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Safety gaps

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Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012 26

Safety gaps

• Dimensioning gas cloud & implication for gap

distance

• Large cloud -> gap -> large impact on DAL

• Small cloud -> gap -> marginal impact on DAL

• Safety gaps can have large cost implications

• Alternative solutions:

• Blast walls, gas migration barriers or water curtains

Seminar on Management of the Gas Value Chain, Jakarta, Indonesia, November 27-28, 2012

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