safety aspects of floating lng facilities€¦ · safety aspects of floating lng facilities mike...
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www.gl-nobledenton.com
Safety Aspects of Floating LNG Facilities Mike Johnson, 29th April 2013
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1) Background
2) Major accident events
3) FLNG characteristics
4) Control of hazards
5) Summary
Introduction
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1) Background
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GL Noble Denton
LNG & gas processing skills
Hazard & risk assessment
Subsea engineering
Project management
Marine consulting
Subsea engineering
Marine engineering
Naval architecture for FPSOs and
drill ships
+
+
=
6,800 employees
235 offices
80 countries
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GL Noble Denton – LNG Experience
• Involved in LNG since the first LNG import terminal at Canvey Island, UK
in 1964
• GL Noble Denton has worked on
• 34 LNG liquefaction projects worldwide including 6 with offshore
elements
• 38 LNG regasification projects worldwide including 7 offshore
• 10 peakshaving and satellite plants
• We have worked for over 30 clients across more than 20 countries
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Example - Pre-FEED FLNG Project
• Confidential client, offshore Australia
• Awarded to GL Noble Denton in June 2010
• 35,000 manhour study over 9 months
• 2 million tonnes/year of LNG production
• Hull dimensions 400 metres long, 60 metres wide
• Internal turret
• Side by side loading of LNG and LPG
• Tandem loading of condensate
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GL Noble Denton – LNG Experience
Offshore LNG project LNG Liquefaction project LNG Regasification project
Ichthys NWS
QCLNG
PNG
Confidential
W Africa
Scarboro
Confidential
Australia
Excelerate
SBS transfer
Adriatic LNG
Cyprus LNG
Confidential
Greece
OLT
Confidential
Mexico
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2) Major Accident Events
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Risks for FLNG Facilities
• Project risk
• Risks to personnel
• Process hazards
• Transportation
• Occupational risk
• Risks to the asset
• Environmental hazards
• Financial risk
• Reputational risk
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Hazard Types
• What hazards can you see in this picture?
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Hazard Types
Onshore gas terminal
experiencing sand production
into the slugcatcher
Operator installed temporary
hydrocyclone on boot of
slugcatcher
Remotely operated Emergency
Shutdown Valves (ESDVs)
required
Slugcatcher
ESDVs
Hydrocyclone
Sand Removal ESDVs are closed
automatically if leak occurs
Gas
Liquid
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Hazard Types
• What hazards can you see in this picture?
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Hazard Types
• What is in place?
• A manually operated valve
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Hazard Types
• Experienced spurious closures of
ESDV in operation
• Spare not available, manual valve
fitted as replacement
• Valve would be inaccessible if a
leak occurred on the temporary
pipework
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Hazard Types
• Why was this
important?
• Temporary pipework
adjacent to high
pressure large
inventory slugcatcher
• Failure to isolate could
result in a fire
escalating to failure of
the slugcatcher
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Hazard Types
There are different types of hazards
Occupational health & safety
• Understood and often apparent
• Relatively frequent events usually with limited consequences
Major accident hazards
• Low frequency but high consequence
• Risks are not obvious
Controlling occupational hazards does not control major hazards
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FLNG Process Hazards
Loss of containment events
• High pressure gas
• LNG
• Refrigerant
• LPG
Hazards
• Gas dispersion
• Fire
• Explosion
• Cryogenic
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LNG Spills
Liquid LNG leak Pool Fire
Jet Fire
Vapour leak
Vaporisation
Spill on Water RPT
Explosion
Dispersion into
Confined/Congested Area
Escalation
(e.g. BLEVE)
Dispersion Flash Fire
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Experimental Research
Large scale experiments at GL Noble Denton Spadeadam Test Site in UK
Spadeadam Test Facility
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• Low temperature LNG vapour is initially denser than air and spreads along the ground
• As it warms, it becomes lighter than air and rises
• The white cloud/plume is water vapour condensing out of the air
• If the release is at high pressure, a jet of vapour may result
• The may be liquid droplets of LNG within the jet which can “rain out” onto the ground
Gas Dispersion
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• Jet Fire
• Ignition of a high pressure release
• Highly directional
• High thermal flux
• Pool Fire
• Liquid spill onto ground will start to vaporise
• Ignition of the vapours gives a fire across the surface of the pool
Fires
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Jet Fire
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Impacting Jet Fire
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• The heat of the fire encourages further vaporisation
• Diameter of pool depends on:
• Bunding and topography
• Release rate
• Mass burning rate
• Time of ignition
• Large pool fires create dense black smoke as insufficient oxygen gets to the centre of the flame
Pool Fire
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Ignition of vapour cloud over open ground gives a flash fire - no blast
In certain conditions an explosion will occur:
• Cloud confined – expansion from combustion cannot escape so pressure rises
• Cloud engulfs a congested area of pipes and vessels – cause the flame front to accelerate
Delayed Ignition of Vapour Clouds
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Flame Acceleration
• A characteristic of vapour
cloud explosions is that the
release usually occurred in
congested process areas
• Research examined the
effect of pipework in the gas
cloud
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Flame Acceleration
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Experimental Arrangement
Ignition
45m
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Flame Acceleration
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• Natural gas is the most benign of common hydrocarbons
• LNG vapour is mostly methane, so similar to lean natural gas
• Liquefaction usually introduces more reactive fuels such as propane, ethane and ethylene
• Explosion severity increases
• We will return to this topic
Delayed Ignition of Vapour Clouds
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3) FLNG Characteristics
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Size
Q-max LNG Ship (354 m x 54 m)
138,000 m3 LNG carrier (278 x 42 m)
300,000 dwt VLCC (470 m x 60 m)
Shell Prelude FPSO
475 m x 75 m
13000 TEU Container Ship (380 m x 54 m)
Oriana Cruise Liner (260 m x 32 m)
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Size
Oman LNG
3.6 mtpa
Liquefaction
120 x 270 m
Utilities
80 x 250 m
Shell’s proposed
3.5 mtpa FPSO
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• Very complex, congested plant
• Similar to Snohvit
• Built in Spain
• Transported to Arctic Norway by
Barge
Complexity
Oman LNG Snohvit
Liquefaction plot
270 x 120 m
Liquefaction plot
154 x 54 m
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• The crowded nature of the facility can increase the severity of any loss of containment incident
• This is combined with the presence of more reactive higher hydrocarbons in the refrigerant or in LPG extraction
• Potential for escalation must be minimised
Implications for Process Hazards
0.0%
50.0%
100.0%
150.0%
200.0%
250.0%
300.0%
350.0%
400.0%
450.0%
Dual N2 SMR DMR
No
rmal
ised
Ave
rag
e R
isk
Low Escalation Risk
High Escalation Risk
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FLNG and Major Accident Hazards
FLNG is:
• A complex LNG production area squeezed into a smaller footprint
• …..placed on top of the storage tanks
• …..with personnel working and living very close
• …..in the middle of the sea
The only advantage is that there is no off-site public hazard
Control of major hazards is of key importance
• Prevention of escalation from initial incident is critical
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4) Control of Hazards
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Control of Major Hazards in Design
Philosophy
• Inherently safer
• No matter what, the option is safer than other approaches
• Prevention
• Measures that prevent a hazard being realised
• Control
• Measures that control a major hazard event
• Mitigation
• Measures that reduce the consequences
Examples
• Inherently safer • N2 compared to SMR liquefaction • Layout
• Prevention
• Design and material selection
• Control
• ESD and blowdown • Spill containment
• Mitigation
• Preventing escalation (e.g. passive fire protection), protecting people
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Safety Concept – Option Development and Selection
• Inherently safe design is the preferred approach
• If all other things are equal, then the decision is simple
• In reality:
• More often than not ‘other things’ are not equal
• It may also not be clear which option is lowest risk
• We are now balancing risks and benefits
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Example of Risk vs Benefit
• Average risk to personnel
affected by:
• Liquefaction cycle choice
• Whether to extract LPG
or not
• These decisions can have
significant operational and
commercial implications
• Quantified analysis
supports the decision
making process
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
120.0%
140.0%
160.0%
180.0%
Dual N2 SMR DMR
No
rmal
ised
Ave
rag
e R
isk
LPG Extraction
Other Units
Results from Quantitative Risk Assessment (QRA)
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• A flame will accelerate as it burns through a vapour cloud engulfing a process region
• As the flame speed increases it generates increasing pressure
Explosions in Congested Process Areas
congested region length > critical runlength
Distance
Overp
ressure
at
flam
e f
ront
threshold
value
congested region
critical
runlength
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Mitigation through Design
• Minimising congestion and spacing out process regions reduces the explosion hazard
congested region length < critical runlength
Distance
Overp
ressure
at
flam
e f
ront
threshold
value
congested region
Distance
Overp
ressure
at
flam
e f
ront
threshold
value
congested
region
congested
region
• This is difficult and expensive on floating facilities
• If we get it wrong, very high flame speeds can be produced as the flame passes from one region to another
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Flame Acceleration – Congested Region
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Flame Acceleration – Congested and Partially Confined
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Escalation Example - Buncefield
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Buncefield Damage
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Layout
Internal Turret
Hg / Acid Gas
removal
Dehydration
Condensate Stab & LPG
fractionation
Liquefaction
Exchanger
Refrigeration 1
Accommodation and
helipad
Acid Gas Regen
Boil Off Gas /
Fuel Gas
Feed Gas
Compression Primary
Separation
Refrigeration 2
Flare
LNG Offloading
Condensate
Offloading
Utilities
• Most hazardous at stern (LPG)
• Least hazardous at bow (Utilities)
• Only exception is turret which for marine
reasons needs to be towards the front
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Cryogenic Spill Management
1) Send overboard immediately
• Cryogenic effects on vessel hull
• Location of spill discharge –
deck level or sea level
• RPT
2) Contain and controlled disposal
• Volume of spill to be contained
• Effects of wave motion
• Cryogenic effects on local steel
• Need to control vaporisation
(foam)
• Large fire if bunded area ignites
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Escalation Prevention
• Need to avoid escalation from collapse of structures or equipment
spreading fires or damaging the storage tanks
• Measures
• Safety gaps – best but limited
• Reduced inventory of hydrocarbons, especially LPG
• Passive fire protection – much more needed than a typical onshore site
• Increased structural integrity – more steel (and weight)
• Deluge and water curtains – effective but
• an active system and
• interaction with cryogens
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Escape and Evacuation
• Each module has stairways forward and
aft
• Escape routes run along both sides of the
main deck
• Enclosed or open?
• Difficulties in evacuation for remote
locations
• Prime means of escape is by helicopter
• Lifeboats are available forward of the
accommodation block and at the aft
refuge
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Summary
• There are significant major accident hazards associated with LNG operations
• Fires
• Explosions
• Cryogenic liquid hazards
• Move to smaller footprint facilities makes potential interactions and escalation a key concern
• Preference is for inherently safer options
• The decision is generally not clear cut
• Weigh risks against benefits
• Risks can be mitigated by
• Understanding the hazards and their potential consequences
• Developing appropriate control measures
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What Mass of Gas Caused This?
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Thank you for your attention.
Mike Johnson
Principal Consultant, Safety and Risk
GL Noble Denton
01509 282559
www.gl-nobledenton.com