www.gl-nobledenton.com

Safety Aspects of Floating LNG Facilities Mike Johnson, 29th April 2013

1) Background

2) Major accident events

3) FLNG characteristics

4) Control of hazards

5) Summary

Introduction

1) Background

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

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

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

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

2) Major Accident Events

Risks for FLNG Facilities

• Project risk

• Risks to personnel

• Process hazards

• Transportation

• Occupational risk

• Risks to the asset

• Environmental hazards

• Financial risk

• Reputational risk

Hazard Types

• What hazards can you see in this picture?

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

Hazard Types

• What hazards can you see in this picture?

Hazard Types

• What is in place?

• A manually operated valve

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

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

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

FLNG Process Hazards

Loss of containment events

• High pressure gas

• LNG

• Refrigerant

• LPG

Hazards

• Gas dispersion

• Fire

• Explosion

• Cryogenic

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

Experimental Research

Large scale experiments at GL Noble Denton Spadeadam Test Site in UK

Spadeadam Test Facility

• 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

• 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

Jet Fire

Impacting Jet Fire

• 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

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

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

Flame Acceleration

Experimental Arrangement

Ignition

45m

Flame Acceleration

• 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

3) FLNG Characteristics

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)

Size

Oman LNG

3.6 mtpa

Liquefaction

120 x 270 m

Utilities

80 x 250 m

Shell’s proposed

3.5 mtpa FPSO

• 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

• 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

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

4) Control of Hazards

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

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

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)

• 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

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

Flame Acceleration – Congested Region

Flame Acceleration – Congested and Partially Confined

Escalation Example - Buncefield

Buncefield Damage

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

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

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

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

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

What Mass of Gas Caused This?

Thank you for your attention.

Mike Johnson

Principal Consultant, Safety and Risk

GL Noble Denton

01509 282559

mike.johnson@gl-group.com

www.gl-nobledenton.com