University of Technology

Gothenburg

SHIPPING AND MARINE TECHNOLOGY

MARTIME ENVIRONMENT AND ENERGY SYSTEMS

Cecilia Gabrielii Lecturer, PhD

Agenda

LNG - what is it?

Why LNG as a marine fuel?

Production, storage, transport

Properties, characteristics and behavior

Hazards

What is LNG?

Natural gas that is converted to liquid for ease of storage/transport

LNG takes up about 1/600th of the volume of natural gas.

Natural gas becomes a liquid (LNG) at approximately -162°C

Transported and stored at around -162°

LNG’s extremely low temperature makes it a cryogenic liquid.

LNG constitutes mostly of methane

LNG – produced for transportation purposes

Gas market is often far from the natural gas source

LNG offers greater flexibility than pipeline gas

There are challenges with storing / transporting LNG…

Outside of storage tanks

LNG quickly warms back into natural gas

Volume expansion 600

Inside storage tanks

LNG eventually warms back into natural gas

so called Boil Off Gas – BOG

Volume expansion 600

Tank pressure increases

20°C

-162°C

LNG as a marine fuel

A way to reduce air pollution

Emissions from ships running on fuel oil

SOx - sulphur oxides

NOx - nitrogen oxides

PM - particles

CO2 - carbon dioxide

Negativ impact on the environment and/or health

SOx

PM CO2

NOx

SOx (sulphur oxides) emissions

Regulations on SOx emissions from ships

SECA

GLOBAL

Sulphur emissions control areas (SECAS)

2015: max 0.1% sulphur content in the fuel

Different ways to comply with SECA 2015

Continue running on high-sulphur fuel oil and install exhaust

gas cleaning equipment - scrubbers

Run on low-sulphur fuel oil with 0,1% sulphur

New types of fuel, LNG or Methanol (no sulphur)

What about the other emissions?

CO2: Demand for reduction of Green House Gases

EEDI (energy efficiency design index) for new ships

PM: Expecting new regulations

NOX:

SOx

PM CO2

NOx

Regulations on NOx emissions from new ships

2011: 20% reduction - global

2016: 80% reduction – only in ECA

Emission controlled areas (today)

Expected future ECA for NOx

Governing factors for selecting “future” marine fuels

Max 0.1% sulphur fuel in SECA - from 2015

Max 0.5% sulphur fuel globally - from 2020/2025

80% reduction in NOx emissions (from 1 Jan 2016, new ships, ECA)

Demand for reduction of Green House Gases – lowest possible EEDI

Expecting new special limits for PM

Emissions from LNG fuelled ships - compared to MDO

SOx – practically zero

NOx – 80-90 % reduction

PM – negligible

CO2 – 25-30% reduction

Net reduction of Green House Gases: 15-20%

Green house gases (GHG)

Methane is a 25 times stronger green house gas than CO2

Due to a small amount of unburned methane in the engine the net

reduction of GHG emissions is ”only” 15-20%

From gas field to users

Exploration/production

Natural gas reservoirs

Conventional gas - porous reservoir with sufficient permeability to allow

gas to flow to producing well

Unconventional gas - Deposits in relatively impermeable rock formations

artificial pathways have to be created

What is natural gas?

Crude oil and natural gas constitute of hydrocarbons

Gas from different sources have different chemical composition

Methane is by far the major component, over 80%

Typical natural gas composition

And impurities such as hydrogen sulphide, water and mercury

From the natural gas production/exploration plant

Natural gas is transported in pipelines to the processing and liquefaction plant

Composition before

Composition after

Processing and liquefaction plant

Processing and liquefaction plant

-162°C

Processing before liquefaction

Removing of impurities

hydrogen sulphide (H2S) and mercury

Removing components which would freeze at the liquefaction

water vapour and carbon dioxide

Removing heavier hydrocarbons

raw materials to industry or used as fuel at the plant

Liquefaction

The gas is cooled down in stages until it is liquefied, at -162°C

Nitrogen removal

Nitrogen decreases the energy content in LNG

Nitrogen

Typical LNG composition

Others:

Ethane < 4%

Propane < 1%

Butane < 0.5%

Nitrogen < 0.5%

LNG can now be transported wherever needed

Transport of LNG

By truck

very short distances

specialised, double-skinned tank trucks

By ships

long distances in a special purpose LNG carrier

good insulation and a double hull design

LNG Carriers – 50 years ago

Methane Princess - the first ship built purposely for transport of LNG

Capacity of 27 000 m3

LNG Carriers - today

350 carriers - average capacity of 150 000 m3

Specifically designed to contain LNG at or near atmospheric pressure

at a cryogenic temperature of approximately -162°C

How to keep LNG in its liquid form?

Tank insulation

will not keep the LNG cold enough to remain as a liquid by itself

Auto-refrigeration

LNG stays at near constant temperature if kept at constant pressure.

Achieved if the LNG vapour boil off (BOG) leaves the storage tank

20°C

-162°C

How to handle the boil-off?

Use it as fuel in the propulsion machinery

Steam turbine propulsion

Dual fuel engines

Re-liquefy and send back to the LNG tanks

Disposal of boil-off gas to atmosphere

Only in an emergency situation

LNG Carriers – two different tank systems

Spherical

Membrane

Spherical - self-supporting - tank

Tank shell: 30 mm aluminium or 9% nickel steel

Insulation: 220 mm of e.g. polystyrene foam

Spherical; high degree of safety against fracture or failure

Membrane tanks

not self-supporting - the inner hull forms the load bearing structure

very thin primary barrier - 0.7 to 1.5 mm stainless steel or nickel alloy

utilize the hull shape more efficiently – larger cargo capacity

must always be provided with a secondary barrier

Secondary barrier

temporary containment of a leakage of LNG through the primary barrier, and

prevent a too low temperature of the ships structure

Which type is ”the best”?

Spherical

Simple construction

Independent from the ship's hull

Can be partially pressurised

Membrane

Larger cargo capacity

Less tank weight

Lower windage area

LNG has arrived at the import terminal!

Onshore terminal or floating (FSRU)

Feeder vessel to intermediate terminal

Feeder vessel

Regional distribution of LNG

Typical cargo capacity: 7000 - 20000 m3

At the receiving terminal (import / intermediate)

LNG is either

re-gasified into natural gas

delivered to the gas grid

or LNG is

delivered to a truck or bunker vessel

which deliver it to a LNG fuelled vessel

LNG is re-gasified just before entering the engine

”Components” at the terminal

Unloading arms

Cryogenic pipelines

Storage tanks

Boil-Off Gas (BOG) compressors and re-condensers

Pumps

Vaporisers (re-gasifiers)

Onshore terminal storage tanks

Flat bottomed tanks (FBT) - stores LNG under atmospheric pressure

Semi-pressurised tanks - stores LNG under pressure (approx. 10 bar)

withstand cryogenic temperatures

maintain the liquid at low temperature

minimize the amount of evaporation (BOG)

Example of LNG bunkering terminal

From the atmospheric FBT :

High pressure pump

Regasification

To the natural gas grid

From the semi-pressurised tanks:

To truck or bunker vessel

Storage tanks – how to prevent leakage of LNG?

LNG tanks have more than one means of containment.

Primary

the tank which holds the LNG, with insulation

Secondary

dikes, impoundment dams around storage tanks, or:

second tank around the primary storage tank

Atmospheric pressure tanks (FBT tanks)

Large tanks (>10 000 m3)

Built on site on flat-base concrete foundations

A system for BOG is needed

Different ”types”

Double containment

Full containment

Double containment tank

In case of failure/leakage:

LNG is contained by a concrete bund wall

But…uncontrolled release of LNG vapour to the ambient

Full containment tank

In case of a failure / leakage

The outer tank - concrete wall - is capable of containing both LNG

and LNG vapour (controlled venting of the vapour)

Handling of the Boil-off Gas (BOG)

0.05 - 0.1% of the total tank content per day

This gas is captured and

sent to the pipeline (gas grid), or

re-injected into the LNG carrier during the unloading of the ship, or

re-condensed and sent back to the storage tank, or

sent to the flare - only in abnormal or accidental situations

-162°C

Handling of the Boil-off Gas (BOG)

BOG

Regasification

LNG is warmed back to natural gas and delivered by pipeline to consumer.

The atmospheric storage tanks are equipped with submerged

pumps that transfer the LNG towards high-pressure pumps.

Regasification

The pressurised LNG is then turned back into a gaseous state

in vaporizers (warmed by seawater).

Regasification

Example of LNG bunkering terminal

From the semi-pressurised tanks:

To truck or bunker/vessel

Pressurised tanks

Small scale tanks - typically 1000 m3

Cylindrical tanks designed to resist pressures of up to approx. 10 bar.

The BOG can “remain” in the tank

Simple tank arrangement

Two ”types”

Double integry

Full integry

Double integry pressure tank

In case of a failure/leakage

a pool / collection basin directing any spillages away in a safe location.

Full integrity pressure tank

In case of a failure/leakage

Both the inner and the outer containment are constructed from

cryogenic steel being able to hold the LNG.

Example of LNG bunkering terminal

From the semi-pressurised tanks:

To truck or bunker/vessel

Bunker vessel

Smaller and more manoeuvrable compared to an LNG feeder vessel

Typical cargo capacity: 500- 6000 m3

Bunker vessel bunkering LNG-fuelled ship

Floating LNG Terminal (FSRU)

FSRU - Floating Storage and Regasification Unit

170 000m3 membrane tanks

FRSU

Bunker vessel loading at FSRU

Chemical and physical properties

fundamental for understanding and predicting LNG behaviour

distinguish between the properties as a liquid and as a gas/vapour

the properties which make LNG a good source of energy can also

make it hazardous if not adequately contained

properties, characteristics and behaviour of LNG differ significantly

from conventional marine fuels

Chemical and physical properties

Chemical composition

Boiling point - cryogenic

Density – volume expansion

Flammability

Others

LNG´s principal hazards result from its

Cryogenic temperature

Flammability characteristics

Vapor dispersion characteristics

If an LNG release occurs, there is an immediate potential for a

range of different outcomes and types of consequences.

”Typical” chemical composition of LNG

others:

Ethane 4%

Propane <1%

Butane < 0.5%

Nitrogen < 0.5%

Hydrocarbons in LNG

Name of the hydrocarbon

Number of carbons

Boiling point atm. pressure

Methane

1

-162°C

Ethane

2

-89°C

Propane

3

-42°C

Butane

4

0°C

Nitrogen: -196°C

Boiling point at atmospheric pressure

Outside of storage tanks LNG quickly warms back into natural gas

water 100°C

LNG -162°C

GAS

LIQUID

Higher pressure – higher boiling point

Temperature [°C)]

LNG is always stored at its boiling point!

Density

A liquid has a higher density than a gas/vapour!

Liquid

Gas

Volumetric expansion

1 m3 LNG corresponds to around 600 m3 natural gas

The reason why natural gas is stored and transported as LNG

A small leakage of LNG results in a large (flammable) gas cloud

Density – LNG (liquid)

Lower density than water, i.e. LNG floats on water

But becomes a vapour pretty soon…

Water: 1000 kg/m3

LNG: 450 kg/m3

Density – LNG vapour (natural gas)

At temperature below -110°C: LNG vapour is heavier than air

LNG vapour blankets the ground, the cloud travels with the wind

At temperature above -110°C: LNG vapour is lighter than air

LNG vapour will rise when sufficiently warmed by ambient air

How to recognize LNG (natural gas)?

colourless and odourless

The white clouds that form at a leakage of LNG is not LNG/natural gas

Cold LNG vapours will make the moisture in the air condense

causing the formation of a white cloud (fog)

This is not a leakage of LNG…

The cold LNG pipe will make the air moisture to condense

What about flammability?

Yes, natural gas burns - this is why it can serve as a fuel!

LNG (liquid form) does NOT burn

But, LNG begins vaporising immediately upon its release…

Flammability properties

Flashpoint

Flammability range

Auto ignition temperature

Minimum ignition energy

The fire triangle

Fuel (flammable vapor)

Air (oxygen)

Heat - source of ignition

e.g. spark, open flame, high temperature surface

Flash point – flammable vapour

The lowest temperature at which a liquid gives off sufficient vapour to

form a flammable mixture with air above the liquid surface.

Ships using fuels with flashpoint < 60°C must comply with a new

international regulation - IGF Code

LNG MDO & HFO

Flash point -187°C >60°C

20°C -43°C >60°C

Flashpoint

LNG: -187°C

Flammability range - mixture with air

LNG MDO, HFO and gasoline

Flammability range Vol% in air

5-15% 1-7%

LNG flammability range: 5-15%

Above UFL (above 15%): not flammable

In a closed storage tank, the percentage of methan is almost 100%

Below LFL (below 5%): not flammable

A small leakage of LNG from a tank in a well-ventilated area is likely

to rapidly mix and quickly dissipate to lower than 5% in air.

The fire hazards differs from other fuels due to its vaporisation and dispersion behaviour.

A leakage of LNG evaporates to an elongated gas cloud that spreads

by the wind until it warms and becomes buoyant and rises

A small leakage of LNG will disappear rather quickly

The visible fog is a reasonable indication of the boundaries of the

flammable mixture.

Engine room fire – oil fuelled ships

80% of all fires in the engine room start with fuel coming in contact

with hot surface as a result of pipe failure

LNG fuelled ships: the risk for engine room fire is SMALLER, why??

Auto ignition temperature – ignition without flame/spark

The lowest temperature at which the gas will be ignited by a hot surface

LNG has a higher auto-ignition temperature than conventional marine fuels.

not easily ignited by hot surfaces

And, smaller risks for fuel leakage from pipes

Double pipes

LNG HFO, MDO

Auto ignition temperature 540°C 250-400°C

Minimum ignition energy - ignition by a flame or spark

The minimum ignition energy for LNG is 100 times lower than for HFO

LNG releases are not easily ignited by hot surfaces but low energy

sparks represents a higher risk

Electrical spark, static electricity

LNG HFO/MDO

Minimum ignition energy in air 0.27 mJ 20 mJ

Flammability properites - summary

LNG MDO/HFO

Flammability range (in air) 5 - 15% 1 - 7.5%

Flashpoint -187°C >60°C

Auto ignition temperature 537°C 250 - 450°C

Minimum ignition energy in air 0.27 mJ 20 mJ

( )

( )

LNG´s principal hazards result from its

Cryogenic temperature

Flammability characteristics

Vapor dispersion characteristics

If an LNG release occurs, there is an immediate potential for a

range of different outcomes and types of consequences.

LNG spills – consequences depends on:

Leakage on ground or sea

Atmospheric or pressurised tanks (pipe)

Ignition source or not

Confined or unconfined

Small or large leakage

LNG spills – on ground or sea

LNG vaporises five times more quickly on water than on land

LNG spill

Sea

Quick evaporation

Ground

Slower evaporation

Quick evaporation- Rapid Phase Transition

A spill of a large quantity of LNG in a “hot” fluid like the sea

Sudden phase change from liquid to gas

Can result in a damaging physical explosion (pressure pulses)

Like the small explosions when heating cooking oil with small amounts of water inside

LNG vaporises instantaneously from pressurised tanks

LNG spill - from atmospheric or pressure tanks

LNG spill

From atmospheric tank

Evaporation rate depends on water /

ground

From pressurised tank

Instantaneous evaporation and

larger vapour release

LNG spill

Flammable LNG vapour

Ignition source:

Fire

No igntion source:

Evaporates and rises until the pool is gone

LNG spill - ignition source or not

Different types of fire after ignition

Flash fire (vapour cloud fire)

Pool fire

The type of fire depends on

Early or delayed ignition

Atmospheric or pressurised leakage

Jet fire

BLEVE (”fire ball”)

Pool fire - early ignition of atmospheric LNG spill

A leakage forming a liquid pool on water surface or on ground

Some of the liquid will evaporate quickly

if flammable vapour finds an ignition source there will be a pool fire

High radiant heat

The fire burns until the fuel is consumed

Flash fire - delayed ignition of the vapour cloud

No ignition source at the place of LNG release

Before the vapours reach -110°C they disperse along the ground

Vapour clouds may ignite at the edge if they meet an ignition source

the smallest spark capable of igniting is not visible in daylight

Pool fire after vapour cloud fire (flash fire)

The ignited dispersed cloud may “burn backward” to the release point

Ignites the vapour above the pool and generate a pool fire

Summary - Pool fire and vapour cloud fire (flash fire)

Some words about fire fighting

Remove the fuel source (i.e. stopping the leak)

Do not extuingish with water

may cause the fire to flare up and intensify

The fires are very hot

Water can be used to

cool surfaces around the fire

divert the vapours away from possible ignition sources

Ignition – atmospheric or pressurised

LNG spill

Flammable LNG vapour

Flash Fire

(Vapour cloud fire)

Pool fire

Pool fire Jet Fire

“Fire Ball”

Early ignition Delayed ignition High pressure

leakage

Jet fire - direct ignition, pressurised leakage

burning jets as the results of gas or liquid release from pressurised

systems (pipes, hoses, tanks) that are directly ignited

High velocity and very hot

Local effect

For LNG stored at low pressures as a liquid this type of fire is unlikely.

could occur during unloading or transfer operations when

pressures are increased by pumping

LNG trapped in piping (bunker lines)

LNG is not, unlike HFO och MDO, a static liquid, which can ”be stored”

(remain) in pipes and flanges

LNG trapped in the piping :

heat ingress will cause a pressure build-up (volume expansion 600)

can cause a pipe burst

Example 70 bar pressure after one hour

Ignition – atmospheric or pressurised

LNG spill

Flammable LNG vapour

Flash Fire

(Vapour cloud fire)

Pool fire

Pool fire Jet Fire

“Fire Ball”

Early ignition Delayed ignition High pressure

leakage

BLEVE (”Fire Ball”) - fire outside pressurized tank

BLEVE: Boiling Liquid Expanding Vapour Explosions

A fire close by heats the pressurized tank

LNG will evaporate and raise pressure on the inside.

In the event of a tank rupture:

the boiling liquid simultaneously expands and ignites

LNG spills – consequences depends on:

Leakage on ground or in water

Atmospheric or pressurised tanks (pipe)

Ignition source or not

Confined or unconfined

LNG vapours are NOT explosive in open air

the radiant heat of LNG fires is considered the primary hazard

Confined or unconfined LNG spill

Flammable LNG vapour

Fire

Explosion - Flash fire or pool fire

- continue to as a pool fire until the pool is gone.

Evaporates and rise until the pool is gone

Ignition

Confined Unconfined

No ignition

Environmental consequenses of a spill

Methane is a 25 times stronger green house gas than CO2

Venting LNG (natural gas) to the atmosphere shall always be avoided!

Spill LNG MDO/HFO

Ocean Negligible

Significant impact

Atmosphere Significant impact as greenhouse gas

Volatile organic compound

LNG (spill) - Cryogenic hazards

Material- brittle fracture

Human – cold burns

Cryogenic brittle fracture

If LNG spilled on unprotected carbon steel

Cryogenic burns

LNG in contact with skin will cause “cold burns”

Treating a cold burn on the skin:

Warm with the hand or wollen material.

Place in warm water, at about +42°C for 15-60 minutes.

Or, wrap in blankets and let circulation reestablish naturally.

Other health aspects

Non-toxic

Non-carcinogenic

Asphyxiate -suffocating

LNG HFO/MGO

On your hands Causes frost bites Can be carcinogenic

Toxic No Yes

Carcinogenic No Yes

Asphyxiate Yes, in closed spaces No

Oxygen deficiency - asphyxiation

If oxygen is displaced from a space by LNG vapours or inert gases

Summary: Characteristics that make LNG safer than conventional marine fuels:

Non-toxic

Vapours are lighter than air (>-110 °C)

Storage tanks are thick, double walled

Double pipes

Not explosive in open air

Less flammable

High auto-ignition temperature