pressure enthalpy diagram methane

Pressure Enthalpy Diagram Methane

Cool Down Time & Temp drop

The amount of LNG used for cool down is proportional to the

surface to be cooled down; brought down to the m3 of tanker

capacity, examples :

40000 m3 = duration 12 hours – LNG consumed 450 m3

125000 m3 = duration 12 hours – LNG consumed 700 m3

=> it is less for large tankers.

Indicative cool down duration : (atmosphere change in LNG cargo tanks

(order of magnitude)) – Case of a 125000 m3 LNG carrier

Tanks technique Standard Gaz Transport Moss Rosenberg

Duration (h) :

Stripping – heating

Inerting

Gassing

Cooling-down

48

30

12 to 20

130

30

12

40 to 60

Quantity of LNG required for tanks cooling down (m3)

750 2300

LNG use for Cool Down

Cooling Down

• Cargo tank cooling-down reduces temperature into hold space or interbarrier spaces causing pressure drop.

• Pressure drop into interbarrier or hold space should be compensated with Nitrogen / Inert gas or dry air as appropriate

• During cooling down moisture content or remaing inert gas could couse big problems (pumps, valves and other equipment could stuck up)

• Avoid excessive tank pressure

Primary Insulation Space Management during LNG Transport

Nitrogen Flow Rate at Different Stages in the Operational Cycle

LIQUID HEADER

VENT HEADER

INERT GAS HEADER

CONDENSATE RETURN LINE

Reliquefaction

VapourCompressor

L.P.G.Vaporizer

Inert Gas Generator

L.P.G.Heater

Air Blower

VAPOUR HEADER

liquid vapour

Cooling down using liquid from shore, vapour return to shore

20°C

20°C

5°C

19°C

Cool-down - process

Spray Rails Membrane tanks

0 GRADE A

Effect of Temp. on various steel grades

• Carbon steel becomes brittle at cryogenic temperatures (No strength against cold temp)• Special metallurgy required• Stainless steels 304L/316• Aluminium• 9% or higher Ni

What type of containment system

Material–Mild steel–Arctic steel–Aluminium–Invar–Austenitic stainless steel

Minimum Temp0 °C-55 °C-163-163< -163

Metal low temperature Tolerance

Source: Liquefied Gases Marine Transportation and Storage

Brittle Fracture

ESD & Comms Cable

Pre transfer meeting

Ship/shore check list

Steam off main engine

Stop burning gas

Tank gauging (CTS)

Manifolds connected

Purge with N2 & Press Test

Hot ESD test

Water curtain on

Cool arms & lines

Cold ESD test

Start Loading

Preparation for Loading

Ship/Shore Safety Checklist

Loading the cargo

• Ship / shore safety checklist

• Preloading plan

• Prior loading Pay attention to…….• Safety valves settings and h.p. alarm settings

• Remotely operated valves

• Reliquefaction equipment

• Gas detection system

• Alarms and controls

• ESD (Emergency Shut Down)