pressure enthalpy diagram methane
TRANSCRIPT
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)