Gassing Up

Why to Gas up?

Tank will be cooled to well below dew point temperature

Dry Ice deposition from CO2 (IG contains 15% by volume) occurs at -78°C

(opposite is sublimation, dry ice turns to vapour without passing through the liquid phase)

Gassing-up

• Process of replacing inert gas with Methane

• Inert gas contains uncondensable gases

• Nitrogen and CO2 can not be condensed by ship’s reliquefaction plant

• Venting to atmosphere is subject to MARPOL Annex VI

• Return to shore until tank is full with next cargo vapour

Gassing-up

• Gassing-up at sea only available to fully or semi-pressurised vessel (often with deck tanks)

• Gassing-up using cargo from shore

• Before commencing gasing-up O2 contents must of tanks should be less then 5% by Volume.

• Compressors for re-liquefaction can be started after gas concentration into tank reach at least 90%

Time

% O

2

1.5%

20.8%

5%

Gassing Up

Time

Gassing Up

Inert Gas LNG

Steam

VaporiserVent (or ashore)

Inert Gas

LNG

Steam

LNG Vaporiser

Gassing Up

Liquid at -160°VaporTemp?

Max temp +80°C

Min temp +10°C ?

Methane entersthe tank throughthe vapour line atthe top of the tankand exits throughthe liquid fillinglines to the ventriser or ashore.

Compressor & Motor Room Arrangements

•Gas Tight Seal through bulkheads (10.2.4.2, 10.2.4.3)

•Positive and negative ventilation (12.1.4, 12.1.5)

•Entry via airlock (3.6)

•Trip of non approved electrical power on loss of positive pressure (3.6.4)

Airlock

Suction from top and / or bottom

MAIB Tanker Awareness by WMA

High Duty Compressor

760 kw3570 rpm

9552 rpm

Nitrogen

Air

Compressor Inlet Guide Vanes

Inlet Guide Vanes

Minimum +80° Maximum -30°In line with shaft 0°

HD Compressor Alarms and Trips

Lube Oil Lo Lo 90kPa

Nitrogen seal pressure Lo 10kPa

Lube oil inlet temp Hi 65°C

Excess vibration 80µm

Discharge gas temp Hi 100°C

Bearing Lube oil temp Hi 105°C

Rotor axis excess position +/-0.2mm

Bulkhead seal temp Hi 120°C

Bulkhead seal press Lo 3kPa

Differential pressure

vapour header / atmospheric = 0.3kPa

Vapour header / IBS pressure header = 0 kPa

Any tank very high liquid level

Oil temperature

Oil pressure

High gas discharge temperature

Low seal gas pressure

Electric power failure

Motor room ventilation failure

Cofferdam Heating NO96 System

Cofferdam Heating MKIII System

CONDENSATE RETURN LINE

VENT HEADER

INERT GAS HEADER

LIQUID HEADER

Reliquefaction

VapourCompressor

L.P.G.Vaporizer

Inert Gas Generator

L.P.G.Heater

Air Blower

VAPOUR HEADER

liquid vapour

Gassing-up Liquid Supply from Shore Vapour Return Shore