Preparation for discharging LNG cargo - gas carrier guide
Fig:Liquid line cooling by LNG ship before discharging cargo
Before arrival at a terminal prior discharging
The following checks and procedures are to be regarded as the minimum before cargo operations can commence.
Preparation for LNG discharging
When terminal regulations allow, ship lines are to be cooled prior to arrival alongside. The operation is normally commenced 2 hours prior to arrival. LNG is normally supplied to the cargo liquid lines by one of the spray pumps. It is required that the pipelines be thoroughly circulated and cooled until final custody transfer measurement.
To avoid accident the best procedures is to circulate from the spray tank and back to the same spray tank. This avoids the risk of overflow. Once the vessel is berthed alongside the ships side water curtain should be started. The cargo arms can now be connected.
The manifold connection should be purged with N2 gas until the O2 contents is <1%. The manifold should be leak checked by N2 pressurization from shore and standard soapy water. Gas burning should be stopped prior to initial gauging.
After completion of CTM, manifold ESD valves should be opened and a warm ESD test carried out. Re-open ESD valves.
Confirm setting of all ship and shore valves are correct after notifying terminal start spray pump and slowly open the liquid manifold cool down valves.
If required, increase the flow from the spray pump by increasing the motor load, or increasing the spray line pressure. During this operation monitor the liquid header temperature to ensure it remains sufficiently cold. Shore will inform when they consider arm cool down as complete. Stop spray pump and carry out cold ESD.
Below is our additional guideline for handling LNG cargo:
Procedures for LNG cargo discharging
Precautions for LNG carrier during loaded passage
Preparation for loading LNG cargo
Drying of Cargo Tanks and preparation for loading LNG cargo
Inerting of Cargo Tanks prior loading LNG cargo
Gassing-up requirement for cargo tanks
Initial Cool Down of cargo tanks
LNG spill risk during marine transportation and hazards associated
Toxicity and associated health hazards in liquefied Gas Carrier
Safety check items prior loading LNG cargo
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