This exercise focuses on the operation of cooling down cargo tanks onboard an LNG carrier. When the vessel is en route to the loading port, there is typically some quantity of heel remaining in the cargo tanks. The vessel uses this heel to cool down the other tanks, which are in a warm-up condition due to the length of the voyage.
This operation is similar to the extended cool-down from shore; however, the key difference is that the LNG used for the cooling process is sourced from the onboard heel, rather than from the shore.
Liquid LNG is introduced from the Heel tank with the help of the Spray Pump and directed toward the cargo tanks via spray lines, which contain spray nozzles inside the tanks. The LNG is sprayed into the tanks, gradually lowering the temperature. The goal is to reach a loading temperature of -130°C inside all cargo tanks. The vapor pressure inside the tanks is managed by running the LD compressor and consuming in the Engines.
Prepare the high-duty compressor and generators for operation. Connect the spool pieces. Ensure the correct valves are lined up to direct the LNG into the tanks via the spray lines.
The assessment begins once the lineup is complete and all equipment is ready for operation. The LNG flow is started from the spray pump, and the user must achieve a temperature of -130°C inside the tanks. Throughout the assessment, the user must maintain the correct LNG flow in order to achieve the temperature drop in the requisite time period and respond to any rising tank pressure by operating the LD compressor appropriately. The Gas Combustion Unit is put on standby in case required.
The exercise is considered complete when the target temperature of -130°C is reached inside all cargo tanks within the stipulated time. The user is assessed based on their response to various remarks, cautions, and alarms presented during the exercise.
