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.

Exercise Overview:

1. Initial Setup:

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.

2. System Preparation:

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.

3. Assessment Process:

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.

4. Completion Criteria:

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.

Learning Objectives for the Exercise

Participants will be able to effectively demonstrate the process of cooling down cargo tanks on LNG ships when at sea, understanding the necessary safety protocols, operational procedures, and the importance of achieving the required temperatures for safe LNG loading.

Key Components:
Understanding Cooling Down:

• Explain the purpose of cooling down cargo tanks to prepare them for LNG loading.
• Identify the significance of achieving appropriate temperatures to prevent thermal shock and ensure safe operations.

Operational Procedures:

• Detail the step-by-step process for cooling down cargo tanks, including:
• Preparation of cooling equipment and systems.
• Controlled introduction of LNG or cold nitrogen into the tanks.
• Monitoring the temperature drop and managing flow rates to prevent rapid cooling.
• Explain the importance of maintaining proper tank pressure and venting as necessary.

Monitoring and Verification:

• Demonstrate the use of temperature gauges and pressure monitoring systems during the cooling down process.
• Describe how to ensure that temperatures are within safe operational limits before loading LNG.

Practical Demonstration:

• Simulate the cooling down process in a controlled environment or through hands-on training exercises.
• Role-play scenarios to address potential challenges or deviations from the procedure, emphasizing critical thinking and teamwork.

Assessment Criteria:

• Ability to articulate the significance of cooling down cargo tanks.
• Accurate execution of the cooling down procedure and effective monitoring.

By achieving this objective, participants will gain the knowledge and skills necessary for safely and efficiently cooling down cargo tanks on LNG ships while at sea, ensuring operational readiness for LNG loading.

Extended Cooldown at Sea-Intro and Line up

Extended Cooldown at Sea-GCU Test Run

Extended Cooldown at Sea-Spray pump Initialization

Extended Cooldown at Sea-Operations and Assessment

Milestones:

• Learning and Training Phase – Pre-Requisites for the start of operation:

1. Prepared Generators for use.
2. Test Run Gas Combustion Unit.
   • 2A: Start Gas Combustion Unit.
   • 2B: Increase GCU Output (2600 kg/h).
   • 2C: Turn Off Gas Combustion Unit.
   • 2D: Perform N2 Purging In GCU.
3. Open Required Valves For Line Up.

• Assessment Phase – Operational flow and Assessment:

4. Start Spray Pump In Cargo Tank 4.
5. Start LD Compressor When Required.
6. Obtained required temperatures inside the tanks.
   • 5A: Achieved -30°C in all three tanks.
   • 5B: Achieved -100°C in all three tanks.
   • 5C: Achieved -140°C in all three tanks.

Actions During the Exercise:

Deviation From Exercise:

• After starting or resuming the cooldown, the user should not open any non-required valves or close any required ones. A caution message will be displayed to undo the previous action. Failure to correct it will result in exercise termination.

Reduce Temperature Drop Rate During Stage I:

• If the temperature drop exceeds -15°C: Caution message.
• If the temperature drop exceeds -20°C: Low-priority warning.
• If the temperature drop exceeds -25°C: High-priority alarm.
• Continued cooldown with caution alarm for 5+ minutes: Low-priority alarm.
• Continued cooldown with low-priority alarm for 5+ minutes: High-priority alarm.
• Failure to reduce the drop within 1 minute of high-priority alarm: Exercise termination.

Reduce Temperature Drop Rate During Stages II & III:

• If the temperature drop exceeds -11°C: Caution message.
• If the temperature drop exceeds -13°C: Low-priority warning.
• If the temperature drop exceeds -15°C: High-priority alarm.
• Continued cooldown with caution alarm for 5+ minutes: Low-priority alarm.
• Continued cooldown with low-priority alarm for 5+ minutes: High-priority alarm.
• Failure to reduce the drop within 1 minute of high-priority alarm: Exercise termination.

Close One Nozzle in Cargo Tanks Below 0°C:

• Remark issued when tank temperature reaches 0°C.
• Remark unresolved for 5+ minutes: Low-priority alarm.
• Low-priority alarm unresolved for 5+ minutes: High-priority alarm.
• Failure to close nozzle within 1 minute of high-priority alarm: Exercise termination.

Start LD Compressors:

• At 14 kPa pressure: Caution alarm to start one LD compressor. Failure to comply within 1 minute: Exercise termination.
• At 16 kPa pressure: Caution alarm to start the other LD compressor. Failure to comply within 1 minute: Exercise termination.

Alarms & Remarks

Step By Step Procedure

• Learning and Training Phase – Pre-Requisites for the start of operation:

Preparing Generators for Use:

• Navigate to the PMS page through the side navigation.
• Turn on one of the three generators that are not currently running. (By default, one generator will already be running.)

Open all required valves for the line-up.

• Open the following required valves.

• • Access valves across various pages as necessary.

Test Run GCU:

• • Navigate to the Gas Combustion Unit (GCU) page via the side navigation.
  • Prepare and start the GCU.
  • Increase the GCU output to 2600 kg/h and maintain for a specific duration.
  • Stop the GCU and perform GCU purging.

• • Assessment Phase – Operational flow and Assessment:

Start Spray Pump in Cargo Tank 4:

• • Navigate to the Cargo Tank 4 page via the cooldown or side navigation.
  • To start the spray pump:
    • Open Valve CS401 to 25%-30%.
    • Open Valve CS400 to 95% or greater.
    • Ensure at least two generators are running.
  • Ensure Cargo Tank 4 Spray Pump Master Valve CS403 is closed or set to 5% or less.
  • Start the spray pump, then open the master valve and close the return valve to initiate cooldown.

Cooldown Process:

• • Adjust the pump flow rate to avoid exceeding drop rate thresholds.
  • Avoid deviations from required procedures or exceeding temperature drop limits.

Completion:

Achieve -130°C in all three tanks to complete the exercise.

Proper line up for CT cooldown at sea: