Aeration of cargo tanks on board an LNG carrier is the final step in preparing the vessel for its upcoming dry dock. In this process, the inert gas generator onboard is operated in dry air mode. Dry air with a low dew point of -45°C is introduced into the tank from the top, while the heavier inert gas is extracted from the bottom of the tank and released into the atmosphere. This process, known as the displacement of inert gas with dry air, ensures that the cargo tank is safe for manned entry and subsequent inspections or repairs. This operation can also be carried out while the vessel is at sea.

Exercise Overview:

1. Initial Steps:

• The exercise begins with the prerequisites for performing aeration inside the tank.
• Portable multi-gas detectors and dew point meters are used to monitor the atmosphere during the process.
• The correct lineup of valves and connection of school pieces is carried out.
• The inert gas generator is prepared in dry air mode, ensuring that the power generators are operating efficiently.

2. Assessment Process:

• The assessment begins when the dry air is introduced into the tank from the inert gas generator.
• Continuous monitoring is required, using various sampling points and gas detectors, to ensure that the air is effectively replacing the inert gas inside the tank.
• The user must also ensure that the tanks are within the prescribed pressure range.

3. Completion Criteria:

• The exercise is considered complete when the following criteria are met:
• Oxygen content: Greater than 20% by volume
• Methane content: Less than 0.2% by volume
• Carbon dioxide content: Less than 0.5% by volume
• Carbon monoxide content: Less than 50 ppm
• The final evaluation occurs when the required dew point has been achieved, and the gas measurements confirm that the tank is ready for manned entry.

4. Evaluation:

• The user will be evaluated on their ability to navigate the process, including responding to various remarks, alarms, and cautions throughout the exercise.
• Successful completion will depend on the user’s ability to follow the procedure efficiently and maintain safety standards throughout the exercise.

Trainees will be able to effectively demonstrate the process of Aeration of cargo tanks on LNG ships, understanding the importance of safety protocols, operational procedures, and regulatory compliance.

Key Components:

1. Understanding the Importance:
   • Explain why Aeration of cargo tanks is critical for safety and operational efficiency.
   • Identify potential hazards associated with moisture in LNG tanks.
2. Practical Demonstration:
   • Simulate the entire Aeration process in a controlled environment or through a hands-on training exercise.
   • Role-play different scenarios that may occur during the drying process, emphasizing problem-solving and decision-making skills.

Assessment Criteria:

• Ability to articulate the significance of Aerating cargo tanks.
• Completion of each step in the Aeration process with accuracy.

By achieving this objective, participants will gain practical knowledge and skills necessary for safely and efficiently Aerating cargo tanks on LNG ships.

Aeration-Intro and Line up

Aeration -Starting IGG in Dry air mode

Aeration-Operations and Assessment

Milestones : 

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

1. Start The Portable Multi Gas Detector And Dew Point Meter.
2. Install The Spool Piece And Open Required Valves To Connect Inert Gas Line To Vapour Header Line.
3. Install The Spectacle Flange On The Emergency Vent Line To No.1 Vent Must.
4. Set The Cargo Tank Vapour Valves.
5. Set Cargo Tank Liquid Valves.
6. Set The Vapour Line To No. 1 Vent Mast Regulating Valve.
7. Prepare Inert Gas Generator In Dry Air Mode.

• Assessment Phase – Operational flow and Assessment:

8. Start Inert Gas Generator In Dry Air Mode.
9. Oxygen Content > 20% By Volume.
10. Cargo Tank Carbon Dioxide Content < 0.5% By Volume.
11. Cargo Tank Carbon Monoxide Content < 0.50ppm.
12. Maintain Cargo Tanks Pressure Between 5kPa And 7kPa.
13. Check The Sampling Point On Liquid Line In All Cargo Tanks.

When The Required Dew Point Has Been Reached For All Cargo Tanks And Piping , Stop The Dry Air Supply.

Actions During the Exercise

Deviation From Exercise

• Restriction: After starting the aeration process, the user must not open non-required valves or close required ones.
• Consequence: A caution message will instruct the user to undo the action. Failure to correct it will result in exercise termination.

Not Maintaining IGG Outlet Flow and Flow to Atmosphere

• Requirement: Maintain inert gas generator outlet flow and flow to atmosphere between 15,500 kg/h and 16,500 kg/h.
• Consequence: If a high-priority alarm is triggered and the user fails to maintain the flow within 1 minute, the exercise will be terminated.

Alarms & Remarks

Step By Step Procedure

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

1. Start the Portable Multi Gas Detector and Dew Point Meter

1. 1. Navigate to the “Miscellaneous Equipment” page through the side navigation menu.
   2. On the page, press and hold the power button for “Portable Multi Gas Detector” and “Dew Point Meter” for 2 seconds.
   3. Once both devices are started, this milestone is complete.

2. Install the Spool Piece and Open Required Valves

• • Connect the spool piece above valve CL701 to connect the IGG outlet and vapor header.

3. Install the Spectacle Flange on the Emergency Vent Line

• • Connect the spool piece below valve CL700 to connect the liquid line and No. 1 vent mast.

4. Set Cargo Tank Vapor Valves

5. Set Cargo Tank Liquid Valves

6. Set the Vapor Line to No. 1 Vent Mast Regulating Valve

7. Prepare the Inert Gas Generator in Dry Air Mode

1. 1. Set Generator Mode to “Dry Air” by clicking the label or dragging the lever to the right.
   2. Set Operating Percentage to “100%” by clicking the label or dragging the lever to the left.
   3. Set Fuel Pump to “Off” by clicking the label or dragging the lever to the right.
   4. Set IG Chiller Unit to “On” by clicking the label or dragging the lever to the left.
   5. Once these settings are achieved, this milestone is complete.

• Assessment Phase – Operational flow and Assessment:

8. Start the Inert Gas Generator in Dry Air Mode

1. 1. Wait until the IG chiller unit outlet temperature drops to 3°C or below.
   2. Click the “Start” button to activate both air blower units and open the air delivery valves.
   3. The drying process begins as the inert gas flows through the cargo tanks.

9. Achieve Cargo Tank Oxygen Content > 20% by Volume

• • Observe the oxygen content using the Portable Multi Gas Detector at the vapor line sampling point. Once it exceeds 20%, this milestone is complete.

10. Achieve Cargo Tank Carbon Dioxide Content < 0.5% by Volume

• • Observe the carbon dioxide content using the Portable Multi Gas Detector at the vapor line sampling point. Once it is below 0.5%, this milestone is complete.

11. Achieve Cargo Tank Carbon Monoxide Content < 0.50 ppm

• • Observe the carbon monoxide content using the Portable Multi Gas Detector at the vapor line sampling point. Once it is below 0.50 ppm, this milestone is complete.

12. Maintain Cargo Tank Pressure Between 5 kPa and 7 kPa

• • Regulate the vent mast valves to ensure the tank pressure remains between 5 kPa and 7 kPa during the aeration process.

13. Check the Sampling Point on Liquid Line in All Cargo Tanks

• • During or after aeration, check the liquid line sampling points for dry air properties using the Portable Multi Gas Detector and Dew Point Meter.

14. Stop the Supply of Dry Air

1. 1. Navigate to the IGG System Page.
   2. Click “STOP” under the Delivery section.
   3. Close the vent mast regulating valve (CG702).
   4. A remark will be displayed indicating the completion of aeration.

Proper line up for aeration: