Nitrogen padding or blanketing is a vital safety measure used in chemical tanker operations. Nitrogen, a colorless and odorless gas, is employed to dilute the action of oxygen in air, reducing the risk of fire and explosion during cargo handling and storage. Familiarity with the properties and handling of nitrogen is essential for maintaining safe working conditions and preventing potential hazards.
Properties of Nitrogen:
- Nitrogen is chemically inert due to its non-polar nature and high ionization energy.
- It is slightly soluble in water and acts as a food antioxidant.
- Exposure to nitrogen can lead to cyanosis, where the skin turns dark blue due to lack of oxygen and loss of red blood.
Uses of Nitrogen in Tanker Operations:
- Quality Control: Nitrogen is used to reduce oxidation in cargo, ensuring its quality during transportation.
- Retarding Dangerous Reactions: Blanketing with nitrogen prevents dangerous reactions between the cargo and air or water.
- Removing Moisture: Nitrogen is used to remove moisture from the tank, preventing the risk of cargo contamination.
- Avoiding Explosions: Nitrogen inerting is employed to create an inert atmosphere, reducing the risk of explosions during cargo handling.
Handling Nitrogen Padding:
- Nitrogen Bottle Bank: Chemical tankers carry nitrogen bottles for padding purposes. The total capacity of nitrogen bottles should be at least 5% of the total volume of cargo space to be inerted. Bottles must be stored below 52°C.
- Nitrogen Supply: Nitrogen is supplied from bottles via a filter, regulator, and relief valve system. The pressure is reduced from 200 bars to 4 bars and then to 0.15 bars for topping up at sea or padding in port. There are two lines, one for emergency use.
- Blanketing After Loading with Open Venting/Gauging: Nitrogen is used after open venting to prevent air or water ingress. Care must be taken to prevent cargo overflow.
- Blanketing After Loading with Controlled Venting/Closed or Restricted Gauging, Without Vapour Return: Pressure gauges are used, and the nitrogen supply should not exceed the vent capacity of the cargo tank.
- Blanketing After Loading with Controlled Venting/Closed or Restricted Gauging, With Vapour Return: Nitrogen is supplied while maintaining the vapour return system open. Careful monitoring of pressure is required.
Handling Nitrogen During Voyage:
- Nitrogen blanket with positive pressure should be maintained always, as specified by the Charterer or regulatory requirements.
- Regular readings of pressure and oxygen content must be recorded and monitored.
Nitrogen padding is a critical safety measure in chemical tanker operations. Understanding the properties of nitrogen and following proper procedures for handling, supply, and monitoring are crucial for ensuring safe and efficient cargo transportation and storage. Regular checks, record-keeping, and adherence to safety guidelines are essential for the successful implementation of nitrogen blanketing.