Session 12: Inert gas system

Question 1

What is inert gas system?

Answer 1

-A gas that doesn’t react easily with other substances. These gases are often stable and don’t change or combine with other elements. For example Nitrogen doesn’t react easily with other substances.

Question 2

Where can we find inert gas ?

Answer 2

-flue inert gas - main or auxiliary(supporting) boiler (exhaust gas)

-Inert gas generator - burns the diesel oil and generate controlled level of oxygen

-bottled nitrogen - used in product or chemical tanker

Question 3

what are the SOLAS requirement for tankers?

Answer 3

-fitting of a fixed inert gas system will be required for tankers of 8,000 dwt and over, and carry cargo flash point below 60 degrees Celsius

-with the requirements of fire safety systems code (FSS)

-tankers operating with a cargo tank cleaning procedure using crude oil washing shall be fitted with an inert gas system

-complying with the fire safety system code(FSS Code) and with fixed washing machine

Question 4

what are the general requirement of inert gas system?

Answer 4

-shall be capable of inerting, purging

-and gas-freeing empty tanks

-maintaining the atmosphere in cargo tanks with required oxygen content (less than 5%)

Question 5

What is inerting and purging in simple terms?

Answer 5

Inerting is the process of filling the cargo tanks with a non-reactive gas to prevent combustion,

while purging is the act of removing flammable gases or oxygen from the tanks, often by replacing it with an inert gas, to make them safe for entry or cargo operations.

Question 6

What is flue inert gas?

Answer 6

-Flue inert gas is a gas taken from the exhaust (flue) of a ship’s boiler or engine and then cleaned and treated to remove harmful components.

-This cleaned gas, is then used to fill cargo tanks on oil tankers.

-By filling the tanks with this inert gas, the risk of fires or explosions is reduced because the gas prevents the formation of a flammable mixture with the oil vapors inside the tank.

-So, in essence, flue inert gas is like a safety blanket for oil tanks on ships.

Question 7

Tell me the 9 steps of how the inert gas system works

Answer 7

1.Fuel gas comes from the boiler through uptake to Scrubber Tower

2.Gas is cooled, cleaned and dried through the demister in the scrubber tower

3.Blowers propel the gas towards the tank. The capacity of blower is a at least 125% of maximum discharge rate

4.There is fresh air inlet in between Scrubber tower and blower which is used to gas free empty tanks

5.If you want to control the gas pressure, it can be recirculated to the tower

6.After blower gas passes through the deck water seal which works as non return valve

7.From deck water seal gas goes towards cargo tanks passing through two isolation valves

8.There is the pressure vacuum breaker to stop any back flow into the system

9.Mast riser can vent the gas in the atmosphere

Question 8

What does the scrubber tower do?

Answer 8

Here, think of it as a shower for the air; it cleans the air by removing any dirt or impurities.

Question 9

What does a demister do?

Answer 9

After its shower in the scrubber tower, the air might still have tiny water droplets, so it passes through the “Demister.” This is like a towel drying off any leftover moisture.

Question 10

What does the deck water seal do?

Answer 10

Before the air can be sent to the cargo tank, it passes through the “Deck Water Seal.” Imagine this as a security checkpoint ensuring that no unwanted gases return backward.

Question 11

What does the pressure vacuum valve do?

Answer 11

In simple terms, this is a safety mechanism for tankers to release excess pressure and prevent potential hazards.

Question 12

when following the alarms on IG system what must be monitored?

Answer 12

-percentage of oxygen
-Inert gas temperature
-inert gas pressure

Question 13

What is inerting by dilution?

Answer 13

Inerting by dilution is like adding water to a strong drink to make it weaker. Instead of water and drink, you mix a non-reactive gas (like nitrogen) with a flammable gas to reduce its ability to catch fire or explode. By adding enough of the non-reactive gas, the mixture becomes too “diluted” to ignite.

Question 14

What is inerting by displacement?

Answer 14

Inerting by displacement is like emptying a cup of water and then filling it with juice. Instead of water and juice, you “push out” or “displace” a flammable gas or air from a space using a non-reactive gas (like nitrogen). Once the space is filled with the non-reactive gas, there’s little to no chance of a fire or explosion because the flammable substance has been removed or greatly reduced.

Question 15

which 5 circumstances do you need inert gas on tankers?

Answer 15

1. Loading: When loading cargo, the inert gas is used to ensure that the vapor space in the tanks remains non-flammable.
2. Ballasting: When tanks are emptied of oil and filled with ballast water, inert gas is used to keep the tank atmosphere safe.
3. Tank Cleaning : After discharging, tanks may be cleaned. During and after cleaning, it’s essential to maintain an inert atmosphere to prevent flammable gas mixtures.
4. Purging: Before gas-freeing operations or before entering the tank, the volatile hydrocarbon content must be reduced. Inert gas purging ensures that the hydrocarbon concentration is minimized.
5. Topping up: To maintain the desired inert atmosphere in the cargo tanks, especially when there’s a drop in tank pressure or when the concentration of oxygen increases beyond the permissible limit.

Question 16

In case of failure of IG system, what actions should a OOW take?

Answer 16

1. Inform the Master: Immediately notify the ship’s Master or Chief Engineer about the IGS failure.
2. Stop Operations: If the vessel is engaged in cargo operations, consider stopping them until the issue is resolved, especially if the IGS failure compromises the safety of ongoing operations.
3. Check Alarms: Identify the specific problem by checking the IGS alarm system and relevant indicators.
4. Log the Event: Make an entry in the ship’s logbook detailing the time, nature of the fault, and any immediate actions taken.
5. Isolate the System: If there’s a risk of backflow from the cargo tanks to the IGS, isolate the system by closing necessary valves.
6. Ventilate the Space: If safe to do so, consider ventilating the space to prevent accumulation of flammable gases, but always ensuring it doesn’t create a flammable atmosphere.
7. Check Backup Systems: If the vessel is equipped with backup systems or alternative means of inerting, consider deploying them.