Ch 5- Inert Gas Systems (c)

Question 1

What are the two inert gases?

Answer 1

• Nitrogen
• Flue gas

Question 2

Which inert gas is readily available and cheap?

Answer 2

Flue gas

Question 3

Which inert gas is expensive?

Answer 3

Nitrogen

Question 4

Which inert gas is more suitable for high-quality cargo or as an emergency supply?

Answer 4

Nitrogen

Question 5

Where is flue gas sourced from?

Answer 5

Exhaust from a boiler

Question 6

What is an inert gas generator?

Answer 6

A device in which fuel is burnt to create exhaust gases which contain less than 5% oxygen

Question 7

What is the purpose of a scrubbing tower?

Answer 7

• Cools the flue gas
• Cleans the flue gas

Question 8

How many blowers must you have in an IG system?

Answer 8

Two (or one plus spare parts)

Question 9

What is the minimum capacity of blowers?

Answer 9

125% of MAXIMUM cargo discharge rate

Question 10

What does a blower do?

Answer 10

Directs IG to tanks

Question 11

What is a deck seal?

Answer 11

It prevents backflow of vapour from cargo tanks to the gas free area

Question 12

What is the most common type of deck seal?

Answer 12

Wet

Question 13

What is the more reliable type of deck seal?

Answer 13

Non-mechanical

Question 14

What does a liquid-filled P/V breaker do?

Answer 14

• Prevents over or under pressurisation of cargo tanks
• Actuates at pressures in excess of PV valve settings but less than tank test pressures

Question 15

What is a liquid filled P/V breaker filled with?

Answer 15

Fresh water or anti-freeze

Question 16

Describe what happens in a liquid filled P/V breaker when there is positive pressure?

Answer 16

Pressure acts on the liquid within the P/V breaker
This forces liquid up the central column

Question 17

What is a mast riser used for?

Answer 17

Venting excess pressure
Keeps vented gas clear of deck

Question 18

What is at the top of a mast riser?

Answer 18

Flame screen

Question 19

Describe using IG in a voyage cycle

Answer 19

• Primary inerting (8% O2 and positive pressure)
• Loading (vent off excess pressure)
• Top up on passage if required
• Discharge (system fully running)
• Tank washing
• Purging for gas freeing

This then repeats.

Question 20

What are the steps of action in event of IG failure with crude oil?

Answer 20

• STOP all operations
• Close IG deck isolation valve
• Open vent between isolation valve & gas regulating valve to relieve pressure
• Fix the problem or obtain an alternate supply

Question 21

What are the steps of action in the event of IG failure with products?

Answer 21

• STOP all operations
• Decide if repair is practicable & availability of alternative supply of IG
• If repair not practicable operations can resume but:
• Check flame arrestors on vents are in good condition
• Open vent risers
• Do not allow free fall of water or slops
• Take anti-static precautions when ullaging, dipping or sampling
• Additional precautions if tank cleaning

Question 22

Describe the order of an IG system (12)

Answer 22

1. Exhaust gases source
2. Inert gas isolating valve
3. Scrubbing tower
4. Demister
5. Gas blower
6. I.G pressure regulating valve
7. Deck seal
8. Mechanical non-return valve
9. Deck isolating valve
10. PV breaker
11. Cargo tank isolating valves
12. Mast riser