1. Cargo Tank Venting &
Inert Gas System &
Equipment

2. On board cargo equipment 2
Inert Gas System Introduction

3. On board cargo equipment 3
Introduction to Inert Gas System
 Introduction
 Flammability
 Flammable Range
 Effect of Increasing Oxygen
 Suppression of Flammability by IG
 Combustion& Explosion
 Inert Gas Prevents FIRE & EXPLOSION

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Suppression of Flammability by IG

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Suppression of Flammability by IG

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Effect of Oxygen on Flammable Range

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Inert Gas Definitions

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Inert Gas Must On Tankers
 Required Under Regulation 60 of SOLAS
 For All Petroleum Tankers more than 20,000 DWT –
Keel laid after 1-9-84
 Exception for Existing Tankers (Keel Laid prior 84)
- i) Tank Washing Machine Capacity less than 60 Cubic
Meter/Hour &
- ii) Unreasonable & Impracticable due to design determined
by Administration
- iii) For Product Tankers between 20-40,000DWT tank
washing Machine Capacity less than 60 cubic meter/Hour
 Tankers fitted with IGS to keep COT inerted at all times

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Inert Gas Production

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Inert Gas System
 Flue Gas Uptake Valves
 Scrubber
 I.G. Fans (Blowers)
 Gas Regulating Valve
 Deck Water Seal
 Non Return Valve
 Deck Isolating Valve ( Manual)
 P/ V Breaker
 Instrumentation
 Tank Atmosphere Analyzers (Oxygen
Analyzers) Fixed & Portable

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Inert Gas System Layout

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Inert Gas System Flow Sheet

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Inert Gas Lay Out

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Inert Gas Layout System
From
Flue Gas Uptake

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Deck Distribution of Inert Gas System

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I. G. S. LAYOUT

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Deck Water Seal Requirement
•Regulation 62 requires that Inert Gas system is
equipped with two Non return devices one of
which shall be water seal to prevent the return of
hydrocarbon to Gas safe spaces
•In addition Regulation 62 requires that
arrangement of Deck Water Seal Shall be such
that it will prevent back flow of hydrocarbon
vapours and ensure proper Functioning of Seal
Under Operating Conditions.

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Deck Water Seal Wet Type

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Deck Water Seal Semi Dry

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Deck Water Seal Dry Type

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Deck seal
 Deck seal prevent flow back
from deck pipe line to flame
area of boilers or scrubbers
 Water column works as non
returning valve

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Principle of IG Scrubber

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IG Scrubber

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IGS types: Inert Gas Generator (FTU) construction -Scrubber

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Inert Gas System Non Return Devices
 Reason for Non Return Devices
 N/R Consist of Deck Water Seal & Deck
Mechanical N/R Valve
 Deck Water Seal is a Principal Barrier
 Incase of water drop, there should be
Low Water Alarm but Seal Should not
become Ineffective
 Heating Arrangement For Deck Water
Seal
 Sight Glass & Inspection Opening
Provided
 Function of Deck Mechanical N/R V/V
 Purpose of Separate Deck Isolating Valve

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Deck Water Seal Wet Type

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Deck Water Seal Semi Dry with Heating System

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Pressure-Relief & vacuum protection Systems
 Principal work of
liquid filled
pressure – vacuum
deck breakers: in
case P/V v/v fails
to operate
– Over pressure by
IG or Vapour and
blow out liquid on
deck
– Suction ambient
air in gas line and
liquid in tank

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Liquid Filled pressure vacuum breaker

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 The Pressure-Relief and Vacuum-Protection
System gives an automatically controlled
protection against too high or too low pressure
within the cargo-handling system
 Pressure-relief piping system
 Pressure-Relief & vacuum protection System for
All Cargo Tanks, as per IMO rules.
Pressure-Relief & vacuum protection Systems

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P/V & High Velocity Valves

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Pressure-Relief & vacuum protection Systems
 P/V valves

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Pressure-Relief & vacuum protection Systems
 High velocity vents valve
combines the best of modulating
valves and full-lift valves.
 Valve creates "delayed" blow
down of cargo tanks. It reduces
vapor loss during low filling rates
(and due to sloshing) until venting
takes place at full rate when vapor
loss is less important.
 Valve provides active protection
from fire and explosion regardless
of pipe configuration.
 Valve operates in freezing
conditions without heating
arrangements.

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Pressure-Relief & vacuum protection Systems
 Common liquid P/V

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Pressure-Relief & vacuum protection Systems
 1,2 Pressure house; Adapter
 3,4 Pressure disc and seat
 5,6 Booster
 7,8,9 Sleeve / Weight / Stem
 10 Check lift (pressure unit)
 11,12,13 Vacuum house, disc,
seat
 14 Filter element
 15 Venting cover
 16 Check lift (vacuum unit)

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Methods of Gas Replacement
 DILUTION
 DISPLACEMENT
 Dilution is mixing process, where velocity
of incoming Gas is High
 Displacement is a Layering Process,
where IG has Low Entry Velocity , to
enable stable horizontal interface

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IGS – Arrangement for Gas Replacement

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IGS – Arrangement for Gas Replacement

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IG Application

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Requirement for I G Main
 Means for Isolating Each Tank
 Breathing Possible when Tanks Isolated from IG Main
 Blank Flanges for Slop Tanks & Isolation for OBOs
 External IG Supply Connection
 Mast Riser or High Velocity Vents Provided for
Vapour Displacement
 Purge Pipes as Far as practicable from IG inlet
 Effective Isolation between IG Main and Cargo piping
 One or More P/V Breakers
 Provision of Continuous pressure indication of IG

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Tanker Cycle

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Inert Gas Application to Various Shipboard Operations

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IGS types: Flue Gas System
 Flue Gas Systems cool and clean flue gas from the ship's boilers, and deliver it to
deck, typically during cargo unloading and tank washing.
 Flue gas already contains less than 5% oxygen, which is the IMO higher limit for
inert gas, no further treatment is therefore necessary.
 The main components are the scrubber unit, inert gas blowers, the deck water seal,
main non-return valve, the pressure/vacuum breaker, valves, instrumentation and
the control system.
 Surplus gas is automatically re-circulated back to the scrubber unit, and gas
production hence follows gas demand.
 The system can also, like the other variants dealt with in this presentation, be
preset to deliver fresh air for gas-freeing purposes.

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IGS types: Inert Gas Generator
 Inert Gas Generator Systems is used when no existing supply of
flue gas is available.
 The scrubber unit of the flue gas system is here integrated into a
generator unit consisting of a combined burner part and scrubber
part, both sea water cooled. MDO or HFO fuel is burning in the
horizontal combustion chamber to produce flue gas with an
oxygen content of typically 2-4%.
 The gas then enters the scrubber part, where it is cooled and
cleaned by sprayed sea water before being piped to the deck area.

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Tank Pressure & Oxygen Concentration

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MMC Ullaging Device

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Flammability Composition Diagram

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Isolation of Cargo Tanks from IG Deck Main

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Cargo tank vent system

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Monitoring of IG Plant

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Inert Gas systems
 Carbon dioxide (IG) generation system
– Burning fuel for generation carbon dioxide gas is
common procedure on gas tankers
– Take off carbon dioxide gas form boilers
 Inert Gas (IG) is sent via drier / non returning valves
and used for replacing air to prevent explosion
concentrations :
– in Cargo Tanks and
– in Ballast tanks (some times).
 IG can be supplied from the shore facilities in
emergency condition

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IGS types: Flue Gas System

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IGS types: Flue Gas System with Topping Up Generator
 This alternative consists of a flue gas system supplemented
by a separate small (500Nm3/h) inert gas generator, and is
often preferred to aboard OBO and VLCCs
 The flue gas system covers the bulk of the inerting during
cargo unloading etc., and the topping up generator tops up
tank pressures during the sea voyage.

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IGS types: Inert Gas Generator (FTU) construction
- Panel
- Generator
- Fan
- Scrubber

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IGS types: Inert Gas Generator (IGG)
Moss Inert Gas Generators for Oil/
Chemical/ Products
Moss Inert Gas Generators for
LPG/LNG

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IGS types: Flexinert
 Flexinert is a fuel-saving combination of a flue gas system and an
inert gas generator.
 As long as sufficient boiler flue gas is available, Flexinert works as
a flue gas system. When no basis gas is available, it works as an
inert gas generator, and when high-oxygen exhaust gas from the
main engines or diesel generators is available, it afterburns this
gas to produce inert gas with the acceptable oxygen content.
 Afterburning saves fuel since the combustion "air" already has a
reduced oxygen content.

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Inert Gas Generator (IGG) – output
 Oxygen: 0.5% - 1%
 Carbon Dioxide: ~ 14 %
 Nitrogen: ~ 85%
 Carbon Monoxide, oxides of
Nitrogen and Sulphur
Dioxide: ~ 0,5%
– Carbon Monoxide: Max 100
ppm
– Oxides of Nitrogen: Max 100
ppm
– Sulphur Dioxide: Max 1 ppm
 Moisture: Dew Point of -45C
Modes: Inerting

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Deck seal

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Deck seal

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Ballast tank inerting
 Ballast tanks are inerted in
emergency conditions
 Flexible Hose used for inerted
operation
 Pressure 250 mmWC,

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Pressure-Relief & vacuum protection Systems
 Vent riser