Principles of Explosion Protection

In general, three conditions need to be met at the same time for explosion to occur; presence of ignition source, flammables and oxygen. Explosion of cargos is likely expected when an ignition source (e.g. spark) is present in cargo tanks where flammable gasses and oxygen are mixed in high concentration. In other words, explosion can be controlled or prevented as far as oxygen concentration is kept low enough even if a spark is stricken. The inert gas systems thereby fill the free space in cargo tanks with the inert gas and lower the oxygen concentration in the tanks to prevent fires and explosion, ensuring safety of the crew and the ship.

Types of Inert Gas Systems

Comparison of Inert Gas Systems
Adaptability	IGS	IGG	Membrane N2	PSA N2
Crude oil tankers	◯	△	▲	▲
	Utilizes the exhaust gas from boilers. The most economical.	Burns fuels to generate cleaner inert gas, but less economical than IGS	Generates much cleaner inert gas than IGS/IGG, which does not necessary for crude oil tankers. Less cost effective.
Product tankers	△	◯	◯	◯
	Produces impurities entrained in the inert gas generated by combustion process. Care should be taken not to contaminate the cargos.	Generates cleaner inert gas than IGS by combustion process which inevitably produces small amount of impurities.	Generates much cleaner inert gas which gives less impact on the cargos, but is more costly than IGS/IGG.
Chemical tankers	▲	△	◯	◯
	Not recommended since contamination of the cargos with the impurities in the inert gas is highly expected.		Recommended since much cleaner inert gas with very low oxygen content can be generated.
◯ most applicable, △ appliable, ▲ not suitable

We have four types of the system available: Inert Gas System utilizing the exhaust gas from boilers, Inert Gas Generator System burning fuel oil separately to generate combustion gas with low oxygen content, and two different N2 Generator Systems which separate N2 from air.

The latter can generate cleaner inert gas than the former one. Various systems are available for your ships depending on the flammable substances to carry, such as crude oil or high-purity chemical products.

N2 Generator Systems – Membrane and PSA

	Membrane N2 Generator System	PSA N2 Generator System
Equipment overview
Configuration	Compressor Air treatment system (filters) Purging (unnecessary gasses) Membrane N2 gas (95~99.9% purity)	Compressor Air treatment system (filters) Purging (unnecessary gasses) Adsorption columns N2 gas (95~99.99% purity)
N2 generation	Employs the difference of the permeability through the membrane to separate N2 from other gasses in the air.	Employs the difference of the adsorption characteristic to the porous adsorbing materials to separate N2 from other gasses in the air.
Control	Pressurized air is filtered to remove dusts and continuously fed to the membrane to extract high-concentration N2 gas that does not permeate the membrane.	Pressurized air is filtered to remove dusts and fed to the adsorption columns to extract high-concentration N2 gas that is not adsorbed. Pressurization/adsorption and depressurization/desorption process are alternately repeated in the two columns to reactivate the adsorption materials.
Purity	High (~99.9%)	Ultra-high (~99.99%)
Capacity	95% purity: 70~4,500Nm3/h (discharge pressure: approx.1.1MPa) 99.9% purity: max. 540Nm3/h (discharge pressure: approx.1.1MPa)	95% purity: 10~4,500Nm3/h (discharge pressure: approx.0.7MPa) 99.9% purity: max. 1,500Nm3/h (discharge pressure: approx.0.7MPa)
Power consumption	High; air needs to get pressurized to 10~15bar	Low; air needs to get pressurized to 7~10bar
Installation	The system consists of separated several modules, enabling flexible installation even in small spaces.	The system is heavier and requires much space.
Maintenance	Its simple control and configuration require less maintenance.	It has a lot of automatic control valves which require more complicated maintenance than the membrane system.
Running cost	Almost the same as PSA at 95% purity, but goes up as the purity is elevated.	Lower at higher purity