27-09-2012, 05:29 PM
Inert Gas System
Proposal for inert gas generator.docx (Size: 174.51 KB / Downloads: 25)
INTRODUCTION
With an inert gas system, a tank is protected from exploding by introducing Inert gas into it to keep the oxygen content low and to reduce to safe Proportions the hydrocarbon gas concentration of its atmosphere.
Flammable Limits
* A mixture of hydrocarbon gas and air cannot ignite, unless its composition lies within a range of gas-in-air concentrations known as the flammable range.
* The lower limit of the range, known as the “lower flammable limit”, is any hydrocarbon concentration below which there is insufficient hydrocarbon gas to support combustion.
* The upper limit of the range, known as the “upper flammable limit”, is any hydrocarbon concentration above which air is insufficient to support combustion.
* The flammable limits vary somewhat for different pure hydrocarbon gases and for the gas mixtures derived from different petroleum liquids; in practice, however, the lower and upper flammable limits of oil tanks can be taken, for general purposes, to be 1 per cent and 10 per cent hydrocarbon by volume, respectively.
Effect of Inert Gas on Flammability
* When an inert gas is added to a hydrocarbon gas/air mixture, the result is an increase in the lower flammable limit concentration and a decrease in the upper flammable limit concentration. Figure 1 illustrates these effects which should be regarded only as a guide to the principles involved.
* Any point on the diagram represents a hydrocarbon gas/air/inert gas mixture, specified in terms of its hydrocarbon and oxygen content.
* Hydrocarbon/air mixtures, without inert gas, lie on the line AB, the slope of which shows the reduction in oxygen content as the hydrocarbon content increases.
* Points to the left of AB represent mixtures whose oxygen content is further reduced by the addition of inert gas.
* As indicated in Figure 1, as inert gas is added to hydrocarbon/air mixtures, the flammable range progressively decreases, until the oxygen content reaches a level generally taken to be about 11 per cent by volume, at which no mixture can burn.
Proposed Sources
How to produce Inert gas on ships? To answer this question is our ultimate goal.
The production of inert gas is carried out by various sources.
• Inert Gas Generator (IGG)
• The uptake from the ship’s main or auxiliary boilers
• A gas turbine plant equipped with an afterburner