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LIQUIFIED PETROLEUM GAS(L P G)
LPG marketed
in India confirms to Indian Standard Specification IS-4576. Some of the important
properties and their bearings are :
LIQUID
DENSITY
LP gases in
the liqud state are nearly half as heavy as water. Specific gravities range from
0.55 - 0.58. Knowledge of this property helps us in calculating the safe quantities
that can be filled in a given container whose volume is known. An LPG container
should be filled in such a way that there will be a 5% ullage left at the design
temperature, otherwise, as temperature rises excessive pressures are likely to be
encountered leading to bursting of cylinders.
CO-EFFICIENT
OF EXPANSION OF LIQUID
Approximately
12 times that of water. This property in conjunction with liquid density should
be taken into consideration for arriving at safe filling capacities of containers.
VAPOUR
SPECIFIC GRAVITY
LPG vapour is
nearly 1 1/2 times to 2 times as heavy as air. This would mean that any escaping
vapour of LPG would tend to settle down. Hence, there should be adequate ground
level ventilation where LPG cylinders are stored.
For this very
reason LPG cylinder installations should not be undertaken in cellars or basements
which have no ventilation at ground level. Also, cylinders installation should not
be within 1 meter of drain opening.
VAPOUR
PRESSURE
The vapour of
LPG in equilibrium with its liquid exerts a pressure called the vapour pressure
and the magnitude of this pressure is dependent on the ambient temperature and not
on the quantity of the contents. Vapour pressure increases rapidly with temperature.
Boiling point of a liquid is that temperature at which the vapour pressure of the
liquid equals atmospheric pressure. Since boiling point of LPG is below 0 deg. C
the pressure inside a cylinder is always higher than the atmospheric pressure for
temperatures above 0 deg C and hence, this is the reason that gas gushes out of
a cylinder when the valve is opened.
Hence, an external
equipment i.e. pressure regulator is needed for obtaining gas at a constant pressure
for use in appliances irrespective of the ambient temperature.
EXPLOSIVE
LIMITS
Combustible
gases will only ignite with air when mixed with it in certain proportion.
As a combustible gas is gradually mixed with air in increasing proportions, a concentration
is reached at which the mixture just becomes explosive i.e. ignitable. This is called
the " Lower Explosive Limit"
As concentration
of the gas is further increased, a point is reached at which the mixture ceases
to be ignitable, and the concentration of the gas just before this point is called
the "Upper Explosive Limit"