Project Report onON

Liquefied Petroleum Gas Cylinder

By

NAME ROLL NOVishnu RC Vijayan 69

Under the guidanceOf

Prof. Rafael Fernando

DON BOSCO INSTITUTE OF TECHNOLOGYPREMIER AUTOMOBILES ROAD

KURLA(W)MUMBAI – 400070

INTRODUCTION

Liquefied petroleum gas cylinders are manufactured and tested under stringent norms before they get certified by Bureau of Indian Standards (BIS) for market use. These LPG cylinders are designed and manufactured as per Indian standard. Normally, cylinders are manufactured in batches from raw material specified in Indian standards and tested before dispatching to market. As a part of design , cylinder thickness is calculated based the shape of the cylinder dome and cylindrical portion of the dome. Cylinders are then produced through various stages and tested before BIS certifies a lot.

REVIEW OF CYLINDER MANUFACTURING PROCESS

LPG cylinders are manufactured either in two piece or three piece construction. Body parts of the cylinder are explained in the fig.1.

In two piece construction, cylinders are fabricated by welding two domed ends directly together. A three piece cylinder is fabricated by joining two domed ends to a cylindrical body as shown in fig. 1.

The domed ends can be Tori-Spherical, Semi- ellipsoidal or Hemi-spherical in shape as shown in Fig.2

Wall thickness is primary factor to be arrived while designing a cylinder. In order to design the thickness, a test pressure 23,53 bar, and a minimum yield strength is 240 Mpa is considered as per Indian standard IS3196 part 1. Further, weld joint factor to be considered as 1.0, 0.9 and 0.7 depends on type of radiographic examination adopted to check the welds during and after manufacturing.

Thickness of cylindrical portion is calculated using formulas.

Thickness of cylindrical portion

Or

And

Where,

=calculated minimum wall thickness, in mm.

=calculated wall thickness of doom, in mm.

= Test pressure , in Kgf/cm

=inner diamer in mm

=outer diameter in mm

=external height of doms in mm

=internal height of domed ends in mm

=yield strength in mm

=weld joint factor

= 1.0 for fully radio grapged weld.

=0.9 for two piece cylinder

=0.7 for all other cases.

=ratio

=dishing radius in mm.

=knuckle radius

=length of straight flange i mm

Thickness of tori-sherical cylinder dome is

thickness of semi-ellipsoidal cylinder dome is

As per the Indian standards IS 3196 minimum cylinder thickness should be 2.4.

Once the design is finalized, a prototype cylinder to be produced and to be subjected to various tests to ensure deemed fit.

RAW MATERIAL

Special grade steel complies with Indian standard IS6240, Hot rolled steel plate(upto 6 mm) sheet and strip for the manufacture of low pressure liquefiable gas cylinders is used for cylinder body.

The bung or valve pad should confirms to class 1A or class2 of IS 1875, carbon still billets, blooms, slabs and bars for forging or IS 2062.

Valve protection ring, foot ring should confirm to Grade 0 of IS 1079, Hot rolled carbon steel sheets and strips.

TESTING OF CYLYNDER

Normally one cylinder in alot of 202 is subjected to acceptance test. Similarly out of 403 or less lot size one cylinder is subjected to hydrostatic test as per IS 3196 part3. IN addition to that , cylinders are subjected to various destructive and non-destructive tests, to get Bureau of Indian certification for marketing.

following are the essential tests to be conducted before they get certified by Bureau opf Indian standards.

Acceptance test Burst and volumetric expansion test

Hydostatic stretch test and burst test Pneumatic leak test radiographic examination Fatigue test.

LPG PROPERTIES

LPG is a mixture of commercial butane and commercial propane having both saturated and unsaturated hydrocarbons. LPG marketed in India shall be governed by Indian Standard Code IS-4576 (Refer Table 1.0) and the test methods by IS-1448.

PHYSICAL PROPERTIES AND CHARACTERISTICS

DENSITY

LPG at atmospheric pressure and temperature is a gas which is 1.5 to 2.0 times heavier than air. It is readily liquefied under moderate pressures. The density of the liquid is approximately half that of water and ranges from 0.525 to 0.580 @ 15 deg. C.

Since LPG vapour is heavier than air, it would normally settle down at ground level/ low lying places, and accumulate in depressions.

VAPOUR PRESSURE

The pressure inside a LPG storage vessel/ cylinder will be equal to the vapour pressure corresponding to the temperature of LPG in the storage vessel. The vapour pressure is dependent on temperature as well as on the ratio of mixture of hydrocarbons. At liquid full condition any further expansion of the liquid, the cylinder pressure will rise by approx. 14 to 15 kg./sq.cm. for each degree centigrade. This clearly explains the hazardous situation that could arise due to overfilling of cylinders.

FLAMMABILITY

LPG has an explosive range of 1.8% to 9.5% volume of gas in air. This is considerably narrower than other common gaseous fuels. This gives an indication of hazard of LPG vapour accumulated in low lying area in the eventuality of the leakage or spillage.

The auto-ignition temperature of LPG is around 410-580 deg. C and hence it will not ignite on its own at normal temperature.

Entrapped air in the vapour is hazardous in an unpurged vessel/ cylinder during pumping/ filling-in operation. In view of this it is not advisable to use air pressure to unload LPG cargoes or tankers.

COMBUSTION

The combustion reaction of LPG increases the volume of products in addition to the generation of heat. LPG requires upto 50 times its own volume of air for complete combustion. Thus it is essential that adequate ventilation is provided when LPG is burnt in enclosed spaces otherwise asphyxiation due to depletion of oxygen apart from the formation of carbon-dioxide can occur.

ODOUR

LPG has only a very faint smell, and consequently, it is necessary to add some odourant, so that any escaping gas can easily be detected.

Ethyl Mercaptan is normally used as stenching agent for this purpose. The amount to be added should be sufficient to allow detection in atmosphere 1/5 of lower limit of flammability or odour level 2 as per IS : 4576.

COLOUR

LPG is colourless both in liquid and vapour phase. During leakage the vapourisation of liquid cools the atmosphere and condenses the water vapour contained in them to form a whitish fog which may make it possible to see an escape of LPG.

TOXICITY

LPG even though slightly toxic, is not poisonous in vapour phase, but can, however, suffocate when in large concentrations due to the fact that it displaces oxygen. In view of this the vapour posses mild anaesthetic properties.

LPG SPECIFICATIONS

Sr No

Characteristic

Ref. to IS:4576

Requirment

Butane-Propane Mixture

1Vapour pressure at 65 deg. C kgf/cm.g.

16.87 Max

2Volatility: evaporation temperature in deg.C, for 95 per cent by volume at 760 mm Hg pressure, Max

2

3 Total volatile sulphur percent by mass, Max

0.02

COMPOSITION OF LPG

LPG is primarily composed of propane, butane, isobutane and mixtures of these gases. LPG exists as liquid or gas (vapour), depending on pressure and temperature. LPG has many properties including density (specific gravity), flame temperature, boiling point, flash point,

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vapour pressure, odour, appearance, energy content, gaseous expansion, combustion formula, limits of flammability, nomenclature and molecular formula.

LPG Boiling Point

Water boils at 100°C or 212°F, becoming a gas (steam).   In contrast, LPG boils at -42°C or -44°F, becoming gas vapour. LPG stays liquid because it is under pressure in a gas cylinder. 

As a liquid, it looks a lot like water. It is colorless and odorless in its natural state.  LPG Pressure Varies with Temperature As previously mentioned, when LPG is stored in a gas bottle, it is under pressure. 

The term “pressure” refers to the average force per unit of area that the gas exerts on the inside walls of the gas bottle. 

(LPG Pressure-Temperature Chart shown)

Pressure is measured in kilopascals (kPa) or pounds per square inch (psi).

“Bar” is yet another unit of measure for pressure. 

1 Bar = 100 kPa, so it is metric based but not an SI unit of measure.

LPG pressure can vary greatly based on temperature, as shown in the chart.

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The level of fill in the gas bottle comes into play when the LPG is being used, as it affects the rate of vaporization. 

DETAILS OF LPG PUMP

A diaphragm pump (also known as a Membrane pump) is a positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable valves on either side of the diaphragm to pump a fluid.

There are three main types of diaphragm pumps:

1. Those in which the diaphragm is sealed with one side in the fluid to be pumped, and the other in air or hydraulic fluid. The diaphragm is flexed, causing the volume of the pump chamber to increase and decrease. A pair of non-return check valves prevent reverse flow of the fluid.

2. Those employing volumetric positive displacement where the prime mover of the diaphragm is electro-mechanical, working through a crank or geared motor drive, or purely mechanical, such as with a lever or handle. This method flexes the diaphragm through simple mechanical action, and one side of the diaphragm is open to air.

3. Those employing one or more unsealed diaphragms with the fluid to be pumped on both sides. The diaphragm(s) again are flexed, causing the volume to change.

When the volume of a chamber of either type of pump is increased (the diaphragm moving up), the pressure decreases, and fluid is drawn into the chamber. When the chamber pressure later increases from decreased volume (the diaphragm moving down), the fluid previously drawn in is forced out. Finally, the diaphragm moving up once again draws fluid into the chamber, completing the cycle. This action is similar to that of the cylinder in an internal combustion engine. Diaphragm Pumps deliver a hermetic seal between the drive mechanism and the compression chamber, allowing the pump to transfer, compress, and evacuate the medium without a lubricant.

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Figure 1: Type 2 Pump

An elastomeric diaphragm can be used as a versatile dynamic seal that removes many of the limitations found with other sealing methods. They do not leak, offer little friction, and can be constructed for low pressure sensitivity. With the right material consideration, diaphragms can seal over a wide range of pressures and temperatures without needing lubrication or maintenance.

Diaphragm pump characteristics:

Have good suction lift characteristics, some are low pressure pumps with low flow rates; others are capable of higher flow rates, dependent on the effective working diameter of the diaphragm and its stroke length.

Suitable for discharge pressure up to 1,200 bar

Have good dry running characteristics.

Can be used to make artificial hearts.

Are used to make air pumps for the filters on small fish tanks.

Can be up to 97% efficient.

Have good self priming capabilities.

Can handle highly viscous liquids.

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CONCLUSION

In this report cylinder design calculations are aimed to find thickness, which is calculated separately for cylindrical and domes portions and finalized, through various processes. Once the design is finalized, cylinders are produced from a specified raw material through various processes. Internal stresses in cylinders are relieved in heat treatment process. Cylinders are marked with unique serial number and tare weight. after various tests cylinders can be send to the the market.

REFERENCES

Websites

1. en.wikipedia.org/wiki/Liquefied_petroleum_gas2. www.iocl.com/products/lpgspecifications.pdf3. www.elgas.com.au/blog/453-the-science-a-properties-of-lpg4. edugreen.teri.res.in/explore/n_renew/lpg.htm

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