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Chapter 13LIQUIFIED PETROLEUM GAS

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Liquefied petroleum gas

Liquefied petroleum gas (LPG) is the name given to a whole group of gases. These are gases that are stored as a liquid (under pressure and temperature).

Propane is the most common LPG marketed throughout Australia.

Autogas is a blend of propane and other LPGs, such as butane. It cannot be used in domestic applications.

LPG—Propane• Can be stored as liquid, and will vaporise rapidly so

that it can be burnt as a gas.

• Boiling point of propane is -42°C.

• Pressure within a propane cylinderTemperature Vapour pressure

0°C 372 kPa

15°C 627 kPa

4 0°C 1247 kPa

When liquid propane changes from a liquid to a gas, it expand 273 times.

One litre of liquid LPG expands to 273 litres of vapour.

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Vaporisation rates

The vaporisation rate of propane is determined by the following:

1. The volume of liquid in the cylinder (wet area of the cylinder).

2. The temperature to which the cylinder is exposed.

It is important that the volume of gas being drawn off from the cylinder does not exeed the vaporisation rate from the energy being conducted through the cylinder from the surrounding air.

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Icing up of cylinders

The liquid propane in a cylinder absorbs energy from the air surrounding the cylinder and therefore contains energy. If gas is drawn off faster than the air surrounding the wet area can vaporise it, the energy contained within the liquid will be used to assist with the vaporisation.

This will cause the temperature of the liquid propane to drop.

When it reaches the temperature of the dewpoint of the air surrounding the cylinder, condensation will form on the cylinder.

If the draw continues and the liquid temperature continues to drop the condensation will ice up.

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Decanting procedures

• Decanting is the transfer of liquid from cylinder to cylinder or tank to cylinder without the use of a pump.

• Following correct procedures when decanting is undoubtedly a most important safety factor when handling propane.

• Cylinders of 9 kg or less are generally filled by decanting. The correct fill level is 83% (approx).

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Cylinders and pressure relief valves

– Cylinders to be constructed and tested to comply with Australian Standards.

– Pressure relief valve to be fitted to vapour section of cylinder.

– Cylinder relief pressure 2585 kPa.

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Twin-cylinder installation

Comprises:• Regulator

– Manual changeover– Automatic

changeover

• Pigtails• Cylinders• Base• Pipework

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Location of cylinders—Refer to AS 5601

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Multiple-cylinder installations

• Cylinders’ manifold connections.

• Regulator sized to cope with load.

• Multiple-cylinder installation may require local authority approval.

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Caravan installations

Location of cylinders, pipe work, appliances and ventilation to comply with AS 5601 and applicable state laws.

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Marine installations

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Tank installations

1. Liquid filling valve

2. Service line valve

3. Stage one regulator

4. Expansion loop

5. Liquid level gauge

6. Pressure gauge

7. Pressure relief valve

8. Medium pressure line

9. Valve

10. Stage two regulator

11. Internal installation

12. Tank earthing

Installation of LPG tanks must comply with AS 1596.

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LPGas—Summary

• LPG types: propane, butane, autogas.

• LPG is transportable, contained in cylinders and stored as a liquid under pressure.

• One litre liquid expands to 273 litres vapour.

• LPG installations can be single or multi-cylinders or bulk tanks.

• Also used in caravans and marine applications.

• Installations to be in accordance with AS 5601 and/or AS 1596.

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