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Chapter 1GAS TYPES

MARKETED

IN

AUSTRALIA

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Gas types

Marketed in Australia for gas appliances:

• Natural gas (NG)

• Liquified petroleum gas (LPG)

• Tempered liquified petroleum gas (TLP)

• Simulated natural gas (SNG)

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Natural gas

• Formed by:– decaying organic matter– compressed by sediment layers– build-up of pressure and heat converted to:

gas oil

• Gas production– Exploration– Drilling– Production wells– Treatment– Delivery

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Formation of natural gas

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Liquified petroleum gas (LPG)

Types of LPG– Propane – Butane– Autofuel

Produced by:– by-product of natural gas wells– oil refineries

• Stored in cylinders by moderate pressure.

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Tempered liquified petroleum gas (TLP)

Developed to replace towns gas in small provincial cities.

Towns gas substitute produced by using propane or butane as a feedstock and mixing it with precise amounts of air.

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Simulated natural gas (SNG)

Used where natural gas is expected to become available.

– Produced by using propane or butane as a feedstock and mixing it with precise amounts of air.

– When natural gas arrives installations and appliances can be connected with minor adjustments.

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Other gases

• TOWNS GAS– Produced from coal.– Later produced from oil.

– Gas contained condensate (tail pipes required).– Toxic gas.

• PROCESSED NATURAL GAS– Produced from natural gas to produce simulated towns gas

until converted to natural gas.

These gases no longer available in Australia.

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Properties of gases

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Characteristics of gases

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Heating value

This is the measurement of the amount of energy liberated when one cubic metre of gas is completely burnt in air under standard test conditions.

Measured by the number of megajoules (MJ) in a m³.

Natural gas 38 MJ/m³

LPG (propane) 96 MJ/m³

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Relative density

This is the weight of gas relative to the weight of air.

Air = 1

Natural gas RD 0.6 (lighter)

LPG (Propane) RD 1.5 (heavier)

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Burning velocity

(also known as flame propagation)

This is the speed at which the flame can consume the gas.

Natural gas 400 mm/second

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Air requirements

Air must be available for complete combustion to take place.

Air to gas ratio =

natural gas 9.5:1 (gas)

LPG (propane) 24:1 (gas)

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Ignition temperatures

The air–gas mixture must be ignited by sufficient ignition temperature.

Natural gas 680°C

LPG (propane) 490°C

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Flammability limits

(Also known as explosive limits)

Not all air–gas mixtures are combustible.

Lower explosive limits(LEL)

This is the minimum percentage of gas mixed in air that will burn or explode e.g. NG 5%

Upper explosive limits(UEL)

This is the maximum percentage of gas mixed in air that will burn or explode e.g. NG 14%

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Toxicity

This is whether gas is toxic or non-toxic (poisonous).

Natural gas non-toxic

LPG non-toxic

Towns gas toxic

Note: Although some gases are non-toxic, it must be remembered that an escape of gas can result in fire, explosion and asphyxiation.

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Odourants

All gases have odour added before distribution to the customer.

Odour is added to gas sufficient to be detected

at one fifth LEL by smell.

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Gas types—Summary

Natural gas and LPG (propane) are the most common types of gas available in Australia for appliance installations.

Consideration of gas types is an important part of installation, appliance design and operation.

Installers must understand how the different gas types work to ensure the installation and appliance operate safely.

Safe work practices must be followed while working around gas.

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