Gas appliances need to be configured for a specific range of pressure and gas compositions. Safe operation of gas appliances can only be maintained for a small range of pressure and chemical mix as represented by the Wobbe Index.
Natural gas domestic installations are normally supplied at the outlet of the meter with a prescribed pressure of 1.25 kPa. The gas installation piping is normally sized to ensure that a pressure of 1 kPa is available to each appliance connected to the installation. This ensures that all appliances operate safely and perform adequately.
Where high pressures are available in the reticulation system, Natural Gas domestic customers can be supplied at the outlet of the meter with a pressure of 2.75 kPa. This higher pressure allows the installation piping to be reduced in size as a greater pressure drop can be allowed across the installation.
LP Gas installations normally operate at a pressure of 2.75 kPa. This pressure is set at the gas pressure regulator adjacent to the cylinder or tank. The installation piping is usually sized to ensure a pressure of 2.75 kPa is available at the appliances.
Chemical composition / Heating effects
The heating effect or value of hydrocarbons increases with molecular weight i.e. propane burns hotter than methane. Gas appliances are configured for a given range of Wobbe Index. Operating outside these parameters can cause inefficient or even unsafe combustion.
Natural Gas is predominantly hydrocarbons mostly methane with smaller amounts of ethane, propane, propene or butane and other gases nitrogen, carbon dioxide and possibly hydrogen.
Methane liquefies at minus 161 degrees Celsius. Natural Gas from the Carnarvon basin offshore gas field is liquefied at the LNG plant at Dampier, Western Australia prior to being shipped overseas by special tankers to Japan, China and other countries.
A parameter that gives a relative measure of the mix/heating value is the Wobbe Index. For Western Australia, the Wobbe Index ranges from 46.5 MJ/Cu m and 51.0 MJ/Cu m.
LP Gas is a mix of hydrocarbons propane, propene, butane or butene.
Both Natural Gas and LP Gas are colourless, odourless and tasteless and have an odorant added to aid the detection of leaks by making the gas easy to detect by smell.
Pressures are monitored throughout the gas distribution system by the network operator. Consumers who believe that they are not receiving the correct pressure or quality of supply should contact their gas retailer.