AS 4564:2020 General-purpose natural gas.
AS 4564 encompasses the range of Australian natural gases in general-purpose use at the time of publication.
In order to retain the greatest flexibility of supply no attempt has been made to detail the composition of the gas beyond those compounds normally regarded as gas contaminants and which have a detrimental effect on the properties of the gas.
Specification limits are generally consistent with overseas practice. The limit test gases used for the assessment of gas appliances to Australian standards are specified to match this specification, refer to AS/NZS 3645. In this respect the specification is intended to cover only those gases that are primarily methane. This specification does not cover other gases such as LP Gas/air mixtures and synthetic natural gas.
Requirements relating to limits on particular characteristics and components are contained in Table 4.1. More information on those characteristics and components and on contaminants is provided in this Appendix.
In any natural-gas specification, a balance must be achieved between optimum performance, which requires the narrowest possible combustion limits, and cost of supply, which if possible, requires no limits at all so that any available gas can be used. In an endeavour to resolve this issue, the limits are set as wide as possible while still maintaining safe combustion performance in gas burning appliances certified for use in Australia. If the specification of gas deviates from these limits both safety and performance may be compromised. This is dependent on the duration and extent of the deviation.
Although rate of change of variables within the limits is not addressed in this specification, it may be relevant to the performance of combustion control systems particularly in lean burn and low NOx applications. In addition, rapid changes in Wobbe Index for example may lead to customer complaints, as there may be a noticeable change in performance with some appliances.
A.3 Characteristics and components
A.3.1 Relative density
It is expected that for all practical gases available, or likely to be available commercially, relative density
values would be in the range of 0.55 to 0.70.
A.3.2 Wobbe Index
The Wobbe Index is a measure of the energy input rate to a burner at constant supply pressure and also relates to the combustion characteristics of the burner. A change in the Wobbe Index of the gas will result in a proportional change in the energy output of all gas appliances and equipment supplied, and in the energy carrying capacity of gas pipelines and distribution networks.AS 4564 pdf download.