Uncertainty analysis of energy measurements in natural gas transmission networks

The value of natural gas depends on the energy obtainable from its combustion. Despite this, natural gas measurement and billing are normally performed using volume measurements subsequently converted into base conditions.Thus, to correctly achieve network balancing and accurate billings, both civil and industrial natural gas consumptions should be measured in energy. Unfortunately, energy measure- ments for natural gas are actually possible only in an indirect way by means of complex measurement chains with a flow-meter, a volume conversion device and a gaschromatograph or gas analyzer. Moreover, for technical and economic reasons, gas quality is often considered as constant and known despite the unavoidable variations due to the mixing of gases from different origins and type (i.e. importations, national productions, liquefied, biogas). In this paper the authors present the results of a detailed metrological experimental analysis of the typical energy measurement plants installed in natural gas networks. Modern networks are character- ized by a wide variety of flow-rate measurement principles, constructive technologies and plant configurations. Therefore, flow regimes, thermodynamic conditions and chemical properties of the gas play a crucial role in determining metrological performance of natural gas energy measurements and uncertainties can become critical for inaccurate billing and unaccounted for gas.