Uncertainty associated with the energy content in flow measurement of natural gas including real-time correction for fluid properties

A procedure is proposed to calculate the uncertainty of the energy content associated with real-time flow measurements of natural gas. The procedure was applied to a measuring scheme consisting of an arrangement of orifice plate meters installed in parallel, coupled to an on-line gas chromatograph and a real-time data processing flow computer. Two distinct sources of natural gas with appreciable fluctuations in chemical properties were considered. The analysis suggests that the uncertainty depends mainly on these fluctuations, on the flow regime and on systematic errors. The work also suggests that the chemical analysis-sampling rate plays an important role in the overall uncertainty budget.