Advances in metrology for energy-containing gases and emerging demands

Abstract

Metrological services from National Metrology Institutes related to energy gases have been supported by the programme of key comparisons of the Gas Analysis Working Group of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology since its conception in 1993. Most of the key comparisons have been performed on natural gas composition measurement, which is key to the calculation of natural gas properties, thereby facilitating fiscal metering and the trade in natural gas. In the recent years, non-conventional energy gases and natural gas substitutes, such as refinery gas and biogas have been addressed. The paper gives an overview over the achievements in this area from the first key comparison (CCQM-K1) onward and outlines the current challenges to the metrological community. The ongoing energy transition towards renewable energy gases is at the centre of these challenges. The associated emerging challenges primarily concern the measurement of the concentrations of impurities, such as silicon in biomethane and upgraded biogas, carbon monoxide in hydrogen, and many others. The paper presents the first results of the development of measurement standards and methods for impurities in biogas, biomethane and hydrogen and the implications for the programme of key comparisons.

Bilateral comparison VSL-NPL on primary gas standards for the siloxane content in biomethane

“…Both institutes maintain PSMs for the amount fractions of siloxanes in methane [7]. If so required, these amount fractions can be converted into concentrations for, e.g., the purpose of conformity assessment in relation to the biomethane specification [1,2].…”

“…Over the course of the comparison the stability of Mixture 2 was evaluated using three different PSMs prepared in 2017, 2019 and 2021 (see figure 3). The limits used in figure 3 have been obtained from the development work [7] and do not only account for the stability of the amount fraction of the siloxanes over time, but also between-cylinder effects.…”

“…These measurement or test methods require metrologically traceable calibration of the instrumentation used, for which CRMs are needed. Substantial work in the development of the primary standard gas mixtures (PSMs), needed to facilitate the production and supply of CRMs, has been undertaken [4][5][6][7]. As the specification for the silicon concentration in biomethane is very low (down to 0.1 mg m −3 [8]), and siloxanes (and other silicon-containing volatile organic compounds (VOCs)) are reactive, it is challenging to develop and maintain such PSMs.…”

On modelling of artefact instability in interlaboratory comparisons

“…For circulating artefact comparisons, [12,13] consider linear trend models. In [14], several studies on the stability of gas mixtures are discussed and, in addition to model choices that account for instability, a fixed or random effects model is considered (see also [13,15]). For a discussion on random stability effect models, we refer to [16,17].…”

Dark uncertainty in key comparisons in the gas analysis area

“…In this paper, we compare the Bayesian hierarchical model developed previously with the evaluation using independent reference values, in this case reference values obtained from static gravimetric gas mixture preparation [9,10], which has been widely applied in key comparisons [11,12]. For this comparison, the data sets from previous natural gas key comparisons CCQM-K16 and CCQM-K23 [4][5][6] have been chosen, as these enable a detailed comparison with the results of CCQM-K118 [3].…”