Validation of ISO 6974 for the measurement of the composition of hydrogen-enriched natural gas

Hydrogen gas is considered as one of the means to store electrical energy generated from wind or solar sources. The produced hydrogen gas could be injected into natural gas grids and thus utilised. Currently, most fiscal metering systems for natural gas are not configured for measuring the hydrogen content, notwithstanding that hydrogen is found in some natural gases in low fractions. Neither do the current documentary standards ISO 6974 and ISO 6975 cover hydrogen levels above 0.5 cmol mol−1. To support fiscal metering, measurement standards and validated methods are needed to facilitate accurate composition and energy content measurement. The aim of this work was to develop measurement standards for hydrogen-enriched natural gas with uncertainties for the amount-of-substance fraction hydrogen similar to the analysis of methane and nitrogen in natural gas, as well as to validate ISO 6974 for use in this power-to-gas application. Measurement standards have been developed with state-of-the-art uncertainty for the composition for hydrogen fractions between 3 cmol mol−1 and 16 cmol mol−1. A natural gas analyser configured according to ISO 6974-3 was used to confirm the composition of the measurement standards. We conclude that the scope of the current ISO 6974 can be extended to cover natural gas compositions with hydrogen amount-of-substance fractions of up to 20%. The best measurement capability obtained is 0.12% (k = 2), expressed as relative expanded uncertainty.