Comparative Evaluation of Hydrogen Emission Quantification Methods at the Component Level Using Controlled Releases

Hydrogen (H₂) is widely regarded as a promising energy carrier for the energy transition, as it can be produced from renewable energy with low direct greenhouse gas (GHG) emissions and offers strong potential to decarbonize sectors that are difficult to electrify. Consequently, H₂ production is expected to increase in the coming decades. However, H₂ burden in the atmosphere indirectly contributes to climate change by extending the atmospheric lifetime of methane and leading to the formation of stratospheric water vapor and tropospheric ozone. The 100-year global warming potential of H₂ is estimated at 11.6±2.8. As the smallest naturally occurring molecule, H₂ is highly prone to leakage, and intentional releases may occur for operational or safety reasons. Despite this, anthropogenic H₂ emissions from non-combustion sources are poorly known, limited by the lack of availability of precise measurement solutions.

This study reports on a controlled release experiment to assess the performance and limitations of H₂ component-level quantification methods. Seven different methods are compared: a bagging method (leak enclosure with a controlled carrier gas flow), two high-flow sampling (HFS) methods (concentration measurement in high-flow rate suction of the leaking gas), and four acoustic imaging methods (converting sound levels in a microphone array into volumetric flow). The controlled H₂ releases are performed on a test bench at the Enagas Metrology & Innovation Center in Zaragoza, Spain. 15 blind controlled releases up to 313 g·h⁻¹ are generated on typical H₂ industry components, including a flange, a valve, and open-ended lines. Leak-rate restrictions are imposed on the instruments for safety reasons. The maximum measurable leak rate is 216 g·h⁻¹ for bagging, 35 g·h⁻¹ for HFS while acoustic cameras have no limitations.

Early results of the intercomparison suggest that the most accurate methods are one HFS method and bagging, with mean relative errors of 13 and 25%, respectively. The second HFS method exhibits a higher mean relative error of 38%.  In contrast, the acoustic camera methods show higher errors of 63%, 98%, 443%, and 1240%.

In conclusion, bagging, although time-consuming, provides reliable measurements across a wide range of leak rates. HFS delivers fast measurements with high accuracy for moderate leak rates but may be limited at very high rates. Acoustic cameras allow rapid detection without upper leak-rate restrictions. However, their quantification accuracy varies widely among methods making some more suitable for leak detection than precise measurement.