Assessment of the Hi-Flow Sampler Characteristics and Potential Failure Modes when Measuring Methane Emissions

The Bacharach Hi-Flow Sampler (hi-flow) has been widely used to monitor methane (CH4) leaks from various industrial sources, however CH4 emission estimates calculated from these measurements have recently been challenged due to possible issues with instrument performance. This study focused on improving the understanding of the performance of the hi-flow by investigating both its characteristics and potential failure modes. The hi-flow was tested in a laboratory by delivering test gases directly to the measurement sensor thus bypassing high volumes of test gas and flow rate dependency of leaks. We split the hi-flows sensor into three modes, catalytic oxidation (CO), thermal conductivity (TC) and a middle region. Our results showed good linear performance in the CO and TC modes with reasonable uncertainty, however the calibration factor changes from experiment to experiment thus highlighting the importance of regular calibration. Measurements in the middle region are dominated by noise with poor linear results. Results showed that instrument failure due to high non-methane hydrocarbons (nmHC) only occurred sometimes. A hypothesis to explain this was demonstrated both experimentally and theoretically. We found the hi-flow to be a suitable instrument for measuring methane emissions if operated correctly and with knowledge of its limitations.