Methane emissions at pressure-regulating stations in China: A comparative analysis of various quantitative methods.

As a key component of the distribution system, metering and pressure-regulating (M&R) stations provide an opportunity for effective mitigation of methane emissions. Given that these stations are readily accessible, above-ground facilities, routine methane emission monitoring can identify issues and with repair or upgrades this can lead to reduced methane emissions. This practice has become an important measure for addressing climate change. China aims to actively promote the monitoring, evaluation, and inventory improvement of distribution systems. In this study, methane detection and analysis were conducted at 11 pressure regulation-metering stations operated by a company in North China and Central China. Methane emissions were estimated using the dynamic flux chamber method, the inverse Gaussian plume modeling method (OTM33A), and the stochastic Lagrangian (LS) inverse modeling method. The results of the dynamic flux chamber method indicate that flanges, instrumentation and meters, and connectors are the primary sources of methane emissions at pressure-regulating stations, with emission factors of 0.0034 kg/h (CI: 0.0030-0.0038 kg/h), 0.0022 kg/h (CI: 0.0018-0.0025 kg/h), and 7.1e-04 (CI: 6.3e-04-8.0e-04) kg/h, respectively. The correlation between detected concentration and emission rate was weak. The cumulative fluxes calculated by the three methods were 0.109 kg/h (CI: 0.094-0.125 kg/h), 0.143 kg/h (CI: 0.015-0.337 kg/h), and 0.125 kg/h (CI: 0.035-0.218 kg/h). The results of controlled tests and field measurements suggest that the LS method offers a more reliable and physically accurate analysis of methane fluxes for pressure regulating-metering stations with limited measurement distances (typically less than 30 m) and small continuous emissions. The emission factor for the pressure-regulating stations in this study is 0.013 kg/h (CI: 0.008-0.023 kg/h) using the bootstrap Monte Carlo method. This research provides guidance for operators to implement fixed monitoring, which is crucial for building emission inventories and ensuring production safety.