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High-volume sampling system to measure methane emissions from natural gas refueling infrastructure

University of British Columbia

Natural gas has gained attraction as an alternative fuel for heavy-duty vehicles due to its lower prices and carbon dioxide (CO₂) emissions as compared to diesel. However, methane is the main component of natural gas, and it is a potent greenhouse gas (GHG). The global warming potentials (GWPs) of methane are 86 and 34 times as high as those of CO₂ in 20- and 100-year horizons, respectively. The potential of natural gas to reduce GHG emissions from heavy-duty vehicles can be undermined if enough methane is emitted along the natural gas supply chain. A high-volume sampling (HVS) system was developed to accurately quantify methane emissions from the pump-to-tank (PTT) segment or the natural gas refueling infrastructure. This segment is the least documented portion in the life cycle analysis of natural gas. The accuracy of the HVS system was validated by comparing the measurements with known flow rates of injected methane and CO₂. The results showed that the HVS system was capable of measuring steady-state leaks and transient emissions with a maximum uncertainty of 6.6%. The utility of the HVS system was demonstrated to measure methane emissions from a pilot and fully-operational time-fill compressed natural gas (CNG) refueling station. A data set of component-level emission rates from compressors, component and nozzle leaks, and nozzle venting events was generated. The results showed that compressors were a significant source of emissions in the pilot station, contributing 88.6% to the annual emissions. Prior to regularly scheduled maintenance, compressor emissions and nozzle leaks in the fully-operational station contributed 32.9% and 66.6% to the annual emissions, respectively. The PTT methane emissions from the pilot and fully-operational stations were 1.4±0.8% and 0.7±0.7% of the total throughputs, respectively. Using these data, practical solutions were recommended and implemented to reduce the PTT methane emissions by 80±20% and 98±2% in the pilot and fully-operational stations, respectively. The HVS methodology presented in this study can be applied to accurately quantify methane emissions from a wide range of natural gas refueling infrastructure including fast-fill CNG and liquefied natural gas (LNG) refueling stations, and LNG bunkering facilities.

Text

2020-05-13

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/74430

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/