Feasibility Study of a Fugitive Methane Emissions Sensor (23.RP1.0171) – Completed

The challenge

Methane emissions are the second largest contributor to greenhouse gas emissions. In natural gas production and processing, where methane is the main component, fugitive emissions from incomplete combustion, venting and methane slip, are critical issues.

A wide range of measurement methods have been tried on-site to understand the severity of this issue; however, those results were inconsistent each other. Thus, a feasibility study on current methane emission sensing methods was deemed essential, with sensing performance to be evaluated with respect to minimum detection limit, accuracy, response time and repeatability.

The solution

The first phase of this work implemented an evaluation kit of a commercial methane sensor — Molecular Property Spectrometer^TM (MPS^TM) flammable gas sensor, manufactured by NevadaNano — to test with nominated gas mixtures. Sensor response time was one of the key metrics, including ppm level of methane in gas mixtures, both in the presence and absence of a membrane. Dependence on configuration – how the components were installed in a sensor unit housing –  was followed by an uncertainty analysis of methane detection to understand the variability of results.

The second phase introduced a plume experimental setup designed to better represent real-world conditions, that addressed the limitations of the earlier lab-scale tests. Key activities included the construction of a new test rig, which focussed on sensor sensitivity between 200-400 ppm, conducting dynamic testing protocols, and performing parallel measurement comparisons with the MPS Dev Kit, Woodside Intellisense Pulse Unit, and IRwin GC benchmark. The plume simulation setup featured a 2-metre pipe and controlled methane injection, enabling accurate assessments of the sensors’ initialisation periods and detection limits at a varied methane concentration.

The outcome

Through a series of systematic testings with varying temperature conditions, membrane installation configurations and methane concentrations, a deep understanding of the commercial methane monitoring sensor’s capabilities and limitations was achieved. The project found that the NevadaNano MPS sensor was not able to detect methane concentration at 200 ppm despite measuring after enough warm-up time (30 min prior to the test). This raises the sensor’s sensitivity and reliability issues, especially for detecting low methane concentrations.

Outcomes indicated the reliability of the nominated sensor and gave guidance on its mechanical design for on-site use. Dynamic tests simulated real-world scenarios with varying methane concentrations, revealing critical insights into the sensor’s performance.

While the sensor demonstrated consistent response times across different temperatures and configurations, notable deviations in measured concentration were observed, particularly with certain membrane installation configurations. The configuration with the membrane attached to a spacer exhibited significant inaccuracies in methane concentration readings in some instances, highlighting the importance of proper installation methods.

While the inability of the sensor to detect methane concentrations of 200 ppm is a significant limitation, the NevadaNano MPS sensor could be used for methane detection, particularly in high-methane concentration environments.

The impact

The key findings underscore the importance of thorough testing to ensure reliable and consistent methane detection, and the importance of proper initialisation protocols to ensure reliable methane detection in field applications. The project also highlighted the critical importance of proper membrane installation to ensure accurate methane concentration measurements.

Next steps

Further investigation is needed to (i) understand the underlying causes behind why the sensor struggles to detect these concentrations and (ii) a pilot-scale test to identify potential limitations for field uses.