Quantifying Methane Emissions

Rapid reduction in methane emissions is a crucial step to limiting climate change and its impacts. But identifying where and when methane leaks, and accurately quantifying emission rates requires new ways to measure plumes.

UQ’s Gas and Energy Transition Research Centre (UQGET) has developed an autonomous system using a quantum gas LiDAR working closely with QLM Tech the LiDAR developers. The system can safely identify, visualise and accurately quantify methane emissions at a local scale filling an important gap in fugitive monitoring and provides a step change in methane measurement accuracy.

Our research includes successful controlled release trials to verify the system’s accuracy with range, windspeed and weather conditions, with a journal publication in preparation. During remote field trials in autonomous mode the system identified, visualised and quantified emissions 24/7 through sun, wind and rain.

Measuring fugitive emissions rates is inherently difficult and for methane it can be potentially dangerous. Current approaches include measuring changes in atmospheric methane concentrations at multiple point locations or require natural daylight to help illuminate plumes or use infra-red to detect temperature contrasts in gas plumes. When benchmarked, many of these methods have been shown to have large errors for rate estimation.

Quantum gas LiDAR

The UQGET LiDAR system comprises a methane LiDAR mounted on a mobile trailer that provides a stable elevated observation platform with data logging, power and communications. The LiDAR comprises an eye safe tuneable diode laser that performs absorption spectroscopy and differential absorption LiDAR to detect and discriminate methane in air to measure its three-dimensional distribution. The single photon avalanche diode sensor enables rapid detection that combined with laser scanning optical system provides the ability for 20x zoom and measurement of low leakage rates (<10 L/min, 0.4 kg/hr, 3.8 Tonnes/yr, 0.2 TJ/yr) at distances over 100 m. The UQGET methane LiDAR system provides 4-D visualisation of potential methane sources with the capability to autonomously scan, focus and record over hours and days. The system provides detailed information of what is emitting methane, when, where, for how long and at what rates.

Objective

The objective of the UQGET methane LiDAR system is to safely visualise and accurately quantify methane emissions over minutes, hours and days. This provides insight on how emission rates vary and on mechanisms causing fluctuations and the information necessary for prioritising emission abatement and to test whether abatement works.

Application

Known sources of methane include livestockagriculture (ruminants), manure and silage, landfills, bio-digesters in waste and water treatment, natural gas extraction, transmission and use, coal mining and anerobic decomposition in surface waters.

The UQGET methane LiDAR system complements top-down space or aerially based fugitive monitoring platforms that are increasingly available to provide emission estimate snapshots during daylight. Satellite methods can rapidly survey large areas for methane concentration but suffer from high detection limits and typically rely on regional scale weather information to estimate emissions. Further research and partners are needed to test the systems abilities for longer duration, and more accurate plume detection and quantification, than other local survey methods such as drones or hand-held methane detection equipment.

This work is funded by UQ Gas and Energy Transition Research Centre.