Infrared differential absorption Lidar (DIAL) measurements of hydrocarbon emissions

Abstract

We report the application of an infrared (IR) differential absorption Lidar (DIAL) system (also capable of ultra violet measurements) built at the National Physical Laboratory (NPL), UK, to field measurements of total site emissions (controlled and fugitive) from petrochemical and landfill installations. The validation of the IR-DIAL was carried out via a series of controlled field experiments including comparison to GC analysis and tests against controlled methane releases from a test stack, all detailing agreements on the order of ±20%. In volatile organic compound (VOC) measurements at a UK petrochemical site it was found that the American Petroleum Institute's methodology of the time for calculating the emitted flux underestimated by a factor of 2.4. Also, in a similar field trial it was found that scaling traditional point measurements at easily accessible flanges and valves to represent all flanges and valves on a site led to an underestimation by a factor of 6. In addition to petrochemical examples we also report field measurements from a landfill site to demonstrate the advantageous of the DIAL technique for monitoring area emission sources. In this case study it was found that active (still being filled) cells resulted in significantly greater VOC emission rates (30 kg h(-1)) than closed (≤ 10 kg h(-1)).

Field Validation of Remote Sensing Methane Emission Measurements

“…The individual DIAL emission rate values were determined by combining the 2D methane distributions with the wind profile information using NPL's in-house processing suite which implements the processing steps described in Reference [8]. This processing is carried using a set of scripts within the MATLAB™ package.…”

“…Data capture is started by a data acquisition trigger synchronized to the firing of the infrared source, with up to 16,000 samples acquired (per laser shot) with each sample spaced by a Lidar range of 3.75 m. The digitized data is averaged, typically for 500 laser shots (250 pulse pairs), to reduce random noise. More details of the NPL DIAL capability are given by Robinson et al [8]. It should be noted that the system deployed in these field campaigns is a newer version of the facility described in this paper; however, the relevant details of its operation and application are unchanged.…”

“…Many developers of emission measurement instrumentation, using both remote and in-situ sensing techniques, have gone to significant lengths to ensure the quality of their measurements. Such quality assurance methods include the use of internal calibration gas cells [8], testing with external gas cells [9], inter-comparisons between different methods [10], and measurements of known point releases [11]. However, there are a number of limitations in these processes.…”

“…However, it has been shown that with such approaches there is a significant risk of underestimation. For example, it has been found that measuring leaks at easily accessible flanges/valves and scaling these up to represent all flanges/valves on a site can lead to as much as a six-fold underestimation in site emissions [8].…”

Differential Absorption Lidar (DIAL) Measurements of Landfill Methane Emissions

“…The scanner system directs the output beam and detection optics, giving hemispheric coverage in both the horizontal and vertical planes. For more information about the system, see Robinson et al [14].…”