Quantitative optical gas imaging, or QOGI, can serve as an additional measurement method for leak detection in industrial facilities. Several studies under laboratory and field conditions have examined how reliably the technology can detect and quantify fugitive hydrocarbon emissions.
Leak Detection Compared with Method 21
A study funded by Concawe and conducted at VITO in Belgium compared an early QOGI system with Method 21 using 61 controlled hydrocarbon releases. According to the study, the QOGI system detected all of the leaks examined. Quantification errors ranged from -23 to 69 percent, with an average error of 6 percent.
For Method 21, the study reports an error range of -92 to 667 percent and an average error of 31 percent. For the QOGI system examined, the temperature difference between the gas and the background was a factor. The study describes reliable performance at a difference of at least 5 °C (9 °F).
Measurement Conditions Affect QOGI Results
Further studies show that measurement accuracy does not depend on the technology alone. In a study in Zaragoza supported by the European Gas Research Group, the values determined with QOGI were typically within a factor of three of the actual emission rates. Release rate, background, ambient conditions, and operator procedures and preparation all influenced the results.
Tests at Colorado State University’s METEC also illustrate this relationship. In 357 measurements across 26 release scenarios, 75 percent of the QOGI quantifications were within a factor of three of the actual emission rate. Better results were achieved with low wind speeds and clear skies, among other conditions. Taking measurements from multiple positions also helped reduce outliers.
QOGI as a Building Block for LDAR and MRV
In the Alberta Methane Field Challenge, QOGI was used at around 50 oil and gas sites. There, the technology served purposes including screening and the creation of site-specific emission profiles. The study reports an overall error of 18 percent.
The studies described thus provide indications for the use of QOGI in leak detection and repair programs as well as in measurement, reporting, and verification. At the same time, they show that measurement procedures, ambient conditions, and user qualifications must be taken into account when evaluating the results.
QOGI can make emission sources visible and quantify their magnitude. However, the available studies also reveal the method’s limitations and influencing factors. For operators, a defined approach to carrying out measurements and evaluating them is therefore particularly relevant, in addition to the measurement technology itself.
