(390c) Infrared Optical Imaging for Advanced Gas Leak Detection

Infrared imaging technique is used in industry as a method to detect fugitive leaks from equipment and pipeline systems. Optical imaging is considered as a smart LDAR (Leak Detection and Repair) because it can scan a large number of equipment in relatively short time compared to detection using Total Vapor Analyzer (TVA) or ?gas sniffer'. In addition, the ability of infrared optical imaging system to visualize the gas plume which is not visible to naked eyes offers another advantage. However, this novel technique poses a lot of challenges in its application due to many uncertainties related to the sensitivity of the camera and factors which may affect measurement. Infrared imaging technique has been used in this research to detect methane gas leak from pipelines and monitor LNG plume from LNG spill. In this work, some significant factors affecting measurement such as gas emissivity, atmospheric attenuation, and stimulated radiation from other objects than the target are being evaluated. Furthermore, potential use of infrared imaging technique for methane gas emissions estimation is proposed in this research. This is carried out by assessing the sensitivity of the infrared camera during monitoring the gas release in order to obtain the minimum detectable gas concentration that still can be observed by the camera under real meteorological conditions. From this test, the correlation of mass flow rate and distance to minimum detectable concentration will be withdrawn. Prior to the test, discharge and dispersion simulation of methane gas at various pressures, temperatures and leak sizes is performed to calculate the gas release rate and predict the downwind concentration of methane gas. Several types of infrared imaging technique also have the capability as a non-contact temperature measurement and thus they can provide a spatial temperature distribution of a target object. This facility is used in this research to demonstrate the temperature profile of LNG gas plume in case of accidental spill of LNG on the ground. However, there is a high discrepancy of the cloud temperature measured using infrared camera to the thermocouple reading. This research has been able to identify the most significant uncertainty which comes from unspecified emissivity of the LNG cloud. The methane gas emissivity is not included in the detector's algorithm and therefore the apparent target temperature shows much higher value than the actual one. In this study, the methane gas emissivity as a function of temperature at different optical depth is analyzed using band absorption model.