Infrared Optical Imaging Techniques for Gas Visualization and Measurement

Advancement in infrared imaging technology has allowed the thermal imaging to detect and visualize several gases, mostly hydrocarbon gases. In addition, infrared cameras could potentially be used as a non-contact temperature measurement for gas and vapor. However, current application of infrared imaging techniques for gas measurements are still limited due to several uncertainties in their performance parameters. The aim of this research work was to determine the key factors in the application of infrared imaging technology for gas visualization and a non-contact temperature measurement. Furthermore, the concentration profile and emission rate of the gas are predicted by combining the application of the infrared imaging method with gas dispersion modeling. In this research, infrared cameras have been used to visualize liquefied natural gas (LNG) plumes from LNG spills on water. The analyses of the thermograms showed that the apparent temperatures were different from the thermocouple measurement which occurred due to the assumption of that the object emissivity was always equal to unity. The emissivity for pure methane gas and a mixture of methane and atmospheric gases were then evaluated in order to obtain the actual temperature distribution of the gas cloud. The results showed that by including the emissivity value of the gas, the temperature profile of the dispersed gas obtained from a thermal imaging measurement was in good agreement with the measurement using the thermocouples. Furthermore, the temperature distribution of the gas was compared to the concentration of a dispersed LNG vapor cloud to obtain a correlation between the temperature and the concentration of the cloud. Other application of infrared imaging technique was also conducted for leak detection of natural gas from a pipeline. The capability of an infrared camera to detect a fugitive gas leak was combined with the simulation of vapor discharge and dispersion in order to obtain a correlation between the emission rates and the sizes of the gas plume to the minimum detectable concentration. The relationship of the methane gas cloud size to the gas emission rate was highly dependent to the prevailing atmospheric condition. The results showed that the correlation were best to predict the emission rate less than 0.2 kg/s. At higher emission rate, the increase in gas release rate did not change the size of the cloud significantly.