| Summary: | 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.
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