Methane Gas Visualization Using Infrared Imaging System and Evaluation of Temperature Dependence of Methane Gas Emissivity

Infrared (IR) camera has been used widely in the industry to visualize gases that cannot be seen by the naked eye or a visual camera. The use of an infrared camera for gas imaging offers several advantages such as faster locating of gas leaks and easier understanding on how the gas travels and disperses. In addition, several types of infrared cameras have the capability to measure the temperature of target objects especially solid body objects. However, this facility has not been applied for measurement of gas temperature clue to complex analysis on the physics of infrared imaging and some uncertainties related to the radiation heat transfer processes during temperature measurement that have not been well underslood. The objective of this research is to make use of the infrared or thermal imaging, system to provide a concise temperature distribution of a methane gas plume presented in the infrared image. However, the current technology in infrared imaging cannot provide the true temperature of a gas plume because the emissivity value is always assumed as unity, and the actual emissivity value of the gas is not integrated in the camera's algorithm. The visualization of dispersed liquefied natural gas (LNG) vapor from LNG spills on the ground using a midwave thermal camera is presented in this work. Two types of infrared cameras were used: Amber Radiance 1 and GasFindIR, also known in industry as hydrocarbon camera. The infrared images or thermograms show that several factors affecting the temperature measurement are weather conditions, wind rose, atmospheric attenuation due to the presence of other radiation absorbing gases along the optic path, and gas emissivity. Gas emissivity is the main uncertainty in gas temperature measurement using thermal cameras. This research proposed a method to correct the gas temperature measured by a thermal camera by applying the emissivity factor calculated from a theoretical analysis on methane gas emissivity using the band absorption method. The study demonstrates that methane gas emissivity is a strong function of gas temperature; however, the effect of optical depth is insignificant. Because in this work, the infrared camera is used to visualize the LNG vapor, temperature dependence of methane emissivity at temperatures 110-300 K is evaluated and presented in this paper.