Experimental study of flammability limits of methane/air mixtures at low temperatures and elevated pressures

Abstract

During the production of LNG, explosion hazards may occur in the top of the distillation column in the low-temperature liquefaction of oxygen-bearing coal-bed methane. Because of the lack of flammability limits at low temperatures, in this study, an experimental setup was built to measure the flammability limits of methane/air mixtures at a wide temperature range from 123K to 273K and pressure range from 0.1MPa to 0.9MPa. The results show that the trend of flammability limits at the initial low temperature and pressure is the same as that at high temperatures. With the increase in the initial temperature or pressure, the range of flammability limit becomes wider. The upper flammability limit (UFL) or lower flammability limit (LFL) linearly correlates to temperature. The UFL shows a logarithmic trend with the initial pressure, whereas the LFL is unaffected by the initial pressure. A significant difference is observed between the flammability limits obtained in this study and other studies because of the electrode position, size of explosion vessel, and criteria for explosion. In the top of the distillation column, the methane content is within the flammability limits, and explosion hazards may occur. Therefore, proper safety measures should be taken to solve this problem.