Performance of Gas Mixing in a Flux Chamber

Abstract

Flux chambers are often employed in measuring the surface emissions of methane, carbon dioxide, and other minor species, such as volatile organic compounds, from municipal landfills. In this study, several operational parameters, including arrangement of sweep air tubes, control of exhaust flow, and installation of a mixing fan, were elucidated for the mixing of a flux chamber. Toluene was used as a tracer gas as it is one of the most commonly found volatile organic compounds (VOCs) in landfill gas. Air samples were collected at the exhaust line of the chamber using a vacuum sampling box and Tedlar bags. The samples were then analyzed by a gas chromatograph equipped with mass spectrometer. The measured concentrations of the samples were compared to theoretical calculation based on the completely flow stirred tank reactor (CFSTR) model. The results from this study revealed that control of exhaust flow produced interference to the mixing of air in the chamber, no matter that the sweep air tubes were arranged in vertical or horizontal style. However, as the exhaust flow was left without control, a horizontal arrangement of the sweep air tubes was capable of creating a well-mixing environment for the chamber after 2 chamber’s retention time. The system was also tested with an addition of quartz sand under the chamber. A well-mixing situation in the chamber was also observed for the new system, indicating that the tested operational parameters may be applied to the measurement of surface emissions of VOCs in municipal solid waste landfills.