TDLAS Detection of Propane/Butane Gas Mixture by Using Reference Gas Absorption Cells and Partial Least Square Approach

Propane/butane gas mixtures are frequently used in the petroleum industry and sensors that provide early warning of the concentrations of such mixtures are essential for avoiding explosion hazards. Tunable diode laser absorption spectroscopy (TDLAS) underpins this paper, exploiting infrared absorption spectroscopy and providing the potential to provide a highly accurate, in situ and intrinsically safe method for the detection of propane/butane gas mixtures. In consideration of the significant spectral overlap of the absorption spectral features of propane and butane, an experimental approach using reference gas cells has been proposed to remove the severe absorption spectral overlapping that occurs by using known samples of both propane and butane gas in the reference gas cells. The partial least squares method was used to calculate the concentrations of propane and butane individually in the mixture. The spectral overlapping can be effectively removed, resulting in all the fitting correlation coefficients for the spectral extraction being higher than 0.96. A field test carried out using simulated gas samples shows that near both the first and second alarm values set, high accuracy can be obtained in the measurement, with all the relative errors in the calculated concentrations of propane and butane (in the gas mixture samples) below 3% lower explosion limit, which meets the requirement of the detection standards in the petroleum industry. This paper provides an experimental verification which then supports this being an effective TDLAS-based field sensor system for the petroleum industry to be used in practice.