Concentration Measurement Technology for Ternary Gas Mixtures Using a Thermal Conductivity Gas Sensor

A method has been established to determine the ratio of each gas in a mixed gas containing CH4, CO2and H2using a thermal conductivity (λ) gas sensor composed of a silicon oxynitride membrane integrating Pt heater/thermometer lines encapsulated by reduced TiO2−δ. The sensor was operated by simply applying three different DC voltages (2, 3 and 5.8 V) to the Pt heater and its temperature (T) was measured in CH4, H2, CO2, and their gas mixtures. The results confirm that the theoretical λ of an ambient gas exhibits an almost completely linear correlation (coefficient of determination is almost 1) with the experimental quantity of ΔR−1, which represents the reciprocal of the rate of change in the Pt resistance. Two calculated λ (λcal) results for a gas mixture at two differentT’s yield two possible lines in the triangular λ-CH4, CO2and H2composition map and the intersection of the two lines determines the composition ratios. The error is within 4 vol% when the difference inTis large enough. These results suggest that the proposed method can provide a simple and robust approach for real-time gas composition monitoring in practical process environments, such as CO₂ methanation systems.