Multi-component photoacoustic gas analyzer for industrial applications

We present here a diode laser based photoacoustic system for multi-component analysis in a carrier gas with widely varying composition and prove its practical applicability. The selected application of the system is the analysis of the side products of experimental hydrogenation reactions for converting waste hydrocarbons into utilizable compounds in the oil industry. The requirement for our system is therefore the capability of simultaneous and continuous monitoring of the concentration of all main side products, i.e. methane, water vapor, carbon dioxide, carbon monoxide in the presence of heavier hydrocarbons, in the hydrogen carrier gas. The analysis of the four different compounds is carried out using two near-infrared distributed feedback (DFB) diode lasers (with 1371 nm and 1581 nm wavelengths). The system contains a resonant photoacoustic cell with two resonator tubes for the two light sources in which the measuring microphones are separated from the sampled gas by a membrane in order to prevent damages caused by precipitation of heavier hydrocarbons. The minimum detectable concentrations were determined to be: 0.003% for water vapor, 0.13% for carbon monoxide, 0.16% for carbon dioxide and 0.06% for methane. The system is operated continuously at an experimental reactor and there is a good agreement between its readings and the results of off-line gas chromatographic analysis.