Investigation of the operation of thermocatalytic sensors in explosion hazard monitoring systems for technogenic objects

Purpose. The research aims to theoretically and experimentally investigate the operation of thermocatalytic sensors in the entire range of possible concentrations of explosion-hazardous vapors and gases to assess the unambiguous operation of explosion protection equipment. Methods. Analytical methods, classical provisions of electrical engineering, thermodynamics and catalysis, experimental studies of serial single-chamber pellet-type thermocatalytic sensors with a platinum-palladium catalyst, as well as the evaluation and generalization of experimental results are used in the research. Findings. It has been found that when monitoring the explosion hazard of gas mixtures using thermocatalytic sensors, the maximum measuring bridge output signal value is observed at a concentration of combustible gases where the complete reduction of oxygen sorbed by the catalyst is ensured. However, at higher concentration of combustible gases, when insufficient oxygen is available on the catalyst surface for complete oxidation, a decrease in the measuring bridge output signal value is observed. It is shown that, unlike gas-air mixtures, it is impossible to reduce the bridge output signal to zero in the region of high fuel-vapor concentrations, and the minimum bridge output signal value depends on the partial pressure value of oxygen in the fuel-air mixture when it is saturated with fuel vapors, which ensures the unambiguous operation of explosion protection equipment in the entire range of possible explosion-hazardous concentrations of fuel vapors. Originality. It has been determined that when using thermocatalytic sensors to control the explosion-hazardous medium during the oxidation reaction of the fuel-air mixture in the diffusion region at the stoichiometric value of the diffusion fluxes of combustible components and oxygen to the surface of the catalytically active sensor element, short-term dips in the measuring bridge output signal of gas analyzers are observed. At high concentrations of fuel vapors, when oxygen becomes a limiting agent in the mixture, the bridge output signal is inverted, which is a consequence of a more active oxidation reaction on the comparative thermocouple. Practical implications. The conducted research allows us to recommend thermocatalytic sensors for use in explosion hazard monitoring systems of oil-fuel complex facilities, the main tasks of which are to control the explosion hazard of the medium and timely adoption of control decisions aimed at eliminating the threat of explosion, and to substantiate their power supply modes.