Fedorenko A. Thermophysical processes of flameless combustion of flammable gas impurities on a dispersed catalyst

The dissertation is devoted to the research of processes of influence of combustible gas thermodiffusion, porosity and size of catalyst, schemes of parallel reactions to critical conditions of catalytic spontaneous combustion and ignition of small contents of combustible gases (on the example of ammonia and hydrogen oxidation reaction on platinum dispersed catalyst) in the air; analysis of the phenomenon of self-acceleration of oxidation reactions in determining the conditions of hysteresis of heat and mass exchange and flameless combustion of gas and air mixtures; study of hysteresis modes of heat and mass exchange and flameless combustion of gas and air mixtures with impurities of combustible components. The hysteresis regions of heat and mass exchange of particles (darts) of the catalyst during the catalytic oxidation reaction with the consideration of the thermal diffusion of hydrogen in air are suggested to be described analytically in parametric form. The lower limit of the concentration of combustible gas impurity in the cold gas and air mixture is identified. This limit is determined as the potential for the realization of self-supporting stable catalytic combustion of gas mixtures at room temperature. This mode is applicable as a result of catalytic forced ignition by pulse preheating of the filament (par-ticles) above the ignition temperature. The dependence for determining the ignition tem-perature on the basis of the catalyst size is proposed. The specified temperature enables to estimate analytically the time of catalytic spontaneous combustion of the gas and air mix-ture at room temperature. The dependences of the stationary resistance of the platinum dart of the catalyst on the temperature of the gas and air mixture and the concentration of hydrogen impurities showing a hysteresis character were obtained analytically. This method is suggested to be used for research of the thermokinetic characteristics of the catalytic oxidation of carbon monoxide, hydrocarbons (methane, benzene, propane, butane), the synthesis of ammonia from nitrogen and hydrogen. The role of each of the parallel reactions of catalytic oxidation of ammonia (before the formation of nitrogen and nitric oxide) on a platinum dispersed catalyst in the thermophysical processes that ensures the implementation of stable stationary modes, catalytic spontaneous combustion and quenching (critical catalyst diameters, mixture temperature and combustible gas impurity concentration) under critical conditions are analyzed. The dependences of the critical temperatures of spontaneous combustion and quenching of the gas mixture, the critical concentrations of combustible gas impurities on the reduced diameter are minimal. The influence of particle porosity on the dependence of spontaneous combustion and quenching concentrations on the reduced particle diameter is investigated. The expression for analyzing the effect of porosity on the minimum concentration of combustible gas, above which spontaneous combustion of gases on the surface of the catalyst particle occurs is obtained.