Effect of Electrophysical Factors on Formation of Noxious Emissions during Combustion of Gaseous Hydrocarbons

Abstract

At present, many problems of detoxification of noxious emissions generated on burning of hydrocarbon fuels (HF) cannot be solved successfully without a detailed theoretical analysis of the combustion process and without taking account of the physicochemical processes that lead to uneven distribution of various components in the gas stream as well as to a change in th e composition of the gas and the internal state of its atoms and molecules. Attempts to apply traditional semiempirical methods of control of noxious emissions produced during use of hydrocarbon fuels (HF) in practice, in general, lead to large expenditures on material resources and greatly impede development and introduction of high-efficiency industrial technologies [1‐6]. The HF combustion process may be regarded as a stream of multicomponent gases undergoing exothermic chemical reactions, and so this process can be described with certain approximations taking recourse to the kinetic theory of gases. The basic equations of gas dynamics based on the Boltzmann equation are the fundamentally important outcome of this theory, which made it possible to establish an unbroken link between the macro- and microprocesses in the stream. This allows one investigating streams of chemically reacting multicomponent gas mixtures to theoretically calculate internal flow, to determine the transport factor as a function of temperature, pressure, molecular weights of the gas components, and parameters that describe the laws of molecular interaction, and to determine the effect of external forces on the multicomponent gas mixture through interaction between the individual components of the gas mixture. We shall make an attempt, on the basis of solution of the Boltzmann equation for slightly unsteady and nonequilibrium states of a gas mixture, to determine the internal microstreams of a flame of gaseous hydrocarbons and the effect of these proce sses on the yield of individual components in the combustion process [1‐3]. The factors affecting the internal stream and the un balanced yield of individual components during combustion of gaseous HF arise from the process of combustion in the stream itself. A steep rise in the internal energy of the stream causes accelerated motion of the gas mixture and separation of the gas components. Moreover, in the space where combustion takes place, there appears thermal inhomogeneity, and if the relationship of the rate of formation of nitrogen oxides (NO x ) with the gas temperature is nonlinear, the yield of nitrogen oxides goes up beyond what is possible thermodynamically. Acceleration of the stream and the consequent thermal inhomogeneity alter the electrophysical parameters of the flame. Consequentially, the key factors affecting the increase in the yield of individual com ponents as a result of internal streams in the flame are thermal, gas dynamic, and electrophysical [1‐5]. These factors lead to disruption of the thermodynamic equilibrium in the combustion process. Even though occurrence of chemical reactions in a gas mixture may disrupt the Boltzmann energy distribution, investigations of the effect of chemical reactions on the transport factors however demonstrate that in many cases [4] this effect can be ignored. Analysis of the solution of the Boltzmann equation shows that in a multicomponent gas mixture diffusion of the components relative to the basic mass may occur due to pressure, temperature, and concentration gradients as well as due to the action of mass forces. These factors are interrelated and affect each other. In a first approximation, the dependence of the d iffusive stream of the components on the gradients of these parameters is linear. Note that if there are no external mass forces , the diffusive streams arising due to gradients of pressure, temperature, and concentration of the individual components do not give rise to macromotion of the system. In the end, they may merely counterbalance each other, and the time and extent of this balancing depend on specific interactions between the particles of the components. For example, in the case of accelerated