DETERMINATION OF KINETIC CHARACTERISTICS OF SOLID FUEL.

Abstract

The combustion process begins with the ignition of the fuel - bringing it to the auto-ignition temperature, which is one of the important components of the kinetic characteristics of the fuel.

Fuel ignition does not occur immediately - but after a certain period, during which activation energy is accumulated: heat or active centers, depending on the mechanism of the process - thermal-kinetic or chain-kinetic, sufficient to overcome the potential barrier. At the same time, the period of reaching the self-ignition temperature is the induction period of this reactive system: for self-ignition or the ignition time during ignition.

The purpose of the work is to substantiate the kinetic characteristics of the fuel: self-ignition temperature and induction period, methods of their experimental determination for solid fossil fuels and biomass waste.

According to the methodology, an installation was created for the experimental determination of the self-ignition temperature and the induction period of solid fuel in the layer.

Studies of such fuels as anthracite, hard coal, buckwheat husk, millet, oats, flax husks, birch wood, peat, and paper showed the dependence of the self-ignition temperature on the degree of metamorphosis and volatiles. With an increase in the degree of metamorphism and a decrease in volatiles in solid fuel, the self-ignition temperature increases. However, the self-ignition temperature does not depend on the size of its particles, their number in the layer and the temperature of the oxidizer.

The above allows us to conclude that the self-ignition temperature depends only on the conditions of heat exchange (accordingly, on aerodynamics), and the absolute value of the auto-ignition temperature for an infinite space, in the absence of a jet stream, is a constant value, and only then, in the presence of heat exchange (with velocity gradients) , takes one or another value.

It was found that the induction period depends only on the initial temperature of the process, the induction period decreases with increasing temperature. This is due to the more intensive transfer of heat to the fuel particles due to the increase in the temperature gradient and the acceleration of the development of the oxidation reaction.

The induction period, as shown by the conducted experiments, does not depend on the size of the particles. This can be explained only by the fact that the rate of thermal destruction of the fuel is close to the rate of its heating. The burning time of coal particles, on the contrary, depends on the size of its particles.

Expressions for determining the autoignition temperature and the induction period were obtained based on the processing of the results of the conducted experiments.

The results of the work can be used in combustion technologies, in which self-ignition of fuel is one of the main components of the process - it ensures combustion in the self-ignition mode of fuel when in contact with an oxidizer.