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[References: 42 tit.]

The results of experimental studies of the ignition processes of a large set of particles (from 100 to 500) of wood-coal composite fuels under conditions of high-temperature radiation-convective heating are presented. The ignition of wood-coal fuel mixture fuel particles was studied under the conditions of their free fall along the quill ceramic cylinder passage in a high-temperature oxidizing medium (air). Such a configuration provides the conditions that most closely match the heating conditions of actual furnaces of heat generating installations.The experiments have been carried out on the mixtures of particles of subbituminous coal (that is quite typical of coal-fired power industry) with the particles of woody biomass of three types: birch, pine and larch, which are widely spread in the territory of many states of the northern part of the Earth hemisphere. The recording of the heating and ignition processes of the fuel mixture particles was carried out with a high-speed Photron FASTCAM CA45 (500 fps) camera. The air temperature in the passage along which the particles moved varied in experiments from 873 K to 1273 K. The purpose of the experiments performed was the ignition delay time (tign). The main variable factors are the ambient temperature and the concentration of woody components. The consistent errors in determining the main characteristics of the process did not exceed 5%, the random ones did not exceed 13%. The size of coal particles in the experiments did not exceed 60 ?m, and of the wood - 5 mm.

It has been established that in such a fuel system one of the fuel components of the coal particle is "conducting" (or leading), and the second is "conducted" in the reaction of the thermochemical response of the fuel mixture with air oxygen. According to the results of experimental studies, the ignition delay times for the wood-coal particle mixtures have been stated. The increase in the concentration of small-sized coal particles in fuel mixtures from 0% to 100% leads to the decrease in the entire induction period (up to 20%) at the relatively cold temperatures. It was also found that with typical sizes of coal particles up to 60 ?m, stable ignition of sufficiently large wood particles (up to 5 mm), present in the mixture, is provided. The conditions and characteristics of ignition of wood-coal mixtures hardly depend on the type of wood, which is the second component of the mixture.According to the results of the research conducted and following the requirements for optimizing the processes of fuel combustion, the use of mixed coal- and wood-based fuels in boilers of large and small power plants is justified.