Vol 53, No 1 (2019)

The thermal decomposition of the mixtures of two types of dispersed coals and shredded wood in a temperature range until the complete pyrolysis of the organic matter of both components at different concentrations was experimentally studied in order to evaluate the prospects of using these fuels as composite fuels for large- and small-scale power plants (combustion in the furnaces of steam and hot-water boilers). It was established that the joint thermal decomposition of a mixture of coal and wood particles leads to a significant change in the pyrolysis temperature range and the release of anthropogenic gases (sulfur and nitrogen oxides) in the case of the high-temperature heating of such a mixture based on lean coal. A similar effect, but on a much smaller scale, was detected for a mixture based on long-flame coal. A hypothesis on the mechanism of sequestering sulfur and nitrogen oxides on the thermal decomposition of a mixture of lean coal and wood particles as a result of the interaction of intermediate gaseous and solid products of coal and wood pyrolysis in a temperature range to 1000°C was formulated. The possibility of using a mixture of crushed coal and wood as fuel for steam and hot water boilers was substantiated. With a certain decrease in the energy characteristics of such fuels compared to homogeneous coals, the environmental and economic characteristics of fuel burning processes were significantly improved. It was shown that a significant synergistic effect of co-combustion of particles of coal and wood is achieved only in certain coals.

The results of a study of the steam gasification of carbonized brown coal samples at 700°C depending on the composition of mineral components, textural properties, structural ordering of the organic matter, and the type of a gasifier are reported. It was found that the native calcium content is the main factor responsible for the reactivity of carbonized brown coal. Treatment with acid solutions led to the almost complete extraction of calcium, which was accompanied by a sharp decrease in reactivity upon gasification. It was hypothesized that the found behavior was associated with the participation of native calcium compounds (in oxide and/or carbonate forms) in the catalysis of carbon gasification reactions with water vapor.

The paper analyzes the processes occurring on the interaction of high-power nanosecond laser pulses with a coal–water mixture prepared from gas-coal waste. It was found that the rate of production of a mixture of CO and H₂ sharply increased at a laser radiation intensity higher than 8 J/cm². This was expressed in a sharp increase in the concentration of the combustible components of synthesis gas (CO, up to 0.57 vol %) and in a noticeable acceleration of the growth of the mass of a gas–aerosol fuel mixture upon the absorption of laser pulses (by 40%). At low pulse energy densities, the generation of a finely dispersed (particle size, 30–70 μm) fuel aerosol was a predominant process. Gasification came into play above the effective ablation threshold when the weight ratio between synthesis gas and the sprayed aerosol reached 1 : 3. Thus, the action of laser pulses makes it possible to convert coal preparation wastes into a highly flammable gas–aerosol fuel mixture.

The samples of granulated (2–3 mm) active carbon were prepared by the alkaline activation of a mixture of soot and oil pitch (50/50) followed by washing and drying (the first stage). At the second stage, the prepared granules were steam activated at temperatures of 700–750°C. As a result, samples with a carbon loss of 10–56% were obtained; in this case, the specific surface area increased from 423 m²/g for a sample not subjected to steam activation to 723 m²/g for a sample with a carbon loss of 56% (the specific surface area increased by 70%). An analysis of the dependences of the specific surface area and strength on the carbon loss showed that both pitch coke and the material of soot particles reacted with water vapor in the course of activation. Taking the first order of reaction with respect to water vapor, we determined the apparent kinetic constants of the rate equation of a reaction of water vapor with the material of carbon granules. The low activation energy (202 kJ/mol) indirectly indicated a high reactivity of the granules obtained; this allowed us to perform steam activation at a temperature 100–150°С lower than that in the case of traditional activated carbons.