Sharabura T. Improving the processes of thermal treatment of coal-water fuel from low-grade coal and coal refinement waste

The dissertation focuses on studying the processes of thermal treatment of coal-water fuel produced from low-grade coal and coal refinement waste, considering its thermokinetic transformations and thermophysical properties for effective substitution of natural gas in boiling houses and other power units. The correlations between heat conductivity coefficients of coal-water fuel and solid phase-water ratio, coal metamorphosis stage and mineral impurities content within the temperature range 40…150оС were established experimentally. It was proved that heat conductivity coefficient of coal-water fuel increases in comparison with that of coal and alternates within the range 0,4…0,8 W/m·К depending on coal metamorphosis stage, and it grows as the temperature rises in the stated range. Experiments and theoretical research allowed to define the laws of thermokinetic transformations under the influence of thermal impact within the set temperature range and pressure from 0,1 to 5 МPа applied to the coal-water fuel produced from coals at different metamorphosis stages. It was established that thermal pre-treatment of coal-water fuel at 150…200оС results in changes in the organic fuel substance with formation of combustibles constituting 38…44% from the total amount of steam-gas phase, which improves parameters of its flammability and increases efficiency of its burning under further thermal treatment. Processes of thermal treatment of coal-water fuel from low-grade coals and coal refinement waste were numerically computed for conditions of double-shaft cyclone gasifier, considering thermokinetic transformations, thermophysical properties and specifics of thermally pre-treated coal-water fuel burning. Rational modes of gasification processes and coal-water fuel combustion ensuring carbon conversion degree to 89…96% have been worked out. Generator gas, obtained as a result of air gasification at 900…1050оС, contains 24…30% of combustibles and its caloricity is 4,3…5,5 MJ/m3, for oxygen gasification - 61…68% of combustibles and caloricity is 10,9…12,5 MJ/m3 accordingly. Research into the process of thermally pre-treated coal-water fuel allowed to determine rational modes ensuring steady burning at 1100…1350оС with dry ash removal. The process of thermal treatment of coal-water fuel at 900…1500оС was ecologically assessed which enabled to define characteristics of sulfur- and nitrogen-containing components forming in the generator gas under air and oxygen gasification, as well as in the combustion products of coal-water fuel and purified generator gas. Thermotechnical computational theoretical research into the peculiarities of small capacity and medium capacity steam boilers (of ТП and ДКВР types) operation resulted in the development of mode cards and recommendations regarding shifting of these power units to burning coal-water fuel from low-grade coals and coal refinement waste, as well as the products of its thermal treatment.