Dunayevska N. Scientific and technological principles of combustion processes of non-designed fuels in boilers of thermal power plants

A number of actual and critically important theoretical and applied problems aimed at the formulation of the technological fundamentals of the off-design fuels (the fuels whose characteristics were not taken into account at the stage of boiler design) combustion in the existing boilers of TPP and CHP are solved. The processes of high-ash anthracite, "salty" coal of the Northern Donbas, separate biomass, mixtures of biomass and anthracite effective combustion in existing boilers and technologies for their realization were deeply analyzed. As a result of this the following technologies of domestic coal use are properly substantiated: thermochemical preparation of anthracite (TCP); preliminary partial removal of Cl and Na from salty coal; co-combustion of anthracite, biomass and bituminous coal in existing boilers. The prospects and expediency of their practical introduction are proven. The limiting parameters and the natural gas / coal consumption ratio (~ 0.6% for heat) have been theoretically and experimentally proven for the optimum thermochemical preparation of anthracite group coals, which provides the optimal degree of autothermicity of the process and the optimum residence time (0.1 c) of coal particles in the high temperature zone that minimizes the consumption of natural gas at the TCP, which in turn makes possible the determination of the operating parameters and geometry of TPPs burners. The proposed modernized burner with TCP has been installed on the operating boiler ТПП 210 A boiler and effectively burned anthracite group coal with the extremely high ash content (up to 30%) which is well above the design value. The modernized burner has been in the operation for 1,5 years and has shown a reduced natural gas consumption for "backlighting" (from 10% to 0.6% on thermal base), reliable slag removal, including that whilst on reduced loads. For the first time, the technology and original burner for the combustion of natural gas in the dust-coal-air stream have been developed. Its aerodynamic and thermophysical parameters, the limits of stable combustion have been determined. The prototype has been created and tested on the active equipment. Based on theoretical and experimental research of burner with thermal capacity of 70 MW and calculations of in-furnace processes, the reduction (up to 20%) of total emissions of nitrogen oxides was substantiated. It has been shown for the first time that the technologies of combustion of solid biomass and anthracite in pulverized coal boilers significantly expand the scope of energy use of biomass compared to the foreign practice of co-firing exclusively with bituminous coal and semi-anthracite. It has been experimentally established that the addition of solid biomass improves the conditions of anthracite ignition, including the coal with the increased ash content, while emissions of pollutants per the share of the involved biomass are reduced. For the first time, a synergistic effect was observed with the co-thermolysis of biomass and high-ash anthracite (4-10% additives misbalance on a solid residue) due to the influence of volatile biomass and their interaction with coke anthracite. The effect is confirmed by two independent experimental methods - thermogravimetric and spectroscopic. The kinetic constants of the processes of dehydration, the yield of volatile and combustion of the coke residue of coal of varying degrees of metamorphism, the heterogeneous solid biomass and their mixtures were determined based of the thermogravimetric and Isothermal reactor techniques. The Arrhenius rate coefficients and frequency factors were determine within the differential and integral approach. The kinetic constants were used in the determining of the minimum fuel residence time in the furnace, material balance of the components and the duration of the constituent processes of the combustion. The calculations aimed at the obtaining of maximum combustion efficiency. The design of the burner itself and the technological scheme of its the implementation within the anthracite - biomass co-combustion technology in the ТПП -210A boiler have been developed. The technology of biomass combustion in communal boilers using natural gas has been developed. The original pre-furnace for the ДКВР-2.5 boilerwere designed and manufactured. The growth (on 10-17%) of the burnt-out of increased ash content anthracite mixture with gas coal in the flow reactor within the studied ratios (10-30% of bituminous coal) has been observed. For the first time, a comparative analysis of native minerals of aqueous extracts of salt coals of domestic deposits was performed. It has been shown that the NaCl content ranges from 66 to 91% by weight. The technology of water desalting of the coal of the Northern Donbas has been improved by combining the enrichment and washing functions of the jigging machines.