To solve the problem of further improving the efficiency and reliability of solid fuel generation in the Russian Federation, it is necessary to solve a number of main problems: ensuring environmental safety, export-oriented nature of the coal industry, low reliability, efficiency, high emissions of NOx , SO2 and particulate matter of existing obsolete equipment. In modern conditions, these problems can be solved comprehensively with the use of relatively low-cost methods in the case of using highly reactive coals, which at the same time have an increased explosion hazard (coals of explosiveness groups 3 and 4). For this reason, currently a large number of coal-fired power plants (mainly in Siberia and the Urals) experience a global transition to the combustion of highly explosive Kuznetsk coal of grades D, G, GD. In the present work, analysis is undertaken of methods and technologies to ensure the explosion and fire safety of fuel preparation systems for combustion at thermal power plants during the transition to these types of fuels, since most of these thermal power plants were initially designed for explosion-proof types of coal (T, 1CC, AH). A number of additional recommendations are developed to the current "rules of explosion safety", taking into account the specifics of technological schemes and the operation of a large number of these thermal power plants, a number of design solutions for equipment that improve the explosion safety of their dust treatment plants. For systems of preparation of finely crushed fuel (5–15 mm), boilers with circulating fluidized bed that are promising for the Russian power industry, and the use of drying installations at thermal power plants to ensure crushing of ordinary high-humidity fuels entering thermal power plants, a number of measures have been proposed that increase the fire safety of such installations.

A relationship for determination of the complex efficiency hcom of a separator, which graphically reflects the effectiveness of its operation from the standpoint of both output of prepared dust with an assigned amount retained on a sieve, and also with consideration of the extent to which fine fractions of final dust are excluded from the return, is presented on the basis of analysis of existing methods of determining classifier efficiency, experience with their use in power engineering, and the function of dust separators of coal-pulverizing mills in the production process of boiler plants at TPP. A procedure is proposed for determination of the value of hcom when an assigned amount of final dust is retained on a sieve during operation. The possibility of determining complex separator efficiency for mills with a built-in separator is analyzed.Keywords: separators for coal-pulverization mills, boiler units, complex efficiency, fineness of millings, grindability of fuel.At the present time, it is accepted to consider weighed amounts of particles coarser than 90 mm (retained on the 90-mm sieve -R 90 , %), and coarser than 1,000 mm (retained on the 1,000-mm sieve -R 1000 , %) as basic parameters from which the quality of fuel dust prepared in the dust systems of boiler units is evaluated for combustion in chamber furnaces. The distribution function of the dust fractions is also a critical characteristic of the coal-dust fuel.The dust system is built with a certain structural and quantitative safety factor [1] in conformity with active standards; in the majority of cases, therefore, removal of dustpreparation equipment from service for restoration can be compensated by an available reserve (including the burning of reserve fuel). Since at the same time, the performance of the furnace determines the effectiveness of the boiler's operation, the quality of fuel dust should, for the most part, correspond to current requirements ensuring optimal conditions for the heating process [2, 3], even when economic and reliable operation of dust-preparation equipment is considered.Selection of dust fineness for optimal in-service performance is established on the basis of regime-adjustment tests, and is regulated in [1 -4] in the design stage. Based on conditions of combustion efficiency and ignition stability, and depending on the type of fuel and the design of the furnace unit, the fineness of the fuel dust, which is selected in the design stage of the boiler unit, should satisfy the values presented below in conformity with the methodical recommendations outlined in [2,3].

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Ensuring environmental safety for energy companies in accordance with the requirements of Federal Law No. 219 of 21.07.2014 is a top priority task today. Experimental studies and industrial experience show that one of the main factors for the formation of virtually all toxic fuel combustion products in boiler plants is the ignition conditions in each burner of the furnace: the fuel-air ratio in the ignition zone, the proportion of primary air, the ratio between the secondary and primary air velocities, etc. However, according to the current regulations, the calculation of emissions of fuel oxides of nitrogen, as well as benz(a)pyrene, is based on averaged values for all burners of the furnace, and the influence of the most important factor — the uniformity of the distribution of fuel and air over the burners — on their formation is not taken into account.In the work presented, a calculation analysis is performed of the effect of uneven distribution of solid fuel on the burners of boiler plants on emissions of nitrogen oxides, as well as benz(a)pyrene, in combustion products. A calculation procedure has been developed and the dependences of the change in NOx emissions on the nonuniformity of the Δg distribution, the average air excess factor in the αG burners, the number of burners and the dust distribution models have been obtained. It is shown that with the value of the parameter Δg <10%, the uneven distribution of fuel has practically no effect on emissions of nitrogen oxides and benz(a)pyrene, and Δg5 (at which the increase in NOx emissions due to uneven distribution of dust does not exceed 5%) should make: for two burners — 22% ... 27%, four — 12% ... 22%, six — 11% ... 13%. At higher values of Δg and with increasing α, there is a significant increase in emissions of nitrogen oxides and benz(a)pyrene. It is obtained that simultaneously there is a simultaneous increase in NOx and BP. Recommendations are given on the use of dust distribution circuits and designs of dust dividers that meet the requirements to ensure that the uneven distribution of fuel over the burners would not affect emissions of nitrogen oxides.

Translated from Élektricheskie Stantsii, No. 7, July 2008, pp. 10 -23.The successful introduction and setup of new designs for dust separators in Russian and foreign 200 -800 MW coal-fired power production units is described. Results from mathematical and physical modelling of these designs, as well as data on their operation in test stands, are presented. Recommendations are given for the most suitable equipment and configurations of new dust distribution systems in dust preparation systems.Keywords: dust-gas flow mixing distribution systems, introduction and setup, design models, test stand studies, mechanism for motion of stable dust layers, equipment recommendations.Operating experience and industrial research show that the operational efficiency and reliability of furnace systems, the explosion safety and operational reliability of dust preparation, the reliability and operating lifetime of heating surfaces, and the amount of nitrogen oxide emissions depend on the degree of uniformity of the distribution of fuel and air over the burners in a furnace. Failure to meet the required fuel-air ratio in the burners leads to a deterioration in ignition stability, reduced fuel burnup, and increased yield of toxic combustion products [1 -4]. Elevated concentrations of dust in the dust ducts can lead to dust deposits in the ducts or even to blockage of individual lines, which increases the explosion hazard for the system and reduces the productivity of the dust system [5 -7]. Nonuniform heating in different burners causes greater distortions in the temperature over the cross section and height and may make the flare stretch into the upper part of the furnace and cause a rise in the temperature at the furnace outlet; this sharply reduces the service lifetime of the heating surfaces and causes slag buildup on them [1,3,8,9].During operation of dust preparation systems this nonuniformity can be extensive (up to 100%) owing to different fuel dust feed rates at various outlets from the system: three-way distribution feeds, turns, separators, etc. Even with a uniform distribution over the outlets for the transport air, the dust can fall into one or several outlets as it is extruded toward the channel walls [9]. If the dust system includes dust ducts with greatly differing lengths and configurations, as is typical of most coal-fired thermal power plants with highpower energy production units, an additional nonuniformity is imposed on the distribution of air over the outlets.It should be noted that efforts to introduce new technologies and equipment for fuel burning may not yield the expected theoretical effect, if the specified distribution of fuel feed rate over the burners is not ensured. These problems are especially pressing in connection with the tasks now facing the national power generation system of enhancing the steam parameters (which requires the elimination of temperature distortions at steam superheater surfaces) and meeting modern ecological standards (through use of stepwise combustion and the strict need to ma...