Complex efficiency indicator for separators in dust-preparation plants

Abstract

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].