TECHNICAL SOLUTIONS FOR DECREASING NOX EMISSIONS AT COAL THERMAL ELECTRIC POWER STATIONS

Abstract

Most power-generating units at the Ukrainian thermal electric power stations were designed to burn hard coal mined in Ukraine, but today due to physical depreciation of the stations, those units are in non-project manoeuvring peaking operation what leads to the increase in both the specific fuel equivalent consumption and in harmful environmental emissions. The purpose of the research is to develop recommendations on the selection of optimal technical solutions aimed at reducing NOx emissions of oxides at the operating boilers of Burshtyn thermal electric power stations (TEPS) under the conditions of regime-technological measures. The article analyzes the main approaches to developing and selecting technological methods aimed at reducing emissions of coal thermal power stations and identifies prospects for their work in accordance with modern environmental requirements. The mechanisms of the transformations the organic fuel bound nitrogen undergoes when heated are determined. To reduce the amount of NOx emissions in combustion products, it is offered to apply the regime-technological mode of the preliminary heating the pulverized coal mixture. The results of thermo chemical studies of coal samples used at Burshtyn TEPS are presented. The temperature ranges are determined at which the maximum emissions of volatile combustible compounds takes place before to the upper flammability limit of the pulverized coal mixture is reached. It was determined that under the conditions of actual burning process, there is a clear sequence: a release of volatile components and burning of the coke residue; heating of the pulverized coal mixture; emission of volatile combustible compounds; their burning; heating of the coke residue up to initiation of its combustion; the coke residue burning-out. A pulverized coal stream is brought into the furnace without being preliminary mixed up with air. While burning the pulverized coal stream, fuel particles are heated and degassed in the zone immediately adjacent to the burner section where there is a shortage of oxygen, whereas the oxygen concentration in the flow is a gradually increasing. The regime-technological measures that are aimed at inhibiting NOx oxides formation by preliminary heat treatment of the pulverized coal mixture; they make it possible to obtain the maximum emissions of volatile combustible compounds before the upper flammability limit of the pulverized coal mixture is reached. It was found out that heat treatment should be carried out at temperature from 540-580° C. This is the temperatures range when the maximum emission of volatile combustible compounds takes place. After this combustion occur in an environment that is practically devoid of oxygen, where competing reactions of formation of volatile components and molecular nitrogen occur simultaneously. Thereafter, combustion can proceed in the practically oxygen-free environment with competing parallel reactions the forming volatile components and molecular nitrogen. This method allows to almost halving the concentration of nitrogen oxides in flue gases.