Investigation into the Influence of Temperature on the Formation of Nitrogen Oxides during the Staged Combustion of Low-Reactive Coal with the Use of Direct-Flow Burners

Abstract

Coal remains one of the main types of mineral fuel in Russia, especially in the Siberian and Far Eastern federal districts. At the same time, the requirements for reducing emissions of harmful substances into the atmosphere, including nitrogen oxides NO_x, are becoming tougher both in Russia and around the world. In this regard, it is promising to use the vortex method of coal combustion using slot burners and collective action nozzles with a stepped air supply for combustion. However, when burning low-reactivity coal, it becomes necessary to achieve high combustion efficiency, which can only be ensured with the correct organization of the furnace aerodynamics, including the location of burners and nozzles, as well as with the optimal distribution of the shares of primary, secondary, and tertiary air. Using the example of vortex combustion of lean Kuznetsk coal using direct-flow burners and nozzles, the possibility of reducing nitrogen oxide emissions during staged fuel combustion is considered. A boiler with a steam capacity of 500 t/h with solid ash removal was taken as an object of the study. Two schemes of coal combustion were chosen earlier with the help of numerical and physical modeling. According to the calculations, both schemes provide low heat losses with mechanical underburning, at the level of 0.7–1.9%. Numerical modeling of the vortex combustion process showed that high maximum temperatures in the fuel ignition zone at low air excesses do not contribute to the formation of nitrogen oxides, but, on the contrary, contribute to their suppression due to the increased concentration of pyrolysis products in the main combustion zone. The temperature at the initial stage of combustion should be approximately 2000 K, and this figure is more important than reducing the excess of primary air from 0.3 to less than 0.1.