Influence of furnace combustion conditions on NOx emission from lignite flames

Abstract

Coal combustion in boiler furnaces is followed by emission of pollutants, i.a. NOx compounds. The appropriate activities have been conducted lately for lowering this emission and satisfying the ecology requirements. Therefore, the knowledge of NOx formation mechanism in furnace conditions is of great importance. In the paper presented are the results of an application of the developed model on the computation of the chemithermodynamic equilibrium of a system formed by compounds and elements contained in the Kolubara basin lignite and the combustion air, at temperatures from 800 to 1700 K, pressure 1 bar, for two lignite compositions at excess air α = 1,25. The briefly outlined developed mathematical model used for shaping the computation algorithm takes into account only the thermal oxides formation mechanism which is for Kolubara lignites, having low nitrogen content, the dominant NOx formation mechanism even at lower combustion temperatures. The results obtained are of use, as thermodynamic indicators, for lowering NOx emission by adequately organizing and conducting the combustion process, i.e. by preventing formation of temperature zones with NOx emission above the allowed values. A sample computation of the equilibrium composition of the system has been performed for the stoichiometric combustion case, thus illustrating the possibility of NOx emission lowering by applying the so-called sub-stoichiometric combustion.