A study of the effect of air temperature on the possibility and rate of formation of nitrogen oxides in boiler flue gases

Abstract

We consider the mechanisms of formation of nitrogen oxides in boiler flue gases. Thermodynamic calculations are used to determine the possibility and rate of formation of nitrogen oxides in the temperature range from 25 to 2000°C. We apply the methods of geometric thermodynamics to demonstrate the changes in the Gibbs free energy of nitrogen oxides formation reactions and determine the conditions of achieving the chemical equilibrium for these reactions. An analysis of concentrations of formed nitrogen oxides and temperatures of the jet flame under different conditions of mixture formation was performed. We produced and analyzed a number of diagrams of distribution of the flame temperatures and nitrogen oxide concentrations in the calculation area for the temperatures of the oxidant of 20, 60, 100, 150 and 200°C. Mathematical simulation of the process of gaseous fuel combustion was performed using FlowVision software package. The analysis of the results showed that the decrease in the temperature of the air supplied as an oxidant results in a considerable drop in the concentration of nitrogen oxides in flue gases without any significant impact on the changes of the flame temperature. The results of the study can be used in addressing the problems of optimization of boiler plants in order to reduce harmful flue gas emissions.