Formation Characteristics of No and N2o During Air-Staged Combustion of Pulverized Coal

Abstract

In this study, air-staged combustion experiments of pulverized-coal were carried out using a down-fired furnace, the effects of furnace temperature, air staging degree, and injection position of the burnout air on the formation pattern of NO and N2O were preliminarily explored, and macroscopic patterns of changes in the concentration of the components inside the furnace chamber were obtained. The results indicate that under air-staged combustion conditions, NO always appears before N2O, and the reduction of NO is accompanied by the generation of N2O at higher concentrations. The strong multiphase reductive environment likely causes the formation of N2O due to the reduction of NO. There is a reciprocal pattern in the concentration changes of NO and N2O along the pathway, primarily because there is an interconversion relationship between NO and N2O under high-temperature of air-staged combustion conditions; N2O formation is always accompanied by the production of high concentrations of CO, representing the reductivity of the combustion atmosphere. Different furnace temperatures directly affect the intensity of combustion, with an increase in temperature facilitating the formation of NO, while the formation of N2O decreases as the temperature rises, mainly due to temperature control. The degree of air staging determines the strength of the multiphase reductive environment in the reduction zone, further affecting the formation of NO and N2O. The change in the injection position of burnout air mainly influences the length of the reduction zone in air-staged combustion, thereby impacting the reduction of NO and the formation of N2O. By establishing a multiphase flow reaction model for the formation and reduction of NO and N2O under the air-staged combustion of pulverized coal, the deficiencies of the original model were remedied, and the formation of N2O and the second rise of NO were successfully predicted.

Keywords: Air-staged combustion, NOx, Model, High temperature, Coal