Numerical investigation on IRZ dimension and optimization of a 0.3MWt swirl oxy-firing flame in high confinements

Abstract

In oxy-coal combustion, the Internal Recirculation Zone (IRZ) can effectively improve the flame stability and propagation. Therefore, it is necessary to investigate both the formation of the IRZ and the optimization of the oxy-firing flame in high confinements. The present work investigates the primary four factors which significantly affect the formation of the IRZ and the optimization of the oxy-firing flames. These factors include the V-type flame holder, the secondary stream (SS) swirl number, the recycle ratio, the oxygen pressure fraction in the primary stream (PS). The numerical object is a new swirling oxy-burner for the 0.3MWt pilot-scale facility in HUST. In the procedure of the numerical investigation, the important chemical reaction scheme needs to be considered for oxy-firing flames, including the four-step global reaction mechanism in the Finite-Rate and Eddy-Dissipation (FRED) model and the gasification reactions with H2O and CO2. The conclusions are that these four factors significantly affect the formation of the IRZ and the optimization of a 0.3MWt swirl oxy-firing flame can be obtained in high confinements. Both the pressure fraction of oxygen in PS and the recycle ratio can seriously affect the flame stability and propagtion. The V-type flame hold can significantly affect the maximum recirculation rate (qmr/q m0)max. The maximum IRZ dimension can significantly keep the flame stability and propagation. Correspondingly, the stabilized flame belongs to the Flame type-II. © Tsinghua University Press, Beijing and Springer-Verlag Berlin Heidelberg 2012.