Search

The burner tilt angle has a significant influence on the combustion characteristics of a furnace, but few studies have focused on this topic. In this study, a numerical model was developed and validated to investigate the effect of the burner tilt angle on the combustion and NOX emission characteristics of a 700 MWe pulverized-coal-fired boiler with deep-air-staging technology. The turbulence, heat transfer and chemical reactions in the furnace were reproduced in detail by the model. Deep insight into the effects of burner tilt angle on combustion and NOX emission characteristics was acquired. The results show that the turbulence intensity in the burnout zone of furnace increases as the burner tilt angle increases, leading to a significant increase in the reaction rate of CO combustion. Hence, the level of CO emission is continuously reduced. The char burnout rate changes little with increasing burner tilt angle since the kinetic reaction rate and oxygen diffusion rate increase while the particle residence time decreases. The NOX emission increases as the burner is tilted farther upward because of an enhancement in fuel NO formation and a decrease in NO reburning. This study provides useful guidelines for improving the performance of deep-air-staged tangentially coal-fired boilers.

Coal combustion is one of the major pathways by which lead (Pb) enters the ecological environment. An effective method to control Pb emissions in a furnace is to transform the Pb from vapors to particles using Si-Al-based sorbents. However, the high price, poor thermal stability, and difficult molding of sorbents limits their application. Fly ash cenospheres (FACs) prepared from the waste of coal-fired power plants, which are mainly composed of SiO2 and Al2O3, are ideal materials for Pb sorbents because of their high strength, light weight and low price. In this study, the adsorption and reaction mechanisms of FACs and several Si-Al-based sorbents for Pb vapors were investigated in a two-stage fixed-bed reaction system, and the thermal stability and regeneration characteristics of FACs were tested. The results indicate that the adsorption capacity for Pb vapors is FAC > kaolin > SiO2 > γ-Al2O3. The acidic sites, such as Si-O and Al-O bonds in FACs, were the main reaction sites for Pb adsorption and captured Pb in the form of stable Pb compounds (Pb2+). As the temperature increased from 700 to 1200 °C, the Pb adsorbed by FACs increased, and 55.21% of the Pb in the simulated flue gas was removed at 1200 °C. Kaolin is an excellent sorbent for Pb vapors. The adsorption capacity of kaolin for Pb first increases and then decreases with increasing temperature, and the maximum removal rate occurs at 1000 °C, reaching 33.46%. In addition, FACs are thermally stable and reusable. Therefore, the high-temperature application of FACs to remove Pb vapors has good prospects.