Numerical Study On The Aerodynamics During Pulverized Coal Combustion Process And Its Application

The aerodynamics during the pulverized coal combustion process plays a very important role in determining processes of coal devolatilization, burnout and pollutant emission. In this dissertation, coal combustion processes in the swirling burner and in the blast furnace were numerically studied, respectively. For the burner, the inner relationships among NO_x emission, gas flow and gas/particle mixing characteristics were systematically analyzed. As for the pulverized coal injection (PCI) system of blast furnace, effect of various structures, operating parameters on the combustion in the zones of the tuyere and raceway was investigated as well.During the simulation of the burner, relations among the coal particle size, its residence time inside the inner recirculation zone (IRZ) and the effective time of IRZ were given. By monitoring the oxygen concentration distributions along the coal particle trajectories, the coal combustion characteristics for different particle sizes and swirling numbers were quantitatively discussed. Further, research of their effect on the NO_x production was conducted.In most reported study of char combustion, the energy distribution between the gas and solid phase always unreasonably neglects the effect of gas combustion inside the boundary layer of the char particles. In regard to such shortcoming, the energy distribution coefficient (Xc) was carefully discussed in present study, where the homogeneous oxidation of CO and the surface reduction of CO2 were taken into account. And, impacts of the coal property and coal diameters on energy distribution coefficient were investigated in detail. All these efforts are committed to providing more precise prediction of the char combustion.The Discrete Transfer Method (DTM) has great advantages in industrial application to calculate the radiative heat exchange, but its detailed application procedure in three-dimensional cylindrical media has not been reported. In this study, a new method for DTM used in three-dimensional cylindrical system was developed. By transforming the cylindrical coordinates to Cartesian coordinates, the radiation ray equation was easily developed and the intersection points of the radiation rays in all three-dimensional angles with various radiation unitary bodies at all emission points were determined. The distance between the emission point and intersection point was obtained easily. With the intersection points being arranged in proper order according to the distance values, the DTM can be used for the radiative heat transfer in a three-dimensional cylindrical system efficiently.A three-dimensional multi-phase model using Eulerian approach has been developed to simulate the coal heat transfer, devolatilization and combustion process inside a blast furnace tuyrere. The model was applied to predict the coal combustion characteristics and effect of coal properties, particle diameter and injection angle on the coal volatile matter released rate and coal burnout inside a blast furnace tuyere.Numerical simulation has been conducted to study the coal devolatilization and combustion process inside tuyere and raceway for different tuyere diameters. The velocity field, temperature distribution, and combustion characteristics have been determined to provide a better understanding of PCI process inside blast furnace.A 3-D computational fluid dynamics (CFD) model was developed to predicate the pulverized coal injection (PCI) process in the blowpipe, the lance, and the tuyere. The parametric studies were carried out to study the effect of the blast temperature and coal injection rate on the heat transfer and coal devolatilization. The computational results provide useful information for trouble shooting and optimization of the coal injection system.