Evaluation of Drag Coefficient of Coal Ash Particles

A type of coal ash particles, fragments of sintered fly ash masses, can travel with flow in the furnace and settle on key places such as catalyst surfaces. Computational fluid dynamics (CFD) models are often used in the design process to prevent the carry over and settling of these particles at key locations. Particle size, density and drag coefficient are the most important hydrodynamic parameters involved in CFD modeling. The objective of this study was to experimentally determine particle size, shape, apparent density, and drag characteristics for sintered fly ash particles from a power plant. Particle size and shape were characterized by digital photography in three orthogonal directions and computer image analysis. Particle apparent density was also determined by volume and mass measurements. Particle terminal velocities in three directions were measured in water and each particle was also weighed in air and in water. The experimental data was analyzed and a method was developed to calculate particle equivalent diameter, equivalent ellipsoid size, apparent density, and drag coefficient distributions. Discussions were focused on developing a practical method that can characterize the aerodynamic properties of porous, sometimes skeletal particles