A dimensionless factor characterizing the ignition of pulverized coal flow: Analytical model, experimental verification, and application

An analytical model describing the ignition process of pulverized coal is proposed, and a dimensionless condition number (Ncom) is obtained to describe the comprehensive effect of factors governing the ignition of pulverized coal flow, such as the initial temperature of flow, the sectional heat load of the furnace, and the flux of primary air, secondary air and recirculation flue gas. An optimized concentration of pulverized coal flow is derived explicitly, upon which the earliest ignition of pulverized coal flow is possible. The model is verified in a hot furnace experiment, where it is shown that the derived criterion (Ncom) can be used for different kinds of coal and different types of burner. For given coal and sectional heat load of furnace, when the value of Ncom increases, the condition of ignition is improved and both unburned carbon and NOx emission are reduced. The employment of Ncom in the optimization of burner operating conditions is demonstrated through two applications. In practice, the criterion Ncom can be used to guide the selection of the concentration and type of pulverized coal, as well as the choice of burner and desired aerodynamic field, so as to achieve an optimized performance. Copyright © 2008 John Wiley & Sons, Ltd.