OCR Text |
Show Pulverized-Coal Combustion Model With Finite-Rate Carbon Monoxide Oxidation R. A. Wessel and W. A. Flveland THE BABCOCK & WILCOX COMPANY, Research and Development Division Alliance Research Center, Alliance, Ohio 44601 Presented to the American Flame Research Committee Pittsburgh, Pennsylvania, October 4 - 6, 1988 ABS'l'RAC'l' RDTPA 88-36 A numerical model was developed to predict pulverized-coal (PC) combustion and carbon monoxide (CO) oxidation. The combustion model is a part of the three-dimensional furnace model which simulates the various interacting processes of turbulent flow, heterogeneous and homogeneous chemical reaction, and heat transfer. Homogeneous combustion of the fuel is characterized by a two-step process. In the first step, fast chemistry is used to describe the reaction between the gaseous fuel and oxygen to form CO and other products. The second stage of combustion involves the kinetically-controlled oxidation of CO. The impact of turbulent fluctuations on temperat 1re and instantaneous species concentrations is considered for determining the local average rate of CO oxidation throughout the furnace. Forward and reverse CO oxidation reactions are simulated based on kinetic rate measurements in the literature. The average CO reaction rate is calculated by integrating the instantaneous Arrhenius expression over a probability density function, in terms of the mixture fraction. Fluctuations in the CO reaction progress variable are neglected in the averaging process. The concentration for CO is then described by the Favre average, general convection transport equation with appropriate boundary conditions and is solved by standard finite difference methods. In this paper, CO formation and oxidation are investigated for staged combustion in a 6 MBtu/hr pulverized-coal-fired furnace. Numerical results for flow, heat transfer, and CO combustion are compared with pilot-scale test data and agreement is favorable. NOMENCLA'l'URE Symbol units Definition a Coefficient of finite difference equation Pre-exponential factor Initial particle diameter Activation energy 1 |