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Show INTRODUCTION The Tennessee Valley Authority (TVA) has assumed a lead role in the demonstration of atmospheric fluidized bed combustion (AFBC) technology for application in large utility boilers. As a first step in this program, TVA has constructed a 20-MW(e) pilot plant to develop basic data for utility AFBCs. TVA and the Electric Power Research Institute (EPRI) are currently cosponsoring operational testing of this unit. The TVA Energy Demonstration and Technology Division enlisted the assistance of Oak Ridge National Laboratory (ORNL) in providing technical support and services for the pilot plant according to the interagency agreement between TVA, the Department of Energy (DOE), and ORNL (TV 48 296A, Subagreement 5). Under this agreement, ORNL developed a computer model to simulate the steady-state operation of the TVA pilot plant. One of the key components of this model [which is described more fully by Wells et al. (1)] is the calculation of the devolatized char combustion rate. Combustion kinetics data available in the literature do not cover the fuel type and range of conditions appropriate for the TVA pilot plant. Thus the reliability of the preliminary kinetics expression used in the model was unknown. This study was initiated to experimentally determine a kinetic expression for the combustion of devolatilized Kentucky No. 9 coal, which will be the primary fuel burned in the TVA pilot plant. Of greatest concern was the separation of external mass transfer effects from the effects due to intraparticle processes (i.e., pore diffusion and chemical reaction). This is important because each of these terms varies differently with bed conditions and must be calculated separately in the computer model. THEORETICAL BACKGROUND The Limiting Regimes of Combustion It is usually convenient to separate heterogeneous solids combustion into three basic steps: (1) diffusion of mass species (both 3 |