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Show modeling effort have been directed toward determining the feasibility of such a model. The destruction model used was designed to predict minimal combustor performance. For example, a standard exists for incinerators requiring 99.99 percent DRE for any combination of waste and equipment; however, all combinations cannot be tested. Experience in a current program (Ref. 1) indicates that industrial flames nominally achieve only 90 to 99.9 percent destruction. Thus, at least some destruction must be sought in the postflame region if the 99.99 percent destruction goal is to be reached. Finally, the postflame region is not subject to the great complexity of physical and chemical interactions of turbulent flame behavior. It was therefore decided to limit the model to a description of the postflame furnace environment. A postflame simulation can approach the needs of the user by providing a conservative estimate of waste destruction. Thus the current model underestimates actual combustor efficiency by intent. 5.2 PROGRAM STRUCTURE The model program consists of two modules, as shown in Figure 1. The first module calculates a single average gas temperature, Tj, for each axial zone, j, into which the furnace is subdivided. An energy balance is performed on each zone. Figure 2 shows the principle energy flows into and out of a furnace zone. Radiative heat transfer dominates the heat losses from the gas phase. Separate radiative and convective terms describe the losses to the waterwall and refractory wall components of the firebox surface. The output bulk gas temperatures can be compared directly to the pilot-scale furnace measurements. The second module uses the output from the first module as input. It extrapolates the single-zone temperature to an axisymmetric radial temperature profile for the zone. The algorithm is based on an empirical description of the pilot-scale thermal boundary layers. Simple fluid mechanics of laminar and turbulent flows applied to the bulk flow properties and boundary layer temperatures produces a radial velocity profile for each zone. The residence time for a fluid particle which travels through an annul us i (always traveling parallel to the furnace wall) to reach a zone j, T^J, follows directly. The concentration of the principal waste component, C-jj, can then be calculated by overlaying simple global kinetics on the axisymmetric temperature-time history. 5.5.2 |