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Show Table 4 HEAT TRANSFER DATA million Btu/hr (jjW) Heat Loss within the Convective Boiling Loop 7.5928 2.2237 Heat Loss by Radiation to the Lower Surface of the 0.6148 0.1801 Convective Boiling Loop Total Heat Loss to the Convective Boiling Loop 8.2076 2.4038 Heat Loss to the Walls by Convection and Radiation 1.0954 0.3208 RESULTS Accurate prediction of freeboard combustion and, therefore, temperature is highly dependent on the kinetic rate of char oxidation. Our approach was to use published values of kinetic rates as a first step. There was a wide variation among published kinetic rates (order of magnitude differences at a given temperature). The rates by Sargeant and Smith [12] gave the closest prediction of freeboard combustion, yet it was still 40% overpredicted. With the excess combustion predicted, freeboard temperatures would have been approximately 200°F (111°K) higher than actually measured. Since fuel nitrogen release is proportional to the coal weight loss, accurate prediction of combustion is critical to the NO modeling. Temperatures are also used for the kinetic rates of the NO production and reduction reactions. To get the correct nitrogen release and temperatures, char oxidation kinetic rates were adjusted downward. There was agreement in the activation energy in the published rates by Sargeant and Smith versus Combustion Engineering data [13]. The pre-exponential factor was reduced by 40% while the activation energy was held constant. When this was done the predicted carbon burnup was 399 lbm/hr -22- |