| OCR Text |
Show • Refractory temperature • Air preheat • Waterwall temperature • Refractory emissivity • Speckledness The following inputs influence not only temperature, but also residence time: • Feed rate • Excess air • Furnace surface area The following inputs influence not only temperature, but also oxygen concentration: • Excess air • Fuel moisture content • Fuel C:H ratio The latter two lists contain the parameters whose effects on destruction efficiency are most difficult to determine without benefit of a well-defined numerical model. 5.4 COMPARISON WITH PILOT-SCALE EXPERIMENTS The model was run with inputs corresponding to a range of firing conditions in the experimental test matrix. Furnace diameter, furnace length, waterwall temperature, refractory emissivity, waterwall emissivity, refractory conductivity factor, speckledness, and soot mass loading were the same for every model run. Firing rate, excess air, fuel composition, fuel moisture content, waterwall surface area, flame diameter, and refractory/gas temperature difference were matched to experimental observations. Approximations were necessary for certain furnace design variables. For simplicity, the refractory/bulk gas temperature difference was fixed at ~110°C (200°F) over the length of the firebox for the case with all waterwalls present, and ~-170°C (300°F) with no waterwalls. The average waterwall temperature was fixed at ~77°C (170°F) by solving an energy balance on a panel. Because of the dependence of radiant transfer on the difference in temperatures raised to the fourth power, however, this value is not crucial to the model. The waterwall emissivity was fixed at 0.81, the average normal emissivity of a steel sheet with a rough oxide coating (Ref. 4). The emissivity of different refractory types varies widely. White refractory 5.5.25 |
