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Show EXPERIMENTAL Pulverized coals were fired in the PSU-FCL plane flame furnace, shown schematically in Figure 2. The construction of the furnace permits a nearly complete characterization of the pre-to-post combustion regime. Despite its rather diminutive dimensions [1-2 orders of magnitude smaller than a typical utility boiler], the PSU-FCL plane flame furnace adequately simulates the thermal and temporal combustion environment of a full- 4 scale boiler: heating rates of 10 °K/second; peak gas temperatures of 1400-1500°K; and residence times of 1-2 seconds. It purposaly does not, however, recreate the turbulent aerodynamics within an industrial fireball. Rather, the furnace has been designed to generate a microturbulent flame of essentially one-dimensional geometry. The flat flame structure is generated by close control of mixing of secondary air and adiabatic combustion products. To achieve such an environment, premixtures of pulverized fuel and primary air [ca. 15% of the required combustion air] pass through a water-cooled tube bank before flowing downward into the combustion chamber. This key furnace component helps to prevent combustion flashback into the mixing chamber and streamlines the velocity profile of the freely-falling pulverized coal/air cloud into plug flow. Flat flames stabilize at different positions downstream of the down-fired burner primarily as a result of different compositional (volatile matter) and physical (particle size, reactivity) characteristics of the pulverized fuel. Because of the "once through" flow, all fuel particles experinece a nearly identical time/temperature history as they vertically traverse the combustion zone. Hence, thermal and chemical profiles of the combustion environment can be well-controlled and rather unambiguously resolved as a function of time. Ignition of a pulverized test fuel was accomplished by preheating the internal refractory fire-brick walls of the plane flame furnace with a natural gas/air flame to a set limit temperature profile below which a self-sustaining flame of that fuel would not develop. The plane flame furnace had been previously calibrated according to its time/temperature preheat history so that this standardized ignition procedure could be executed; at e.g., 500°C, 700°C, or 900°C, the natural gas flame had to be fired for 0.5, 1.0, or 7.0 hours, respectively. After yes/no 17-10 |