| OCR Text |
Show Pulverized Coal Combustion Nonswirling pulverized coal combustion (see Figure 6A) was modeled and (27) compared with the experimental data collected by Thurgood . Modeled conservation equations were solved for the gas and particle processes as described before. The modeled geometry is shown in Figure 6B. A list of test conditions is shown in Table 4. Coal particles and air are injected through a central nozzle at a rate of 0.00121 kg/sec and 0.0056 kg/sec, respectively, at a velocity of 33.51 m/s. The oxidant streams through an annulus at a mass rate of 0.0361 kg/s corresponding to a velocity of 34.1 m/s. The flow was nonswirling. For combustion calculations, a nonuniform 30 x 31 grid was used as shown in Figure 7. Inlet velocity, turbulence energy, and dissipation profiles (see Table 5) were those recommended in Reference 29. Particle size and spatial distributions at the inlet have been discretized as listed in Table 6. As indicated, 50 streams were modeled - five sizes at 10 locations. All particles enter the combustor at 356°K. A vector plot of the flow field is shown in Figure 8. Arrows on the figure are proportional to the flow velocity. The strong inlet jets of fuel and oxidant dissipate quickly, and a one-dimensional flow is established about half way down the combustor. Combustion occurs in this one-dimensional region; thus, the weak recirculation near the inlet does not significantly affect the combustion results. Figure 9 shows contour maps for coal-gas mixture fraction and isotherms. The contours of coal-gas mixture fraction indicate that there is no devolatilization in the inlet regions of the combustor. At the midpoint, most of the volatiles are released and distributed downstream by turbulent mixing. The contours of the isotherms suggest a relatively uniform temperature until devolatilization occurs, after which the temperature rises rapidly due to combustion. The predicted location of this point (X/L = 0.78) agrees well with experimental data. -22- |
