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Show was 6.36mm. The primary stream was pulverized coal conveyed by argon at approximately 310K, and the secondary (oxidant) stream was composed of preheated steam and argon. The main reaction chamber was heated from the outside so that the temperature distribution inside the chamber was approximately uniform. The reactor operation condi tions were varied to study the effects of reaction pressure, P r, temperature Tr, and the gas residence time, tgr' on the gasification process. The experimental ranges of these parameters were: Pr = 8 to 62 atm, Tr = 1089 to 1644K, and tgr = 2 to 10 sec., respectively. Montana Rosebud subbituminous coal .was used with an average proximate analysis of 43.29,45.31, 9.76, and 1.64 weight percent fixed carbon, volatile maner, ash, and moisture, respectively. For the simulations reported here an average proximate analysis of 4&.05, 40.55, 10.37 and 1.64, respectively, from an earlier test series was used. An apparent density of 0.7 gm/cm3 was used in the calculations instead of the true density, 2.0 gmlcm3. The apparent density takes particle porosity into account The particle size distribution was in the range from 10 to 250 microns. This was represented in the calculations by five discrete sizes so that the mass weighted mean diameter matched the experimental value of 56 ± 5 microns. For further details of the computer simulations, the reader is referred to Celik and Chattree (1988). Figure 2 shows a typical calculated flow pattern where the stream function \f values are normalized by the primary mass flow rate. m accordance with the design criteria, the flow in the quarl section was highly turbulent and it caused rapid mixing of the coal conveying and the oxidant streams. A corner recirculation zone was predicted as identified by the dashed line in this figure. Recirculation wnes can have significant effects on particle mixing and residence time if the volume of this zone is large compared to the total reactor volume (See Celik, 1988) for the present cases, the recirculation wne volume varied between 10-20 percent of the reactor volume. The gas flow downstream of the recirculation wne can be characterized as a fully developed low Reynolds number turbulent pipe flow. 4.0 CALCULATION OF PARTICLE-RESIDENCE TIME Particle trajectories and particle residence times were calculated from the computer simulations. For each particle size dj and starting location (St. Loc.) Yi at the inlet of the reactor, there is a corresponding trajectory. In the present calculations, 50 trajectories (10 starting locations and 5 particle sizes) were used to represent the residence time distribution. Examples of calculated particle trajectories are shown in Figure 3. The 25 -5- |