OCR Text |
Show -13- of symmetry at the top boundary, and steam is injected through a 2.87 cm diameter secondary annulus. The bottom of the computation mesh is an outflow boundary at which a constant pressure boundary condition is maintained. Coal, oxygen, and argon are injected through the primary nozzle at the rates 24.5, 22.6, and 3.41 kg/hr, respectively. The mean velocity of this primary flow is 36.57 m/s. Steara enters through the secondary annulus at the rate 6.73 kg/hr and with velocity 6.725 m/s. The temperature of the injected fluid is 370 K, while the initial temperature of the fluid in the system and the confining walls is 1500 K. The coal is injected in the form of parcels of coal particles. The particles within each parcel are of uniform size, but with a size distribution among the parcels that corresponds to Soelberg's [17] measured distribution (except that particles with diameters less than 10 ym are neglected). There are 11 different particle sizes, ranging from 11.39 era to 110.00 cm in diameter. As indicated above, the number of particles in each parcel is chosen such that the mass of each parcel is the same. Figure 1 shows the nonuniform fluid computation mesh, with finest resolution near the nozzle inlet and expanding radially and axially from this region. The left boundary is an axis of symmetry, while the top and right boundaries border rigid walls. A uniform pressure condition is applied to the bottom boundary. The velocity distribution at a time of 13.9 ms is shown in Fig. 2. These velocities indicate a large radial expansion of the flow at the inlet nozzle, followed by an axial flow with a gradually expanding radial dimension. The radial turning just below the middle of the mesh results from buoyancy generated by a region of high temperature. Fluid is then carried back up to the top of the mesh in a recirculating pattern, although the vectors at large radii are too small to be visible in this plot. The effect of this recirculation is apparent in the particle plot of Fig. 3. Each dot in this figure is a parcel of coal particles. These particles show their greatest concentration near the axis of symmetry, but with a disperse radial distribution that results from the buoyancy generated recirculation pattern and from the turbulent fluctuating particle velocities. A plot of the specific internal energy at this time in the calculation is shown in Fig. 4. This plot shows a cold inner core that results from the cool injected flow, and a region of high temperature below the middle of the region that results from the burning of devolatilized fluid. The fluid density plot in Fig. 5 shows a high density inner core of injected fluid and a region of relatively uniform density elsewhere. The pressure contour plot in Fig. 6 shows the |