Fluid Flow in a Combined Top and Bottom Blown Reactor

Abstract

Physical modeling was done to study the flow field in a cylindrical bath agitated by bottom purging, top lance blowing and a combination of both injection types. A particle image velocimetry (PIV) system has been used to capture the velocity field of all three cases mentioned above. Special attention was paid to the recirculation loop. Top blowing creates a re-circulation loop in a relatively small volume close to the surface, compared to bottom-and combined-blowing. Increasing bottom flow rate moves the center of the re-circulation loop downwards into the liquid. When top blowing is combined with bottom blowing the center of the re-circulation loop is moved downwards into the liquid with increasing top lance flow rate.KEY WORDS: fluid flow; reactor; bottom purging; lance blowing.ISIJ International, Vol. 46 (2006), No. 8, pp. 1137No. 8, pp. -1142 was set to 50 mm above the undisturbed bath surface. Also, when used, the bottom nozzle (f2 mm) was placed in line with the center axis of the cylinder. The tracer substance used was a polymer from MCI GEL ® with model name CHP2OP. It has a density of 1.03 g/cm 3 and a diameter distribution of 75-150 mm. Before the tracer particles were added to the de-ionized water, they were subjected to Ethanol in order to remove trapped air inside the particles. This is important since trapped air causes unwanted buoyancy. Before each experiment there was a short time to let the flow field stabilize, this time was small, usually less than 5 min.Three cases have been studied: 1. Top blowing 2. Bottom blowing 3. Combined top-and bottom blowing Each case has a number of conditions set, which can be seen in Table 1. Equations UsedCylindrical coordinates are used in order to describe the system, where u, v and w are the velocity components in the radial, azimuthal and axial (r, q, z) directions respectively. Only the axial and the radial velocity components were registered in the experiments. The mean velocities; U, W are calculated as follows: where N corresponds to the number of data samples. ResultsSince the bubbling jet affects the laser the readings on the left side of the axis are less accurate (see Fig. 1 for the setup). Accordingly, the right side of the flow field has been the main viewpoint. The flow field in the bath can be classified as having a number of regions i.e., the momentum-, the transition-, the buoyancy-and the surface-region as well as the re-circulation region.7) The first four regions describe the bubbling jet and the re-circulation region is outside the bubbling jet. Figure 2 shows a vector plot of the mean velocity in a two-dimensional plane where the symmetry plane is to the left and the vessel wall to the right, which is the same for all figures. Data are presented for a case when only bottom purging through a centrally placed nozzle was used and for the following gas flow rates, Vol. 46 (2006) 49.5 cm 3 /s and (c) 92.0 cm 3 /s. As can be seen the water is lifted up towards the surface due to buoyancy forces resulting from the gas that is injected. Therea...

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