MICROMIXING EFFECTS ON BARIUM-SULFATE PRECIPITATION IN AN MSMPR REACTOR

The Effects of non-ideal and nonhomogeneous mixing on barium sulfate p recipitation in an MSMPR reactor were observed experimentally and anal yzed theoretically. To generate nonhomogeneous mixing the unmixed feed streams were fed to the reactor at the same location (joint feeding m ode) or a plug how reactor was connected to the MSMPR reactor. These n onhomogeneous mixing conditions resulted in significant reductions in particle size and increases in particle numbers. These non ideal mixin g effects were dependent on the impeller speed, feed stream velocity a nd residence time in the connected plug flow reactor and are believed to result from elevated supersaturation levels in a premixing zone whi ch are controlled by turbulent micromixing. To model the effect of non homogeneous mixing (premixing) in the MSMPR reactor a plug flow-stirre d tank reactor series model was developed. The plug flow reactor repre sents the premixing region of the MSMPR reactor in which turbulent mic romixing is important, and the stirred tank reactor describes the homo geneous mixing region of the MSMPR reactor where particle growth is im portant. The model predicts that the premixing effect is strongly depe ndent on micromixing of the feeds in the premixing region, and thus, a s the turbulent mixing intensity in this region is increased, the part icle size in the product suspension is reduced and the particle popula tion is increased. These predictions of the model are in good agreemen t with the experimental data. An interesting prediction of the model i s that as the impeller speed increases, the precipitation of barium su lfate in an MSMPR reactor deviates increasingly from the precipitation in a perfectly mixed (ideal) reactor.