Chemical Engineering Science, Vol.61, No.9, 3033-3043, 2006
Reactor performance with high velocity surface feed
Reagents have traditionally been fed into the impeller region of stirred tank reactors to utilize the high levels of turbulence, improve mixing rates and hence reduce mixing limitations. There are; however, numerous operational problems associated with submerged feed with dip tubes so surface feed is still preferred by operations staff. One alternate way of adding reagents into a stirred tank is to feed at the liquid surface using a high velocity jet. The ability of a high speed jet mixed feed stream to reduce mixing limitations has been investigated in this study. While most previous studies report results in the laminar flow regime (even for mesomixing limited operation), the present investigation presents data for much higher feed velocities. Experiments revealed that with reduced feed time, there is a local maximum in byproduct formation and the product quality initially improves with faster feed once this point is reached. However, other factors (primarily macromixing issues) limit the maximum improvement that can be achieved and in fact at very short feed times the byproduct formation increases again. Analysis of the design based on mixing and turbulent jet constraints shows that it is very difficult to obtain a fully turbulent jet because this leads to very short feed times (and associated convective stoichiometric limitations), very high feed stream velocities (where the feed stream overshoots the impeller) or very small feed pipe diameters (giving a large pressure drop through nozzle). Feed jets at high velocities are difficult to achieve under reasonable operating conditions and do not provide any Substantial improvement in performance. (c) 2005 Elsevier Ltd. All rights reserved.