Particle flow modelling in slurry-fed stirred vessels

Abstract

In this paper experimental information on the retention time distribution (RTD) of solid particles in a high-aspect-ratio vessel, stirred by three equally spaced Rushton turbines, is presented. The relevant data were obtained by a special technique named twin system approach (TSA) that greatly simpli+es the handling of particle-laden streams and is therefore particularly suited for investigating particle RTD in 9ow systems. The technique fundamentals are +rst summarized, together with the data analysis procedure. This lastly requires a numerical deconvolution operation that is easily performed with the help of Z-transforms. Two di;erent approaches for excluding the spurious contributions of the external piping required for the experimentation are tested and discussed. Particle tracing was performed by an e;ective particle-coating/optical-detection technique that allows particles recovery and reuse after each experimental run. The RTD data obtained indicate that a cascade of ideally mixed tanks with back9ow results into very good agreement with experiment, with practically any number of tanks in series but one, provided that the back9ow rate parameter is chosen accordingly. In all cases, the recirculation is large enough for the resulting 9ow model to be quite close to a single perfectly stirred vessel.