Predicting bulk powder flow dynamics in a continuous mixer operating in transitory regimes

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 9970 a b s t r a c tOver recent years there has been increasing interest in continuous powder mixing processes, due mainly to the development of on-line measurement techniques. However, our understanding of these processes remains limited, particularly with regard to their flow and mixing dynamics. In the present work, we study the behaviour of a pilot-scale continuous mixer during transitory regimes, in terms of hold-up weight and outflow changes. We present and discuss experimental results concerning the start-up dynamics of a Gericke GCM 500 mixer, for which a specific experimental protocol has been developed to determine the evolution of the hold-up in the mixer and the real outflow. Empirical relationships are derived so as to link hold-up weight variations with operating conditions. A simple stochastic approach, based on a non-homogeneous Markov chain, is developed to simulate the bulk particle flow and transport in the continuous mixer at a macroscopic level. Although this simple model is only based on the start-up behaviour, it provides a full description of the mixer dynamics in response to strong perturbations on the flow rate or on the rotational speed of the stirring device, such as negative or positive steps. This model is validated experimentally for a wide range of operating conditions, and constitutes a first approach to process control.

Perspectives on the continuous manufacturing of powder‐based pharmaceutical processes

“…Blenders have been modeled with a variety of approaches, including DEM simulations, population balance models, hybrid models combining DEM and PBM, Markov chain models, and residence time distribution models . Adam et al proposed an integrated quality‐by‐design (QbD) approach toward the design space definition of a blending unit operation with DEM.…”

Continuous powder mixing of segregating mixtures under steady and unsteady state regimes: Homogeneity assessment by real-time on-line image analysis

“…However, none of the above-mentioned studies have been dealing with the transitory dynamics of such technological systems, despite of their industrial significance. In our previous recent works [22,23], we investigated the transitory dynamics of bulk solids flow in a Gericke GCM500 continuous mixer, using single powders (no mixture). The transitory phases that correspond to mixer start, emptying, as well as step changes in inflow rates or rotational speeds, have been studied in terms of outflow rate and hold-up weight variations.…”