Theoretical interpretation of residence-time distribution measurements in industrial processes

Processes - The Residence-Time Distribution (RTD) is a chemical engineering concept introduced by Danckwerts in 1953. It has been described in a multi tude of scientific papers and applied for various industrial processes. The development of Computer Fluid Dynamics will improve the comprehension and optimisation of such processes. However, this approach remains difficult in case of complex industrial processes. Therefore, the extension of the RTD concept is an alternative way to obtain hydrodynamic data and help for impr ovement of the processes. Actually, the models derived from tracer experiments are often restricted t o the use of simple elementary reactors such as perfect mixing cells in ser ies or plug flow with axial dispersion. The resulting information is often not sufficient for the understanding of complex processes. Better understan ding may be obtained by the creation of complex networks of interconnected elementary reactors. However, that can lead to two problems to be solved: t he first one is the possibility to realise an easy simulation of any comple x network, the second one is to create realistic models on a sound physical basis. Indeed, complex models contain so many parameters that two different models may give the same result or the same model may give an identical result wi th different sets of parameters, A software package has been developed to s imulate the response to an input of any complex network of elementary react ors properly interconnected. Processes with multiple inlets or outlets can be modelled convolution and optimisation procedures. The software may, equa lly be used to determine the parameters of different models giving the same response, and the subsequent examination of the physical soundness of thes e parameters leads to the choice of a realistic model In addition, local me asurements may be validated through the possibility to simulate the local r esponse within the model and to optimise the corresponding parameters. Also, a general procedure has been developed to optimise the different flow rates of models in complex industrial processes with many undetermined rec irculation flow rates. Future developments including RTD under transient st ate and automatic generation of flow models are also presented. They are il lustrated through experiments and literature analysis. Finally, different p erspectives of recent concepts are suggested.