RICERCA ITALIANA     

Advanced modelling and validation based on detailed experimental analysis of the fluid dynamics of stirred gas-liquid reactors for chemical and biotechnological processes

Università degli Studi di Bologna

Abstract

The objective of this research project is the modelling of gas-liquid mixing processes in stirred vessels for reliable prevision of equipment behaviour as well as for deeper understanding of the physical basis of their behaviour. In addition, the influence of the fluid dynamics on selected issues regarding their performance in important areas like biotechnology will be analysed. The study will be based on experimental, modelling, fundamental and numerical activities.
The programme will be centred on four interconnected lines, namely: (a) CFD simulation of stirred gas-liquid reactors and results validation with experimental data, (b) Experimental investigation on the fluid dynamics of gas-liquid stirred reactors, (c) Fundamental analysis of bubble motion in the liquid, (d) Investigation about the influence of the fluid dynamics on selected issues related to reactor performance.
Item (a) is the main, reference objective of the study and will regard two types of gas-liquid vessels – sparged reactors and self-induced reactors. The CFD simulations will be carried with commercial CFD codes that will be implemented with models of bubble coalescence/break-up, bubble drag in a turbulent liquid, etc. The results of the simulations will be analysed in terms of liquid phase flow pattern, bubble velocity distribution, spatial gas hold-up, local bubble size distribution as well as the progress of the liquid homogenisation at selected positions in the presence of the gas >>>

Principal Investigator

Franco MAGELLI Università degli Studi di BOLOGNA

Research Objectives

The aim of the whole research project is the modelling of gas-liquid mixing processes in stirred vessels for reliable prevision of equipment behaviour and, thus, safer equipment design, scale-up and operation. The study will be effected through concerted actions of the four participating groups on selected topics. It will be based on experimental, modelling, fundamental and numerical activities.
The programme will be centred on four interconnected aspects, namely:
(a) CFD simulation of stirred gas-liquid reactors and results validation with experimental data (for both sparged and self-inducing agitation systems).
(b) Experimental investigation on the fluid dynamics of gas-liquid stirred reactors.
(c) Fundamental analysis of bubble motion in the liquid (as a means to provide information for more reliable equipment modelling).
(d) Investigation about the influence of fluid dynamics on selected issues related to reactor performance (limited to some aspects of mass transfer and material deterioration).

Item (a) is the main, reference objective of this study, while items (b-d) provide important, complementary information as well as tools for more effective modelling. From this point of view, this programme is an extension to gas-liquid systems of previous activities developed by some of the applicants in the area of solid-liquid mixing (e.g.: Montante et al.,Chem. Eng. Res. Des., 79, 1005, 2001; Cerbelli et al., Int. J. Multiphase >>>

Timescale

24 months

National and international background

The use of multiphase equipment and reactors in industrial operation is of paramount importance and for this reason they have been the subject of extensive research for several decades. In spite of this, the knowledge achieved so far is far from being satisfactory and the prevision of full scale apparatus behaviour is still affected by significant uncertainties [1]. This proposal is centred on the study of gas-liquid contactors that are relevant for the accomplishment of processes in the chemical, specialty, pharmaceutical, biotechnological industry as well as for environmental applications. Equipment like mechanically stirred tanks (either sparged or self-inducing), bubble columns, air-lift reactors, plunging jets, etc. have been and are used in these areas.

The subject of this project is the study of the fluid dynamics of gas-liquid stirred tank equipment [2], which strongly affects mass transfer, chemical and biochemical transformations and possible materials damage. The main aspects regarding the sparged tanks are: the overall fluid dynamic behaviour (with parameters like power consumption, mixing time, gas holdup, which the design methods are heavily based upon), the characterisation of the local flow field (especially with reference to impeller and blades) and modelling. The power consumption depends on both aeration rate and impeller speed and usually exhibits a drop, relative to the ungassed case, with an increase of the former and/or a decrease of >>>