RICERCA ITALIANA     

Studies into key mechanisms affecting fluidized bed behaviour and their incorporation into numerical simulation codes for process industry applications.

Università degli Studi de L'Aquila

Abstract

The proposal is for a coordinated and wide ranging programme of research into industrially important aspects of fluidization dynamics. The interlinked topics which make up the programme having been chosen as representing areas where essential information is lacking, both with respect to experimental data and closure relations for the relevant force interactions. The particular areas, all of which involve the participation of a number of the individual research units taking part in this application, may be considered under the following headings.
(i) Homogeneous fluidization: its occurrence in gas- and liquid-fluidized systems; its characterisation in terms of particle mobility, evaluation of the relevant wave velocities; its induction in normally bubbling systems by imposed force fields, and in vibrating beds of fine powders.
(ii) Suspension rheology: experimental measurement of apparent suspension viscosity in gas- and liquid-fluidized systems and in modified shear cell devices; its model based correlation in terms of generalised momentum diffusion phenomena.
(iii) Binary particle fluidization: experimental evaluation of the relevant force interactions in gas- and liquid-fluidized beds of binary particle mixtures.
(iv) Simulation code development: the provision of closure relations for conventional and non standard fluidized bed applications (much of the work of the above areas relates to this point); development and enhancement of multi-phase >>>

Principal Investigator

Lorenzo Giovanni GIBILARO Università degli Studi de L'AQUILA

Research Objectives

The object of the proposed research programme is to carry out a detailed and closely coordinated investigation into industrially important aspects of fluidization which, for one reason and another, have received scant attention in the research literature.

The decision to embark on this course was taken in December 2004, at a meeting held at the University of L'Aquila to review progress and discuss developments at the completion of the first year of the PRIN 2003 programme (Experimental characterization and simulation models for fluid-particle systems in the process industry). The five research units of this present application all participated in that meeting and gave presentations of their work in progress and intentions for the remaining year, which we decided to make generally available on the web. It may be viewed on: www2.ing.univaq.it (click NEWS; click PRIN). During discussion on specific aspects of the ongoing research that followed the presentations, a number of clear indications emerged regarding this present application:
(i) that a successor programme should be firmly focussed on the fluidization process itself;
(ii) that it should be tightly coordinated, with individual topics being covered by a number of the participating research units, each from their own particular perspective;
(iii) that the dissemination of results and experiences among the participating units - essentially a dedicated workshop session - had proved >>>

Timescale

24 months

National and international background

All the research groups involved in this funding application have been involved in related work on fluidization and fluid-particle interaction processes of industrial significance for the past twenty years or more. A fairly comprehensive account of the work conducted at the University of L'Aquila, much of the time in close collaboration with a group in the Chemical Engineering Department at University College London, is the subject of a recently published book (1) and forms the background to much of the programme now being proposed. An initial focus was the primary interaction forces between the solid particles and the fluidizing medium - whether a gas or a liquid - which may be considered to comprise essentially the effect of the mean fluid pressure field in the bed and the drag forces which comes about as a result of local distortions of the flow field due to the presence of the particles. This work led to a unification of the separate treatments for energy dissipation for flow through beds of spheres, commonly estimated by means of the well established Ergun equation, and the steady state expansion characteristics for homogeneous fluidization, which obey the equally well established Richardson Zaki law (2, 3). It also provided a fully predictive constitutive expression for the total primary fluid-particle interaction force on a fluidized particle.
The derived interaction force was applied to the prediction of the stability of the homogeneously fluidized state >>>