ARR - Annual Report

This report is the annual statement of progress on the Loughborough powder flow project. The project concerns the aerated flow of powders, that regime of flow where the voidage of the bed increases and the resistance of the powder to flow is greatly reduced. This investigation is a broad topic and may be considered to have three broad perspectives:

• Measurement of aerated flow of properties
• Manipulation of material properties and behaviour
• Behaviour of materials in engineering situations

Overall Objectives of Programme

TO develop:

1. means of predicting particle attrition in process equipment based on unambiguous small scale tests.
2. Insight into the influence of
• particle design and
• equipment design and operation on attrition.

This is the annual progress report on the Particle Attrition project which is being partially carried out at the University of Delft. The project is part of a collaborative effort, at present a complementary project is being carried out at the University of Birmingham. The project was started in February 1982.

The project follows the initial literature survey made by Dr. J. van Brake1 of this University of Technology. In that report the sub-division of the subject was identified as being basically in three parts:

1. Tests on Single Particles
2. Tests on Groups of Particles
3. The Attrition Behaviour of Particles in Kcal Systems

In this department we are currently concentrating on the relationship between the tests on single particles and the behaviour in real systems. This necessarily means that such a relationship will most easily be established for particle handling systems in which the particles are in diluted phase. The two systems in which we have made measurements of particle attrition are in a pneumatic conveying line, where the criteria of lean phase is maintained and in a fluidised bed where the process is more complicated. In defining the objects of this programme there is of course no real distinction between the attrition of particles and the fracture of particles. In our minds we basically perceive the fracture as being the splitting of particles to a number of fragments of roughly comparable size, while the attrition behaviour on the other hand is the gradual wearing away of one large particle. In real processes both features are occuring simultaneously.

At the Clausthal meeting in June 1982 the overall objectives were defined as follow:

• To develop
• means of predicting particle attrition in process equipment based on unambiguous small scale tests.
• insight into the influence of particle design and equipment design and operation on attrition.

This is the third phase of the research performed on agglomeration of particles in fluidized bed systems including both theoretical and experimental work on aggregating fluidized beds. The report contains an updated review on high temperature agglomerating fluidized beds with emphasis on fluidized bed conbustors. The report also includes a detailed comparison between predicted and measured minimum gas velocities necessary to keep a bed of sticky (wet) or sintered granules in the fluidized state.

The experimental procedure using a dilatometer to measure the apparent surface viscosities of sintering particles is described together with measurements to determine agglomerate strength. These quantities must be known before any theoretical model which predicts defluidization in fluidized beds can be applied. Furthermore, a theoretical model based on the growth of vertical channels in a defluidized bed to predict refluidization of a defluidized (packed bed) is described. Future theoretical and experimental work on the project is also outlined.

Friction losses were determined for titanium dioxide suspensions at concentrations of 17.5, 22.3, 25.3 and 33.9 percent by volume, flowing through 1 inch and 2 inch standard 45 deg. and 180 deg. bends, and 90 deg. bends of various radii of curvature, and also through gate and globe valves and Venturi meters. Pertinent suspension properties, which were measured, included particle size distribution, suspension pH, zeta potential, sedimentation behavior and sediment volume and rheological behavior. The rheological behavior was shear-thinning at low shear rates, and shear- thickening at high shear rates. Preliminary analysis and correlation of the rheological data included determination of the power-law parameters over appropriate ranges of shear rate, which were used to define a generalized Reynolds number for correlation of the friction loss data.

Introduction

The knowledge of strain distributions of granular materials is required in various kinds of particle handling processes in chemical, ceramic, food processing and other related industries. However, it is very difficult to obtain such a knowledge as compared with the case of fluids. If we want to obtain a velocity distribution of a gas or liquid flow, we can utilize the Navier-Stokes equation. We have had, however, no basic equations for the corresponding calculation of granular materials. The aim of this paper, is therefore, to derive a new equation for granular materials like the Navier-Stokes equation for fluids.

I will derive a new simple equation for obtaining the strain-distribution based on the classical hydrodynamics. Then, the equation will be applied to simple one-dimensional problem, and compared with the experimental results.

SUMMARY The objectives of our project are to establish an industrial estimation method for any powder bed yield loci and to develop a design procedure for an industrial powder process by use of the yield loci. In this report, research works on the phenomena of powder, in which fluidization, packing structure, adhesion and agglomeration, mechanical yield etc. are contained, are systematically reviewed. Examples of the application of the method for estimating powder bed yield loci to actual particulate processes are discussed. Finally, the transmission of particle bulk density in powder is described qualitatively and experimentally.