ARR - Annual Report

Removal of liquid from filter cakes can be accomplished by mechanical or hydraulic methods after cake formation is The local porosity in porous beds (Tiller and Cooper, 1962) is a complete. This paper deals with the latter procedure.

Function of Hydraulic Pressure Distribution

Function of hydraulic pressure distribution and cake compressibility. Calculation of average porosity requires an integration of local values as determined by liquid flow patterns. As most compressions of filter cakes are irreversible, the local porosity is a function of the maximum effective pressure (frictional pressure loss) reached during cyclical operations.

Reversal of Flow

Reversal of flow through a cake develops radically changed pressure distributions which can be utilized to reduce local porosities. Analytical expressions are presented for reduction of average porosity brought about by reversing flow of liquid in plate-and-frame and recessed plate filter presses.

A general discussion of deliquoring operations

A general discussion of deliquoring operations is given as an introduction to a more complete analysis made at the University of Houston of three different types of hydraulic deliquoring. Objectives and deliquoring methods are listed. A short discussion of solid-liquid separation provides a general background in relation to the topic under consideration.

Cake structure

Cake structure as affected by particle size and shape is discussed. The simplest method of reducing average porosity consists of increasing applied filtration pressure. Unfortunately, for compressible difficult-to-dewater materials, increasing pressure neither decreases liquid content nor increases flow rate after a usually relative low pressure is reached.

Hydraulic deliquoring methods

For such materials the hydraulic deliquoring methods discussed in the attached thesis hold considerable promise. The three methods are:

• Reverse flow
• Right-angled or three-dimensional flow
• High viscosity deliquoring

Mechanical expression, deep cone thickening, dispersion, and centrifugal drainage are briefly treated.

An art review on the measurement of various agglomerate strengths in Japan, as the request of IFPRI, has been already reported on 20th April, 1982. The present paper deals with the experimental results of some agglomerate strengths for polymeric materials such as polypropylene of polyethylene particles. These agglomerates of polymeric particles were produced by hot fluidized beds at The City College of The City University of New York.

As indicated in the preliminary IFPRI report (Gabriel Tardos, Dominick Mazzone and Robert Pfeffer: Agglomeration of Particle Systems in Fluidized Beds - Phase 31, Tardos, G. et al. made a detailed investigation into the minimum sintering fluidization velocity necessary to keep a bed of sticky or agglomerated particles in the fluidized state. In this connection, three samples of agglomerated polymeric particles were sent from New York to Tokyo in order to obtain agglomerate strength data at several temperatures between 80 and 170°C.

Unfortunately, the usual strength testing procedure regarding a cylindrical agglomerate with the diameter/length ratio about half does not apply to three samples of agglomerated polymeric particles because of irregular shape. An advantage of agglomerate strength measurements in this work, for this reason, is that the presumed tensile strengths of the agglomerates can be calculated from experimental results of interparticle forces at temperatures ranging from 80 to 170°C. In addition to this measurement, a new method for measuring the breakage strengths of three samples in streams of hot air was introduced into this work.

The aim of the following study is the evaluation of the feasibility of electrostatic classification in the size range below approx. 1 um. The study has been subdivided into the following chapters:

chapter 2: Outline of the problem

chapter 3: The classification zone, theory and dimensioning

chapter 4: The particle feeding and dispersion zone

chapter 5: The charging zone

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.