Positron Imaging Studies of Rotating Drums

D J Parker1, R N G Forster1, P Fowles1, Y Ding2 and J P K Seville2 1 Positron Imaging Centre, School of Physics and Astronomy

2 School of Chemical Engineering

University of Birmingham, Birmingham B15 2TT, UK, d.j.parker@bham.ac.uk

ABSTRACT

The University of Birmingham Positron Imaging Centre has pioneered the application of the radioisotope tracer technique of positron emission tomography (PET) to study industrial processes, and has developed the related techniques of positron emission projection imaging (PEPI) and positron emission particle tracking (PEPT). All three techniques rely on detecting the pairs of back- to-back D-rays, produced from annihilation of positrons with electrons, using a “positron camera”. Typically in PET or PEPI a single component of a multi-phase system is labelled and its distribution imaged in 3D or 2D respectively, whereas in PEPT a single labelled particle is tracked. In 1999 a new positron camera was acquired which has sensitivity 10 times that of the previous system and can generate data at 20 times the previous rate.

The potential of this new system will be illustrated with reference to a series of laboratory scale studies on particulate motion in rotating drums, operating either in batch or continuous flow modes. Such drums are in widespread use in industry, for example as rotary kilns in which, for optimum product quality, it is important to ensure good mixing and narrow residence time distributions. Sand grains, glass beads and TiO2 granules down to 0.5mm diameter have been labelled and used for these studies. Using PEPT the transition between rolling and slumping modes has been identified and the velocity profile within the active layer has been determined for a range of drum diameters, enabling validation of theoretical models. PEPI has been used to measure and explain residence time distributions. All three techniques have been used to study segregation based on particle size, both radially and axially within the drum.

A novel rotary gas/solid contactor has recently been proposed in the literature, in which a horizontal drum is divided into two by a longitudinal partition to which are fixed a series of inclined baffles. As the drum rotates the baffles cause material to be transferred continuously from end to end of the drum. Using PEPT, the first detailed investigation of particle motion in such a device has been undertaken.

Keywords PET, PEPT, radioactive tracers, particle tracking, rotating drums