Many materials are either processed or sold in the form of particulates. Particle processes such as granulation, tabletting and mixing have been studied. The group currently has a strong interest in rotary kiln operations. Rotary kilns are used extensively in the solid processing industry, such as cement production, drying, and titanium dioxide manufacture. Granular materials are fed continuously into an inclined cylindrical kiln, rotating slowly along its axis. A heat source is often provided by a counter-current flow of hot gases in the freeboard space above the granular bed.
Previous studies have concentrated on the motion of the granular materials inside the kiln. This includes the investigation of different granular flow regimes, axial segregation of binary mixtures, non-steady systems, and flow behaviour during the filling and emptying phases of kiln processes. A numerical model, with no free parameters, has been developed to predict accurately the behaviour of the granular bed when subjected to step changes in the operating conditions. Collaboration with the Positron Imaging Centre at the University of Birmingham allows the motion of granular materials to be studied, using a technique called Positron Emission Particle Tracking (PEPT). This involves tracking an individual particle inside the rotary kiln using a radioactive tracer.
Current research focuses on heat transfer from the freeboard gas to the granular bed inside the rotary kiln. At low to medium temperatures, the main heat transfer mechanisms include convection from gas to solid, convection from gas to the exposed kiln wall, and via regenerative heat transfer, where the granular bed is heated at the base by the covered kiln wall. The group aims to establish the relative importance of these mechanisms through experimental work and theoretical modelling.
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