Flow patterns in rotary cement kiln models.

The work carried out for this thesis represents part of a larger study being followed in the Department of Chemical Engineering, University of Surrey into the processes of heat transfer taking place in rotary kilns with particular emphasis being placed on those in the Cement Industry. A widely used method of investigation of the performance of furnaces is that of partial modelling of the flow taking place within the system. This approach allows predictions to be made from model work concerning the shape and length of the flame within the real furnace. In cases such as the rotary kiln, where the flame may be defined as a turbulent jet diffusion flame, the mixing of the oxidant (air) with the fuel is of the utmost importance in dictating the flame characteristics. Consequently the approach of isothermal partial modelling has been applied to an accurate model of a specific industrial installations from which general conclusions concerning flow patterns in kiln systems can be made. The two most important aspects of such modelling procedures are firstly to obtain an accurate geometric model, and, secondly, to ensure that the flows produced in the model system are representative of actual practice. The first of these is relatively simple to attain; the second is more difficult. In order to overcome the limitations of published literature concerning flowrates in kiln systems, original industrial data was obtained and analysed in some detail, using relevant jet theories to produce a range of operating conditions suitable for use in the model. Isothermal model systems operating on air and water have been designed and constructed. Prom these flow pattern diagrams have been produced and presented in the results. The model studies indicate that the degree of recirculation in kilns is low to moderate and does not take place symmetrically about the kiln axis. The primary jet is deflected by the asymmetry of the secondary flow, the distribution of which is determined by the inlet geometry to the kiln. Jet deflection increases as the velocity ratio, uo /ua is decreased. The flow patterns are of sufficient generality for wide application for within the limits of the rules of isothermal modelling