Abstract
The Fuels and Energy Research Group at the university of Surrey (FERGUS) have been investigating the heat transfer and energy utilisation within rotary cement kilns since the early 1970's. One such project has been the study of chain systems in cement kilns. The work presented in this thesis is an investigation of a chain system for dry process cement kilns. A review of the literature has highlighted that there is a general paucity of experimental work on cement kilns, and in particular, very little on the role of chain systems. This lack of applicable results is due to the fact that experimentation on this type of full-sized plant is exceedingly difficult. In modelling the convective heat transfer in a chained dry process cement kiln the analysis of Gardeik and Jeschar (1979) has been applied. These authors have developed an expression which enables the regenerative nature of a chained rotary kiln wall to be quantified. The similarity criteria utilised to scale down a chain system is that of equal voidages between the model chainbank and its industrial counterpart. This modelling criteria was developed by Patterson (1980) through air and water modelling experiments on different chain systems. In order to generate the basic heat transfer data a 1/8th scale, indirect fired, model of the chained section of Chinnor No. 1 Kiln of the Rugby Portland cement p.l.c. has been constructed. Clean low momentum flue gas from a vortex combustor has been used to heat, countercurrently, raw meal cement nodules for a range of gas and solid flowrates at different kiln rotational speeds. As with most experimental rotary kilns working at elevated temperatures (400ºC) many difficulties have had to be overcome, with a consequent alterations to the original design. The problem of continuous monitoring of temperature within the model kiln has been solved by the use of a programmable data recorder and a gold slip ring assembly external to the kiln. This system has simplified the acquisition, storage and retrieval of temperature data from a rotating kiln. Experiments have been performed with the model kiln operating without and with a chain system to quantify the swirl produced by the combustor and the regenerative action of the chainbank, respectively. The direct heat transfer coefficients between gas and wall have been determined as well as the overall heat transfer coefficient. Correlations of the data have been presented and where possible the results have been compared with the literature and to commonly used equations. For the model kiln operating with a chain system the gas to wall heat transfer has been correlated to yield: NU = 0.00661 Re1.15 Pr.33 and the overall heat transfer coefficient by: Keff = 0.002188 Re1.28 Significant enhancement in heat transfer to, a moving bed of solids has been achieved by using swirling flows in tandem with a chain system.