Abstract
This paper presents work focused on the development, evaluation and use of a 3D model for investigation of the radiative heat transfer in rotary kilns. The model applies a discrete-ordinates method to solve the radiative transfer equation considering emission, absorption and scattering of radiation by gas species and particles for cylindrical and semi-cylindrical enclosures. Modelling input data on temperature, particle distribution and gas composition in the radial, axial and angular directions are experimentally gathered in a down-scaled version of a rotary kiln. The model is tested in its capability to predict the radiative intensity and heat flux to the inner wall of the furnace and good agreement was found when compared to measurements. Including the conductive heat transfer through the furnace wall, the model also satisfactorily predicts the intermediate wall temperature. The work also includes a first study on the effect of the incident radiative heat flux to the different surfaces while adding a cold bed material. With further development of the model, it can be used to study the heat transfer in full-scale rotary kilns.
Highlights
Rotary kilns are cylindrical, tilting and slowly rotating furnaces, and the first patented invention resembling a rotary kiln was created in 1885 by Frederick Ransome, which was introduced to the cement industry [1]
Applying a discrete-ordinates method (DOM), the examined enclosure is divided into a number of three-dimensional cells and the radiative transfer equation (RTE) is solved for a set of weighted discrete directions for each cell
The authors have previously published a paper on the heat transfer modelling within a full-scale rotary kiln for iron ore pelletizing using a DOM [32], and the aim of this work is to describe the detailed radiative heat transfer model used, for a pilot-scale rotary kiln, and validate it by comparing it with measurement data
Summary
Rotary kilns are cylindrical, tilting and slowly rotating furnaces, and the first patented invention resembling a rotary kiln was created in 1885 by Frederick Ransome, which was introduced to the cement industry [1]. The rotary kilns have been developed and are still used for cement production and several different other industries, such as pulp and paper and for iron ore pelletizing. The heat transfer within the kiln is complex, since it includes convective, conductive and radiative heat transfer, but heat is transferred in the angular and axial directions as the wall rotates and the bed mixes. Several researchers have examined the heat transfer mechanisms within the kiln freeboard, bed material and walls. Many studies have focused on the development of different models, while others have conducted experiments in smaller furnaces. Cross and Young [2] examined flame characteristics and pellet throughput in a rotary kiln for oil and gaseous flames employing a one-dimensional flame model assuming grey radiative properties
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