A heat-transfer model for the rotary kiln: Part II. Development of the cross-section model

Abstract

A model of rotary kiln heat transfer, which accounts for the interaction of all the transport paths and processes, is presented in a three-part series. In this second paper, the development of a unified model for heat transfer at a kiln cross-section is described. Heat transfer within the kiln refractory wall was solved using a finite-difference approximation for one-dimensional transient conduction. A ray tracing technique was applied to derive coefficients for radiative heat transfer in the kiln freeboard, and the finite-difference model was extended into the contacting bed ma-terial in order to calculate the exchange between the covered wall and the bed. The cross-section model is shown to simulate the measured thermal performance of the pilot kiln for several feed materials: fine and coarse sand, limestone, and pctroleum coke. The interaction among the heat-transfer processes at cross-sections of the pilot kiln was examined, and explanations were made for both the observed close coupling of the bed and inside wall temperatures and the high rates of heat input to the bed occurring near the kiln entrance and in the presence of an endothermic bed reaction. Conclusions regarding the likely effects of kiln internal devices on heat transfer to the bed and the importance of preheaters are reached from the model predictions for a 4 m I.D. prototype kiln.