A heat-transfer model for the rotary kiln: Part I. pilot kiln trials

Abstract

A model for 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 first paper, the pilot kiln facility is described, and the significant results from the heat-transfer trials are identified. Limestone, Ottawa sand, and pctroleum coke were heated using a range of firing rates, while other operating variables were held nearly constant. Measurements were made to obtain the net rates of heat transfer for the bed material, freeboard gas, refractory wall, and, unique to the study, the radial heat flux at the inside refractory surface as a function of circumferential position. High rates of net heat input to the bed material, occurring very near the feed end, were found to decline quickly with distance, and for an inert bed, leveled out at a value well below the rate of loss through the kiln wall. The onset of an endothermic bed reaction resulted in sharp increases in both the temperature cycling at the inside refractory surface and the net heat input to the bed, but no corresponding jump in the kiln wall heat loss. The temperatures of the bed material and inside refractory surface always were coupled closely, even in the presence of bed reaction. Regenerative heat transfer from the covered wall to the contacting bed material was not a major component of the net input to the bed, and for the inert bed, negative regeneration was en-countered beyond the kiln midpoint.