Analysis of Cycle Formation in the Clinker Burning Process

Abstract:
Most of today’s worldwide cement production takes place in rotary kiln plants. A powdery raw meal is being fed into the kiln via a preheater. The kiln itself is heated by a coal, oil or gas flame and the hot flue gas flow is directed opposite to the solid flow. This counter current configuration permits the formation of cycles of volatile substances within the kiln. These substances are brought into the process by the raw meal and by the fuels. Vaporizing in hot regions of the kiln they are being transported back to cooler regions together with the gas phase and there they precipitate again. These cycles cause heat losses by consuming energy for vaporization. Moreover the liquid precipitate melt sticks together the powdery solid and thus enhances the formation of coatings on the kiln walls, which causes holdups. Using SimuSage a cell model of the cement process has been derived which is capable of caculating the formation of cycles depending on the composition of the incoming raw meal and fuel streams. The kiln and the preheater are subdivided into several zones of different temperature. Within each of these zones thermochemical equlibrium is assumed to establish due to the high temperature. The zones are interconnected by streams in order to map mass transport within the kiln. A database comprising thermochemical data of 13 elements has been used for calculations.

Keywords:
Computational thermochemistry, minor components, cement clinker burning, rotary kiln