Computer Simulation of Heat Transfer in Alumina and Cement Rotary Kilns

This paper presents computer simulation of heat transfer in alumina and cement rotary kilns. The model incorporates radiation exchange among solids, wall, and gas, convective heat transfer from the gas to the wall and the solids, contact heat transfer between the covered wall and solids, and heat loss to the surrounding as well as chemical reactions. The mass and energy balances of gas and solids have been performed in each axial segment of the kilns. The energy equation for the wall is solved numerically by the finite-difference method. The dust entrainment in the gas is also accounted for. The solution marches from the solids inlet to the solids outlet. The kiln length predicted by the present model of the alumina kiln is 77.5 m as compared to 80 m of the actual kiln of Manitius et al. (1974, "Mathematical Model of an Aluminum Oxide Rotary Kiln," Ind. Eng. Chem. Process Des. Dev., 13(2), pp. 132-142). In the second part, heat transfer in a dry process cement rotary kiln is modeled. The melting of the solids and coating formation on the inner wall of the kiln are also taken into account. A detailed parametric study lent a good physical insight into axial solids and gas temperature distributions, and axial variation of chemical composition of the products in both the kilns.