Thermodynamic process evaluation of a rotary kiln unit at LKAB Kiruna

Abstract

This thesis describes the development of a thermodynamic model for the Grate-Kiln process. One application of such a process is the thermal treatment of iron ore pellets. The work has been performed in close collaboration with the iron ore producing company LKAB. The model is applied to assess the process in terms of heat and mass flows. The thermodynamic assessment is carried out on an overall basis and for each of the three main process parts: grate, kiln and cooler. The results reveal that the oxidation of the magnetite, contained in the inlet pellets, to hematite is the main heat source of the process. The heat release during the combustion of coal inside the kiln contributes to the remaining one third of the total heat supply. Half of the provided heat leaves the process as hot off gases. Thus, measures to improve the energy efficiency of the plant should focus on either reducing the mass flow of air that is heated by the process or making better use of the hot off gases. In order to shift the models usability towards quantitative application, different measures could be taken. Among these, improvements in the data for validation, and enhancements in the modelling of the chemical properties of the iron ore pellets promise the greatest benefits.