EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

Outotec is a pioneer in rotary kiln direct reduction with coal offering the well-proven SL/RN and the more recent SL/RN-Xtra technologies. The SL/RN-Xtra technology uses hot offgas from the rotary kiln to pre-harden green pellets on a travelling grate, before they are fed to the rotary kiln. This not only increases energy efficiency of the process, but also the production rate of the standard SL/RN module to more than 200,000 tons DRI per year per strand. Over the past years, Outotec has developed a complex mathematical in-house model to improve the understanding of kiln operation. The model incorporates complex physical and chemical phenomena occurring in the kiln such as heat transfer, granular transport of bulk material, fluid dynamics in the freeboard, and chemical reactions in bulk, freeboard, and at the bulk’s surface. The model has been mainly developed for the SL/RN and SL/RN-Xtra technologies for the production of DRI as well as for Ilmenite processing in rotary kilns for the production of synthetic rutile for the pigment industry. However, the model can also be applied to other similar rotary kiln processes. To operate rotary kilns for direct reduction of iron ores in an energy efficient way within a specified and trouble-free temperature window is a challenging task due to the complex physical and chemical processes taking place within the kilns. This is why Outotec’s in-house model was not only developed to design new rotary kilns, but also to provide strong support in the operation and trouble-shooting of existing rotary kilns. This applies particularly to plants where changes in the raw material occur. An important basis for all model calculations are the raw material’s physical (e.g. particle size distribution) and chemical (e.g. distinctive kinetics of iron ore and coal) properties that are determined and provided by our research center in Frankfurt, Germany.