Modernizing batch-wetting systems at sinter-production machines

Abstract

Sintering plants 2 and 3 at OAO Magnitogorskii Metallurgicheskii Kombinat (MMK) were designed and built in the 1950s. In this simple technology, the batch is sintered without a base layer, and cake processing is minimal: crushing and classification at a stationary screen. Since 2000, sinter production at OAO MMK has been under reconstruction, with the assistance of Uralmash Metallurgical Works; the modifications are tailored to the existing structure, foundations, and supply lines. In 2007, the sintering plants were fitted with sinter-stabilization equipment, for cooling of the crushed cake in annular units without preliminary screening; the crushed cake is sorted on vibrational screens. This significantly improves the quality of commercial sinter. However, the formation of a large quantity of small sinter fractions prior to charging in the cooling unit poses problems. Unsatisfactory batch preparation leads to loss of the cake, as it falls off the sintering-machine belt at extremely high speed; moreover, the sintering process will be nonuniform over the width and over the length of the channel. If the sinter cake contains primary batch components that have not been assimilated by the melt, other problems arise: such components affect the chemical and mineral composition of the sinter and the recycled material, i.e., the content of FeO and also of free CaO and SiO 2 (unbound in sinter minerals), and also the residual content of fuel carbon in the sintering products (especially in the recycled material). To understand and eliminate the large yield of fines, the operation of the mixing and pelletization systems has been investigated by specialists at OOO Uralmash‐ Engineering (a division of Uralmash Metallurgical Works), with the participation of the MMK technologists. The existing wetting system consists of sprinklers installed over the whole length of the drum; they supply water at pressures up to 0.8 MPa. In the new sprayer system designed by OOO Uralmash‐Engineering, a mist consisting of water drops with a radius less than 30 µ m is produced. Such fine spraying is ensured by a direct-flow mixer with transverse water supply (Fig. 1). To investigate mixing and pelletization and the batch supply to the machine, samples are taken successively from the vibrational feeder, beyond the mixing and pelletization system, from the stabilizer (over the width) of the charging car, and from the sinter cars after charging (over the width), by special sampling units of original design. In the tests of the batch-wetting system, samples are taken during operation of the mixing and pelletization units with the existing wetting system (sprinklers) and with the proposed sprayer. The degree of segregation is estimated from the chemical mass, packing density, and granulometric composition of the batch over the bed height and width.