No abstract

Iron ore sinter, constituting a major proportion of blast furnace burden, significantly impacts the blast furnace performance. The chemical composition of iron ore fines, particularly alumina, sinter basicity and sinter MgO together with the thermal conditions that sinter blends are subjected to play an important role in the formation of mineral phases in sinter. To increase the sinter proportion (70-80%) in blast furnace, lowering of CaO in sinter mix is a vital parameter to balance the flux supply without affecting the slag volume and productivity. At present, the alumina content in the sinter grade iron ore fines at JSW Steel varies from 4 to 6%. The quality of iron ore presently being used calls for extensive investigations to produce low basicity sinter with high alumina iron ore. Studies have been carried out on low and high alumina iron ore fines to know the influence of sinter basicity and fuel (coke breeze) addition on sinter mineralogy, properties and productivity. It is found that with increase in sinter basicity, sinter productivity and reduction degradation index (RDI) decreased and tumbler index (TI) increased for both low and high alumina sinter at coke breeze rate of 65 kg t 21 of sinter. The low alumina sinter showed higher productivity and strength, and lower RDI due to the presence of higher silico ferrites of calcium and aluminium (SFCA) and magnetite phase, and lower pore phase as compared to high alumina iron ore sinter. The sinter productivity decreased and physical and metallurgical properties improved with increase in coke breeze addition by increasing the sinter basicity for high alumina sinter.

During the processing of steel in steel mills, iron oxides will form on the surface of the metal. These oxides, known as mill scale, occur during continuous casting, reheating and hot rolling operations. Mill scale is a valuable metallurgical raw material since it contains 65-70% iron. JSW Steel Ltd is a 7 Mtpa integrated steel plant and generates 270 t of mill scale per day. Most of the materials of steel plant wastes are recycled through sinter making in most of the countries. Because of its physical, chemical and mineralogical properties, it can be used as a raw material in a process like sintering. The mill scale contains high amounts of Fe and low amounts of silica and alumina. Thus, recycling it through the sintering process helps in the saving of raw materials like iron ore and limestone. This paper presents preliminary findings of a study that investigates the potential for recycling steel mill scale in the sintering process. Experiments were conducted using the mill scale in sinter making from 0 to 70 kg/t of sinter. The total Fe and FeO contents of the sinter increased with the increase in mill scale addition. The sinter productivity decreased with the increase in mill scale addition due to a decrease in sinter bed permeability. The sinter strength and sinter mean size initially increased and reaches a maximum at mill scale addition of 40-50 kg/t of sinter and afterwards declines with the increase in mill scale addition. Sinter reduction degradation index and reducibility decreased with the increase in mill scale addition due to the increase in FeO content. Except sinter productivity, other desired sinter properties can be obtained with the use of 40-50 kg mill scale per tonne of sinter.

Coke breeze is the most common fuel used in sintering, and its usage depends on the alumina content and fineness of the sinter mix. The coke breeze consumption in the JSW Steel Limited sinter plant was high compared to many other sinter plants in the world, and as there was a local shortage, optimisation in the sinter plants was necessary. FeO is an indicator of the thermal state of the sintering process and is employed as a quality control tool at many plants. Laboratory pot sinters were made, and the variation in FeO was affected by varying the amount of coke breeze in the green mix from 55 to 85 kg t 21 of sinter. The produced sinters were evaluated with respect to productivity, strength (tumbler index), reduction degradation index (RDI), reducibility and microstructural phases in the FeO range between 6?2 and 14?8%. It was found that the sinter with FeO range of 8?60-9?88% showed higher productivity and higher strength with desired RDI of (27% and reducibility of .60%. Analysis of plant data has revealed that the sinter with FeO of 8?5-10?0% showed higher productivity, higher strength and lower RDI.

Dolomite and other MgO bearing materials are being increasingly used as basic flux constituents for production of fluxed sinters. Addition of flux materials in sinter influences the resultant sinter microstructure and chemical properties. The physical and metallurgical properties of sinter mainly depend on mineralogy of the sinter. Dolomite is the source of double carbonate of calcium and magnesium. Recent studies reveal that, apart from the additional fuel needed, the addition of dolomite and MgO bearing material greatly influences the magnetite content and the properties of the sinter produced. The increasing use of MgO bearing fluxes in the blast furnace burden, and the trend to incorporate a major part of fluxes in the sinter mix led to an investigation of the influence of MgO on sinter properties and productivity. In this study, the systematic investigation has been made on the influence of MgO% (1?4 to 2?6) on sinter mineralogy and sinter properties with dolomite. Microstructural examination of dolomite sinter revealed that hematite and calcium ferrite phases decreased whereas magnetite phase increased with increase in MgO percentage in sinter. From the laboratory pot grate sintering results it was found that sinter reduction degradation index improved whereas tumbler index and reducibility decreased with increase in MgO%.