The scarcity of good quality coking coal for the blast furnace (BF) has made steel makers look for an alternative iron-making process that requires little or no coke. The Corex process has been developed as an alternative to BF iron-making, which uses non-coking coal and a small amount of coke as fuel, and pellet/lump ore as iron-bearing feed. JSW Steel operates two Corex units each of 0?8 Mtpa, commissioned in 1998 and 2001 respectively. Iron oxides and non-coking coals have to meet certain physical, chemical and high temperature properties for stable operation and to attain high performance levels. Experience of the Corex operation with various coals and iron oxides over the years has helped in understanding the influence and sensitivity of raw materials on its performance and develop new raw material specifications. Statistical analysis of plant data showed that the significant parameters affecting fuel rate and production are moisture, volatile matter, char strength after reaction of coal, reduction disintegration index (RDI; %, -6?3 mm) of pellets and slag rate. This helped achieve the most efficient operating parameters, surpass rated capacity and utilise steel plant waste. The present paper brings out the impact of various raw material properties, and the modified specifications of coal and iron oxides for Corex.

The blast furnace has been, and is likely to remain, the dominant technology for ironmaking. Coke is fed to blast furnace as a fuel and its quality plays a significant role in controlling the performance of the furnace. The quality of coke depends on the quality of coal or its blend, coking parameters and precarbonisation techniques, if any. With decreasing availability and increasing cost of good quality hard coking coal, coke makers face a tough challenge for production of metallurgical coke at competitive rates. Coke quality has been enhanced in recent times by introduction of precarbonisation techniques, such as compaction of the blend into cakes, so as to improve its bulk density. JSW Steel has adopted the newly developed vibrocompaction precarbonisation technique, along with non-recovery ovens, having a capacity to produce 1?2 Mtpa of coke. Optimisation of coal blend and bulk density of cake produced from vibrocompaction has helped JSW use inferior coals up to 35% in the coal blend, without adversely affecting the coke quality. The present paper discusses the optimisation of bulk density and coal blend, and use of non-coking coals in the coal blend to obtain the desired coke with properties: coke strength after reaction (CSR) exceeding 64%, coke reactivity index (CRI) ,25% and Micum index (210 mm) (M10) ,6%.The high cost coupled with scarcity of good quality coking coal necessitates development of techniques capable of producing superior coke from inferior coals. Precarbonisation techniques have helped improve the bulk density of coal charge which results in good quality coke even from inferior coals/coal blends. The improvement in bulk density leads to closer proximity of the coal particles during softening, which results in development of a stronger bond between the coke cells. The popular precarbonisation techniques include briquette blending, binderless briquetting, selective and groupwise crushing, preheating and stamp charging. A bulk density as high as 1?15 t m 23 could be achieved using the stamp charging technique. 1 Vibrocompaction is the most recent development in the class of precarbonisation techniques, developed by VECON, Germany. Conceptually, this technique is similar to the stamp charging but does not require very fine crushing of coal. 2 Numerous studies 3-6 have been carried out to investigate the influence of noncoking coal in coke making coal blends. Although inferior coals are being used in limited quantities between 10 and 30% by many cokemakers, only limited documentation is available on the subject. In Japan, y30% of hard coking coal is being replaced by medium and weakly coking coals by adopting improved coke making techniques. 7-9 In India, y15% of inferior coals are being used in stamp charged ovens. 10 JSW Steel Ltd has adopted the vibrocompaction technology for its non-recovery ovens obtained from Sesa-Goa. 11 From the experience of operation for more than two years, coal blend specifications for coke making have been developed. A coal cake bulk density of 1?1 t m 23 could be a...

Abstract

The blast furnace coke quality depends on the characteristics of coal blend, precarbonisation techniques adopted such as stamping, vibrocompaction etc., and coking conditions. Of the above, coal blend plays a significant role in the production of quality coke. Furthermore, the quality of the blend depends on the quality of individual coals and their interaction making up the blend. Coal, being a highly heterogeneous material, requires special care for determination of its properties and blending of individual coals for coke making. Coal fluidity is one such important coking property which highly influences the coke quality. The hard coking coals having good fluidity, which yield good coke, however are not only very expensive, but also are limited in reserves. Unlike, other properties, coal loses its fluidity on weathering, i.e. oxidation in presence of air on long storage in the yard, and the fluidity value changes on blending with different coals. To understand the effect of coal fluidity on coal blending and there by the coke quality, studies have been conducted using the industrial scale coals and coal blends. An empirical relation has been developed between actual blend fluidity and calculated fluidity using logarithmic weighted average from fluidity of individual coals. Blending of non-coking coals above 20% with the hard coking coals used in this research decreases the blend fluidity and impairs the coke quality. It was seen that the coals lose their fluidity on weathering, and the value becomes less than half after a two months of storage at site. Weathering appears to be more rapid in case of semisoft than hard coking coals. The present paper discusses the influence of coal fluidity on coal blend fluidity and changes on weathering.

Corex is an alternative smelting reduction ironmaking process where non-coking coal and pure oxygen is used instead of coke and air. The temperature of the tuyere region is much higher than in a blast furnace, and sustainability of tuyeres is a major challenge. At JSW Steel Ltd, almost 15% of the total shutdown is due to burnt tuyere replacement. A detailed analysis of tuyere failure and process parameters effecting tuyere burning was conducted to understand the failure mechanism and the root causes. A common reason does not exist for all types of tuyere failure; however, the collective reasons for failure are excessive coal fines (26?3 mm) and small mean particle size, low back pressure, blocking of tuyeres, scab formation and slip.