Maximisation of non-coking coals in coke production from non-recovery coke ovens

Abstract

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...

Compaction tests on coking coals. Part 1: Laboratory-scale compaction with a 4-ton hydraulic press

“…The d 50 of the Waterberg sscc materials varied between 0.6 mm and 1 mm, whereas the crushing fineness was more than 99% < 3.25 mm. The particle sizes of the coals utilized in this study were similar to those suggested for compaction or stamping by various workers in the field, namely 85% to 99% < 3.25 mm (Dash et al, 2005;Kumar et al, 2008, Tiwari et al, 2012Madias and de Córdova, 2013;Rejdak and Wasielewski, 2015). In the case of the Oaky North sample, the d 50 was 0.7 mm with a crushing fineness of 95% < 3.25 mm.…”

“…A less porous coke product, which is beneficial for mechanical strength (Nishioka and Yoshida, 1983). The decrease in total porosity is indicative of limited swelling, restraining pore enlargement and this, presumably, is attributable to the compact nature of the coal bed under high oven bulk density (Nyathi et al, 2013) Closer proximity of coal particles during softening, which results in the development of a stronger bond between the coke cells (Kumar et al, 2008) The induction of homogeneity throughout the coal cake (Kuyumcu, Rosenkranz, and Abel, 2010) An increase in the proportion of less-reactive carbon forms, and an improved degree of crystallization (Nyathi et al, 2013) Decreased porosity causing an increase in the water saturation index, i.e. filling of the total pore volume (Rejdak and Wasielewski, 2015) Improvement in the coke strength owing to increased coal particle contact and increased coke density (Rejdak and Wasielewski, 2015).…”

Influence of coal fluidity on coal blend and coke quality

“…8 The analysis of coals used for the study is given in Table 1. Coals A, B are hard coking coals, coals C, D are semi soft and coal E is non-coking coal.…”

Understanding the impact of coal blending decisions on the prediction of coke quality: a data mining approach

“…Several models (Bukharkina et al 2012;Dash et al 2005Dash et al , 2012Kishore et al 2011;McKenzie et al 1998;Suresh et al 2012) consider an aggregate of a portion of the vitrinite distribution as an input parameter, in effect creating a weighted R v,max . Kumar et al (2008) reported that the vitrinite reflectance in the range V 9 -V 13 , a commonly used aggregate value, is an improved predictor of the measured Coke Strength after Reaction (CSR) than the mean maximum vitrinite reflectance. The standard deviation or petrographic non-uniformity of the distribution is another attribute used within models, that relates to V-groups and blending decisions (Bulanov et al 2009;Stankevich and Bazegskiy 2013;Stankevich et al 2008;Stankevich and Zolotukhin 2015).…”