importance attached to semi-soft coals for use in cokemaking arises mainly from their lower price. Stamp charging In India the use of appropriate imported coals to provides scope for using inferior coals efficaciously without supplement the inherent deficiencies of indigenous impairing the coke strength and can use a large proportion coals for cokemaking is in vogue. Stamp charging is of semi-soft coals. Tata Steel, having completely replaced very efficacious for inferior coking coals and has conventional charging with stamp charging, is well placed enabled Tata Steel to produce coke of international to maximise the usage of semi-soft coal in the blend. quality. It has been found to offer scope for the This paper describes the experiences of Tata Steel utilisation of less expensive imported semi-soft in replacing imported hard coals in the stamp charging coals to replace expensive imported hard coals. blend14-16 containing high ash indigenous coals (West Extensive tests were carried out to assess the Bokaro, Jamadoba, Bhelatand) without any impairment of blending potential of semi-soft coals for coke strength. The conclusions drawn should be of general cokemaking by stamp charging in a 7 kg mini-oven, interest to other steel plants dealing with the problem of and a 600 kg pilot oven in the laboratory. This was poor quality (high ash content)/scarce coking coal. followed by commercial scale trials. The test results clearly indicated that hard coals can be replaced with 30-35% of semi-soft coals in the stamp CHARACTERISTICS OF SEMI-SOFT COALS BY charging blend at Tata Steel without any SOURCE compromise of coke strength. Semi-soft coals are In India, coals have been categorised as prime coking coal, now in regular use in all Tata's stamp charged medium coking coal, and blendable coal depending on the batteries. I&S/1554 resulting coke quality, while Australian coals are conventionally classified as hard coking coal, semi-soft coking The authors are with The Tata Iron & Steel Co. Ltd, Jamshedpur coal, and thermal coals. The hard coking coals correspond 831 001, India. Manuscript received 10 August 2000; accepted to high quality coking coals, semi-soft coking coals which
Table 1 Design features of top charged ovens at Tata Steel A 1 8 scale perspex model for the top charged coke oven batteries of Tata Steel was installed as a tool Battery 1 Battery 2 for optimisation of coal blend moisture, light diesel No. of ovens per battery 54 54 oil addition, and charging practice to enhance coal Oven dimensions, mm throughput. The coke oven cell could be divided width, ram side 412 370 into 12 subcells to study variations in bulk density, width, coke side 488 430 average width 450 400 segregation, and other properties. The actual coal taper 76 60 blend was used as a medium for experimentation. height 4460 4500 The optimum conditions, as established from model length over sole 13 590 13 590 studies, were employed in plant practice resulting Capacity (dry coal), t/oven 18•5 16•5 Average pushings per day 67 91in about a 10% increase in coal throughput.
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