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Utilisation

Perspectives on the Future of Cokemaking Stuart Nicol and Bob Durie

A few years ago there was talk of the demise of the coke ovens, at least in the developed countries, in favour of new steel-making technologies. This now seems less likely and this article provides an analysis of the future of cokemaking and blast furnace steelmaking.

Background With the advent of a more enviromentally aware society, traditional cokemaking has come under close scrutiny from regulatory authorities with regard to the production of fugitive pollutants and their influence both on plant operators and the community at large. This rightful attention has unfortunately had the effect whereby legislation, or threatened legislation, has impeded the introduction of new facilities. This concern has developed to an extent where the future of ironmaking by the integrated blast furnace route is seriously threatened. The consequences of this have grave implications for not only the coal industry but also for the overall Australian economy. Revenue to Australia from export coking coal amounts to some $3.5 billion in contrast to the lower figure of $2.3 billion for coals consigned to the energy sector (Fig. 1). For this reason, it is important to understand the current status of the coking industry and the reasons leading to its recent problems.

The Production of Coke and its Use Metallurgical coke is traditionally produced by heating carefully formulated blends of coals by indirect heat transfer in a sealed oven. The process is essentially a batch process in which the coked product is 'pushed' from the oven by means of hydraulic rams after a prescribed residence time. This period is

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The Australian Coal Review April 1997

coal blend and oven type dependent and may lie in the range 12-24 hours. The ovens in which the coal-to-coke transformation takes place consist of a series of refractory lined slots which may be up to 0.45 m in width, 6 m high and 16 m long (Fig. 2). Because of the number of battery openings (at the top for charging and at both ends for pushing), the traditional process is prone to leakage of environmentally unacceptable materials to the atmosphere. These materials may be in the form of dust, condensable tars and liquids and gas, particularly in the case of ageing ovens where door seal closures are a particular problem. The coke so produced is subsequently quenched-screened and fed to the ironmaking blast furnace. Within the blast furnace (Fig. 3), the coke not only acts as a reductant and fuel but also, by virtue of its placement in layers (slits), it provides a means of ensuring adequate permeability. This permeability is necessary to enable reducing gases to have access to the ferrous burden. For this reason coke must have specific physical characteristics that ensure that strength is maintained as the coke reacts and descends in the blast furnace. This is necessar y to enable it to support the imposed loads at high temperatures and physicochemical properties which permit the satisfactory progression of the complex chemical reactions within the furnace. Furthermore, the trend toward large blast furnaces and associated coke replacement by pulverised coal injec-


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