Developments in blast furnace process control at port kembla based on process fundamentals
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I. THE BLAST FURNACE PROCESS THE iron blast furnace is in principle a countercurrent gas/solid heat exchanger from tuyere raceway to stockline and a countercurrent oxygen exchanger from fusion zone to stockline.[1] Solid raw materials consisting of iron ore, sinter, coke, and fluxes are charged into the top of the furnace, while air, and sometimes hydrocarbons and oxygen, is blasted through tuyeres near the bottom of the furnace. The retention time of the ore may be as long as 8 hours, while that of the gas is a few seconds. However, the residence time of the coke in the hearth is longer, varying from 1 to 4 or more weeks.[2] The liquid hot metal and slag products are tapped at regular intervals through several tapholes near the bottom of the furnace. The slag is separated from the metal and the liquid metal is transported to the steel plant. In an attempt to gain a better understanding of this complex process in which direct experimental measurement is exceedingly difficult, experimental as well as operating furnaces have been quenched and dissected. Earlier studies by Bosley et al.[3] and Muravev et al.[4] were followed by very detailed and comprehensive investigations in Japan. The results of these studies have been fully documented, summarized, and thoroughly analyzed by a committee of the Iron and Steel Institute of Japan.[5] Largely based on the information gained from these dissections, it has been possible to divide the modern blast furnace for the sake of convenience and further discussion into five different zones.[1,6] (1) lumpy zone (upper stack and cyclic reduction zone), (2) cohesive zone (softening and melting zone), (3) active coke zone, (4) Hearth–Deadman, and (5) tuyere raceways. The verification of the existence of a cohesive zone through the dissection of quenched furnaces gave an enormous boost to blast furnace operational improvements. In this zone, the first slag forms, ferrous materials soften, and melting begins. In the cyclic reduction zone, carbon monoxide reacts with wustite to produce solid iron and carbon dioxide. The carbon dioxide, in turn, reacts with coke to regenerate carbon monoxide and this cycle prevails at temperatures above 1000 8C. Excess carbon monoxide reduces hematite and magnetite to wustite in the upper stack. ROBERT J. NIGHTINGALE, Superintendent of Ironmaking Development, is with BHP Steel, Port Kembla, NSW2505, Australia. RIAN J. DIPPENAAR, Director, is with the BHP Institute for Steel Processing and Products, University of Wollongong, Wollongong, NSW2522, Australia. WEI-KAO LU, Professor Emeritus, is with the Department of Materials Science, McMaster University, Hamilton, ON, Canada L8S 4L7. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS. METALLURGICAL AND MATERIALS TRANSACTIONS B
In the hearth, refining of the liquid metal and final reduction and separation of the liquid slag and metal occur as well as the final carburization of the iro
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