A Study of Scrap Heating By Burners. Part I: Experiments
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IN developed countries with ample steel scrap, electric arc furnace (EAF) steelmaking has increased rapidly over the basic oxygen furnace (BOF) steelmaking; over the last decade, EAF steelmaking has increased from 49 to 61 pct of total crude steel production in North America.[1] The performance of EAF units has improved with a number of new technologies. One of these is the use of oxy-fuel burners to assist electrical heating, which has become standard equipment. The first use of burners was to melt the scrap at the slag door where arc heating is ineffective, but it was quickly realized that productivity could be increased by more burner power. Generally, there are at least three burners positioned in the cold spots between electrodes.[2] Using burners, typical productivity increases are in the range of 5 to 20 pct, as reported by different investigators.[3–5] Despite the importance of burners, there is little information on the efficiency of the heat transfer between the combustion gas and the steel scrap in the furnace. Better understanding of heat transfer phenomena between the combustion gas and the steel scrap could improve the process, for example, by determining the time at which the heating efficiency drops to uneconomical levels or by determining the best scrap size and density to charge near the burners. The present study was aimed at measuring and modeling the heating efficiency for a range of scrap types. The ultimate aim of this research is to assist operators with the selection of energy inputs and scrap grades from different sources so as to optimize the operation for various cost or productivity objectives. The main objective of the present Part I experimental
KAMALESH MANDAL, Senior Metallurgist, is with the Severstal Columbus, Columbus, MS 39703. Contact e-mail: kamaleshm@ gmail.com GORDON A. IRONS, Dofasco Professor of Ferrous Metallurgy and Director, is with the Steel Research Centre, McMaster University, Hamilton, ON, L8S 4L7, Canada. Manuscript submitted September 13, 2012. Article published online October 18, 2012. 184—VOLUME 44B, FEBRUARY 2013
study was to measure steel scrap heating to validate the numerical model, presented in Part II. II.
APPARATUS
The present study focused on the region of the EAF around a burner, isolated from the effect of arc heating and the proximity of other burners, as shown schematically in Figure 1. The aim of the present study was to measure the efficiency of heat transfer between a single burner flame and scrap, not to melt the scrap. A photograph of the scrap heating furnace is shown in Figure 2, along with its dimensions in Figure 3. The furnace shell was made of steel with refractory lining on bottom and the front wall with the burner. There were two layers of refractory on the front wall; the first layer was made of 65-mm-thick insulating brick and the hot face layer was made of 113-mm-thick alumina brick. There was a removable lid with a chimney, which is not shown in Figure 2, but is shown in Figure 3. An in-house designed, premixed oxygen-propane burner, located
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