Heat transfer and lance clogging during submerged powder injection
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I.
INTRODUCTION
O V E R the past ten years powder injection processes in the iron and steel industry have developed to the point where almost all of the industrialized world's steel production is treated by some form of powder injection. Desulfurization of iron and sulfide shape control of steel are the most common refining processes carried out with powders in North America, whereas the Japanese and Europeans are also desiliconizing and dephosphorizing iron before steelmaking. In spite of the widespread adoption of such processes, our understanding of the associated transport phenomena is still at a rudimentary stage. The fluid mechanics has been studied considerably with water models 1-6 and to a lesser extent with liquid lead models. 7 Multiphase mathematical modeling by this author has elucidated the effects of conveying conditions on the flow regime in the liquid, contacting pattern with the liquid, and the depth of penetration of gas-particle-liquid jets. 8 A mathematical model for the ascending three-phase plume was also developed to predict the volume fractions and velocities of the individual phases. 9 The agreement between these models and experiments, in water and lead, was reasonable. There has been no systematic study of the heat transfer aspects of powder injection, although such phenomena are important for several reasons. As will be shown, lance clogging phenomena are a result of the interplay between the fluid dynamics and heat transfer at the lance tip. Additionally, the heat transfer rates determine the time required to heat the particles to reaction temperatures, and this is particularly important for reagents which vaporize such as magnesium and calcium and those which decompose such as calcium carbonate since the gas release should ideally occur deep in the bath. The present work concerns the measurement and calculation of gas, particle, and lance temperatures and the develG.A. IRONS is Associate Professor, Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. Manuscript submitted August 26, 1985. METALLURGICAL TRANSACTIONS B
opment of a model which permits extrapolation to iron and steel systems.
II.
EXPERIMENTAL
A . Experimental D e s i g n
It is obviously very difficult to measure gas and particle temperatures in a flowing stream inside a lance submerged in a liquid metal. A thermocouple in the stream will usually indicate a temperature between the gas and particle temperatures. The approach adopted in the present work was to measure temperatures in the lance wall. The lance was made of mild steel without any refractory coating so that its thermal resistance was small. Consequently, the temperature across the lance wall could be considered constant. (In fact, for the lance used in the experiments, the thermocouple embedded in the inner lance surface was usually less than 10 K cooler than the one in the outer surface when the temperature difference between the liquid lead and the internal gasparticle stream was 375 K
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