Dynamics and control of solidification of molten metal flows
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I. INTRODUCTION
SOLIDIFICATION of turbulent flows in cooled pipes or ducts is a phenomenon that occurs in a wide range of situations. Flow through water pipes in frozen soil, handling of metal and slag flows in metallurgical operations, and magma flows in volcanos can all be affected by solidification. This article focuses on freezing of molten metals in turbulent flow and the application of this knowledge to control the flow rate of metallurgical furnace products, particularly through tapholes. Currently, periodic tapping with an oxygen lance is the most common method for removing molten products from a furnace. The oxygen lance burns a hole in the clay plug blocking the taphole to allow the molten material to flow out of the furnace. Once tapping is complete, moist clay is used to block the taphole. These operations are hazardous to operators as they must work in close proximity to the furnace and the oxygen lance produces a shower of sparks. Due to the corrosive nature of most furnace products, the refractory conduits through which they flow erode quickly, a situation exacerbated by oxygen lancing. There is also no current means of flow control for metallurgical flows through tapholes. This means that the level of product in the furnace fluctuates and the furnace does not always operate at its optimum conditions. By applying a coolant to the outer wall of a tapping tube, it is possible to build up an annular solidified layer of the molten material inside the taphole. This solidified layer can be used to restrict and control the flow. Manipulation of the cooling parameters can be done remotely from the tube using standard process control techniques. The taphole can be frozen shut if enough cooling is applied, though a heating source would normally be required to reopen the pipe. The solidified layer can also protect the taphole lining from A.R. FIRTH, Project Scientist, is with Iron Ore Processing, CSIRO Minerals, New South Wales, 1670, Australia. N.B. GRAY, Associate Professor and Program Leader of the G.K. Williams Cooperative Research Centre for Extractive Metallurgy, and A.K. KYLLO, Research Fellow, G.K. Williams Cooperative Research Centre for Extractive Metallurgy, are with the Department of Chemical Engineering, The University of Melbourne, Victoria 3010, Australia. Manuscript submitted January 25, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
corrosion by the molten material. This removes the need for operators to be near the furnace when tapping, as the process could be performed from a control room. II. PREVIOUS LITERATURE Many previous studies have been done on internal solidification in pipe flow, both experimentally and analytically. The majority of this research has focused on the freezing of water.[1,2,3] Some limited data have been obtained for metals and slags,[4,5] although results obtained using waxes[6,7] can be useful for determining the behavior of slags, to which they are thermally similar. Water data are not relevant to molten metal flows, however, as molten metals have much lower Pra
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