Accretion growth on single-pipe tuyeres: Part I. Model development and preliminary analysis
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I.
INTRODUCTION
S U B M E R G E D gas injection is fundamental to the pyrometallurgical production of a number of metals, including copper, nickel, steel, and lead. Two of the most important problems faced in submerged gas injection are tuyere blockage and refractory erosion. Tuyere blockage is generally thought to be caused by the "back-attack" phenomenon, while refractory wear is the result of a number of factors, including back-attack, thermal stress cracking, and erosion by the bath. While tuyere blockage can be eliminated by the use of high-pressure injection, ~J the protection of the refractory is more complex. The reduction of refractory wear can be approached from two directions. Improved refractory materials may be sought which have a greater resistance to wear and thermal stress cracking, or the refractory may be protected with an accretion. Such an accretion may be formed as a result of the cooling of the bath by the relatively cold gas or as a result of the deposition of a reaction product around the tuyere. In cases where an exothermic reaction occurs between the gas and the bath, the freezing of the bath may require the use of an inert or hydrocarbon shrouding gas, as in Q-BOP tuyeres. In cases where a hydrocarbon is used, an enhanced cooling effect is obtained from endothermic dissociation. It should be noted that, in some cases, accretion formation is considered to be detrimental to the process. This is particularly the case in nonferrous processes, where the A . K . K Y L L O , Graduate S t u d e n t , is with the Centre for Metallurgical Process Engineering, University of British Columbia, Vancouver, BC Canada V6T 1Z4. G.G. RICHARDS, formerly Associate Professor, University of British Columbia, Vancouver, is Senior Research Scientist, Cominco Metals, Trail, BC Canada VIR 4L8. Manuscript submitted October 16, 1992.
METALLURGICAL TRANSACTIONS B
injection pressure is lower and tuyere blockage by accretions is a significant problem. However, as noted previously, when properly formed, nonblocking accretions can be critical to efficient process operation. The formation and growth of accretions are subjects about which little detailed information is known. If properly understood, substantial improvements, particularly in terms of reduced refractory wear, could be made. While there have been significant advances in tuyere design (i.e., shrouded tuyeres, multihole plugs, and porous plugs), there is still only a rudimentary understanding of how these work to control accretions. As a result, progress in the development of injection technology is hindered. Essentially, three basic types of accretions have been reported in metallurgical processes using submerged injection. These are the pipe, the hemisphere, and the hollow-cored hemisphere, which are shown schematically in Figure 1. Each of these types tends to form under specific conditions. The pipe is generally found in cases where a reactive gas is injected through an unshrouded tuyere; for example, in copper and nickel converting. The hemisphere is us
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