Experimental and theoretical analysis of zinc updraft sintering
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I.
INTRODUCTION
T H E pyrometallurgical production of zinc involves the reduction of zinc oxide in a blast furnace (imperial smelting process). The operating efficiency of the blast furnace requires prior sinter-roasting of the ore burden in order (1) to eliminate the sulfur present in the ores (blende and galena) and to facilitate the reduction reaction and (2) to increase the mechanical strength of the blast furnace burden. The present article describes a mathematical model of the zinc sulfide ore sinter-roasting operation and experimental studies undertaken to clarify the physical phenomena involved in the process.
A. The Updraft Sinter-Roasting of Zinc Sulfide Ores The sinter-roasting of zinc sulfide ores is usually carried out in a Dwight-Lloyd type mobile sintering strand, as shown in Figure 1. The charge material is composed of pellets with a mean size of about 4 ram, comprising three constituents: (1) the ore mixture (zinc and lead sulfides, with a ratio P b / Z n = 0.5), (2) the fluxes (silica, calcium carbonates), and (3) returned fines (recycled sinter material too small for the blast furnace and other recycled materials). A thin layer of charge material, about 3-cm thick, is first deposited on the grid, then ignited with gas burners to initiate the highly exothermic sulfide oxidation reaction. The remainder of the sintering mixture is then discharged onto this "ignition" layer, to form a pellet bed about 30-cm deep. Air blown up through the bottom of J.P. BELLOT, Assistant Professor, F. PATISSON, Research Assistant, Centre National de la Recherche Scientifique (CNRS), and D. ABLITZER, Professor, are with the Laboratoire de Science et Grnie des Matrriaux Mrtalliques (LSG2M), Ecole des Mines, 54042 Nancy Cedex, France. Manuscript submitted May 10, 1991. METALLURGICAL TRANSACTIONS B
the grid ensures propagation of the reaction through the bed. The high temperature attained (1300 ~ to 1400 ~ induces partial melting of the solids and sintering of the pellets to produce an agglomerate with an appropriate texture, which is recovered at the end of the strand. Figure 2 shows a cross section of the bed and reveals several characteristic zones: (1) a wet zone, where the moist pellets are dried by the hot gases, (2) a heating zone, where the dried pellets are further heated by the passage of the hot gases, (3) a reaction zone, where exothermic oxidation of the sulfides produces a sharp temperature rise, leading to partial melting of the solids, and (4) an agglomerate zone, where the sinter formed in the reaction zone is cooled by the cold air draft through the pans.
13. Literature Survey Due to the limited number of updraft Dwight-Lloyd plants devoted to the roasting of zinc ores, relatively little work has been done on the mathematical modeling of the process. In the early 1980s, Prrignon developed a simplified model, tq In 1981, in the case of the closely similar process involving the roasting of mixed lead and zinc ores (Pb/Zn = 1), Cumming and Batterham I2j described a model whose approach is similar to th
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