A mathematical model of the nickel converter: Part I. Model development and verification
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I.
INTRODUCTION
THE converting
of nickel mattes has been carried out for over 90 years. The general principles of the process are similar to that of the slag blow in the copper converter; iron and sulfur are removed by reaction with air. It is not normally practical, however, to blow down to nickel metal due to the high temperatures that would be required, tll Although the essential chemistry of the process has long been understood, it is only recently that some of its peculiar differences from copper converting have been explained, tll As a result, there have been few efforts to write a comprehensive model of the process, accounting for both process chemistry and heat transfer. This is in contrast to the large effort which has gone into developing quantitative models of different aspects of copper converting. These include impurity behavior, t2-51 heat transfer, t6] and bath and surface motion. 171 It is interesting to note, however, that few models of the bulk process chemistry based on basic principles have been published. Only two models attempt to reproduce the overall material balances during the standard copper converting operation, and of these, only one includes a simultaneous heat balance. This may be, in part, a result of the fact that the rate of converting is largely limited by factors other than chemistry. Nonetheless, process models of this type are important, especially when it is necessary to operate outside of the bounds of normal practice, for example, to assess the effect of major changes in matte grade, quantities and compositions of reverts, or the use of a carbonaceous fuel for submerged combustion/reduction.
A.K. KYLLO, Research Engineer, and G.G. RICHARDS, Associate Professor, are with The Centre for Metallurgical Process Engineering, The University of British Columbia, Vancouver, BC V6T lW5, Canada. Manuscript submitted April 30, 1990. METALLURGICAL TRANSACTIONS B
II.
PREVIOUS WORK
Of the mathematical models published to date which consider the converting process, only two consider the particular chemistry of the nickel converter. One of these calculates only the instantaneous oxidation path of an iron-nickel-sulfur system Ill in equilibrium with a fayalite slag with a fixed F e O / F e 3 0 4 ratio. Although it does not include a heat balance, it can be used to make predictions about the fundamental chemical operation of the converter and the effect of some of the variables on the oxidation path. In particular, this model introduces the concept of the "limiting converting path." This is a compositional path which the converter follows after initially correcting for any sulfur excess or deficiency. The path is dependent on the temperature of the bath, as well as some of the other converting variables, especially those relating to the oxygen content of the gas. The other model of nickel converting is an empirical model developed by Falcobridge Limited, Falconbridge, ON, Canada. [8] The compositional variations of the bath are calculated based on curves fitted to plant data. The heat b
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