CFD modelling of fluid flow in a Peirce–Smith converter with more than one injection point
Introduction
Copper conversion is the selective oxidation of iron and sulphur with oxygen enriched air (up to 35 vol.% O2) injected laterally into a molten matte by means of a series of submerged tuyeres aligned on one side of a cylindrical vessel named converter. Nearly all the copper obtained by smelting and converting is processed in Peirce–Smith (PS) converters. In spite of its high productivity, the PS converter has some technical issues:
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Clogging of tuyeres as a result of accretions growing on the tip of them.
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Erosion on the refractory lining around the tuyeres due to localised thermal gradients.
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Inefficient SO2 capture in the off gases.
This type of furnace has not experienced significant technological improvements over a century of operation, which opens the door for upgrading it (Navarra and Kapusta, 2009). This can be overcome with the use of computational tools and physical modelling of such reactor.
On the other hand, gas injection is vastly used in process metallurgy; a significant amount of analytical and experimental work has been published on this subject. Extensive reviews were made by Brimacombe et al., 1991, Brimacombe, 1996, Kellog and Díaz, 1992, Mazumdar and Guthrie, 1995, and more recently by Lehner and Samuelsson (2009) and Mackey and Campos (2001). In all these reports it has become evident the need to further explore fluid flow phenomena at operating conditions in order to minimise as possible the extent of refractory wear and accretion growth in PS converters, in addition to splashing and slopping of the bath.
In this paper we present some CFD results of the fluid flow within a converter, after injecting gas with one and three tuyeres. Most of the reports existing in literature refer to a single injection point; however, given the nature of the converter, more information on flow patterns and velocity fields is needed when more than a single injection point is used.
Section snippets
Model description and geometries used
Fluid flow is described by Navier–Stokes (NS) equations, which are expressed in vector form as follows:where ρ is the fluid density, u is the fluid velocity (vector) (m/s), t is time (s), p is pressure (Pa), μ is the fluid viscosity (Pa s) and g is the gravitational acceleration (m/s2). To maintain the mass balance in the system, the continuity equation must be solved as well:which under isothermal conditions can be simplified to:
In current copper converting
Results and discussion
Fig. 2 shows the evolution of the plume as gas is injected into the matte with just one tuyere. The morphology of the plume indicates that it is symmetrical and that in principle there would be no effect from the tuyeres placed in each side of the injection point.
In terms of fluid flow, it can be noticed in Fig. 2 that shortly before one second of jetting, the air reaches the surface of the matte causing flow of the melt towards the wall over the tuyere and also in the direction opposite to
Conclusion
Numerical simulations of air blowing into a copper matte have been conducted. The effect of the number of tuyeres used to inject the gas was studied. As more tuyeres are used to blow the gas, the more chaotic the fluid flow within the vessel it becomes. Turbulent effects are magnified due to different flow paths, resulting in localised eddy formation; as the number of eddies increases, the less efficiently the volume of the converter is occupied, as flow recirculation takes place, limiting the
Acknowledgement
Financial support from IPN Grants is greatly appreciated.
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