Hanna, Keith
(1990).
Transport phenomena at elevated temperatures - studies related to direct polymetallic smelting.
University of Birmingham.
Ph.D.
Abstract
The modelling of two key areas of transport phenomena in a new polymetallic smelter has been achieved by using both mathematical andphysical models to investigate optimum operating conditions. A study of oxygen mass transfer caused by multiple top-blown, subsonic gas jets contacting water flowing in a full-scale channel model of the smelter converting hearth has been carried out. A liquid phase solute mass transfer model that incorporates a flowing liquid phase has been developed. It has been used to compare mass transfer for both open-packed and close-packed multiple lance arrays of 2.26 mm, 4.95 mm, 10.95 mm and 24.40 mm nozzles delivering the same quantity of gas. It was found that for fewer lances of the larger nozzle diameters, up to a 75% reduction in liquid phase mass transfer occurred especially for the close-packed configurations. This restriction of mass transfer will result in reduced metal losses in the analogous smelter situation. Over a wide range of channel flowrates the mass transfer coefficient was found to be independent of water velocity. A computer model that predicts the amount of fog formation in the zinc vacuum condenser of the smelter for binary vapour/gas mixtures has identified operating conditions most susceptible to vapour fogging and subsequent metal losses. A fog problem is most likely to occur in condensable mixtures with high vapour concentrations and low initial quantities of superheat, and at low cooling wall temperatures as well as at high total pressures. Any lead in a Pb/Zn/N\({_2}\) condensable mixture will fog heterogeneously at least 400°C before zinc droplets form and act as condensation nuclei for the zinc vapour. An engineering approach to estimating quantities of homogeneous fog formation has been developed and is used to analyse the performance of the Imperial Smelting Furnace zinc condenser and the Port Pirie Vacuum Dezincing Unit.
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