Sammendrag
During casting of refined ferromanganese alloys in sand beds at temperatures up to 1800oC a considerable amount of very fine brown fume is generated by the active oxidation of the alloy. This fume is difficult to capture because of the large flux of fume generated associated with high evaporation rate of Mn at elevated temperatures, the large thermal plumes over the casting beds, the large surface area of the casting beds and the very fine nature of the fume. This paper describes how the use of fine water sprays along the edge of the roof covering the casting bed has lead to a significant reduction in visible diffuse emissions. The effect of water spray pattern, droplet size, wind direction and ambient weather conditions on Mn oxide fume capture is presented. The flux of fume generation during casting is also markedly reduced when water sprays are used in the vicinity of the casting beds. Possible fume suppression mechanism investigated included the interaction of the moist air stream with the Mn vapor in the boundary layer over the liquid alloy and the resultant formation of a thin layer of Mn oxide on the metal surface that reduces the Mn evaporation flux. Video techniques are used to semi-quantify the flow patterns over the sand bed, to calculate the energy in the fume plumes and to provide input parameters for CFD modelling of air flows over the casting bed. These data are used to optimize the capture of the fume from sand beds both inside and outside the smelter building. The safe use of fine water sprays in the vicinity of liquid metal is considered and practical tips to avoid water / metal contact are presented. The use of fine water sprays represents a cost effective way of reducing fume emissions.