The Role of Expansion and Fragmentation Phenomena on the Generation and Chemical Composition of Dust Particles in a Flas
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DUCTION
THE presence of dust particles in the off-gas stream of flash smelting and flash converting reactors is a common problem during the operation of such furnaces.[1–5] Dust particles in the off-gas stream are undesirable because they cause blockage of the transport system in the waste heat boiler and electrostatic precipitator. They also increase the time and cost of process maintenance. Although a portion of the dust recovered in the bag house is typically recycled to the reactor,[6,7] an inventory of dust must be maintained to keep the process operating under steady-state conditions. Furthermore, the handling of large amounts of dust provides opportunities for the escape of fine particles to the atmosphere, with serious implications CIRILO ANDRE´S DUARTE-RUIZ, Graduate Student, and MANUEL PE´REZ-TELLO, Professor, are with the Department of Chemical Engineering and Metallurgy, University of Sonora, Hermosillo 83000 Mexico. Contact e-mail: [email protected] VI´CTOR ROBERTO PARRA-SA´NCHEZ, formerly Graduate Student with the Department of Chemical Engineering and Metallurgy, University of Sonora, is now Postdoctoral Visiting Researcher with the University of Concepcio´n, Chile. HONG YONG SOHN, Professor, is with the Departments of Metallurgical Engineering and Chemical Engineering, University of Utah, Salt Lake City, UT 84112. Manuscript submitted April 6, 2016. Article published online July 22, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
to the environment and the health of operators, engineers, and the human settlements near the smelter facilities. It is generally accepted that dust is produced by the violent fragmentation of sulfide particles as they undergo oxidation in the reaction shaft of flash smelting and flash converting reactors.[4] However, so far most of the studies regarding dust generation report qualitative information obtained from microscopic observations of reacted particles oxidized under controlled laboratory conditions.[8,9] To the best of the authors’ knowledge, no plant campaign has been reported in the literature that provides quantitative local information on the size distribution of the particle population along the length of the flash converting reactor and the downstream units. As a result, a number of uncertainties prevail. For instance, it is not clear how much of the dust entering the waste heat boiler was produced by fragmentation of the original particles and how much consists of fine particles in the feed that were carried away by the off-gas stream without fragmenting. The composition of dust particles as well as its relationship with the overall composition of the particle population is also unknown. An additional concern stems from the fact that no clear definition of dust has yet been adopted in this area. As an example, plant engineers typically call ‘‘dust’’ all particles entering the waste heat boiler and those collected in the electrostatic precipitator.[1–3,6,7] In VOLUME 47B, OCTOBER 2016—3115
contrast, ‘‘dust’’ has been used by several researchers[4,10,11] to refer to fin
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