Study of Lime Dissolution Under Forced Convection
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THE demands on high-quality steel and optimization of converter process have emphasized greatly the importance of lime dissolution in converter slag. Fast lime dissolution in slag would ensure the power of the slag for dephosphorization, shorten the process, and reduce the consumption of the raw material as well as energy. Although lime dissolution in slag has been a research topic since a few decades ago,[1–9] this topic is becoming more important currently. In 1976, Mstsushima et al.[1] rotated a CaO cylinder mounted between two molybdenum plates in slag. The effect of FeO content, the rotation speed, and temperature were studied. They concluded that the mass transfer was the rate-determining step. Natalie and Evans[2] investigated the effect of lime properties on the rate of dissolution in CaO-SiO2-FeO slag with rotating disk apparatus. They reported that the porosity of lime played important role in CaO dissolution. The current work is a part of a long-term project to study the effects of different parameters on lime dissolution. In a previous work,[3] the dissolution of different CaO samples into molten synthetic ‘‘FeO’’-SiO2 and ‘‘FeO’’-SiO2-CaO slags was carried out. The slag was kept stagnant. The dissolution rate was found very fast in ‘‘FeO’’-SiO2 slag, but slow in ‘‘FeO’’-SiO2-CaO slag. The formation of a dense layer of 2CaOÆSiO2 was responsible for the total stop of the dissolution. To study the lime dissolution by forced convection, a new experimental technique was developed.[4] In this method, a cube of CaO was placed in the slag, which was stirred eccentrically. By freezing the whole system (the sample along with the slag could be quenched), the effect of forced convection on the dissolution and the dissolution mechanism could be revealed successfully. As a continuation of these studies, the current work focuses on the mechanism of lime dissolution when forced convection prevails. The effect of stirring intensity on dissolution is studied also. TENGFEI DENG, Graduate Student, and DU SICHEN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, SE 10044 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted December 6, 2011. Article published online January 19, 2012. 578—VOLUME 43B, JUNE 2012
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EXPERIMENTAL
A. Materials and Slag Preparation Five types of CaO samples were all prepared by Lhoist using lime stone. The CaO sample was in the form of cube, about 9 9 9 9 9 mm in size. The sizes of the cubes varied somewhat because of different preparation procedures. No preparation conditions are to be reported in this article to protect the company’s interest. In view of the great difference between type 1 and type 2 limes, the emphasis of the current work was given to these two types of limes. The chemicals used for the slag preparation are presented in Table I. The purity levels and suppliers are also listed in the same table. The CaO, Fe2O3, and SiO2 powders were dried at 393 K (120 C) for 24 hours to remove moisture. The details of slag prep
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