Improving the Desulphurization in COREX Process by Adjusting the Hot Metal Chemical Composition
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INTRODUCTION
ENVIRONMENTAL pressures and the increasing scarcity of good-quality coking coal have led to the development of ironmaking processes other than the traditional blast furnace route. COREX process has been developed as one of the most acceptable ironmaking process alternatives till now.[1,2] However, the COREX-3000, designed productivity of which is 1.5 million tons per year, still has some disadvantages. For example, the sulfur content of COREX hot metal (HM) is higher on average and has more severe fluctuations than that of the blast furnace (BF). The detailed description of the problem in COREX hot metal and transfer process of sulfur were listed in the authors’ previous paper.[3] For example, much higher sulfur burden and unstable operational parameters resulted in the higher and more fluctuant sulfur content of COREX. Therefore it is necessary to explore measures to improve the desulphurization in COREX process. To the best knowledge of the current authors, a great deal of research work in desulfurization has been carried out over the years. However, these works were mostly LAIXIN WANG, SHENGLI WU, MINGYIN KOU, BINBIN DU, YANAN LU, and KAI GU are with School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, (USTB), 30 Xueyuan Road, Haidian District, Beijing, P. R. China. Contact e-mail: [email protected] Manuscript submitted January 11, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
done in the context of BF slags and ladle slags.[4–7] There was little work regarding the influence of the chemical composition of HM, and the composition of slag in COREX process was different from those of BF and ladle slags. Therefore, it is worthwhile to study the desulfurization in COREX process by adjusting the chemical compositions of hot metal. This study would be beneficial to improving the alternative method of COREX compared with BF. In this paper, a theoretical analysis has been carried out to study the influence of the chemical composition of COREX HM on the theoretical sulfur distribution ratio by adjusting the Si and Mn contents of hot metal. Experiments were then conducted to verify and develop it. The influence of the chemical composition of COREX HM on the desulfurization of COREX process will be verified through this study.
II.
THEORETICAL BACKGROUND
A. Calculation of LS When discussing the desulfurization between slag and hot metal, the sulfide capacity (Cs) is a critical parameter, and it is deduced from the following important exchange reaction[8] 1 1 ðO2 Þ þ S2 ðgÞ ¼ ðS2 Þ þ O2 ðgÞ 2 2
½1
The equilibrium constant for reaction [1] could be expressed as shown in Eq. [2].
K½1 ¼
aS2 pO2 1=2 f 2 ðpct SÞ pO2 1=2 ¼ S aO2 aO2 pS2 pS 2
½2 a½O
where aS2 and aO2 are the activities of sulfur and oxygen in the slag phase, respectively, and pS2 and pO2 are the partial pressures of S2(g) and O2(g), respectively. fS2 is the activity coefficient of sulfur in the slag phase, and (pct S) is the sulfur content of slag in wt pct. K[1] is the equilibrium
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