Kinetic Study on Desulfurization of Hot Metal Using CaO and CaC 2
- PDF / 3,716,504 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 22 Downloads / 188 Views
NTRODUCTION
LIME and calcium carbide are two of the most commonly used agents for hot metal desulfurization. It is important to have a good understanding of their kinetics and reaction mechanisms to optimize material utilization. Although a number of studies[1–11] have been carried out, it is still difficult to compare the efficiencies of desulfurization using CaO and CaC2. The main reason is due to the scattered and even poor-defined experimental conditions. The general view for hot metal desulfurization with CaO was described by Oeters.[7] Oeters reported that an outer layer of CaS together with 2CaOÆSiO2 was formed on the surface of CaO according to Reactions [1] and [2]. CaO þ S ¼ CaS þ O
½1
2CaO þ Si þ 2O ¼ 2CaO SiO2
½2
Reaction [1] proceeds by diffusion of the reactants (S and O) through the CaS layer whereas diffusion of reactants through the di-calcium silicate layer is slow and therefore, limits the desulfurization.[7] On the other hand, not only di-calcium silicate is formed around the CaO particle but also tri-calcium silicate.[9,10] It is argued that the addition of CaF2[9] or Al[10] helps the formation of a slag layer around the CaO particle and thus increases the reaction rate. Takahashi et al.[11] dipped CaO rods in hot metal with or without slag at 1723 K (1450 °C) under Ar-3 pctH2
DAVID LINDSTRO¨M, Ph.D, Researcher, and DU SICHEN, Professor, are with the Department of Materials Science and Engineering, KTH Royal Institute of Technology, 10044 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted January 30, 2014. Article published online September 25, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
gas atmosphere. No CaS formation on the CaO rod was observed in the absence of slag. They reasoned that solid CaO does not work at all for hot metal desulfurization because of the formation of silicate layer. They argue that CaO has to go into slag before it can have any effect on hot metal desulfurization. On the other hand, Oeters et al. dipped sintered CaO rods in hot metal with and without silicon at 1573 K (1300 °C) and studied the growth of reaction products as a function of time.[6] A layer of 2CaOÆSiO2 was formed inside the outer layer of CaS when the hot metal contained silicon. CaS was the only reaction product in the experiments with silicon free hot metal. They concluded that solid state diffusion was the rate determining step at high sulfur concentrations whereas boundary layer diffusion was rate determining at lower sulfur concentrations. In the case of calcium carbide used for hot metal desulfurization, a layer of CaS forms around the unreacted core of CaC2 according to Reaction [3].[7] CaC2 þ S ¼ CaS þ 2C
½3
[8]
Talballa et al. observed a graphite layer formed between the CaS and CaC2. The authors speculated this carbon layer would slow down the desulfurization process.[8] The contradicting observations reported in the literature are partly due to the difficulties in the experiments at high temperature and partly due to the different experimental conditions employed. The
Data Loading...
