Optimization of CaO-CaF2 Flux to Improve Initial Desulfurization in Carbon Saturated Iron
- Optimization of CaO-CaF2 Flux to Improve Initial Desulfurization in Carbon Saturated Iron
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- The importance of the effective hot metal desulfurization process is increasing today due to several reasons. The sulfur content in hot metal is getting higher because of the depletion of high grade ore with low sulfur, so that the usage of low grade ore with high sulfur is increased. And the demand from the customer for the high quality steel with low sulfur such as line pipe steel is increasing. There is also a demand for the reduction of desulfurization time for the high productivity, because it might take such a long time for desulfurization for a converter process only. Therefore, it is important for hot metal desulfurization process to be more effective for faster desulfurization rate and more desulfurization amount in a short time.
In the present study, in order to further optimize the desulfurization flux without excessive unused CaO, various conditions of desulfurization reactions using the conventional CaO-CaF2 flux were tested in a series of laboratory scale experiments. The desulfurization efficiency (removal rate of S and final concentration of S) was examined by changing various conditions, such as fluorspar proportion, liquid/solid proportion, mechanical stirring, order of addition of fluxes, etc.
Since the initial desulfurization behavior was of our interest, analysis was focused on the initial desulfurization 10~20 minutes after flux injection. From the test results of various conditions, we could obtain followings:
The initial desulfurization rate was dependent on the state of flux, especially liquid slag proportion is important for the initial desulfurization rate. As fluorspar proportion increased, the initial desulfurization rate increased.
However, 20 minutes after injection, the desulfurization due to solid CaO become evident in some conditions such as mechanical stirring was applied and reaction time were given enough, conventional flux which contains more amount of CaO showed even or more sulfur removal efficiency in terms of sulfur contents in equilibrium.
Therefore, 2 step injection method is feasible for application. At initial stage, desulfurization with large amount of liquid slag is favorable and in the middle of the desulfurization, additional solid CaO injection is needed.
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