PURPOSE: To stably and effectively execute continuous molten iron pretreatment by executing de-sulfurizing treatment at the time of high temp. in the initial stage and de-phosphorizing treatment at the time of low temp. in the last stage and adding lime so as to hold the basicity of slag to a suitable value in order to avoid re-sulfurization.
CONSTITUTION: In the pretreatment for the molten iron accommodated in a vessel, such as mixer, etc., the de-sulfurizing agent is injected through lance at the time of high temp. in initial stage to execute de-sulfurizing treatment. Next, at the time of de-siliconizing treatment injecting de-siliconizing agent through the lance, the lime is added, so as to become to ≥3.5 the basicity of slag (%CaO/%SiO2) in order to prevent the re-sulfurization. Next, at the time of de-phosphorizing treatment injecting de-phosphorizing agent through the lance, the lime is added, so as to become to ≥3.0 the basicity of slag - %CaO/(%SiO2+0.634%P2O5 - to prevent the re-sulfurization. In this way, the continuous operation for de-sulfurizing, de-siliconizing and de-phosphorizing treatment can be executed and the effective continuous molten iron pretreatment is obtd.
HIWASA SHOICHI
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