Effect and Requirements of Hot Metal Pretreatment on Refractories

      Taking the pretreatment of molten iron on a torpedo mixed iron tank car as an example, Figure 1 shows the refractory materials used for pretreatment of molten iron. During the pretreatment of molten iron, the carrier gas (nitrogen or air) for the pretreatment agent is sprayed into the molten iron through a spray gun. In order to improve the efficiency of pretreatment, agitating gas is sprayed into the molten iron through the nozzle, or the molten iron is stirred with a stirrer, so that the pretreatment agent and the molten iron are fully mixed, the reaction process is accelerated and the reaction is fully complete.

      In the desiliconization process, iron oxide (FeO) pretreatment agent is used, generally rolled steel scale or iron ore is used as the oxygen source in the pretreatment process, and lime (CaO) is used to adjust the alkalinity of slag. In dephosphorization, lime-based (CaO-CaF₂-FeO) or soda ash-based (Na₂CO₃) pretreatment agents are generally used. When performing desulfurization treatment, use lime series (CaO-CaF₂ and CaC₂). Various pretreatment agents have a strong erosive effect on refractory materials. Especially among soda ash-based pretreatment agents, Na₂O has good dephosphorization and desulfurization effects, but its melting point is very low (852°C), and it has a strong erosion effect on refractory materials. Na₂O is also a strong oxidant that can oxidize graphite and silicon carbide. When using a lime-based pretreatment agent, lime (CaO), fluorite (CaF₂) and iron oxide (Fe₂O₃) are used in combination. Iron oxide and fluorite have a strong erosion effect on refractory materials, but their erosion effect is stronger than that of Na₂O light. In addition, due to the addition of lime during the treatment process, the alkalinity of the slag changes greatly, from acidic slag to alkaline slag, and the refractory material suffers from the erosion of acidic slag and alkaline slag.

(refractory material in torpedo mixed iron tank)

1-Dolomite refractories；2-High alumina refractories；3-Magnesia refractories；4-sealing brick；5-breathable brick；6-CaC₂ spray gun

During the pretreatment process of molten iron, the erosion and damage suffered by refractory materials are mainly:

1. The strong erosion and wear effect of high temperature molten iron and slag.

2. Chemical erosion of various pretreatment agents.

3. Penetration and erosion of slag.

4. Sudden temperature changes caused by intermittent operation.

Therefore, the requirements for refractories for molten iron pretreatment are:

1. High temperature strength, wear resistance.

2. Resistant to the erosion of various pretreatment agents.

3. Good corrosion resistance to slag.

4. Good thermal shock resistance, no cracking, peeling off.

5. It is convenient for on-site application and construction, and has less environmental pollution.

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