Process of continuously converting molten crude iron into steel

摘要

A continuous process for the conversion of crude iron into steel using a gaseous refining agent containing oxygen in free or combined form is carried out in a series of separate reaction zones including at least one prerefining zone and one decarburizing zone in which different temperatures are maintained, and is characterized in that the crude iron is atomized by means of the refining agent on entering at least one of the reaction zones. The heating of the zones is independent of the refining process. When only carbon, manganese and silicon are present in the crude iron, one prerefining zone for removal of manganese and silicon will be adequate, but if phosphorus is present it is eliminated by treatment with lime in a second prerefining zone. In these zones the gaseous refining agent may have a low ooygen content, such as air, or a mixture of oxygen with carbon dioxide or steam. A gas rich in oxygen is used in the decarburizing zone. In the embodiment illustrated in Fig. 1 iron from blast furnace 1 is separated from slag at separator 2 and passes to desulphurizing unit 3 and mixer 4 before entering the first prerefining vessel 5 at 1250 DEG C. Here the iron entering in a vertical jet is atomized by the gaseous refining agent which may also contain iron ore from nozzle 10, and in this stage about 70% of the manganese and silicon are oxidized. Slag and metal leave the vessel 5 together, being separated outside the vessel, and the metal passes to vessel 14, also at 1250 DEG C. where it is again atomized by gas from nozzle 15. In this stage the gas contains iron ore and lime. After leaving this vessel the metal is separated from slag and passes to furnace 21 where it is heated to 1650 DEG C. by electric or combustion means, and then passes to decarburizing vessel 22 where it is atomized by the gaseous refining agent from nozzle 24. Alternatively by using a strongly oxidizing heating flame heating and decarburizing may proceed simultaneously in vessel 22. In this stage the refining agent may be a mixture of oxygen, steam, carbon dioxide, air and ferric oxide suitably adjusted to prevent oxidation of iron. The metal, after slag separation, passes to deoxidizing vessel 32 and is again atomized by a stream of non-oxidizing gas such as carbon monoxide containing powdered deoxidants such as magnesium or aluminium from nozzles 30, 31. Alternatively a deoxidizing slag may be used, the slag forming additions being made with the atomizing gas. The steel finally passes to vessels 41 where the necessary alloying additions are made. The various vessels are normally arranged so that metal passes through them in cascade, but where this is not possible metal may be raised by means of a CO2 gas lift system as at 29. Scrap metal for addition to the system is melted in shaft furnace 42 using carbon monoxide evolved in the refining process.