Refining iron in a converter
The present invention relates to methods of refining iron, whether phosphoric or haematite iron, in a converter. It relates particularly to the case in which such refining is carried out by injecting an oxidising gas, for example pure oxygen, into the molten metal through tuyeres located in the bottom of the converter. In practice, the bottom of such converters is provided with a set of tuyeres having two coaxial ducts, the central duct serving to admit the oxidising gas, whilst the peripheral duct serves to admit a protective fluid, for example a gaseous hydrocarbon, to shield the bottom from the direct action of oxygen. After the blow, the converter is tipped into a suitable position for taking a sample, then raised and tipped in the opposite direction into a position for emptying the steel from the vessel. It is often the case that the converter remains in a vertical position for some time during this operation of raising and tipping into the emptying position. It is therefore necessary at this moment to continue blowing through the tuyeres in order to prevent them becoming blocked with the liquid steel in the converter. In order to carry out this operation, recourse is often made to injection of pure oxygen and natural gas (by the central and peripheral ducts respectively of the tuyeres), or nitrogen injection; however, in the first case such practice leads to an increase in the hydrogen content of the metal, whereas in the second case, if the hydrogen content decreases, the nitrogen content increases. In order to counter this drawback, it has been proposed to carry out this injection by means of argon, which stops any increase in the nitrogen or hydrogen contents of the metal but has the drawback of being particularly difficult in practice. 
    
    
     The present invention provides a refining method in which a steel works converter whose base is provided with a set of tuyeres having two coaxial ducts is used, and in which, during the operation for moving the converter into the emptying position, following its tipped positioning for sampling, a gas substantially consisting of CO 2  is blown through the ducts of the tuyeres. 
     It has been observed that such a method enables any blockage of the tuyeres to be avoided during the tipping of the converter, without running the risk of increasing the hydrogen and nitrogen contents of the steel and without being difficult to put into practice. 
     It has also been found advantageous to carry out this CO 2  injection during any possible pause of the converter, for example in vertical position, during its tipping up, and to continue this operation during the emptying operation itself. 
     This CO 2  injection may also be carried out after any corrective blowing operation carried out directly after the actual blow; this corrective blowing operaton also requires the converter to be tipped up for sampling, and is also characterised in that a strongly oxidising gas is blown through the central duct of each tuyere and a protective fluid, such as a hydrocarbon, is blown through the peripheral duct. 
     According to an advantageous variant of the above method the corrective blowing step is combined with the CO 2  blowing step mentioned above. According to this variant, during the corrective blow, e.g. from the beginning of the righting of the converter up to its emptying position, all or part of the hydrocarbon blown through the peripheral ducts of the tuyeres is replaced by CO 2 , whilst continuing to blow a strongly oxidising gas through the central ducts of the tuyeres, this operation therefore only being followed by emptying of the converter. It has also been observed that such a method also enables a considerable reduction of the hydrogen and nitrogen contents of the steel to be achieved without additional cost.