Application of CO as bottom stirring gas in combined blown converter.

Abstract

At Kakogawa Works, steels of low to high carbon contents are produced by the use of LD converter of top and bottom blowing type. Argon and nitrogen has been used for the bottom stirring gas. In response to the recent increase in argon consumption, carbon monoxide (CO) recovered from LD exhaust gas is now being used to replace argon for bottom stirring.By the COSORB® process using a large scale CO gas generating equipment introduced from Kinetics Technology International Corporation, highly purified CO can inexpensively be produced from LD exhaust gas. The COSORB® process is a gas-liquid absorption method using the COSORB® solution, which is a toluen solution of Cu-AlCl4. By the COSORB® method, the gas having the chemical composition suited for bottom blown gas in the BOF can be produced in large enough quantity.The use CO as the bottom blown gas, particular attention should be paid to the CO concentration in the bulb station room where the possibility of CO leakage is present and to clean the pipe line during the non-blowing period.The characteristics of metallurgical reactions in the converter, for examples [O]F and slag (T.Fe) at turn down, are almost the same as those of argon and nitrogen bottom stirring. However, the carbon content in the molten steel is increased by CO rinsing after the oxygen top blowing; in contrast the carbon content is reduced in the case of argon rinsing.This is attributable to the fact that the decarburization reaction does not occur during CO rinsing due to the presence of CO bubble; otherwise the CO decomposition reaction (CO (gas) in CO bubble→C+O) occurs.At Kakogawa Works, the erosion rate of refractory has been reduced by the development and installation of S.A. tuyere (Single Annular tuyere). By the use of CO as the bottom blown gas, mushroom is formed in a similar manner as in the case of argon blowing. The life of the tuyere can be prolonged 20% as compared with the case of argon blowing due to the cooling effect of CO.By the installation of safety devices, it is possible to substitute CO for argon in order to reduce the gas cost.