Recent progress in top-and-bottom blown converters at Kawasaki Steel Corporation

Kawasaki Steel has developed two types of top and bottom blown converters, K-BOP and LD-KGC. K-BOP blows part of the oxygen gas together with lime through bottom tuyeres. In the LD-KGC, an inert gas is injected through bottom tuyeres and oxygen gas is blown through the top lance. Stirring force was intensified by increasing the flow rate of the bottom-blown inert gas in LD-KGC and by mixing the inert gas with bottom-blown oxygen at the final stage of the refining in K-BOP. The role of the bottom-blown gas for the improvement in metallurgical reactions was studied by changing the partial pressure of CO and stirring force. These studies have revealed that preferential decarburization is more affected by stirring force rather than partial pressure of CO in the bottom blowing gas. In order to quantitatively understand the metallurgical reaction, a new reaction model was developed by considering the stirring effect on changes in carbon and oxygen concentrations. On the basis of the results, carbon monooxide gas in LD-KGC, and carbon dioxide gas in K-BOP have been used in practice. Studies on smelting reduction of chromium ore in K-BOP are also described.