転炉内二次燃焼に及ぼす炉内水素濃度の影響

摘要

転炉において熱余裕度を向上するために，上吹き酸素の二次燃焼は重要な熱源であり，その増大が課題となっている。そこで従来から高い二次燃焼率が得られるノズルの開発などが行われている1，2）。転炉内で二次燃焼を効率的に向上させるためには，ノズルから吹込んだ酸素の流動やCOとの反応挙動の解析が重要となる。しかしながら，上底吹き酸素の吹込み条件3）や使用する炭材の種類4）などにより，二次燃焼挙動が大きく変化する。特に溶融還元吹錬においては揮発成分の高い炭材を用いた場合に二次燃焼が低下することが知られているが4-6），転炉内部の各化学種の濃度を計測し，反応を実験的に検討することは非常に困難である。%In this study, numerical simulation of high temperature combustion in CO-H_2 mixture with oxygen jet has been conducted to consider post combustion in a converter for steel making process. In the numerical model, a detailed reaction model and mixture fraction model were used. The flammability characteristics and flame structure were compared between both calculation results. The influence of H_2 content in the mixture and the reaction mechanism of the combustion were discussed. In mixture fraction model, the post combustion ratio decrease with an increase of H_2 content, but the influence of H_2 content on post combustion ratio is small. On the other hand, in the detailed reaction model, the influence H_2 content on post combustion ratio is bigger, and the post combustion ratio takes its maximum when the molar hydrogen concentration is 2%. When the molar hydrogen concentration is 20% in CO-H_2 mixture, CO_2 is decomposed around the edge of combustion zone, where the endothermic reaction occurs. Resultantly, the temperature in the downstream region is reduced. In the CO-H_2 combustion, water vapor is also decomposed by the shift reaction through CO+H_2O → CO_2 + H_2.