A low coke rate operation in blast furnace is desired to decrease the carbon input and mitigate global warming problem. However, low coke rate operation tends to cause the gas permeability to deteriorate. The mixing of small-size coke (nut coke) including high reactivity coke in ore layer is considered to be a promising way to improve permeability and increase reaction efficiency in a blast furnace. Although adding a nut coke mixing to an ore layer is predicted to be empirically effective in low coke rate operation, there is little actual data on microscopic phenomena of each particle in the packed bed. In the present study, an Euler-Lagrange approach was introduced to precisely understand the influence of the packed bed structure on the reaction behavior of each particle in the three-dimensional particle arrangement.It was observed that the heterogeneity on the reaction rate and temperature distribution was influenced by the particle arrangement. When high-reactivity coke was used at approximately 1 273 K, although CO gas fraction increased, the gaseous phase temperature decreased due to the active solution loss reaction rate of the nut coke in the mixed layer. As a result, the ore reduction rate decreased. The contribution of high-reactivity coke to the ore reduction rate depends on the particle arrangement through the heat transfer and reaction heat. Accordingly, in the case of the mixed charge of the high reactivity nut coke in the ore layer, the design of the packed bed structure is important.
Ryo ShibaSaki, Shungo NatSui, Tatsuya koN, Shigeru ueda, Ryo iNoue and Tatsuro ariyama Synopsis : To decrease the reducing agent ratio in the blast furnace, various measures such as mixed charging are being pursued. Coke mixed charging is considered to improve permeability in the cohesive zone and the reducing behavior of ore particles. Conventionally, these researches were frequently carried out with a small packed bed. However, the information obtained by these experiments was based on a macroscopic analysis. In the present research, a DEM-CFD model developed by the authors was applied to precisely analyze reaction behavior under various packed bed structures, such as that with coke mixing. Moreover, the effect of high reactivity coke on the reduction rate of ore was examined using this model. According to the results, coke mixed charging has little influence on the reduction rate. When high reactivity coke was charged to the ore layer, the particle temperature decreased due to the endothermic reaction by high reactivity coke. Accordingly, the reduction rate of the ore particles was suppressed as a result of the temperature change. This phenomenon was relatively noticeable in the packed bed structure with high reactivity coke set up in the lower part.
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