Recently, low coke rate blast furnace operation has been required in response to the rising cost of coking coal. However, the thickness of the coke layer decreases in low coke rate operation. Since it is known that the gas permeability of the blast furnace deteriorates as the coke layer thickness decreases, it is important to determine the minimum coke layer thickness for stable blast furnace operation. On the other hand, the minimum coke layer thickness has not been clarified due to a lack of equipment capable of measuring the effect of the coke layer thickness on permeability.In this study, a new experimental device called the cohesive zone simulator was developed to clarify the minimum coke layer thickness. In the cohesive zone, gas flows horizontally along the coke layer. In order to quantify the effect of the coke layer thickness on permeability, this horizontal gas flow should be simulated. Therefore, this simulator simulates a horizontal gas flow.Next, the effect of the coke layer thickness was quantified by using the cohesive zone simulator. The results showed that melting iron ore penetrated into the coke layer and closed part of the layer. These phenomena caused a deterioration of permeability under thin coke layer thickness conditions. Finally, a pressure drop estimation model considering penetration of the coke layer by melting ore was developed with the aim of quantifying the minimum coke slit thickness.
The influence of agitating conditions on agglomeration and collapse of wet iron ore mixture was investigated in the view of kinetics and matrix model analysis. At the initial stage of mixing behavior, it was found that average particle size was dependent on the mixing rate constant defined as the deviation degree of particle size and water distribution from initial state. Mixing rate constants of powder and water were almost consistent with each other and expressed by power function of Froude number of impeller. It was presumed that the water and fine particle moved together as wet granules during mixing at a given water level. According to the analysis of entire mixing behavior based on matrix model, it was found that the collapse indexes defined by matrix parameters increased as particle size and impact force increased. Minimum particle size at initial mixing state decreased as collapse index increased and the size of long term mixing state was expected by intrinsic increasing rates defined by maximum eigenvalue of matrix parameters.
Synopsis : To achieve stable operation of high ratio coke mixed charging, it is important to control coke segregation behavior in mixed layer at blast furnace top. In this study, the effect of charging conditions and burden particle diameter of mixed coke ratio at blast furnace top were analyzed by numerical model based on discrete element method (DEM). Rolling friction coefficient was calibrated by experiment and calculation. Then, segregation behavior of coke particle was numerically investigated by using above calculation parameters. As a result, following findings were obtained. 1) At reverse tilting and broad range charging pattern of rotating chute, granular flow to the furnace center was interrupted and mixed coke particle was distributed uniformly for the direction of furnace radius. 2) Coke segregation in mixed layer was decreased by lowering particle diameter ratio between coke and sinter. Therefore, for the improvement of coke mixed ratio in mixed layer, control of particle diameter of coke and sinter is effective.
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