دانلود رایگان مقاله مقایسه مدل کوچک شدن هسته و مدل متبلور شدن برای شبیه سازی پلت سنگ آهن

Abstract

The current study revisits the particle combustion modeling in the simulation of iron ore pellet indurator, which is the process to dry and fire the pellets as a pretreatment for blast furnace. Although the shrinking core model has been frequently used in the previous studies due to its simplicity, its limitation for the porous pellet should have been evaluated. Instead, the grain model could have been used as it conceptually gives the better description. In that context, the shrinking core model is compared against the grain model in the simplified isothermal condition and the complete indurator simulation to demonstrate the applicability. Despite the possible differences in the conversion profiles along the reaction regimes, the models provide apparently reasonable bed temperature results for the normal indurating conditions. However, the shrinking core model needs to be applied with caution and its validity should be questioned when the operating conditions change.

5. Conclusion

Mathematical simulation has widely been conducted for iron ore pellet indurator to understand the internal thermal state and to predict the performance. Simulations for the straight-grate system generally aims to obtain the bed temperature profiles incorporating the heat transfer and the reactions on the pellet. In constructing the bed simulation, the shrinking core model was preferred for the convenience of bed temperature calculations as it gives the simple and analyticalfunction ofthe reaction rate. However,the model has the inherent limitations as a result of the assumption of the coreshell structure in the single species nonporous particle. Hence, the model might have needed caution when itis used for the coke in the pellet, as the small fraction of reactant in the porous agglomerate, which has not been focused sufficiently in the previous studies. Comparison of the shrinking core model with the grain model implies thatthe shrinking core model might have needed a fitting to make the more realistic approximation. Preparing the different rate equation cases for the shrinking core model itself showed the arbitrariness in using the model for coke fraction in the pellet. Despite the possible differences, some of the shrinking core model cases showed the similar bed temperature profiles to the grain model case in the complete model of the conventional indurator condition. The similarity may be largely due to the low coke content and the dominance of the hot gas in the heat transfer to the bed. Moreover, it may also be attributed to the longer duration of the diffusive regime for the reaction, in which the core-shell structure becomes valid as the shrinking core model assumes. Those may explain the plausible temperature results in the previous indurator models using the shrinking core model.