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Development of the Burden Distribution and Gas Flow Model in the Blast Furnace Shaft
Jong-In PARK, Han-Sang OH and Jeong-Whan HAN
(Technical Research Center, Hyundai Steel, Korea.)
(June 20, 2011)
It is important to control the burden distribution, which affects the gas flow pattern in the blast furnace. Therefore, a burden distribution analysis model is needed to predict the burden profile. In this study, the burden descent and gas flow models were developed to complete a blast furnace analysis model. A previous study reported two models based on the burden trajectory and stock model. The burden profile that is due to the burden trajectory was calculated using stock model in the upper part of shaft. The entire burden profile, which is classified into five burden types calculated using the descent model, was used for a gas flow calculation as the initial conditions in the gas flow model. The analysis models were developed using a visual basic based spread sheet, and compared with the 1/12 scaled model experiment. In addition, a GUI (Graphic User Interface) was added for the convenience of the operators.
In the blast furnace (BF), the gas flow pattern is dominatedby the mean thickness of the coke and ore layers, since the permeability and surface area according to the burden type are different and affect the gas pressure loss. Therefore, it is essential to predict and control the burden distribution for an efficiency improvement of iron-making. On the other hand, it is very difficult to measure internal flows directly and understand the phenomena inside the blast furnace because of the high temperature and hazardous conditions. In addition, considerable effort and time is needed to disassemble a BF. Therefore, simulation models are useful for predicting the phenomena inside a BF. Thus far,
1-dimensional based on the kinetics and 1-dimensional dynamic model, 2-dimensional steady state model, three-dimensional steady-state simulation model, and non-steady state model were developed to examine the inner state of a BF. In previous studies, the burden materials are mostly assumed to be a mixed layer of ore and coke. Therefore, it is difficult to examine the gas flow affected by the burden distribution.
A recent study developed a burden trajectory and stock model, and calculated the burden profile at the upper part of the shaft. To complete the analysis model for the burden distribution, the descent model was added. The shape of the burden layer stacked on the upper part changes when the burden descends, because the descending velocity affected by the operating variables is different along the radial direction.
In this study, the descending velocity was calculated using the 1/12 scaled model, and it was applied to the analysis model. The burden profiles calculated from the burden trajectory and stock model were used as initial conditions in the descent model. As a result, the program involving an analysis model for the fall, stack and descent of the burden simulated the behavior of the burden using several algorithms.
Consequently, the overall burden profile was calculated, and used for the gas flow model. After the burden profile calculation, layers including five burden types were divided into cells with information on the properties. For a gas flow calculation, the pressure drop was calculated using Ergun’s Eq. in each cell.
In this study, visual basic based spread sheet was used to develop the burden distribution and gas flow model. This is a widely applied spread sheet that includes numerical analysis for the iron-making process. This analysis model that runs in a spread sheet includes a GUI (Graphic User Interface) developed via visual basic coding. The GUI menu is divided approximately into three parts, calculation conditions, program run and results. The operators can easily set up the boundary conditions, such as the notch angle, charging pattern, shape of a blast furnace and burden properties, in the calculation condition sections. The results section displays the LO/LC graph, burden profile, gas flow distribution, etc.. On the other hand, chemical reactions, such as the reduction of iron oxides, the boudouard reaction are yet to be considered in each cell.
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