Abstract
It is very important for a multilayer pellet bed to have a proper description of the radiant heat transfer and direct reduction process in the rotary hearth furnace. Ellipsoidal pellets may also be used in industrial production. The research on this ellipsoidal pellet bed will provide comprehensive data support for the production process. Besides, the view factor is one of the important factors affecting the heat transfer of the multilayer pellet bed. It is of great significance to study its value and distribution. In this study, the effects of the gas field and the bottom of the furnace on the direct reduction of multilayer ellipsoidal pellets were considered. The local environmental viewing angle coefficient in the model was obtained through the mechanism calculation method, which is more accurate than the calculation through the radiation exchange network. Furthermore, the porosity variation in the pellet during the direct reduction process was also considered. According to the calculation, it was found that the higher initial temperature at the furnace bottom is beneficial to increase the degree of metallization (DOM) and zinc removal rate (ZRR) for all pellets, and is more advantageous to the lower pellets in the material bed. Nevertheless, the reduction degree of the lower pellets is still smaller than that of the upper pellets. The results also show that increasing the offset ξ has a greater effect on increasing the ambient view factor and each position reduction degree in the ellipsoidal pellets layer. Results can be applied for the optimization of pellets distribution in a rotary hearth furnace.
Highlights
With the development of society and the consumption of resources, the demand for sustainable recycling methods is increasing
The direct reduction process based on rotary hearth furnace (RHF) has attracted great attention from researchers due to its high carbon utilization rate, low CO2 emissions, and low energy consumption [1,2]
The model considered the effect of the gas field in the furnace and the bottom region of the furnace on the direct reduction of the multilayer ellipsoidal pellet bed
Summary
With the development of society and the consumption of resources, the demand for sustainable recycling methods is increasing. This paper mainly focuses on the heat transfer characteristics of the multilayer pellet bed in the rotary hearth furnace by establishing the mathematical model. To improve the rotary hearth furnace efficiency and to obtain a high-performance pellet design, scholars have done much work in this area, including research on pellet shape, size, composition, and furnace temperature, etc., affecting the carbon-containing pellets direct reduction process [11,12,13]. Liu et al established a multilayer carbon-containing pellets model, which considered different pellets’ arrangements of the layer to improve the pellets’ metallization degree It did not take into account the heat transfer effect of the furnace bottom. To accurately obtain the reduction process of the multilayer ellipsoid pellets in the rotary hearth furnace, a three-dimensional mathematical bed model was established, and problems arising in the bed reduction process were evaluated in the model. The backward difference formula is used to carry out the separation and iterative calculation
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