Abstract
Abstract Although the conventional blast furnace is still the major iron-making process today, its coexisting coke oven and sintering plant in developed countries are nearly forced to stop establishing due to serious environmental problems. The iron bath smelting process has thus become the major research topics recently. The iron bath smelting furnace is a new process, with FeO dissolved in liquid slag and reduced by coal, to make hot metal directly. In order to reinforce the smelting strength in the iron bath furnace, high smelting-reduction speed is required. Thus bottom-gas stirring of liquid iron and slag phases to achieve a large surface area for FeO reduction has become an important method in the process. Accompanying the reaction CO product gas with the top-blown O2 gas, the liquid slag contains a large amount of gases and it becomes foaming. The control of the foaming phenomenon is one of the important topics in an iron bath smelter. The aims of this study contain effects of amount of bottom-blown N2 gas and the slag basicity on the slag foam strength. The good electric conductivity of high-temperature slag gives an effective measuring of the foaming height. The study also includes the reaction speed of FeO with carbon by measuring the CO gas production speed and the height of slag foaming as a consequence of the FeO-carbon reaction. Since the FeO-carbon reaction is a major way in controlling the process, It is hoped that this study can be a reference for design and operation of the process. Important results in this study are as follows. For MgO-saturated CaO-SiO2-Al2O3-MgO slags (B2 from 0.8 to 1.2) smelted in a MgO crucible with I.D. = 0.1" at 1500 oC, the bottom-blown N2 flow rate of 10 to 100 Nml/min gives a maximum slag foaming height of 1.8 cm, with foaming indices ranging from 0.6 to 1.1 sec. The foam height increases with increasing N2 flow rate, with various critical flow rates with different slag basicity. The critical flow rate decreases with increasing B2 of the slag. However, For N2 gas flow rates less than 50 Nml/min, B2 is the dominating factor for the foam height. On the other hand, B4 is the dominating one for flow rates greater than 50 Nml/min. Experiments show that for a 34.5 CaO-34.5 SiO2-10 Al2O3-21 MgO (wt %) slag with 10 wt % FeO smelted and reacted (with carbon) at 1500 oC, a FeO-C reaction speed constant, k, ranging from 0.136 to 0.159 l/m·s is obtained under the assumption of the reaction being of 1st order. The slag foam height is 9 cm, being higher than that of the N2 gas, and the size distribution of the bubbles in the slag foam is wider than that of the case of bottom-blown N2 gas.