LABORATORY INVESTIGATIONS ON SMELTING REDUCTION ACCORDING TO THE PROCESSES IN MELTER GASIFIERS AND IRON BATH REACTORS

摘要

The application of smelting reduction for di-rect production of liquid iron, or steel from melts containing iron oxide, is currently the object of special developmental efforts. Hence, laboratory experiments on smelting reduction have been conducted with the objective of gaining information on the reaction mechanism. Based on the phase relation in the system Fe-C-0 ideas are developed to obtain conceptions referring to possible reducing agents and paths of reaction. Those considerations are transferred schematically to melter gasifiers and bath reactors. For this purpose, the reduction behaviour of iron oxide melts has been investigated with a supply of carbon monoxide during top blowing, injection, and bottom blowing experiments at 1550°C. Furthermore, solid carbon has been supplied. The complex reduction ratio, reduction velocity, formation of reaction-inhibiting layers, and phase separation of the reaction products have been investigated more closely. Aluminium oxide was employed as crucible material. The use of MgO as a refractory material is also possible. The progress of reduction was determined through gas-volumetrically. Subsequently, the specimens were examined microscopically. During the top blowing experiments, the contact between the liquid oxides and reduction gas occurs at the surface of the melt. It is thereby evident that large quantities of gas results in improved material conversion. After covering of the blowing trough by solid reaction products thus formed, the material conversion is hindered and proceeds only through the spinel layer formed in the proximity of the surface. During the reduction of liquid oxides by injected and bottom blown carbon monoxide, in addition to solid carbon, decided nonsteady-state conditions prevail. Thus, conclusions about reaction mechanisms are all the less feasible. On the whole, higher reduction velocities can be attained during injection and bottom blowing experiments, in comparison with top blowing experiments at the same respective blowing rates and experimental times. Moreover, higher values by far are obtained for the final reduction ratios and reduction velocities during the experiments with solid carbon. Maximal values up to 5%/min are attained. A feature common to all experiments is the undesirable precipitation of solid spinels because of the inevitable presence of Al_2O_3; this effect is caused by the corrosivity "of FeO with respect to the crucible material during the experiments. The hindrance of the reaction by foams containing CO_n is a further adverse effect. Finally, conclusions can be drawn for the experimental development of the testapparatus and the experiments concerning to melter gasifiers and iron bath reactors.