Observation of molten slag surface under gas impingement by X-ray computed tomography

Observation of molten slag at 1673 K was carried out by X-ray Computed Tomography (X-ray CT) to make clear the shape of slag surface where gas was downward blown. X-ray CT scanning of molten slag heated in an electric furnace was conducted to take an image of its cross section. In order to examine the effects of gas momentum supplied on the surface shape, three kinds of inert gases, Ar, He and N-2, were employed as the blowing gas under the several conditions of gas flow rate and gas pipe diameter. The obtained X-ray CT images successfully visualized the cross section of molten slag. The boundary line between gas and slag in the image was concave under the gas blowing, indicating a formation of depression on the slag surface by gas impingement. The concave boundary is completely different from the parabolic shape conventionally evaluated. The depression became larger, not only in depth but also in width, with increasing gas flow rate, whereas drastically smaller with increasing gas pipe diameter. In addition, larger depth was brought by impingement of larger molecular (atomic)-weight gas. These results were well explained by the conservation law of momentum between gas and slag. It was also revealed that the increment in the boundary line caused by formation of depression, which corresponds to an increase in the interfacial area, is in proportion to the depression depth in the range of more than 2 mm, and was independent of the pipe diameter and gas species.