MATLAB-SIMULINK SIMULATION OF SLAG FOAMING CONDITIONS IN EAF PRACTICE
The slag foaming practice in EAF process is very important. For a good slag foaming special conditions are necessary. Simulation with MatLab-Simulink program of slag foaming conditions and slag foam index are made and presented in this paper. It will be shown that in the case of slags with low iron oxide contents slag basicity strongly influences on foam index; increasing the slag basicities decrease foam index. Basicity of slag with high iron oxide contents has no affect on foam index.
Effect of carbonaceous particles on slag foaming
Use of carbonaceous particles such as coke or coal char in controlling slag foaming is of great practical significance for bath-smelting and other steelmaking processes. The foamability of the liquid slag in terms of the foam index has been determined with the presence of different amounts of coke and coal char particles. Different sized and shaped particles were used in the experiments. It was found that the foam index decreased significantly as the ratio of the total cross-sectional area of the particles to the liquid slag surface area increased. When the foam was generated by argon gas injection through an alumina nozzle (i.d. = 1.5 mm), a liquid slag, CaO-SiO2-CaF2-(Al2O3), depending on the alumina content, could have an initial foam index of about 2 to 4 seconds at 1500 °C without any carbonaceous particles. When the slag surface was covered only 15 ~20 pct with either coke or coal char particles, the foam was totally suppressed regardless of the initial foam index. In order to understand the mechanism of the antifoam effect of the carbonaceous particles, interactions of a coke sphere, an iron ore pellet, an alumina tube, and a coal char particle with the liquid slag foam were examined by X-ray observation. It was concluded that the antifoam effect of coke or coal char particles is primarily contributed by the nonwetting nature of the carbonaceous materials with the liquid slag. Possible mechanisms of carbonaceous particles rupturing a slag film could be (1) the rapid thinning of the liquid slag film driven by a difference between the instantaneous contact angle and the equilibrium contact angle or (2) the “dewetting” of the liquid slag from the interface when the film is “bridged” by the particle.
Slag Foaming in Smelting Reduction and Its Control with Carbonaceous Materials
In the smelting reduction process of the thick slag layer type, it is important to keep slag height stably without abnormal slag foaming. This study investigated the mechanism of slag foaming control with carbonaceous materials by experiments using a 1-ton smelting reduction furnace and by X-ray fluoroscopic observation of phenomena occurring in a small graphite crucible. As the carbonaceous material was not wettable with slag, small bubbles coalesced on its surface. Because the large bubbles due to the coalescence of small bubbles rise through the foaming slag layer at a relatively high speed, the foaming of slag may be restrained. It was found that the smaller the size of the carbonaceous material was, the more effective was the carbonaceous material in controlling the foaming of slag. A certain extent of relative motion between carbonaceous material and slag was necessary to promote the coalescence of small bubbles. It was experimentally confirmed that the smelting reduction in 100-ton scale furnace can stably operate under the condition that the carbonaceous material is present in a sufficient amount in the slag.