A low carbon operation is an unfavorable situation for liquid permeability around cohesive zone, because liquid volume will increase against solid coke in there. In order to keep a healthy operation with this technique, information of wetting behavior between liquid iron and coke should be correctly understood. However, there is not enough information about wetting behavior between them, because of many difficulties about wettability measurement from an active reaction between iron and carbonaceous materials. In this study, a sessile drop method with molten sample injection system was applied to measurement of wetting behavior between liquid iron and carbonaceous material at 1 673 K for excluding reaction between samples before starting measurement. Carbonaceous material's substrates were made from mixture powder of graphite and alumina by hot press at 1 873 K. From the results, following knowledge was revealed. Molten iron samples un-saturated with carbon showed bigger values of contact angles, 110°-120°, at initial stage, than apparent constant values of them, 85°-100°, at latter stage. It indicated a reaction between iron and carbonaceous materials had obvious effect on wetting behavior between them due to decrease an interfacial energy during the reaction. Mixed alumina powder in the substrate prevented to wetting behavior of iron sample on carbonaceous materials, and they changed their apparent constant contact angles from 115° to 130°. The alumina powder had effects on not only wetting behavior but also reaction between iron and carbonaceous materials.KEY WORDS: wettability; carbon dissolution; sessile drop method with molten sample injection system; simulant coke; molten iron; carbonaceous material's substrate.

A wetting behaviour of Fe-C sample on carbonaceous materials has been extensively investigated to understand the liquid flow behaviour in lower part of blast furnace. The previous studies reported a large change in apparent contact angle in the initial contact period in the wetting between the Fe-C sample and the carbonaceous materials substrate. The carbon dissolution reaction and the interfacial morphology in the initial contact period would strongly affect the wetting behaviour in this period. To further understand the wetting behaviour between the Fe-C sample and the substrate, the effects of the carbon dissolution reaction on the wetting behaviour in the initial contact period must be considered. 4.26,4.90 mass% C samples were fabricated using a high-frequency induction heating furnace under an inert gas atmosphere. The graphite substrate was made from 99.90% pure graphite powder using a hot press furnace under an argon gas atmosphere. The wetting behaviour of the graphite substrate with molten Fe-C sample is investigated using a sessile drop method with a molten sample injection and quenching systems. The results shown that the apparent contact angles significantly decreased from the initial apparent contact angle. The carbon concentration of the carbon-unsaturated Fe-C sample gradually increased and reached the saturation after the 300 s of contact. The formation of concave was observed and developed in the initial contact period due to the transfer of carbon atoms into the carbon-unsaturated Fe-C sample. The wetting behaviour was dependent on interfacial energy of solid-liquid phases before the formation of concave. After the formation of concave, the wetting behaviour dominantly depended on interfacial morphology change.KEY WORDS: wetting behaviour; initial contact period; sessile drop method with molten sample injection system; quenching system; carbon dissolution reaction; interfacial morphology; formation of concave.

Wetting between liquid iron and coke influences liquid flow in the lower part of a blast furnace, which strongly affects the operation of the furnace. With increasing fluidity, the blast furnace performs more favourably and efficiently. To further improve blast furnace operation, the wetting behaviour of liquid iron on coke must be correctly understood. The effects of ash in the coke on reactive wetting in concave formations, such as holes formed at the contact area, must be considered. This study aims to elucidate the effects of the ash component in coke on the reactive wetting behaviour of carbon-unsaturated liquid iron on a simulant coke substrate and concave formations thereof. In this study, reactive wetting between the iron samples and the substrates was measured by a sessile drop method with a molten injection system at 1 673 K. The results revealed that the apparent contact angle significantly decreased with time in the first 300 s after contact. After 300 s, the contact angle stabilized at a constant equilibrium value. The initial contact angles depended not only on the carbon concentration of the liquid iron, but also on the Al 2 O 3 content in the substrates. Concave geometries formed when the carbon-unsaturated iron samples were wetted on substrates containing 0, 5, and 10 vol% Al 2 O 3 . The effect of Al 2 O 3 on the carbon dissolution reaction was the main factor affecting the reactive wetting behaviour of substrates against liquid iron.

In this research, a new space vector modulation control algorithm is proposed to increase the reliability of the cascaded H-bridge multilevel inverters in case of faulty situations, where one or several power cells do not function. Methods to detect faults ensure finding open-circuit module exactly, which is fast and easy to program. By giving a detailed analysis of the impact of the faulty power cells, optimal redundant level states are chosen such that highest possible output voltage can be achieved, while the balance of the three-phase line-to-line voltage is maintained and common-mode voltage is reduced. The proposed algorithm is generalized so that it can be applied to H-bridge inverters of any level. The validity of the method is verified by numerical simulations and experiment results with an 11-level cascaded H-bridge inverter.

Synopsis : A low carbon operation is an unfavorable situation for liquid permeability around cohesive zone, because liquid volume will increase against solid coke in there. In order to keep a healthy operation with this technique, information of wetting behavior between liquid iron and coke should be correctly understood. However, there is not enough information about wetting behavior between them, because of many difficulties about wettability measurement from an active reaction between iron and carbonaceous materials. In this study, a sessile drop method with molten sample injection system was applied to measurement of wetting behavior between liquid iron and carbonaceous material at 1673 K for excluding reaction between samples before starting measurement. Carbonaceous material's substrates were made from mixture powder of graphite and alumina by hot press at 1873K. From the results, following knowledge was revealed. Molten iron samples un-saturated with carbon showed bigger values of contact angles, 110°~120°, at initial stage, than apparent constant values of them, 85°~100°, at latter stage. It indicated a reaction between iron and carbonaceous materials had obvious effect on wetting behavior between them due to decrease an interfacial energy during the reaction. Mixed alumina powder in the substrate prevented to wetting behavior of iron sample on carbonaceous materials, and they changed their apparent constant contact angles from 115° to 130°. The alumina powder had effects on not only wetting behavior but also reaction between iron and carbonaceous materials.