In-situ observations of the liquid high carbon iron (HCI) and slag flows in coke bed was carried out by using high temperature X-ray fluoroscopy at 1 773 K. Along with the observation, 2-dimensional multiphase computational simulations of the liquid HCI and slag flows in the coke bed was carried out to investigate the effect of the slag on the HCI flow in the coke bed. The liquid HCI cannot pass through the coke bed with the coke diameter of 3-5 mm, however, the HCI can pass through the same size coke bed if the HCI comes into contact with the slag in the coke bed. When the HCI and slag contact each other on the coke surface, the contact angle of the HCI with slag decreases and its wettability increases. On the other hand, the slag's contact angle increases and it changes to non-wettable phase. Based on the experimental and simulation results, it is confirmed that the contact angle change due to the HCI-slag contact makes them pass though the narrow coke slit which is small enough to prevent both of the liquid phases from flowing down if they do not contact each other. Based on the capillary rise model, the driving force of the HCI penetration into the coke bed will be the energy reduction by extending area of the coke surface covered with the liquid HCI.
In-situ observations of metal-slag separation behaviors between CaO-Al2O3 based slag, iron and graphite powder mixed pellets by a confocal laser-scanning microscope (CLSM) have been carried out to find the effective way to use high Al2O3 iron ore in CCA reduction processes. Since a particular type of high Al2O3 iron ore such as laterite contains small amount of NiO and Cr2O3, the effect of NiO and Cr2O3 on the metal-slag separation behaviors were also studied. The observed metal-slag separation behaviors were analyzed based on the equilibrium phase fractions calculated by FactSage and carbon diffusion simulation in an iron sphere particle with a spot carbon source condition. Based on these in-situ observations and carbon diffusion results, starting temperature of metal-slag separation was found to correspond to the eutectic temperature of CaO-Al2O3 based slag. The iron carburization was initiated by slag melting and most of iron particles were melted within about 20 s after slag melting. The rapid carburization after slag melting was introduced by the good wettability between solid iron and molten slag. NiO and Cr2O3 additions did not change the fundamental behaviors of metal-slag separation at least up to about 3 mass%. Based on these results, it was confirmed that high Al2O3 content iron ore can be used in CCA reduction process by using CaO-Al2O3 based slag.KEY WORDS: metal-slag separation; high Al2O3 iron ore; iron carburization; spot source diffusion; CaOAl2O3 based slag.
The effect of graphitisation by the variation of annealing time and temperature on the pore structure and apparent gasification rate at 1200 and 1500°C was investigated. The graphitisation degree of three kinds of coke used in this study was increased with annealing time and temperature. The increase in porosity of annealed coke sample is ascribed to the formation of silicon carbide. Annealing at 1200°C had less significant effect on the change of porosity in comparison with annealing at 1500°C. The mean area of pores was decreased, and pore density was increased with increasing annealing time while annealing had marginal influence on the pore shape. The apparent gasification rates of Coke 1 and Coke 2 with H 2 O were decreased by annealing, but 3 h of annealing increased the apparent gasification rate of Coke 3. The correlation between apparent gasification rate with H 2 O and macroporosity or graphitisation degree was investigated.
In a packed bed system, the interfacial tensions of liquid drops highly affect their flow behavior by changing the direction of the interfacial tensions in the liquid-solid-gas interface. The vertical directional interfacial forces of a liquid drop in a packed bed of small particles were calculated using a 3-D analytic calculation model. Regardless of the wettability of a solid surface, the interfacial tension induces the resisting force against the gravitational force. In short, the interfacial tension limits the flow of a liquid drop along the direction of the gravitational force. In case two liquid drops of different phases directly contact each other in a packed bed, one of the interfaces of each drop is shared, and the influence of the interfacial force decreased so that the liquid drops could move down through the void between particles compared with the case a single drop. If the shared interface of two liquid drops of which one is nonwettable and the other is wettable has lower contact angle than that of the liquid-gas interface of the liquid drop, then the drops experience the downward force along the direction of the gravity in the larger range of the position in the packed bed.
The grain refinement of α-Fe using repeated carburizing and decarburizing at 1 073 K are investigated.It is found that the grain sizes are decreased by carburizing reaction but are increased by decarburizing reaction. Repeated α ↔ γ phase transformations make grain size smaller. However, without pinning elements, the reduction of the grain size has limitation. Sulfur does not have enough effects on the grain growth with the grain size of less than 30 μm. To improve the grain refinement process, Fe3C was introduced by annealing at 873 K along with the carburizing and decarburizing processing. Formed Fe3C can supply a lot of nucleation site for austenite nuclei during the reaustenitizing and retards ferrite grain growth during γ → α transformation by the decarburization reaction. The fine uniform grains of less than 10 μm have been produced by the carburizing and decarburizing processing at 1 073 K along with adjusting the cementite size and the whole volume during the heat treatment at 873 K.
Synopsis :In-situ observations of the liquid high carbon iron (HCI) and slag flows in the packed coke bed was carried out by using high temperature Xray fluoroscopy at 1773 K. Along with the observation, 2-dimensional multiphase computational simulations of the liquid HCI and slag flows in the coke bed was carried out to investigate the effect of the slag on the HCI flow in the coke bed. It is found that the liquid HCI or slag could not pass through the coke bed with the coke diameter of 3-5 mm, however, the HCI can pass through the same size coke bed if the HCI is contacted with the slag through the X-ray fluoroscopic observation and the computational flow simulation. When the HCI and slag contacted each other on the coke surface, the contact angle of the HCI with slag decreased and the initially non-wettable characteristic of the HCI changed to wettable one. On the other hand, the slag's contact angle is increased and changed to non-wettable. Based on the experimental and simulated results, it is confirmed that the contact angle change due to the HCI-slag contact make it possible for the liquid HCI and slag to pass though the narrow coke slit that is small enough to prevent each liquid's flow down if they are not contacted. Based on the capillary rise model, the driving force of the HCI penetration into the coke bed will be the energy reduction by extending area of the coke surface covered with the liquid HCI.
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