CO2 emissions in steel works accounts for about 15% of those in Japan (2015), and most of those are from blast furnace iron-making process. To reduce CO2 emissions, utilization of woody biomass in blast furnace is considered. Woody biomass has the characteristic of carbon neutral and high reactivity. So CO2 emissions can be reduced by the use of woody biomass as coke substitution. High reactivity of reducing agent is expected to decline thermal reserve zone “Trz” temperature, which causes improvement of reaction efficiency in the blast furnace and lowering of reducing agent rate. To verify the effect of the use of woody biomass on thermal reserve zone temperature, we executed experiment to evaluate the effect of charcoal coexisting in the ore layer on reduction behavior of iron oxide with the adiabatic blast furnace inner reaction simulator (BIS). With heat and mass balance analysis, we evaluated the effect of declining Trz temperature on lowering of reducing agent rate and the effect of utilization charcoal as coke substitution on reducing CO2 emissions in blast furnace process.
As a result, charcoal lowered the Trz temperature and carbon consumption. We estimated that charcoal can reduce CO2 the amount of CO2 emissions 33%. So that, we think that charcoal can be used as coke substitution.
Injection of plastics into blast furnaces as an alternative reducing agent has been carried out for the purpose of mitigation of carbon dioxide emissions. Several studies on the pyrolysis of plastic particles have been reported, however flow behavior of plastic particles or unburnt char in actual blast furnace is not clear.
In this study, hotmodel experiments and thermogravimetry analysis were conducted for the modeling of gasification behavior of plastic particles, then flow behavior of plastic particle and unburnt char in a blast furnace was calculated by numerical simulation. According to the observation results of gasification experiment, volatile matter of plastics seems to be evolved at the surface of the particles. Regarding reaction of char derived from plastics, thermogravimetry analysis showed that rate of gasification of unburnt char depended on the rate of heating. Gasification rate in the case of rapid heating condition tended to increase.
As the results of numerical simulations, initial diameter of plastics and char diameter determined the flow behavior in the blast furnace. When relatively small plastic was injected or diameter of unburnt char was small, unburnt char went upward along with gas flow and most of it might be consumed at the cohesive zone. On the other hand, when relatively coarse plastics was injected and diameter of unburnt char was relatively coarse, it was suggested that unburnt char accumulated around the deadman.
Therefore, it is considered that fine plastics injection is desirable for the stable operation of blast furnace.
The effect of adding CaO-based desulfurization flux on desulfurization efficiency in hot metal desulfurization by mechanical stirring was investigated. It was found that desulfurization flux dispersion is enhanced by powder blasting with a carrier gas. In this research, the behaviors of the desulfurization powder under different blasting conditions were investigated, and the optimum blasting conditions for achieving higher desulfurization efficiency were examined. The velocities of the gas jet and particles were measured by pressure measurement by the pitot tube technique and LDV (Laser Doppler Velocimeter), respectively. The results showed that the powder velocity was accelerated by the gas jet, which agreed with the calculated velocity. The condition of powder penetration into the hot metal was examined based on the calculations. As a result, the higher carrier gas flow rate, 200 Nl/min, was categorized as a penetrating condition, and the lower carrier gas flow rate, 100 Nl/min, was not a penetrating condition. The difference in the desulfurization behaviors under those carrier gas flow rate conditions is caused by the difference in the penetrating condition. Based on the obtained blasting conditions, powder blasting tests were carried out in 300 t-scale hot metal desulfurization, and desulfurization flux consumption was decreased by 19% compared with conventional top addition.
Machined surface and chip formation mechanism in pure iron with a single phase and low C structural steel (S10C) with dual phases is discussed, using the Quick Stop Test (QST). On the machined surfaces, chip surfaces and built-up edges of the QST samples, many elongated dimples are found and the dimples suggested that the fracture occurred on both the rake side and flank side of the tool. These results suggested that the chip, surface and Built-up Edge (BUE) formation of pure iron and S10C are formed by accumulation of many fine ductile fractures. Therefore BUE formation is affected by microstructure, because the ductile fracture property is affected by microstructure of steels.
In hot rolling, lubrication oil plays an important role in reducing rolling force and protecting the work roll surface. However, the oil behavior in hot rolling has not been clarified sufficiently. In this work, a numerical analysis of the introduced oil film was attempted. There are no previous reports on numerical analysis of hot rolling lubrication. The analytical results of the introduced oil film thickness showed a good correlation with the experimental results. The numerical analysis of hot rolling lubrication clarified the following points: The introduced oil film did not become saturated even if the oil film thickness increased. The reason for this phenomenon is thought to be because the oil viscosity remains high on the work roll side. It was also found that the gradient of the oil velocity in the thickness direction is not constant and changes greatly on the strip side.
The growth of the recrystallized nucleus in niobium added ultra-low carbon steel was investigated experimentally by restricting the nucleation sites. Moreover, the growth process of the recrystallized nucleus from the layered deformed microstructures with various deformed state were simulated by a multi-phase-field (MPF) method, for comparison with the experiments. The cold-rolled microstructure was a layered structure, consisting of both α-fiber close to cube orientation and γ-fiber, and the re-crystalline nucleus tended to grow up preferentially along deformed γ-fiber. The simulations suggested that the shape of growing nucleus was influenced by the dislocation density or layered distances of deformed structures, which were related to the cold-rolling reduction. Furthermore, the crystal rotation of the re-crystallized grains at the middle stage of recrystallization was tried to be simulated using another phase field simulation.