Yingli Liu

Microstructure evolution during softening and melting process in different reduction degrees

This paper concerns the degree of indirect reduction in a burden rising substantially in an oxygen blast furnace. It studies the pellet, sinter and a mixture of both in different cases. The paper concerns experiments on single particle load softening to investigate the microstructural evolution of different burdens during the softening and melting process. The results of the experiments show that the degree of reduction impacted the softening and melting behaviour. In the case of a low degree of reduction, a slag phase substrate and a myrmekitic iron structure were formed on the periphery area of the molten burden, whereas slag phase substrate and disperse island wüstite structure were formed in the centre area. Both peripheral and central areas had a slag phase substrate and myrmekitic iron texture. The slag–iron distribution had a structure in which the slag phase was cut in the metal iron phase. The content of 2FeO.SiO2 as a low melting point phase in the slag decreased sharply, and this resulted in the increase in slag–iron separation temperature. The variation of the Ca/Si ratio in the interface between the pellet and the sinter indicated that enhancement of the reduction degree caused the initial temperature of the interaction in the mixed burden to rise and the interaction distance to decrease.

Effects of basicity, MgO and MnO on mineralogical phases of CaO–FeOx–SiO2–P2O5 slag

The selective separation phosphorous rich phase from steel slag could be an effective way to utilise the steel slag. The mineralogical phase after cooling of steel slag is essential to selective separation of steel slag. In the present work, the mineralogical phases of CaO–FeOx–SiO2–P2O5 slag after controlled cooling were investigated by X-ray diffraction and scanning electronic microscopy and energy dispersed spectroscopy technique. It was found that the heat treatment at 1573 K would lead to the precipitation of Ca2SiO4–Ca3P2O8 (C2S-C3P) solid solution for all samples. The heat treatment at 1273 K would lead to the precipitation of C2S-C3P, CaSiO3 and Fe2O3. The increase of basicity would promote the crystallisation of CaO–FeOx–SiO2–P2O5 slag. The Effects of additions of MgO and MnO on phase formations of CaO–FeOx–SiO2–P2O5 slag were also studied. Fe2O3 gradually transformed into MgFe2O4 and MnFe2O4 in slag after crystallisation with addition of MgO and MnO, respectively. The sizes of MgFe2O4 and MnFe2O4 crystals increased with increases of MgO and MnO content. The increase of MgO and MnO content would promote the precipitation of MgFe2O4 phase and MnFe2O4, respectively. The precipitation of crystals from slag during cooling was interpreted by the kinetic and thermodynamic factors. It was proposed that addition of MgO and MnO in slag would be beneficial to magnetic separation of steel slag.

Reduction behaviour of ferrous burden under simulated oxygen blast furnace conditions

Abstract The reduction behaviour of sinter and pellets was investigated by a programmable reduction apparatus to simulate the traditional blast furnace (TBF) and the oxygen blast furnace (OBF). The starting temperature for reduction of sinter and pellet in the OBF decreased 60 and 150°C compared with that in the TBF and, by the time the temperature reached 1100°C the reduction degree of sinter and pellet was 100.0 and 98.7% in the OBF compared to 94.0 and 83.1% in the TBF. The trends of the reduction rate of sinter and pellet were consistent in OBF and TBF. There are two peak values at about 60 and 80 min and in the OBF the third peak value of pellet emerged at 40 min. In addition, the mineral microstructures of the ferrous burden were characterised by means of SEM and the area proportion of metallic iron zone was obtained by SEM photos.

Effect of reduction degree on cohesive zone and permeability of mixed burden

ABSTRACT Low-carbon operation, especially low-coke-rate operation, is very important for low CO2 emission in blast furnace ironmaking. Maintaining the permeability of the cohesive zone is required under low-coke operation of the blast furnace. The cohesive zone and permeability are determined by the softening and melting properties of the burden. In this study, the effect of reduction degree on the cohesive zone and permeability was investigated by using different reduction degree mixed burdens. The experimental results showed that as the reduction degree increased, the thickness of the cohesive zone decreased, the position of the cohesive zone moved downward, and the permeability of the mixed burden layer was significantly improved. The weight of the droplet and the carbon content of iron in the droplet decreased with the increase of reduction degree. The results of experiments provided an important guidance for improving the permeability of the mixed burden layer in low-coke operation of the blast furnace.

Dynamic dissolution of CO2/H2O(g)-gasified coke by slag containing FeO

ABSTRACT In top gas recycling-oxygen blast furnace (TGR-BF) and injection coke oven gas-blast furnace (COG-BF), lower coke ratio highlight the importance of coke in the melting and dropping zone. To understand the deterioration of coke in lower blast furnace, the dynamic dissolution of CO2/H2O-gasified coke by slag containing FeO and reaction kinetics were analysed. The results showed that the coke deterioration was more serious in CO2 than in H2O for the same gasification ratio. To understand the internal variation of coke, pore distribution and microstructure of coke were observed using mercury porosimeter and scanning electron microscope (SEM). For the same gasification ratio, pore structure was more uniform in H2O than in CO2. In addition, the kinetics of cokes reaction with FeO in slag was analysed.

Research on the Flow Behavior of Molten Slag Through Pore

In the dropping zone of blast furnace (BF), primary slag absorbing ash of pulverized coal and coke become to be intermediate slag. Due to viscosity and surface tension of slag and the pore between cokes, some slag remained in coke layer and affected the permeability of blast furnace. The flow behavior of slag with different basicity (0.55–1.10) and Al/Si (0.35–0.50) were studied. Meanwhile, the viscosity and surface tension of slag were calculated. The results showed that, with the increasing basicity of slag, surface tension increased and viscosity decreased. With the Al/Si increase, surface tension and viscosity increased. The smallest pore that all slag can pass through was 4.5 mm. However, the height between slag droplets and the bottom of crucible indicated that the ability of slag to pass through pore were weakened with the increasing basicity and Al/Si. Thus, slag which absorbed ash from fuel become difficult to pass through coke layer.

Effect of Lance Configurations on Coal Flow and Combustion Characteristics

Coal burnout strongly depends on the residence time and dispersion of coal particles in the raceway region of a blast furnace. The residence time and dispersion of coal particles are directly related to the lance arrangement. In this work, a three dimensional model was developed to simulate the lance-blowpipe-tuyere-raceway region of a blast furnace. Double lance and eccentric configurations were considered. For the double lance, the double-lance and eccentric double-lance were considered. For the eccentric double lance, the effect of intersection angle of the two lances was investigated.

Comprehensive analysis on material and exergy balances of oxygen blast furnace

ABSTRACT The OBF process is widely studied as an alternative ironmaking process, due to the social pressure of energy and environment at present. A comprehensive mathematical model of the OBF process is established, which is based on material and exergy balances. The process parameters of the OBF with different oxygen enriched blast were calculated through the model. The calculation results demonstrated that the material balance of carbon input in the OBF process decreased by 6.7% (OBF-I) and 22.4% (OBF-II) compared to the TBF process. Also, the industrial oxygen consumption increased from 185.88 m3 (OBF-I) to 228.32 m3 (OBF-II). The exergy output and the total exergy loss of the OBF-I process decreased by 1.5% and 5.6%, respectively, and those in the OBF-II process decreased by 16.60% and 30.81%. Due to the exergy indices in OBF-II process all improved, the OBF-II process was a significantly efficient ironmaking process compared to the TBF.

Investigation on Burden Particle Softening and Melting Process under High Reduction Potential Condition

Abstract The present study using a single-particle softening under a load equipment was designed to better understand the softening and melting process of pellet, sinter and a mixture of both under a high reduction potential condition. Additionally, the experiment was interrupted at different shrinkage stages, and the evolvement of particle structure was analyzed. The softening and melting behavior of ferrous burden in high reduction potential compared with the general conditions was ascertained. In comparison with the general case, the thickness of the iron shell and the fineness of the metallic iron phase increased in high reduction potential. In the general condition the melting process is impacted by the low melting point of the slag with wustite outflow from the metallic iron shell, while in high reduction potential, the higher melting point of the slag without wustite exuded from the metallic iron phase. Under high reduction potential, the liquid slag was distributed in the metallic iron phase, which hindered the interaction between pellet and sinter. Thus, the temperature of interaction in high reduction potential is obviously higher than that in the general condition. The thicker iron shell and the higher melting point of slag lead to the improvement of the softening behavior under high reduction potential.

The Dynamic Dissolution of Coke with Slag in Melting and Dropping Zone

In the process of oxygen blast furnace, the lower coke ratio and the higher coke load make the skeleton coke more important. To understand the dissolution of coke in melting and dropping zone, the influence of FeO content, temperature and reaction time on the dissolution of coke with slag were studied by single-factor experiment. Meanwhile, the three factors and three levels orthogonal were conducted. The dissolution degrees were characterized by the weight loss ratio and diameter variation. The results showed that the weight loss ratio increased and the diameter decreased with the increase of FeO content, temperature and time. The three factors and three levels orthogonal test showed that time was the most significant factor on coke dissolution, FeO content of the second, and finally the temperature. The microstructure of coke after reaction indicated that the dissolution occurred on coke surface.