Mansheng Chu

Non-isothermal reduction mechanism and kinetics of high chromium vanadium–titanium magnetite pellets

Abstract Non-isothermal reduction kinetics and mechanism of high chromium vanadium–titanium magnetite pellets were studied at 400–1100°C, simulating the lumpy zone of blast furnace conditions. The phase transformation behaviour of valuable elements including Fe, Cr, V and Ti and microstructural changes of reduced pellets were examined by means of X-ray diffraction (XRD) and SEM-EDX. The swelling of reduced pellets was highest at 900°C, while cold crushing strength was highest at 1100°C. Phase transformation behaviour of valuable elements in the lumpy zone is as follows: Fe2O3→Fe3O4→FeO→Fe; Fe2Ti3O9→Fe2TiO4→Fe5TiO8→FeTiO3; V2O3→VO; (Fe0·6Cr0·4)2O3→FeO·Cr2O3→Cr2O3. By analysing the non-isothermal reduction kinetics of high chromium vanadium–titanium magnetite pellets, based on the evaluation of reaction activation energy calculated according to Coats–Redfern method, gaseous internal diffusion through solid product layer and interfacial chemical reaction are most likely to be the main rate controlling steps in the reduction process.

Numerical Simulation of Innovative Operation of Blast Furnace Based on Multi-Fluid Model

A multi-fluid blast furnace model was simply introduced and was used to simulate several innovative iron-making operations. The simulation results show that injecting hydrogen bearing materials, especially injecting natural gas and plastics, the hydrogen reduction is enhanced, and the furnace performance is improved simultaneously. Total heat input shows obvious decrease due to the decrease of heat consumption in direct reduction, solution loss and silicon transfer reactions. If carbon composite agglomerates are charged into the furnace, the temperature of thermal reserve zone will obviously decrease, and the reduction of iron-bearing burden materials will be retarded. However, the efficiency of blast furnace is improved just due to the decrease in heat requirements for solution loss, sinter reduction, and silicon transfer reactions, and less heat loss through top gas and furnace wall. Finally, the model is used to investigate the performance of blast furnace under the condition of top gas recycling together with plastics injection, cold oxygen blasting and carbon composite agglomerate charging. The lower furnace temperature, extremely accelerated reduction rate, drastically decreased CO2 emission and remarkably enhanced heat efficiency were obtained by using the innovative operations, and the blast furnace operation with superhigh efficiency can be realized.

Effect of MgO content in sinter on the softening–melting behavior of mixed burden made from chromium-bearing vanadium–titanium magnetite

The effect of sinter with different MgO contents on the softening–melting behavior of mixed burden made from chromium- bearing vanadium–titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening–melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%–3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening–melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO contents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium–titanium magnetite in a blast furnace.

Mechanism of zinc damaging to blast furnace tuyere refractory

The phenomena of tuyere upward-warp have been found at No.6 blast furnace in Kunming Steel Company China after its blow-in, which has made a great impact on the practical production of the furnace. Thus, a number of efforts have been made to elucidate the mechanism of this phenomenon. The results of investigation and tests revealed that the enrichment and expansion of zinc in the tuyere bricks is the main factor leading to the tuyere upward-warp. The eroding behavior of zinc is that the inner structure of the tuyere bricks turns from dense to loose with entering, enriching and expanding of zinc, which forms spot-like→stripe-like→ditch-like→vein-like→tumor-like eroding passage. Additionally, it is found that the sequence of deleterious elements entering the tuyere refractory is K, Na, Zn and Pb, respectively. Finally, the phenomena and process of zinc crystallization and growth in the refractory have been clearly observed and recorded during this investigation.

Oxidation induration process and kinetics of Hongge vanadium titanium-bearing magnetite pellets

The induration process and oxidation kinetics of Hongge vanadium titanium-bearing magnetite (HVTM) pellets have been investigated by employing X-ray diffraction, scanning electron microscope, energy-dispersive spectroscopy, thermogravimetric and differential thermal analysis and thermogravimetric and differential scanning calorimetry. The results indicated that HVTM was a high-chromium vanadium-bearing titanomagnetite containing 1.48 wt-% Cr2O3, and the crystal stock strength was 625 N. The compressive strength of HVTM pellets could be improved by increasing the roasting temperature and roasting time. Under the optimum conditions of oxidation roasting at 1200°C for 15 min, the compressive strength was found to be 2893 N. The phase transformations of the valuable elements could be described as follows: Fe3O4→Fe2O3; Fe2VO4→(Cr0.15V0.85)2O3; Fe2.75Ti0.25O4→FeTiO3→Fe9TiO15; FeCr2O4→(Fe0.6Cr0.4)2O4, Fe0.7Cr1.3O3, (Cr0.15V0.85)2O3. Three stages were identified during the induration process: initial oxidation, later oxidation, and haematite re-crystallisation, poly-crystallisation and induration. The development of strength mainly occurred in the last stage. Kinetic parameters of the oxidation process were determined from heating experiments. The results showed that the average value of activation energy was calculated to be 69.33 kJ mol−1 by the Flynn–Wall–Ozawa methods. This study aims to provide theoretical and technical bases for the effective utilisation of HVTM ore for use in either blast furnaces or shaft furnaces.

Effects of MgO and TiO2 on the viscous behaviors and phase compositions of titanium-bearing slag

The effects of MgO and TiO2 on the viscosity, activation energy for viscous flow, and break-point temperature of titanium-bearing slag were studied. The correlation between viscosity and slag structure was analyzed by Fourier transform infrared (FTIR) spectroscopy. Subsequently, main phases in the slag and their content changes were investigated by X-ray diffraction and Factsage 6.4 software package. The results show that the viscosity decreases when the MgO content increases from 10.00wt% to 14.00wt%. Moreover, the break-point temperature increases, and the activation energy for viscous flow initially increases and subsequently decreases. In addition, with increasing TiO2 content from 5.00wt% to 9.00wt%, the viscosity decreases, and the break-point temperature and activation energy for viscous flow initially decrease and subsequently increase. FTIR analyses reveal that the polymerization degree of complex viscous units in titanium-bearing slag decreases with increasing MgO and TiO2 contents. The mechanism of viscosity variation was elucidated. The basic phase in experimental slags is melilite. Besides, as the MgO content increases, the amount of magnesia–alumina spinel in the slag increases. Similarly, the sum of pyroxene and perovskite phases in the slag increases with increasing TiO2 content.

Reduction mechanism of high-chromium vanadium-titanium magnetite pellets by H2-CO-CO2 gas mixtures

The reduction of high-chromium vanadium–titanium magnetite as a typical titanomagnetite containing 0.95wt% V2O5 and 0.61wt% Cr2O3 by H2–CO–CO2 gas mixtures was investigated from 1223 to 1373 K. Both the reduction degree and reduction rate increase with increasing temperature and increasing hydrogen content. At a temperature of 1373 K, an H2/CO ratio of 5/2 by volume, and a reduction time of 40 min, the degree of reduction reaches 95%. The phase transformation during reduction is hypothesized to proceed as follows: Fe2O3 → Fe3O4 → FeO → Fe; Fe9TiO15 + Fe2Ti3O9 → Fe2.75Ti0.25O4 → FeTiO3 → TiO2; (Cr0.15V0.85)2O3 → Fe2VO4; and Cr1.3Fe0.7O3 → FeCr2O4. The reduction is controlled by the mixed internal diffusion and interfacial reaction at the initial stage; however, the interfacial reaction is dominant. As the reduction proceeds, the internal diffusion becomes the controlling step.

Numerical Analysis of Blast Furnace Performance Under Charging Iron-Bearing Burdens With High Reducibility

The reducibility of iron-bearing burdens was emphasized for improving the operation efficiency of blast furnace. The blast furnace operation of charging the burdens with high reducibility has been numerically evaluated using a multi-fluid blast furnace model. The effects of reaction rate constants and diffusion coefficients were investigated separately or simultaneously for clarifying the variations of furnace state. According to the model simulation results, in the upper zone, the indirect reduction of the burdens proceeds at a faster rate and the shaft efficiency is enhanced with the improvement under the conditions of interface reaction and intra-particle diffusion. In the lower zone, direct reduction in molten slag is restrained. As a consequence, CO utilization of top gas is enhanced and the ratio of direct reduction is decreased. It is possible to achieve higher energy efficiency of the blast furnace, and this is represented by the improvement in productivity and the decrease in consumption of reducing agent. The use of high-reducibility burdens contributes to a better performance of blast furnace. More efforts are necessary to develop and apply high-reducibility sinter and carbon composite agglomerates for practical application at a blast furnace.

Optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite

The optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite was investigated systematically through sinter and pellet experiments. MgO was added in the form of magnesite. When the content of MgO in the sinter was increased from 1.95wt% to 2.63wt%, the low-temperature reduction degradation index increased from 80.57% to 82.71%. When the content of MgO in the pellet was increased from 1.14wt% to 2.40wt%, the reduction swelling index decreased from 15.2% to 8.6%; however, the compressive strength of the oxidized pellet decreased dramatically and it was 1985 N with an MgO content of 1.14wt%. This compressive strength does not satisfy the requirements for blast-furnace production. When all of the aforementioned results were taken into account, the sinter with a high MgO content (2.63wt%) matching the pellet with a low MgO content (less than 1.14wt%) was the rational burden structure for smelting high-chromium vanadium-titanium magnetite in blast furnaces.

Optimization of BF Slag for High Cr2O3 Vanadium-titanium Magnetite

In order to clarify the slag system of high Cr2O3 vanadium-titanium magnetite smelting in BF (blast furnace), the melting properties of slag samples prepared by analyticaly pure reagents were measured. By means of orthogonal test synthetic weighted score method, the optimal slag for high Cr2 O3 vanadium-titanium magnetite was obtained, which contained 10% MgO, 8% TiO2 and 15% Al2O3, with the binary basicity being 1.15. In addition, the effects of basicity, MgO, TiO2 and Al2O3 on slag melting properties were investigated by single factor test, and the results showed that, with increasing the basicity or TiO2 content, melting temperature (Tm) increased, whereas initial viscosity (η0) and highGtemperature viscosity (ηh) decreased. With increasing the MgO content, Tm decreased firstly and then increased. With increasing the Al2O3 content, Tm increased, and η0 and ηh decreased firstly and then increased.