Zhenggen Liu

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.

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.

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.

Fundamental research on iron coke hot briquette – A new type burden used in blast furnace

In order to improve blast furnace efficiency, reduce CO2 emission and accelerate energy utilisation, a new preparation process of iron coke hot briquette (ICHB) based on the raw materials conditions in China, a new type blast furnace ironmaking burden, was experimentally investigated in this paper. The new preparation process was researched and optimised through single factor experiment and orthogonal experiment. Meanwhile, the reactivity and the post-reaction strength of ICHB prepared under the optimised conditions were tested and the effect of ICHB on the thermal performance of conventional coke was researched. In addition, softening and dripping properties of mixed burden with optimised ICHB charging was simultaneously investigated. The results showed that the optimised preparation parameters of ICHB include 15% iron ore, 65% bituminous coal, 350°C hot briquetting temperature, 1100°C carbonisation temperature and 4 hours carbonisation time. The reactivity and the post-reaction strength of ICHB prepared under the optimisation conditions are 62.4 and 10.6%, respectively. ICHB has protective effect on conventional coke and the protective effect is more obvious with 10% ICHB adding. With the increase of ICHB charging ratio, softening interval T40–T4 of mixed burden is widened while melting interval TD–TS (namely cohesive zone) is narrowed. Additionally, the permeability of mixed burden becomes better and dripping ratio is first increased then decreased. The suitable charging ratio of ICHB in mixed burden is about 30%.

Numerical simulation on novel blast furnace operation of combining coke oven gas injection with hot burden charging

A novel blast furnace operation of coke oven gas (COG) injection simultaneously with hot burden charging has been proposed to solve the problem of insufficient heat in the BF shaft zone under the condition of COG injection and make full use of the abundant sensible heat of high temperature burden. In this paper, the novel process has been simulated with a multifluid blast furnace model. The results show that, in comparison with the operation of COG injection only, under the operation of COG injection together with hot burden charging, the temperature in the upper zone of the shaft increases while that in lower zone decreases. Furthermore, the reduction of iron bearing material is improved in the top zone, and the cohesive zone tends to descend and narrow. The coke ratio, fuel ratio and CO2 emissions of the operation of charging hot pellet and coke with the temperature of 800°C are decreased by 4.0, 4.7 and 5.3% respectively, while the hot metal productivity is increased by 7.14%. Therefore, COG injection combined with hot burden charging operation not only increases temperature in the upper part of the blast furnace but also decreases energy consumption per tonne hot metal.

Comprehensive Utilization of Ludwigite Ore Based on Metallizing Reduction and Magnetic Separation

With the aim of high-efficiency utilization of Dandong ludwigite ore, a new process of metallizing reduction and magnetic separation was proposed, and the effects of reduction temperature, reduction time, carbon ratio, ore size and coal size on the efficiency of the process were investigated in details, and relevant mechanisms were elucidated by SEM and EDS. The optimum technological parameters for metallizing reduction and magnetic separation on ludwigite ore were obtained as reduction temperature of 1250 °C, reduction time of 60 min, carbon ratio of 1.4, ore size of 0.500–2.000 mm, and coal size of 0.50–1.50 mm. After adopting the optimum parameters, the iron content and recovery ratio of iron in magnetic substance are 87.78% and 88.02%, respectively, while the recovery ratios of boron, magnesium and silicon in non-magnetic substance are 88.86%, 94.60% and 98.66%, respectively. After metallizing reduction and magnetic separation, valuable elements of ludwigite ore could be separated and utilized in subsequent steelmaking process and hydrometallurgy process.

Novel blast furnace operation process involving charging with low-titanium vanadium–titanium magnetite carbon composite hot briquette

An innovative process of blast furnace (BF) operation involving charging with low-titanium vanadium–titanium magnetite carbon composite hot briquette (LVTM-CCB) was proposed for utilizing LVTM and conserving energy. In this study, the effect of LVTM-CCB charging ratio on the softening, melting, and dripping behaviors of the mixed burden was explored systemically, and the migration of valuable elements V and Cr was extensively investigated. The results show that with increasing LVTM-CCB charging ratio, the softening interval T40 − T4 increases from 146.1°C to 266.1°C, and the melting interval TD − TS first decreases from 137.2°C to 129.5°C and then increases from 129.5°C to 133.2°C. Moreover, the cohesive zone becomes narrower and then wider, and its location shifts slightly downward. In addition, the recovery ratios of V and Cr in dripped iron first increase and then decrease, reaching maximum values of 14.552% and 28.163%, respectively, when the charging ratio is 25%. A proper LVTM-CCB charging ratio would improve the softening–melting behavior of the mixed burden; however, Ti(C,N) would be generated rapidly in slag when the charging ratio exceeds 25%, which is not favorable for BF operation. When considering the comprehensive softening–melting behavior of the mixed burden and the recovery ratios of V and Cr, the recommended LVTM-CCB charging ratio is 20%.

Numerical Simulation on Blast Furnace Operation with Hot Burden Charging

Blast furnace operation with hot burden charging was numerically simulated to preliminarily analyze its advantages and disadvantages. Multi-fluid blast furnace model was utilized to simulate hot burden charging operations under the conditions that the charging temperatures of pellet and coke were supposed separately or simultaneously as 800 °C. The results showed that, with hot burden charging, the furnace top temperature significantly increased in comparison to the conventional operation with cold burden charging. However, in-furnace temperature decreased, which decelerated the reduction rate of ferrous burdens. The concentrations of reducing gases were decreased in the furnace. The height of cohesive zone shifted downwards. When the charging temperatures of pellet and coke were simultaneously 800 °C (PC800), coke rate, fuel rate and carbon emission rate were decreased by 13.4, 22.1 and 19.25 kg · t−1, respectively. The ratio of ore to coke, solid burden charging rate and hot metal productivity were increased by 4.79%, 7.55 kg · s−1 and 38%, respectively. Heat taken away by top gas and energy consumption per ton hot metal were increased by 68.97% and 6.40%, respectively. Generaly speaking, hot burden charging was adverse to energy utilization of blast furnace.

Current status and development trends of innovative blast furnace ironmaking technologies aimed to environmental harmony and operation intellectualization

Blast furnace (BF) ironmaking is dominant for reducing pollution emission and energy consumption in iron and steel industry. Under the increasingly strict environmental pressure, some innovative technologies of BF ironmaking for environmental protection have been developed and applied in actual operating facilities. The current state of BF ironmaking in Europe, America, Japan, and China were briefly overviewed. Moreover, some innovative BF ironmaking technologies aiming at environmental harmony and operation intellectualization in the world, such as waste gas recycling sintering, BF operation with coke oven gas injection, ferro-coke, lime coating coke, BF visualization and intellectualization, were roundly summarized. Finally, some discussion on the technologies was carried out and the development trends of BF ironmaking were pointed out. The review could provide references and supports for the progress of environment-friendly technologies of BF ironmaking, thereby promoting their practical applications and achieving sustainable development of BF ironmaking, especially for Chinese ironmaking industry.