Chenguang Bai

High temperature pyrolysis behaviour and kinetics of lump coal in COREX melter gasifier

Abstract The COREX process is an industrially and commercially proven smelting reduction process producing hot metal of the same quality as blast furnace ironmaking. The high temperature pyrolysis behaviour of lump coal is crucial important in the COREX melter gasifier, which determines energy utilisation and gas composition, as well as metallurgical property and particle size of semicoke produced. In the present study, an experimental study was carried out to simultaneously investigate the pyrolysis behaviour of two Chinese lump coals used in the COREX process at different temperatures, and the effect of pyrolysis temperature on microstructure of semicoke produced was analysed by X-ray diffraction technology. In addition, the pyrolysis mechanics and the kinetics parameters of two lump coals were obtained. The results show the pyrolysis rate of lump coals is very rapid, the required time to completion of pyrolysis decreases with increasing temperature, and the contents of moisture and volatile have a remarkable effect on the maximum weight loss rate. The pyrolysis process of lump coals includes three stages: the first is water release accompanying a small quantity of devolatilisation, the second is devolatilisation, and the third is stabilisation. It is found the stacking height of graphite-like crystallite layer along the c-axis for the produced semicokes gradually increases with increasing temperature, the micro graphite spacing decreases and the crystallite size increases while raising the pyrolysis activation temperature. Three-dimensional diffusion is the primary restrictive link in the whole pyrolysis process of lump coals, the expression 3/2(1−α)2/3[1−(1−α)1/3]−1 is the optimal kinetic mechanical function. The apparent activation energy decreases with volatile increasing.

Determination of optimum blast furnace slag cooling rate for slag recycling in cement manufacture

Abstract The crystallisation behaviour of molten blast furnace slag was observed in situ using the single hot thermocouple technique. Isothermal and non-isothermal experiments were conducted to construct the diagrams for time temperature transformation and continuous cooling transformation. The molten slag should be cooled at a minimum critical cooling rate of 10°C s−1. During crystallisation, melilite is the main crystal phase and rankinite is the primary phase. The crystallisation mechanism of the melilite crystal phase involves one-dimensional direction growth with bulk nucleation, whereas the growth mechanism of the rankinite crystal phase is between the surface nucleation mechanism and the one-dimensional direction growth mechanism. The crystallisation activation energies of the melilite and rankinite crystal phases are 238.07±28.81 and 523.52±58.56 kJ mol−1 respectively.

Influence of bed condition on gas flow in Corex melter gasifier

Abstract The Corex process, which consists of the upper reduction shaft and a melter gasifier is an alternative ironmaking process to the blast furnace. The melter gasifier, where final reduction of iron ore and melting of direct reduction iron take place, plays an important role in the process. In order to evaluate the gas flow under different solid bed conditions in the melter gasifier, a two-dimensional static model has been developed. The results reveal that the bed void which is caused by particle diameter and their manner of packing significantly influences gas flow in the gasifier. A V shaped bed is preferred to provide the optimum gas flow in the gasifier.

Solid state and smelting reduction of Panzhihua ilmenite concentrate with coke

Abstract Solid state and smelting reduction of ilmenite is an important process of upgrading ilmenite to high titania feedstock. In this study, an ilmenite concentrate supplied by Panzhihua Iron and Steel (Group) Co. was first reduced at solid state in an electric resistance furnace, followed by smelting reduction in an induction furnace. The effects of reducing agent (carbon) amount on the chemical composition of the solid state reduction sample and the titania slag reduced from them, were analysed. It was found that the metallisation of iron in the solid reduction samples and the grade of titania slag generally increased with increasing carbon amount from 8 to 12%, and then remained constant when the carbon amount was increased above 12%. The content of metallic iron in the titania slag increased with increasing carbon amount, because the slag viscosity and liquidus temperature increased with decreasing FeO content. It was also known that the content of Ti2O3 increased with decreasing the content of FeO in the slag. Some metallic iron particles were found in the high titania slag samples. The liquidus lines and viscosity of the slag were calculated using FactSage to explain the experimental results. La réduction à l’état solide et par fusion de l’ilménite est un procédé important de valorisation de l’ilménite pour charge d’alimentation à haute teneur en dioxyde de titane. Dans cette étude, un concentré d’ilménite fourni par le groupe Panzhihua Iron and Steel Co. a d’abord été réduit à l’état solide dans un four électrique à résistances, suivi par la réduction par fusion dans un four à induction. On a analysé les effets de la quantité d’agent réducteur (carbone) sur la composition chimique de l’échantillon de réduction à l’état solide et de la scorie de dioxyde de titane réduit à partir de lui. On a trouvé que la métallisation du fer dans les échantillons de réduction solide et la qualité de la scorie de dioxyde de titane augmentaient généralement avec une augmentation de la quantité de carbone de 8 à 12%, et ensuite restaient constantes lorsqu’on augmentait la quantité de carbone au-delà de 12%. La teneur en fer métallique dans la scorie de dioxyde de titane augmentait avec l’augmentation de la quantité de carbone, parce que la viscosité de la scorie et la température du liquidus augmentaient avec une diminution de la teneur en FeO. On sait également que la teneur en Ti2O3 augmentait avec une diminution de la teneur en FeO dans la scorie. On a trouvé quelques particules de fer métallique dans les échantillons de scorie à haute teneur en dioxyde de titane. On a calculé les lignes de liquidus et la viscosité de la scorie en utilisant FactSage pour expliquer les résultats expérimentaux.

Influence of MgO, Al2O3 and CaO/SiO2 on the viscosity of blast furnace type slag with high Al2O3 and 5 wt-% TiO2

The effect of MgO, Al2O3 and CaO/SiO2 on the viscosity of CaO–SiO2–Al2O3–MgO–5 wt-% TiO2 slag was studied in the temperature range of 1673–1773u2005K. At a fixed CaO/SiO2 ratio of 1·17 and 12 wt-% Al2O3, the viscosity of the slag decreased with increasing MgO content because of depolymerisation of the silicate structures. At a fixed CaO/SiO2 ratio of 1·17 and 8 wt-% MgO, the viscosity of the slag increased with increasing Al2O3 content. At 8 wt-% MgO and 12 wt-% Al2O3 wt-%, increasing the CaO/SiO2 ratio from 1·07 to 1·50 resulted in lower slag viscosity. The temperature dependencies of the viscosity on MgO addition, Al2O3 addition, and CaO/SiO2 ratio were analyzed, and the apparent activation energies of each system were found to be between 178 and 232u2005kJ/mol, 273 and 360u2005kJ/mol, and 204 and 233u2005kJ/mol, respectively. Five different viscosity models were employed to predict slag viscosity, and the Riboud model was found to be the best for predicting this parameter.

Gas-Particle Flow and Combustion Characteristics of Pulverized Coal Injection in Blast Furnace Raceway

The two-dimensional steady-state discrete phase mathematical model is developed to analyze gas-particle flow and combustion characteristics of coal particles, as well as components concentration and temperature distribution of coal gas in the process of pulverized coal injection of blast furnace raceway. The results show that a great deal of coal gas discharges on the top of raceway away from the tuyere, and the residence time of coal particles in the region of blowpipe and tuyere is 20 ms or so and 50 ms when it reaches raceway boundary. The pressure is the highest at the bottom of raceway and the maximal temperature is about 2423 K. The char combustion is mainly carried out in the raceway and the maximum of char burn-out rate attains 3×10−4 kg/s.

Mathematical Modeling on the Removal of Impurity Elements from Molten Aluminum

In order to remove impurity elements from molten aluminum, many processes, such as using inert gas, reactive gas, reactive powders, unreactive powders, slag, or their combinations, have been used during the past 30 years. In the current paper, mathematical models on the removal of impurity elements from molten aluminum for these processes were extensively developed, and validated by industrial measurement from literatures. Special parameters were introduced to express the refining efficiency. Mathematical models for the combined processes like inert gas mixed with reactive gas purging, reactive powders injection with inert gas as carrying gas, were also developed. The removal efficiency of impurity elements for batch reactor and continuous reactor were derived for these processes, either the single method or the combined method. The effects of gas flow rate, impellor rotating speed, fraction of reactive gas, injecting rate of reactive powders, and temperature on the removal of impurity elements were discussed.

Dehydrating and sintering of Philippine nickel laterite

Abstract Dehydrating of nickel laterite is necessary when high magnesium laterite ores are treated by pyrometallurgical means. In this work, the Philippine nickel laterite was dehydrated and sintered simultaneously in a laboratory scale sintering apparatus. The original nickel laterite was characterised using thermogravimetric (TG) analysis, differential thermal analysis (DTA) and X‐ray diffraction (XRD) experiments. The measurements indicate that chlorite (Fe,Mg,Al)3(Si,Al)2O5(OH)4 and serpentine Mg21Si2O28(OH)34H2O are the primary phases, while FeO(OH) and (Fe,Mg,)3Si4O10(OH)2 are the minor phases in Philippine nickel laterite. The laterite contains free water, water of crystallisation and hydroxyl group; these can be removed in that order during the heating. The temperature range for the removal of free water is 25–140°C, for water of crystallisation it is 200–480°C, and for hydroxyl group it is 500–800°C. Sintering experiments with various coal additions show that sintering time, sintering product ratio, mass loss and the temperatures of off‐gas and burden increase with increasing coal addition. The sintered samples were analysed using XRD, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results demonstrate that olivine (Mg,Fe)2SiO4 and spinel MgFe2O4 are the main bonding phases during the sintering. La déshydratation de la latérite de nickel est nécessaire lorsque des minerais de latérite à haute teneur en magnésium sont traités par méthodes pyrométallurgiques. Dans ce travail, on a déshydraté et fritté simultanément la latérite de nickel des Philippines dans un appareil de frittage à l’échelle du laboratoire. On a caractérisé la latérite de nickel originale en utilisant des expériences de thermogravimétrie (TG), d’analyses thermiques différentielles (DTA) et de diffraction des rayons X. Les mesures indiquent que le chlorite (Fe,Mg,Al)3(Si,Al)2O5(OH)4 et la serpentine Mg21Si2O28(OH)34H2O sont les phases primaires alors que FeO(OH) et (Fe,Mg)3Si4O10(OH)2sont les phases mineures de la latérite de nickel des Philippines. La latérite contient de l’eau libre, de l’eau de cristallisation et le groupe hydroxyle; on peut les enlever dans cet ordre lors du chauffage. La gamme de température pour l’enlèvement de l’eau libre est de ∼25 à 140°C, elle est de ∼200 à 480°C pour l’eau de cristallisation et de ∼500 à 800°C pour le groupe hydroxyle. Les expériences de frittage, avec additions variées de charbon, montrent que le temps de frittage, le ratio du produit de frittage, la perte de masse et les températures du gaz de dégagement et du lit de fusion, augmentent avec une augmentation d’addition de charbon. On a analysé les échantillons frittés en utilisant la XRD, la microscopie à balayage d’électrons (SEM) et la spectroscopie à dispersion d’énergie (EDS). Les résultats démontrent que l’olivine (Mg,Fe)2SiO4 et le spinelle MgFe2O4 sont les principales phases de liaison lors du frittage.

Effect of burden material size on blast furnace stockline profile of bell-less blast furnace

Abstract The position and profile of the burden stockline are important parameters for blast furnace (BF) control. Theoretical calculations currently determine the position without considering the influence of different sized materials. In order to clarify the effects of different sized materials on the position and compare experimental and theoretical calculated results, a 1/15 scale cold model consisting of an actual 2500 m3 shaft and a bell-less top charging system has been built. The results indicate that (i) the chute rotary speed strongly influences the stockline peak position with different sized materials (ii) the rotary inclined angle and position of stockline peaks are approximately linear. Model predictions of the stockline with material size are poorly related to actual trial results, particularly chute rotary speed.

Radiant Image Simulation of Pulverized Coal Combustion in Blast Furnace Raceway

The relationship between two-dimensional radiant image and three-dimensional radiant energy in blast furnace raceway was studied by numerical simulation of combustion process. Taking radiant image as radiant boundary for numerical simulation of combustion process, the uneven radiation parameter can be calculated. A method to examine thre-edimensional temperature distribution in blast furnace raceway was put forward by radiant image processing. The numeral temperature field matching the real combustion can be obtained by proposed numeric image processing technique.