The Chinese Journal of Process Engineering

Modeling of Slag Entrapment and Molten Steel Exposed to Atmosphere in Refining of 250 t Ladle with Bottom-blown Argon

ZHENG Wan TU Hao LI Guang-qiang CHENG Hui-wu ZHU Cheng-yi GU Ji-gang

. 2014, 14(3): 361-168.

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Experiments in water model and numerical simulation were carried out to study bottom blowing process of argon gas for steel refining in a 250 t ladle in a steel plant. The effects of gas flow rate and slag layer thickness on the slag entrapment, and gas flow rate, slag layer thickness and porous brick permeability on exposed surface area of molten steel were examined. Formation mechanism of slag entrapment was analyzed. The results show that flow rate plays a decisive role on formation of slag entrapment. Slag entrapment can be prevented if the flow rate is controlled below 0.96 m3/h (corresponding to actual flow rate of 69 m3/h). With the increase of flow rate, the exposed bare area gradually increases, and reaches about 14% at the flow rate of 0.70 m3/h, and its increasing amplitude tends to ease off with the further increase of flow rate. With the increase of slag layer thickness, critical gas flow rate of the slag entrapment and bare area decrease. With 37 mm (corresponding to actual layer thickness of 150 mm) slag layer thickness covering, reoxidation of steel can be prevented effectively. Porous brick clogging has a great impact on the bare area of molten steel, two bare bright circles with different sizes form on the top of molten steel, which increases the erosion from ladle wall refractory and contamination of liquid steel. After process optimization, the ratio of ladle nozzle clogging is reduced to less than 0.1%, and the production cost can be reduced.

Enrichment of High Ca-containing Phases in Calcium Carbide Hydrolysis Slag with Hydro-cyclone Method

YANG Hang CAO Jian-wei WANG Zhi CHEN Hua-hui GONG Xu-zhong

. 2014, 14(3): 369-376.

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Hydro-cyclone was used to achieve the deaggregation of agglomerated particles of calcium carbide hydrolysis slag and enrichment of high Ca-containing phases. The enrichment effect was evaluated. The results showed that the main phases in over flow were Ca-containing phases [Ca(OH)2 and CaCO3]. The main phases in bottom flow were Si, Al, Fe and Mg-containing phases (SiO2, Al2SiO5, Fe3O4 and MgSiO3). Ca in over flow increased from 41.73%(w) to 61.78%(w) after enrichment, the enrichment rate was over 50%. Si, Al, Fe and Mg contents in bottom flow increased 15.33%, 6.89%, 3.20% and 1.13%, respectively compared with the slag before enrichment. When the inlet water velocity was 4000 cm/s through acting calculation of forces, the shear stress (66.2 kg/cm2) provided by the resultant action of centrifugal force and Stokes force was greater than the adhesive force (45.3 kg/cm2) between calcium- and Si, Al, Fe and Mg-containing phases, which led to the deaggregation of agglomerated particles in calcium carbide hydrolysis slag. The average particle sizes of Ca-containing phases were less than 75 mm, and those of Si, Al, Fe and Mg-containing phases 106~180 mm. The essence of enrichment of Ca-containing phases was that the radial sedimentation velocity of Ca-containing phase particles was less than that of Si, Al, Fe and Mg-containing ones was.

Heat Transfer Performance of Improved INTER-MIG Impeller in a Stirred Tank with Inner-heating Coil

ZHOU Yong-jun JIANG Bin-wei LU Yuan CHEN Ming-hao

. 2014, 14(3): 377-382.

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The temperature field, temperature boundary layer of the lateral of coil and heat transfer coefficient in a f0.5 m stirred tank with a duplex interleaved and orthogonal design improved INTER-MIG blade system were investigated by both experimental and numerical approaches were. Water was stirred in the stirred tank at different rotational speeds. The results showed that the error of temperature between experimental measurement and numerical simulation was less than 2 K, the temperature in the tank had a rising trend from top to bottom and inside to outside, the maximum temperature difference was kept within 1 K. The heat transfer coefficient of coil tube outer side was correlated from the experimental data by Nu=0.0337Re0.925Pr1/3(d/D)0.1(dco/D)0.5, the average deviation between measurement and simulation was 7.64%. The average thickness of temperature boundary layer of coil tube outer side was 3.66 mm, being in a reasonable range.

Experimental Study on Creeping Flow of Moving Particle Bed in a Standpipe

YAN Xue ZHANG Wan-song LIU Ren-feng YAN Chao-yu WEI Yao-dong

. 2014, 14(3): 383-387.

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Under the condition without negative pressure gradient, experiments were carried out to study the characteristics of moving-bed creeping flow in a standpipe using FCC catalyst particles. The particle velocity in the standpipe was measured with PV6D particle velocity measuring device. The results indicate that there exists an observable creeping flow in the standpipe when the solids flux rate is low. Based on the designed gas-solid Re number, this creeping flow can be divided into intermittent creeping flow (Re<500) and fluctuant creeping flow (5004000. The particle creeping flow results from the discharging and clogging occurring at the orifice alternately, because the particles forms the static arch just above the orifice, and the bridge collapse takes place periodically. And the sliding friction force between the particles and wall also affects creeping flow. It is the evolution of force chain among the particles that contributes to the creeping flow behavior.

Kinetics of Alkaline Leaching of Boron Concentrate and Crystallization of NaB(OH)4

YIN Bao-wen QIN Shi-yue ZHANG Yi-fei WANG Shao-na

. 2014, 14(3): 388-394.

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Decomposition kinetics of boron concentrate in NaOH-H2O system was studied. The shrinking core model with surface chemical reaction control described the process reasonably well under the experimental conditions. Macrokinetic equation of leaching reaction of boron was 1-(1-X)1/3=1.3712′102e-31640/(RT)t with the activation energy of 31.64 kJ/mol. Increasing temperature or initial concentration of NaOH solution intensified the leaching of boron. The experimental results of two-stage leaching via four cycles indicated that under the conditions of 140℃, initial mass fraction of NaOH 25%, mass ratio of liquid to solid 4:1, reaction time 2 h and stirring speed 500 r/min in the first stage leaching while 150℃ in the second one with other conditions being the same as in the first stage, the conversion rate of boron reached 86.84%~96.26% in each leaching. The concentration of boron in the leachate from the second stage reached 27.33~29.84 g/L while the content of Si and Al kept low. The leachate from the second stage, hermetically preserved at 90℃ until faded, was naturally cooled to 25℃, crystallized isothermally for 6 h (stirring speed of 200 r/min) and nearly reached equilibrium after 2 h. Washed with anhydrous ethanol and saturated NaBO2 solution successively and dried for 12 h at 40℃, NaB(OH)4 was obtained, with the purity of almost 90%, crystallization rate of over 70% and sections of parallelogram or hexagon.

Forward Osmosis Performance of Sodium Polyacrylate as Draw Solution

QI Yuan-feng LI Yu-ping LI Hai-bo CAO Hong-bin WANG Shao-na

. 2014, 14(3): 395-401.

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Osmosis property of sodium polyacrylate (PAA-Na) as draw solution was studied, and the forward osmosis performance of PAA-Na draw solution examined with focus on influential factors and mechanism of water flux and reverse solute flux. The results show that the fitting curve of osmotic pressure and PAA-Na concentration matches virial equation, and the second virial coefficient promotes the osmotic pressure dramatically in a certain concentration range; the osmotic pressure of 0.2 g/mL PAA-Na is over 1.3 Osmol/kg, showing the great possibility of PAA-Na as draw solution. The permeated water flux in the forward osmosis process with 0.2 g/mL PAA-Na as draw solution reaches 14.5 L/(m2×h), which is higher than that of NaCl draw solution with the same osmosis [14.0 L/(m2×h)]. The reverse solute flux of 0.2 g/mL PAA-Na draw solution is only 1.6 g/(m2×h), which is much lower than that of NaCl draw solution [16.5 g/(m2×h)]. The water flux increases significantly with the increase of temperature while reverse solute flux remains at low level, indicating that the suitable operation temperature with PAA-Na as draw solute should be higher than that with conventional small molecules as draw solute. PAA-Na is a good potential draw solute due to its great water flux and low reverse solute flux.

Modeling of the Pleated Filter Based on Microscopic Structure and Numerical Simulation of Its Filtration Characteristics

HUANG Nai-jin QIAN Fu-ping ZHA Wen-juan LU Jin-li HAN Yun-long

. 2014, 14(3): 402-408.

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In order to achieve optimal control of randomly arranged fibers, an algorithm that generates the stochastic multilayer fibrous medium was presented based on Poisson stochastic linear process. A 3-D mimicry model of the pleated filter was established. The gas-solid two-phase flow characteristics of the pleated filter were simulated using CFD, and its pressure drop and filtration efficiency under different operating conditions were calculated. And the simulated results were compared with those in the literature. The results show that the simulated values of pressure drop agree with those in the literature, and the pressure drop increases linearly with the filtration velocity, moreover, it decreases firstly and then increases with the pleated corner angle. The filtration efficiency first decreases and then increases with the particle size at the same filtration velocity, and the most penetration particle size (MPPS) exists in the given particle size range. When the particle size is less than 0.5 mm, the filtration efficiency decreases with the filtration velocity. But, when it is over 0.5 mm, the efficiency increases with the velocity. The results also show that MPPS decreases with the filtration velocity. The simulated values of filtration efficiency are consistent with those in the literature. And the filtration efficiency decreases with the filtration velocity when the particle size is less than 1 mm. However, when it is over 1 mm, the efficiency increases with the velocity.

Double-capture Process of CO2 by Gas Hydrate and Aqueous Solution of Ionic Liquid

LI Song BI Yin YANG Cui-lian GUO Kai-hua

. 2014, 14(3): 409-414.

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Double-capture process of CO2 with CO2 absorption in aqueous solution of ionic liquid 1-aminopropyl-3-methylimidazolium bromide ([APMIM]Br) and simultaneous formation of CO2 gas hydrate was designed. Based on the experimental data of CO2 solubility and phase equilibrium data of CO2 hydrate formation in [APMIM]Br aqueous solution, the mass balance of this process under various working conditions were calculated, the effects of water concentration, pressure and liquid gas flow ratio on the CO2 capture rate examined, and the comparative performances of CO2 gas hydrate capture and CO2 absorption by the ionic liquid solution in the process also studied. The results show that at high pressure and high water content, the CO2 capture performance by gas hydrate formation is comparatively higher than that of the absorption by ionic liquid solution, while at lower pressure, the absorption of the aqueous solution plays a major role. The CO2 capture performance of the double-effect process with CO2 absorption plus hydrate formation in the aqueous solution is superior to that of CO2 gas formation in pure water system. When molar content of CO2 in feed gas is less than 65%, the CO2 capture rate of double-capture process is less than 40%. For the feed gas with lower CO2 content, the process approaches to the pure absorption process with the ionic liquid aqueous solution.

Bioleaching of Cu-As-containing Filter Cake Waste

DU Juan LI Yuan-yuan ZHANG Guang-ji YANG Chao

. 2014, 14(3): 415-420.

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Bioleaching was used to treat Cu-As-containing filter cake. The effects of pH value, temperature and strain on the bioleaching rates of Cu and As were studied, and the bioleaching mechanism and feasibility of the harmless treatment of As-bearing residue with bioleaching analyzed. The results show that Sulfobacillus sibiricu enhanced the leaching process. The leaching of As and Cu was carried out by hot acid and then leaching with bacterial suspension, the optimum conditions with the strain were obtained as: temperature of 50℃ and pH value 1.5. Under the optimum conditions, the leaching rate of As and Cu reached 91.33% and 94.22% in 7 d, respectively.

Extraction of Vanadium from Fly Ash of Stone Coal Combustion by Alkaline Leaching

QIU Wei-jia WEI Chang DENG Zhi-gan LI Min-ting LI Xin-bin ZHANG Fan

. 2014, 14(3): 421-426.

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The extraction of vanadium from fly ash of stone coal combustion in China was studied by alkaline leaching. The fly ash was characterized by a relatively high content of V5+ in silicon and aluminum oxides. Based on the existing status of vanadium, the effects of reaction time, ratio of liquid to solid, alkaline concentration and reaction temperature on the leaching rate of vanadium were examined. The results show that the leaching rate is proportional to the four influential factors. The optimum conditions for the alkaline leaching of vanadium are stirring velocity of 500 r/min at 180℃ for 3 h, ratio of liquid to solid 5 mL/g and NaOH concentration of 200 g/L. Under the conditions, the leaching rate of vanadium reaches over 85%. The content of impurity Al2O3, K and Fe in leachate is less than 500, 420 and 9 mg/L, respectively. The leachate is recycled back to the leaching system for full use of surplus alkaline and further enrichment of vanadium in the solution.

Extraction and Separation of Gallium Ion with Iron and Zinc Ions in Sulfuric Acid System with P507

ZHANG Kui-fang LIU Zhi-qiang

. 2014, 14(3): 427-432.

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Separation of Ga3+ with Fe2+ and Zn2+ in sulfuric acid system by P507 was studied. The effects of feed acidity, extractant concentration, time, phase ratio and temperature on the extraction of Ga3+ were examined. The isotherms of the extraction were plotted, and the separation scheme of washing Fe2+and Zn2+ by HCl and stripping Ga3+ by H2SO4 was designed by comparing the performances of three ions stripped by HCl and H2SO4 at different concentrations. The results show that with 40%(j) P507 in sulphonated kerosene as extractant, the extraction rate of Ga3+ reaches 98.48% in four-stage counter-current extraction under O/A ratio of 1:1 at 25℃ for 20 min, meanwhile, 19.56% Fe2+ and 38.42% Zn2+ are coextracted. Fe2+, Zn2+ in loaded organic can be totally washed by 6 mol/L HCl in 3 times. Ga3+ in loaded organic can be stripped using 100 g/L H2SO4 and the stripping rate reaches 97.64% in four-stage counter-current stripping under O/A ratio of 4:1 at 25℃ for 10 min.

Predictive Model for Formaldehyde Emission from Block Board in Indoor Environment

ZHANG Hao ZHU Qing-ming LIU Xiu-yu LIU Ying

. 2014, 14(3): 433-438.

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Environment testing chamber was used to simulate indoor environment, the emission concentration of formaldehyde from block board in the chamber at different environmental temperatures and relative humidities measured, and the emission mechanism analyzed. The experiment of formaldehyde emission from block board in actual indoor environment was carried out and compared with that in the chamber. Grey neural network model was established by gray prediction and neural network models to forecast the emission concentration in actual indoor environment. The results indicated that with the rise of temperature and relative humidity, the emission concentration of formaldehyde increased, and temperature has more significant effect in the active period of emission. The emission concentration was easier to reach stable state at low temperature and relative humidity and proportional to the change of temperature difference between indoor and outdoor, hot-pressing seeping wind affected the emission concentration. The predicted data by grey neural network model agreed with the experimental data, their average absolute error was -0.0007 mg/m3, and relative error 0.208%~5.981%.

Experimental Study on Dehydration Concentration of Tetrahydrofuran by Pervaporation with MOR Zeolite Membrane

JIN Ge ZHOU Zhi-hui LIU Hong WU Jian-xiong GUO Da-peng

. 2014, 14(3): 439-443.

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The secondary growth method was used to prepare mordenite zeolite membrane on a-Al2O3 support without using any organic templating agent. The synthesized membrane was applied in the dehydration concentration of tetrahydrofuran (THF). The effects of operating temperature and THF concentration on the pervaporation performance were investigated. The results indicated that at 60℃ and THF concentration of 90%(w), the permeate flux and separation factor of the membrane reached 0.350 kg/(m2·h) and 9233, respectively. In the THF concentration range from 75% to 97%, the water content in permeate liquid was over 99.6%(w). After concentration of the simulated pharmaceutical waste liquor [97.066%(w) THF/water solution] for 37 h, the THF concentration reached 99.640%(w).

Decarboxylation of γ-Valerolactone into Butenes by Mesoporous SiO2/Al2O3 Solid Acid Catalyst

ZHANG Zhan XIne Jia-yu WEI Ling-chao LU Xing-mei Bao-zeng ZHANG Suo-jiang

. 2014, 14(3): 444-449.

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Mesoporous SiO2/Al2O3 catalyst was prepared by sol-gel method and characterized by XRD, BET and pyridine-FTIR for the decarboxylation of γ-valerolactone to produce butenes. The effects of reaction conditions on the production of butenes were examined, and the decarboxylation mechanism was analyzed. The results showed that the average absorption pore size of the catalyst was 6.8768 nm and its specific surface area 398.4 m2/g, and Lewis and Br?nsted acid sites were found on its surface. The highest yield of butenes of 97% was achieved at 350℃ for 4 h with 5%(w) catalyst. The decarboxylation mechanism was analysed as that γ-velerolactone was firstly converted to pentenoic acids by ring opening, then α and b carbons of pentenoic acid were cracked to produce butenes and CO2.

Purification of Silica by Roasting-Acid Leaching and Transformation of Metallic Impurity Phases

LI Ye WANG Zhi MA Wen-hui SUN Li-yuan

. 2014, 14(3): 450-455.

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In the purification process of silica, XRD and EDS are applied to analyze the existing characteristics of impurities in silica, and a combined purification method of acid leaching and high-temperature roasting is adopted to study the transformation of impurity phases during acid leaching, and the combined purification effect. The results show that the main phases of aluminosilicate are feldspar, illite and kaolinite based on their different contents of elements such as K, Na, Ca, Al and Si. Not only the impurity phases are dissolved in acids, but also the feldspar impurity phases are changed into illite and kaolinite. The purity of silica after pre-acid leaching and high-temperature activation can reach up to 99.995%, and the contents of Al and K in it with pre-acid leaching are decreased by 76.6% and 66.5%, respectively, compared with its purification without pre-acid leaching. High-temperature roasting at 700℃ can obtain the best effect for removal of Al and K as impurity elements in pre-acid leached silica at the removal rates of 85% and 41%, respectively.

Catalytic Pyrolysis Behaviors of Xinjiang Tuoli Oil Sand

ZHANG Chi WANG De-min ZHANG Bei-bei ZHANG Jing LANG Ying ZHONG Mei MA Feng-yun

. 2014, 14(3): 456-461.

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Pyrolysis of Xinjiang Tuoli oil sand was studied in a fixed-bed unit, and the effects of temperature, H2 concentration, catalyst type and dosage, and contact mode of catalyst with the oil sand on its pyrolysis characteristics and oil yield were evaluated, and the activation energy was obtained via a thermogravimetric analyzer. The results indicated that the peak value of oil yield [up to 44.52%(w)] was attained at 550℃ in N2 atmosphere. The decrease of oil yield with the inclusion of H2 into the atmosphere was due to the H2-promoted secondary cracking of saturates that led to more pyrolysis gas. When H2 concentration was 40%(j), the yield of saturates decreased to 28.96%(w), 25.43% lower than that in pure N2 atmosphere. Compared with the value without catalyst, the oil yield increased 15.77%, 16.87%, 3.79% and 5.62% with 2%(w) NiO, WO3, ZnO and nano CuO as catalysts, respectively. The contact mode between oil sand and catalyst affected oil yield obviously. The separate setting of NiO with oil sand in layer-by-layer was beneficial to the improvement of oil yield and quality, while nano CuO and WO3 were more suitable to mixing with oil sand in the pyrolysis process. ZnO, NiO and nano CuO could effectively reduce the pyrolysis activation energy of oil sand.

Consumption Prediction of By-product Gas in Iron and Steel Enterprises Based on PSA-SVRM Model

YANG Bo

. 2014, 14(3): 462-468.

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In order to deal with the problem that empirical model of by-product gas consumption in iron and steel enterprises cannot accurately predict the by-product gas consumption, the analysis of by-product consumption user and its characteristics is carried out. Support vector machine is used to classify the by-product gas consumption. It combines Powell calculation, simulated annealing arithmetic calculation, and support vector regression machine (SVRM), a model of PSA (Powell simulated annealing)-SVRM to predict the by-product gas consumption has been established. By-product gas consumption data in some iron and steel enterprises are used in the model. The results show that the prediction accuracy for sintering, steelmaking and continuous casting processes is 94.8%, 94.9% and 100%, respectively, with the relative mean error of 2.5%, 2.8% and 2.1%, respectively, which indicates that this PSA-SVRM model is suitable to prediction of the by-product gas consumption. Wilcoxon sign rank test proves the effectiveness of PSA-SVRM model.

Transgalactosylation Reaction Catalyzed by Hydrophilic Modified PU Nanofibrous Enzyme Membrane in Oil-Water System

LUAN Pan-pan ZHANG Yu-fei; ZHANG Song-ping JIANG Yan-jun LI Peng-ju SU Zhi-guo GAO Jing

. 2014, 14(3): 469-475.

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Polyurethane (PU) nanofiber with the diameter of 240~300 nm was prepared by electrospinning from 26%(w) PU solution containing LiCl. In order to increase the catalytic efficiency of b-D-galactosidase immobilized on PU nanofibrous membrane, suitable microenvironment on the membrane was pre-created by hydrophilic modification. BSA was adsorbed with LiCl on PU nanofibrous membrane at the high loading of 222 mg/g. The contact angle of modified PU nanofibrous membrane with water was thus reduced from 103.7o to 77.3o. Then b-D-galactosidase was immobilized on the modified membrane and catalyzed the transgalactosylation reaction in hexanol-water biphasic system. The specific activity of b-D-galactosidase immobilized on PU nanofiber membrane was 1.59 U/mg, while the activity of b-D-galactosidase adsorbed on unmodified PU nanofibrous membrane was its 79.2%. Compared with native enzyme, the half-life of b-D-galactosidase immobilized on PU nanofiber membrane incubated at 55℃ was increased 14 times. The storage stability of b-D-galactosidase immobilized on the membrane at 4℃ was also increased obviously, after storage for 45 d, the activity retained over 80%, whereas the activity of native b-D-galactosidase only 16.3%. The activity of b-D-galactosidase immobilized on PU nanofiber membrane was retained 31% after reuse in 42 times.

Expression of Cephalosporin C Acylase by Bicistronic Vector in Pichia pastoris

LIU Yu-shan LI Qiang

. 2014, 14(3): 476-481.

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In order to effectively express heterologous proteins in Pichia pastoris, the plasmid with bicistronic structure that connect two cephalosporin C (CPC) acylase genes with foot-and-mouth disease virus (FMDV) 2A sequence was constructed. After two-copy recombinant plasmid was integrated into the Pichia pastoris genome, positive recombinants were identified with selectable markers and PCR amplification. The optimal CPC acylase productivity of two-copy transformant reached 2810 U/L in shaking flask fermentation, the CPC acylase activity of two-copy transformant was 1.6 times of one-copy one at the same condition of cell concentrate. Thus, the 2A peptide with short structure and effective self-cleavage reaction not only achieved the goal of regulating multiple genes by a single promoter, but also provided a simple and effective thinking for improving expression of heterologous proteins by gene copy number.

Screening of High Yield Propionic Acid Producing Strain and Optimization of Its Fermentation Medium

CHEN Huan-jiao LI Xiao-lian LI Yan-liang WANG Zi-qiang WANG Yun-shan; ZHANG Li-ping SU Zhi-guo

. 2014, 14(3): 482-486.

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A propionic acid-resistant strain Propionibacterium acidipropionici WY320, which could tolerate up to 30 g/L of propionic acid, was obtained by environmental stress screening to reduce the feedback inhibition of propionic acid. Its fermentation medium was optimized by orthogonal experiments to improve the propionic acid yield. The results show that the optimal concentrations of corn steep powder, yeast extract and (NH4)2SO4 were 60, 10 and 7.5 g/L, respectively. The propionic acid production by the propionic acid-resistant strain could reach 49.35 g/L, which had a significant improvement of 72.98%, with a productivity of 0.21 g/(L×h). The scale-up experiment was carried out in a 5-L fermentor. The maximum propionic acid concentration of 51.96 g/L was obtained, and the productivity of propionic acid achieved to 0.31 g/(L×h), increased by 47.62% compared with the result of shaking flask experiment.

Preparation of Nanocomposite Tobermorite Whiskers with Fly Ash by Dynamic Hydrothermal Method and Their Characterization

LV Song-qing MA Shu-hua GUO Xi-yao ZHENG Shi-li GUO Fen

. 2014, 14(3): 487-492.

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Nanocomposite tobermorite whiskers were prepared by dynamic hydrothermal method using ordinary fly ash from somewhere in Shanxi as raw material. The effects of molar ratio of CaO to SiO2, reaction temperature, ratio of liquid to solid and reaction time on the synthesis of tobermorite whiskers were examined. The results showed that nanocomposite tobermorite whiskers with the ratio of length to diameter at over 20 were synthesized under the conditions of molar ratio of CaO to SiO2 at 1, ratio of liquid to solid 25 mL/g, reaction temperature 220℃ and reaction time for 10 h. The nanocomposite tobermorite whiskers were intertwined into hollow spherical particles, and their purity reached over 80%.

Corrosion Resistance of Zirconia-Molybdenum Cermets to Liquid Steel and Molten Slag

GUO Yan-ling TANG Lei ZHAO Hai WANG Yao-jie ZHANG Jie-yu

. 2014, 14(3): 493-499.

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Three ceramics, pure monolithic zirconia (m-ZrO2), 3%(mol) Y2O3 doped partially stabilized zirconia (3Y-PSZ) and 12%(mol) CeO2 doped PSZ (12Ce-PSZ), were chosen for preparing three cermets by adding 30%(j) Mo. The relative density of the cermets was over 95%. Their static corrosion tests were conducted in a tube furnace at 1600℃ for 4 h in molten IF steel and Al2O3-CaO-MgO slag respectively, and their corrosion behaviors observed. The results show that the cermet with pure m-ZrO2 has better corrosion resistance to liquid steel while the cermet with 3Y-PSZ has better corrosion resistance to molten slag. The corrosion of cermet by liquid steel is mainly involved with formation of intermetallic compounds between Fe and Mo, and the corrosion of cermet by molten slag mainly with the reaction of ZrO2 and CaO in slag for formation of CaZrO3.

Effect of CaO/Al2O3 Ratio on Solidification and Crystallization Behavior of Mold Fluxes for High-Al Steel

LIU Qi TAN Wen-feng ZHOU Zhen-yu HUANG Ya-ping TANG Ping WEN Guang-hua

. 2014, 14(3): 500-505.

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For the current problems that SiO2 in conventional mold flux for high-Al steel production can be easily reduced by Al in liquid steel, causing quality defects for the continuous casting strand, and the non-reactive mold flux has disadvantages of low consumption and poor lubrication, based on the phase diagram of CaO-SiO2-Al2O3 ternary system, the CaO-SiO2-Al2O3 mold flux with 20%(w) SiO2 was designed, and the effect of mass ratio of CaO to Al2O3 (C/A) on the solidification and crystallization behavior of experimental slag simulated by hot thermocouple technique examined. The results showed that the crystallization tendency of mold fluxes was enhanced with increasing of C/A, and the mold flux with C/A from 0.7 to 1.3 had smaller solidification fraction and expected to have the similar lubrication action with the conventional mold flux. Comprehensively considering the heat transfer and lubrication, the C/A of mold flux for high-Al steel should be in the range from 0.7 to 1.3.

Research Progress in Chemical Analysis of Several Transition Metallic Elements with Various Valence States in Steelmaking Slag

LI Fan WANG Hui YANG Bai-jun

. 2014, 14(3): 506-515.

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Based on the limitation of present physical quantitative analysis of phases and the necessity of chemical analysis of various ions of transition metals in steelmaking slag, the general designed process of chemical phase analysis is summarized as follows: the total amount of analyzed element and its qualitative and semi-quantitative analysis at different valence states should be obtained first, then the leaching and analysis process of metal element at a mono-valence state in slag or simultaneous leaching of the meatal at different valence states is designed, and selective analytical methods or calculation will be applied in determination of its accurate amount in each state. Morever, the principle and technique progress in chemical quantitative analysis of Fe, Cr, V, Ti and Nb at various valence states in steelmaking slag are reviewed, and the advantages and disadvantages of different methods discussed. The phase transforming and dissolving methods, and electrochemical polarography would be the analysis trend of various ions of transition metals in slag. But it is necessary to analyze the specific research systems sometimes.

Research Progress in Recovery of Al2O3 by Alkali Processes from Aluminosilicate Residue

ZHANG Ran MA Shu-hua CUI Long-peng CHEN Gang LI An WANG Shao-na

. 2014, 14(3): 516-526.

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Based on the basic analysis on domestic Al2O3 industry and output of aluminosilicate residue, the potential value and necessity of Al2O3 recovery from aluminosilicate residue were evaluated. Si was the main impurity during Al2O3 recovery with alkali process, the mass ratio of Al2O3 to SiO2 (A/S) in aluminosilicate was generally about 1. The principle of alkali process was analyzed for low A/S materials and four novel alkali processes based on the improvement of Bayer process for Al2O3 recovery were introduced, hydrothermal process, hydro-chemical/sub-molten salt, sintering and pre-desilicating processes. The equilibrium phases in the hydrothermal and hydro-chemical/sub-molten salt processes turned into Fe-substituted hydro-grandite and NaCaHSiO4 respectively, which had low A/S, by changing reaction conditions. Si was fixed and amorphous SiO2 dissolved in the sintering and pre-desilicating processes respectively via pre-treatment of materials, leading to high A/S in material. Compared with Bayer process, the separation efficiency of Al with Si was promoted effectively in the four processes. Moreover, the contrastive analysis on their Al2O3 recovery rate, application field and industrial application status was done. Finally, in view of the research status of Al2O3 recovery, the further research direction in establishment of novel leaching system by adding new materials was pointed out.

Research Progress in Optimization of the Performance of Microbial Fuel Cell by Decreasing Anodic Activation Overpotential

ZHANG Xiao-ting PENG Luo LI Zhen-lun

. 2014, 14(3): 527-534.

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Recent research advances in microbial fuel cell and the major influential factors on the cell power generation are reviewed. The effect of anodic activation overpotential on cell performance is analyzed. The latest research progress on promotion of its power output by optimizing anodic current-potential curve is summarized. The key measures include increasing exchange current density and enhancing heterogeneous electron transfer, which can be achieved by selecting optimal anodic materials, optimizing the anode surface physicochemical properties and screening efficient anodic electrogens. Anodic materials with advanced geometric structures and highly efficient electrogens, and further understanding on the limiting factors of microbial extracellular electron transfer processes, such as the interactions between nano wire and extracellular cytochrome, will be needed in the future development.

Research Progress in Numerical Models on Gas-Solid Fluidization of Cohesive Particles

ZHANG Yong-jun WANG Jia-jun GU Xue-ping FENG Lian-fang

. 2014, 14(3): 535-540.

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The agglomeration of cohesive particles in fluidization process is due to the inter-particle forces such as van der Waals force, liquid bridging force and electrostatic force, which affects the normal operation of fluidized bed reactors. The continuum, discrete particle and pseudo-particle models have their advantages and disadvantages in investigation of the agglomerating fluidization behavior. The continuum model based on Eulerian method can not describe the specific interaction between cohesive particles, while the numerical model based on Lagrangian method shows great advantages in multi-scale studies on the fluidization of cohesive particles in terms of mechanic analysis, particle collision and agglomeration flow. However, the discrete particle model can only be used to simulate a finite number of particles and the pseudo-particle model only works well for the micro-scale systems, due to the tremendous amount of computing. With the development of high performance computers, the Lagrangian methods will have wide application prospects.

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