Behavior and mechanism of pre-oxidation improvement on fluidization in the fluidized reduction of titanomagnetite

The direct reduction process is an important development direction of low-carbon ironmaking and efficient comprehensive utilization of poly-metallic iron ore,such as titanomagnetite.However,the defluidization of reduced iron particles with a high metallization degree at a high temperature will seriously affect the operation of fluidized bed reduction.Coupling the pre-oxidation enhancing reduction and the particle surface modification of titanomagnetite,the behavior and mechanism of pre-oxidation improvement on fluidization in the fluidized bed reduction of titanomagnetite are systematically studied in this paper.Pre-oxidation treatment of titanomagnetite can significantly lower the critical stable reduction fluidization gas velocity to 0.17 m/s,which is reduced by 56%compared to that of titanomagnetite reduction without pre-oxidation,while achieving a metallization degree of>90%,Corresponding to the different reduction fluidization behaviors,three pre-oxidation operation regions have been divided,taking oxidation degrees of 26%and 86%as the boundaries.Focusing on the particle surface morphology evolution in the pre-oxidation-reduction process,the relationship between the surface morphology of pre-oxidized ore and the reduced iron with fluidization properties is built.The improving method of pre-oxidation on the reduction fluidization provides a novel approach to prevent defluidization by particle surface modification,especially for the fluidized bed reduction of poly-metallic iron ore.

Effects of vacuum pre-oxidation process on thermally-grown oxides layer of CoCrAlY high temperature corrosion resistance coating

The influence of the certain specific vacuum pre-oxidation process on the phase transformation of thermally-grown oxides（TGO） was studied.The CoCrAlY high temperature corrosion resistance coatings were produced onto the nickel-based superalloy substrate by high velocity oxygen fuel（HVOF）.It suggests that the TGO usually consists of a great number of chromium oxides,cobalt oxides and spinel oxides besides alumina during the initial period of the high temperature oxidation if the specimens are not subjected to the appropriate vacuum pre-oxidation process.Furthermore,the amount of alumina is strongly dependent on the partial pressure of oxygen;while the CoCr2O4 spinel oxides are usually formed under the conditions of higher partial pressure of oxygen during the initial period and the lower partial pressure of oxygen during the subsequent period of the isothermal oxidation.After the appropriate vacuum pre-oxidation process,the TGO is mainly composed of alumina that contains lower Y element,while alumina that contains higher Y element sporadically distributes,and the spinel oxides cannot be found.After a longer period of the isothermal oxidation,a small amount of porous CoCr2O4 and the chrome oxide sporadically distribute near the continuous alumina.Additionally,after the appropriate vacuum pre-oxidation process,the TGO growth rate is relatively slow.

Prediction of pre-oxidation efficiency of refractory gold concentrate by ozone in ferric sulfate solution using artificial neural networks

An artificial neural network model was developed to predict the oxidation of refractory gold concentrate （RGC） by ozone and ferric ions. The concentration of ozone and ferric ions, pulp density, oxygen amount, leaching time and temperature were employed as inputs to the network; the output of the network was the percentage of the ferric extraction iron from RGC. The multilayered feed-forward networks were trained by 33 sets of input-output patterns using a back propagation algorithm; a three-layer network with 8 neurons in the hidden layer gave optimal results. The model gave good predictions of high correlation coefficient （R2=0.966）. The predictions by ANN are more accurate when compared with conventional multivariate regression analysis （MVRA）. In addition, calculation with ANN model indicates that temperature is the predominant parameter and ozone concentration is the lesser influential parameter in the pre-oxidation process of refractory gold ore. The ANN neural network model accurately estimates the ferric extraction during pretreatment process of RGC in gold smelter plants and can be used to optimize the process parameters.

Sulfidization regulation of cuprite by pre-oxidation using sodium hypochlorite as an oxidant

The direct sulfidization of cuprite is inefficient because cuprite is a copper-oxide mineral with a strong surface hydrophilicity.In this study,oxidant was used to modify cuprite surfaces to regulate the sulfidization of cuprite.Microflotation tests showed that the flotation recovery of pre-oxidized cuprite was nearly25% higher than that of direct sulfidization flotation,which indicates that the cuprite surface activity was enhanced after pre-oxidation by Cu(Ⅰ) species(weak affinity with sulfur ions) transformation to Cu(Ⅱ)species(strong affinity with sulfur ions).Zeta potential,scanning electron microscopy-energy dispersive X-ray spectroscopy,X-ray photoelectron spectroscopy,and time-of-flight secondary ion mass spectrometry results showed that pre-oxidation improved cuprite sulfidization and promoted the formation of copper-sulfide species on the cuprite surfaces.The mineral surface stability and thus,xanthate species adsorption on the cuprite surfaces were improved.The surface-adsorption measurements and infrared spectroscopy showed that a large amount of xanthate species was adsorbed onto the sulfidized cuprite surfaces after pre-oxidation,which enhanced the cuprite hydrophobicity and improved the cuprite flotation.

Complete stabilization of severely As-contaminated soil by a simple H2O2 pre-oxidation method combined with non-toxic TMT-15 and FeCl3·6H2O

The stabilization of severely As-polluted soil has been a challenge, especially for the extremely toxic As(Ⅲ) contaminants. In this study, soil with a high As concentration(26084 mg/kg) was availably stabilized by a H2O2 pre-oxidation assisted TMT-15(Na3S3C3N3 solution with a mass fraction of 15%) and FeCl3·6 H2O stabilization method. The results showed that the combination of the two stabilizers(i.e., TMT-15 and FeCl3·6 H2O) presented a better stabilization behavior than either stabilizer used individually. The use of the H2O2 pre-oxidation assisted TMT-15 and FeCl3·6 H2O stabilization approach not only converted the As(Ⅲ) to As(Ⅴ) but also reduced the toxic leaching concentration of As to 1.61 mg/L, which is a safe level, when the additions of TMT-15 and FeCl3·6 H2O were 2 mL and 0.20 g, respectively. Thus, using only a simple H2O2 pre-oxidation to combine clean stabilization with non-toxic stabilizers TMT-15 and FeCl3·6 H2O could render the severely As-contaminated soil safe for disposal in a landfill.

Reduction and subsequent carburization of pre-oxidation magnetite pellets

Magnetite is a kind of iron ore that is difficult to carburize.In order to improve the carburizing performance of magnetite pellet,pre-oxidation treatment was carried out,and the oxidation,reduction and carburization behaviors of magnetite pellet were investigated in this study.The magnetite pellet was oxidized in the air and carburized in CO-CO_(2)-H_(2) gas mixtures,the oxidation,reduction and carburization behaviors were demonstrated by detecting phase change,microstructure,carburizing index via thermogravimetry,X-ray diffraction(XRD),infrared carbon-sulfur analyzer,and scanning electron microscope(SEM).The results show that the dense magnetite particles inside pellet are oxidized to porous hematite particles,and the Fe_(3)O_(4) transforms to Fe_(2)O_(3) with high lattice defect concentration during the pre-oxidation process.Then the porous hematite particles and newly formed Fe_(2)O_(3) significantly promote the reduction efficiency.Porous metallic iron particles are produced in the reduction process.Finally,both high reduction efficiency and the porous structure of metallic iron particles dramatically enhance the carburization efficiency of pellet.High preoxidation temperature favors to the carburization of magnetite pellet.However,the carburized index decreases due to the recrystallization of iron oxide when the temperature extends to 1000℃.The optimum pre-oxidation temperature for magnetite pellet carburization is 900℃.

Study on contrast test of PPC pre-oxidation and coagulation for algae removal and deodorization

The effect of treating algae-bearing water and induced odor by use of permanganate potassium composite （PPC） pre-oxidation was investigated, and was compared with the effect of treatments by pre-chlorination, permanganate petassium pre-oxidation and simple coagulation. The results showed that simple coagulation and pre-chlorination were less effective in removing algae and its odor, whereas PPC pre-oxidation was the most effective in algae removal and deodorization. Upon oxidation with PPC, the cells of Oscillatoria agardhic were inactivated and some intra-cellular and extra-cellular components were released into the water, which may help the coagulation by their bridging effect. The efficient removal of algae by PPC pre-oxidation is believed to be the joint contribution of several mechanisms.

Effect of chloride ion on bacterial pre-oxidation of arsenic-containing gold concentrate

The bacterial pre-oxidation process of arsenic-containing gold concentrates and the bacterial activity under different chloride ion concentrations were studied by using a mixture of thermophilic strains TCJ domesticated in production.The experimental result shows that with different samples and leaching systems,the adaptability and Cl- tolerance of bacteria are different,and that appropriate chloride ion concentration is conductive to bacterial oxidation,while higher chloride ion concentration will inhibit the bacterial activity and affect the pre-oxidation performance.Under the present production conditions,TCJ can adapt to the changes of water quality in the source of water and its critical chloride ion tolerance value is 2.7 g/L.

Effect of pre-oxidation on strength and thermal shock behavior of ZrB_2-SiC-graphite ceramic composites

A novelty technique,namely,pre-oxidation,has been proposed to improve the strength and thermal shock behavior of ZrB2-SiC-graphite ceramic composites,which is a promising candidate for ultra-high temperature ceramics (UHTCs) in aerospace engineering. The composite is pre-oxidized at temperatures of 900 ℃ and 1100 ℃ for 1 h and 3 h in air. A theoretical model considering surface heat transfer has been given and analyzed. A water-quenching technique is adopted at different temperatures from 300 ℃ to 600 ℃ in order to investigate the thermal shock behavior of pre-oxidized composites. The critical thermal shock temperature improves more than 40% after pre-oxidizing at 1100 ℃ for 3 h. However,the composites strength is not improved as a result of the insensitivity to surface defects.

Effects of Pre-oxidation Conditions on Adsorption Performance of Activated Carbon Fibers

In order to investigate the effects of pre-oxidation conditions on adsorption performance of activated carbon fibers （ ACFs ）, electrospun polyacrylonitrile （ PAN ） fiber webs were adopted as precursors for preparing ACFs. Firstly, the webs were stabilized under different pre-oxidation conditions; secondly, the pre-oxidative fibers were chemically activated by high temperature treatment in nitrogen. Pre-oxidation temperature, heating rate, and treatment time are the main factors on affecting the adsorption performance of the ACFs. Scanning electron microscope （ SEM）, differential scanning calorimeter （DSC）, and Fourier transform infrared spectroscopy （FTIR） were used to characterize the structure and property of the pre-oxldatlve fibers, and the dynamic benzene adsorption capacity of benzene of ACFs was measured. The results indicate that the moderate pre-oxidation condition is necessary to prepare the ACFs with better adsorption capacity, and the optimal oxidation conditions are to increase from room temperature to 230 ~C with a heating rate of 0.75 ~C ~ min -1 held at the peak temperature for 30min.

The Application of KMnO_4 Pre-oxidation in Emergency Treatment of High-algae Source Water

Mobile emergency pilot water plant was used to carry out pilot study of KMnO4 pre-oxidation enhanced coagulation treating high-algae source water. Research showed that the optimal dosages of coagulant and KMnO4 in the process were 6 and 0. 4- 0. 6 mg / L respectively. Under the dosage,removal rate of water turbidity after precipitation rose by 11% than simple coagulation,and removal rate of algae rose by 15%. Removal rates of total amount of odor and GSM by the process were respectively 73% and 59%. The removal rate of total amount of algae by KMnO4 preoxidation was 40%,and removal effect of THM precursors was obvious.

Revisiting “Non-Thermal” Batch Microwave Oven Inactivation of Microorganisms

Over the last few decades there has been active discussion concerning the mechanisms involved in “non-thermal” microwave-assisted inactivation of microorganisms. This work presents a novel non-invasive acoustic measurement of a domestic microwave oven cavity-magnetron operating at fo = 2.45 ± 0.05 GHz (λo ~ 12.2 cm) that is modulated in the time-domain (0 to 2 minutes). The measurements reveal the cavity-magnetron cathode filament cold-start warm-up period and the pulse width modulation periods (time-on time-off and base-time period, where time-on minus base-time = duty cycle). The waveform information is used to reconstruct historical microwave “non-thermal” homogeneous microorganism inactivation experiments: where tap-water is used to mimic the microorganism suspension;and ice, crushed ice, and ice slurry mixture are used as the cooling media. The experiments are described using text, diagrams, and photographs. Four key experimental parameters are indentified that influence the suspension time-dependent temperature profile. First, where the selected process time > the time-base, the cavity-magnetron continuous wave rated power should be used for each second of microwave illumination. Second, external crushed ice and ice slurry baths induce different cooling profiles due to difference in their heat absorption rates. In addition external baths may shield the suspension resulting in a retarding of the time-dependent heating profile. Third, internal cooling systems dictate that the suspension is directly exposed to microwave illumination due to the absence of surrounding ice volume. Fourth, four separated water dummy-loads isolate and control thermal heat transfer (conduction) to and from the suspension, thereby diverting a portion of the microwave power away from the suspension. Energy phase-space projections were used to compare the “non-thermal” energy densities of 0.03 to 0.1 kJ·m-1 at 800 W with reported thermal microwave-assisted microorganism inactivation energy densities of 0.5 to 5 kJ·m-1 at 1050 ± 50 W. Estimations of the “non-thermal” microwave-assisted root mean square of the electric field strength are found to be in the range of 22 to 41.2 V·m-1 for 800 W.

Benchmark Dose Assessment for Coke Oven Emissions-Induced Mitochondrial DNA Copy Number Damage Effects

Objective The study aimed to estimate the benchmark dose(BMD)of coke oven emissions(COEs)exposure based on mitochondrial damage with the mitochondrial DNA copy number(mtDNAcn)as a biomarker.Methods A total of 782 subjects were recruited,including 238 controls and 544 exposed workers.The mtDNAcn of peripheral leukocytes was detected through the real-time fluorescence-based quantitative polymerase chain reaction.Three BMD approaches were used to calculate the BMD of COEs exposure based on the mitochondrial damage and its 95%confidence lower limit(BMDL).Results The mtDNAcn of the exposure group was lower than that of the control group(0.60±0.29 vs.1.03±0.31;P<0.001).A dose-response relationship was shown between the mtDNAcn damage and COEs.Using the Benchmark Dose Software,the occupational exposure limits(OELs)for COEs exposure in males was 0.00190 mg/m^(3).The OELs for COEs exposure using the BBMD were 0.00170 mg/m^(3)for the total population,0.00158 mg/m^(3)for males,and 0.00174 mg/m^(3)for females.In possible risk obtained from animal studies(PROAST),the OELs of the total population,males,and females were 0.00184,0.00178,and 0.00192 mg/m^(3),respectively.Conclusion Based on our conservative estimate,the BMDL of mitochondrial damage caused by COEs is0.002 mg/m^(3).This value will provide a benchmark for determining possible OELs.

7.63 m焦炉PROven系统固定杯更换的改进

对PROven系统固定杯的更换方案进行了分析,通过优化作业步骤,克服了危险性大、吊装难度高等难题,为焦炉单炭化室压力调节系统的维护作业提供了参考和借鉴。

关于7.63m焦炉上升管结石墨原因分析及治理对策的研究

德国伍德公司开发的7.63 m特大型复热式焦炉在生产过程中上升管根部结石墨严重,成为制约焦炉正常生产的突出矛盾。从焦炉加热水平、焦炉加热制度、装煤量等因素综合分析影响上升管根部结石墨的成因,研究制定降低上升管根部结石墨速率的方法及自动清除上升管根部石墨的装置,达到避免因上升管根部结石墨影响焦炉生产的目的。

提高马钢焦炉K_(3)系数的生产实践

通过分析影响马钢焦炉K_(3)系数的因素,采取优化焦炉生产组织、提高设备保产能力、加强炼焦过程监控、全面对标找差、强化炉体维护等具体措施,使得焦炉K_(3)系数得到了稳定提升。

枸杞烘干箱温度场优化及仿真

目的:提高枸杞干制品品质。方法:采用标准Realizable k-ε湍流模型进行理论分析,利用Fluent软件仿真运算并结合实验验证,探究烘干室换热温度场分布规律,并对换热参数进行优化。以温度均匀性系数以及温度分布云图为评价标准,分析换热板入口流速、换热板流道宽度、换热板流道高度、换热板间距对烘干箱温度场均匀性的影响。结果:对烘干室结构参数进行优化后,温度云图显示出的高温区面积大且比较集中,两端和中间的温度梯度小。优化后的温度标准偏差比优化前降低了0.64%,模拟值与试验值的整体趋势大体相同,其误差值为2.56%。结论:枸杞烘干温度分布均匀性最佳的工艺条件为热水入口流速0.18 m/s,流道高度22 mm,流道宽度35 mm,换热板间距85 mm。

干熄焦放散气代替部分焦炉加热燃气的燃烧过程模拟研究

以JN-70型焦炉混合煤气加热为研究对象,利用Ansys Fluent软件对干熄焦放散气代替部分燃气的燃烧过程进行稳态模拟研究,分析了干熄焦放散气的配入对立火道内压力场、温度场、浓度场的影响。结果表明,在空气中配入5%干熄焦放散气时,立火道的最高温度不变,高向加热的均匀性有所提高,且烟气中的NO_(x)浓度变化不大。因此,焦炉燃烧室配入干熄焦放散气替代部分燃气具有一定的可行性。

试样厚度对105℃烘箱法稻谷含水率定值的影响

在使用105℃烘箱法对稻谷含水率定值的过程中,分别对不同种类、不同含水率的稻谷样品,采用不同的试样厚度进行烘干,研究分析了试样厚度对稻谷含水率定值的影响。试验结果表明,试样厚度应介于2~3mm之间。

小麦系统粉发酵和炉内起涨特性及其与面包烘焙品质关系

以19个小麦加工系统粉样为材料,利用成熟度曲线仪、炉内起涨记录仪研究了其发酵和炉内起涨特性,并分析其与面包烘焙品质的关系。结果表明,面粉生产工艺中各系统粉流的发酵特性、炉内起涨特性及烘焙品质存在明显的差异,即前路粉和重筛面粉具有较好的发酵能力和炉内起涨特性,后路粉的发酵能力和炉内起涨特性相对较差,皮磨系统粉流的面包烘焙品质整体优于心磨系统。成熟度曲线仪测定的面团水平和弹性,炉内涨大仪测定的面团体积和面包体积等与面包品质存在显著正相关性。