Modeling and Analysis on Production Yield and Energy Consumption of Pelleting Process

The existing studies on the pelleting process were reviewed, and then the forming process of pelleting was introduced. Furthermore, the models describing the production yield and energy consumption of pelleting were presented. Based on the models, the influence of the pelleting structure parameters, die speed on the production yield and energy consumption were discussed. The results showed that larger pellet mill was preferred and the proper speed of the die should be selected to increase the production yield and reduce the energy consumption.

Mathematical model of the direct reduction of dust composite pellets containing zinc and iron

Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.

CFD modeling of reaction and mass transfer through a single pellet: Catalytic oxidative coupling of methane

In this study a mathematical model of a small scale single pellet for the oxidative coupling of methane（OCM）over titanite pervoskite is developed.The method is based on a computational fluid dynamics（CFD）code which known as Fluent may be adopted to model the reactions that take place inside the porous catalyst pellet.The steady state single pellet model is coupled with a kinetic model and the intra-pellet concentration profiles of species are provided.Subsequent to achieving this goal,a nonlinear reaction network consisting of nine catalytic reactions and one gas phase reaction as an external program is successfully implemented to CFD-code as a reaction term in solving the equations.This study is based on the experimental design which is conducted in a differential reactor with a Sn/BaTiO3 catalyst（7-8 mesh） at atmospheric pressure,GHSV of 12000 h-1,ratio of methane to oxygen of 2,and three different temperatures of 1023,1048 and 1073 K.The modeling results such as selectivity and conversion at the pellet exit are in good agreement with the experimental data.Therefore,it is suggested that to achieve high yield in OCM process the modeling of the single pellet should be considered as the heart of catalytic fixed bed reactor.

饲料颗粒压缩成型力学行为表征研究

为了解不同湿热处理条件对饲料制粒过程力学行为的影响,利用自主搭建的单颗粒压缩(single pellet press,SPP)试验平台,完成了15%、20%和25%水分饲料在70、80、90℃下经过1、3、5 min热处理的颗粒压缩成型试验。根据应力变化率将饲料的压缩曲线划分为压杆入模、挤压段、屈服段和压紧段4个阶段;采用应变强化非线性弹性元件和牛顿黏滞体并联的方式建立了表征压紧段力学行为的非线性弹塑黏性流变模型,模型的决定系数R2>0.98,平均相对百分误差(e)范围为0.52%~7.13%。湿热处理条件对压紧段流变模型参数的影响分析表明:随着饲料水分和热处理温度的升高,饲料压缩变形中塑性变形所占比例增大;而随着热处理时间的延长,弹性变形比例增大。饲料水分的提高有利于湿热处理后饲料中淀粉、蛋白质等黏结剂成分的表达,高水分饲料的压缩特性对温度的敏感性下降。

有效导热系数模型在核热推进反应堆的应用

核热推进反应堆一般选用氢气做工质,通过堆芯燃料颗粒加热到高温,以实现较高的发动机推力和比冲。基于美国核热推进火箭发动机的典型堆芯设计方案,在高温气冷堆球床有效导热系数模型的基础上,对更小直径的燃料颗粒与更高温度的氢气工质组成的颗粒床混合介质进行了初步计算,获得了燃料种类、颗粒直径、孔隙率等关键参数对堆芯导热能力的影响规律。同时,考虑到燃料颗粒采用多种材料复合而成的包覆型结构,采用均匀化方法对不同材料的基础热物性进行了等效计算,从而为有效导热系数模型提供固体域平均导热参数。从计算结果来看,颗粒直径和孔隙率对有效导热系数的影响更大,特别是高温条件下辐射换热作用占主导,使得材料自身导热系数的贡献很小。

基于DEM的3种匀盘结构的玉米种子丸粒化数值模拟

【目的】解决种子丸粒包衣质量不高、种粉间混合均匀度差的问题。【方法】分析3种匀盘结构的丸粒化机制,模拟玉米种子丸粒化过程;基于离散元软件EDEM建立玉米种子丸粒化的仿真模型,将离散系数作为评价指标研究3种匀盘结构的转速、振动频率、振动幅度对种粉间混合均匀度的影响;通过Design-Expert软件建立玉米种子离散系数的二阶回归方程进行方差分析。【结果】3种匀盘结构的最优工艺参数组合分别为:匀盘Ⅰ的转速为50 r/min,振动频率为10 Hz,振动幅度为6 mm;匀盘Ⅱ的转速为60 r/min、振动频率为15 Hz,振动幅度为6 mm;匀盘Ⅲ的转速为70 r/min,振动频率为20 Hz,振动幅度为8 mm。【结论】当匀盘Ⅰ的转速为56.3 r/min、振动频率为11.5 Hz,振动幅度为5.8 mm时,玉米种子丸粒化效果最优,为玉米种子包衣技术提供理论依据自我评价。

Cooling process of iron ore pellets in an annular cooler

A 3-D mathematical model was presented for the cooling process of iron ore pellets based on the laws of mass, momentum, and heat transfer. The flow, pressure, and temperature fields were obtained by numerical simulation with the commercial software FLUENT. In order to verify the model, a mass and energy balance field test was systematically carried out on an annular cooler in Shougang Mining Company. The maximum relative errors of temperature, pressure, and velocity between computational and testing results are 2.87%, -8.11%, and 7.14%, respectively, indicating the validity of the model. Further, the effects of process parameters, such as pellet diameter, bed thickness, air velocity, and temperature, on the pellet bed temperature profiles were studied.

Reduction kinetics of iron oxide pellets with H_2 and CO mixtures

Reduction of hematite pellets using H2-CO mixtures with a wide range of H2/CO by molar （1：0, 3：1, 1：1, 1：3, and 0：1） at different reducing temperatures （1073, 1173, and 1273 K） was conducted in a program reducing furnace. Based on an unreacted core model, the effective diffusion coefficient and reaction rate constant in several cases were determined, and then the rate-control step and transition were analyzed. In the results, the effective diffusion coefficient and reaction rate constant increase with the rise in temperature or hydrogen content. Reduction of iron oxide pellets using an H2-CO mixture is a compound control system; the reaction rate is dominated by chemical reaction at the very beginning, competition during the reduction process subsequently, and internal gas diffusion at the end. At low hydrogen content, increasing temperature takes the transition point of the rate-control step to a high reduction degree, but at high hydrogen content, the effect of temperature on the transition point weakens.

Mathematical simulation of direct reduction process in zinc-bearing pellets

A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.

Water Transport Models of Moisture Absorption and Sweat Discharge Yarns

An important property of moisture absorption and sweat discharge yarns is their water transport property. In the paper, two water transport models of moisture absorption and sweat discharge yarns were developed to investigate the influence factors on their wicking rate. In parallel Column Pores Model, wicking rate is determined by the equivalent capillary radius R and length of the capillary tube L. In Pellets Accumulation Model, wicking rate is decided by the capillary radius r and length of the fiber unit assemble L0.

Kinetics Analyzing of Direction Reduction on Manganese Ore Pellets Containing Carbon

Using high temperature carbon tube furnace, reduction of manganese ore pellets containing carbon was investigated. The reaction was divided into two stages at five minutes after reaction, and the kinetics model of reduction process was established. The experimental results showed that, the reaction rate in the earlier stage was controlled by the chemical reactions between FeO, MnO and carbon reductant, and the activation energy was 28.85 KJ/mol. In the later stage, as the carbon reductant replaced by CO, the reaction rate was controlled by CO-diffusing in solid products, and the cor- responding activation energy was 86.56 KJ/mol. Reaction rate of the later stage was less than the earlier one.

Thermal performance and reduction kinetic analysis of cold-bonded pellets with CO and H2 mixtures

Cold-bonded pellets, to which a new type of inorganic binder was applied, were reduced by H2~CO mixtures with different HJCO molar ratios （1：0, 5：2, 1：1, 2：5, and 0：1） under various temperatures （1023, 1123, 1223, 1323, and 1423 K） in a daermogravimetric analysis appaxatus. The effects of gas composition, temperature, and binder ratio on the reduction process were studied, and the microstxucture of re- duced pellets was observed by scanning electron microscopy-energy-dispersive spectrometry （SEM-EDS）. The SEM-EDS images show that binder particles exist in pellets in two forms, and the form that binder particles completely surround ore particles has a more significant hin- der effect on the reduction. The reduction equilibrium constant, effective diffusion coefficient, and the reaction rate constant were calculated on the basis of the unreacted core model, and the promotion effect of temperature on reduction was further analyzed. The results show that no sintering phenomenon occurred at low temperatures and that the increasing reaction rate constant and high gas diffusion coefficient could main- tain the promotion effect of temperature; however, when the sintering phenomenon occurs at high temperatures, gas diffusion is hindered and the promotion effect is diminished. The contribution of the overaJl equilibrium constant to the promotion effect depends on the gas composition.

Moving behavior of pellets in a pellet shaft furnace

The downward moving behavior of pellets in a 8 m2 pellet shaft furnace with an internal vertical air channel and a drying bed was studied by means of a visualized model(1-15) and a top model(1-1).The visualized model experiment shows that the downward movement of pellets can be regarded as plug flow approximately inside the furnace except for the lower region of cooling zone due to the influence of the drained hopper.The top model experiment reveals that the pellet sizes increase along the moving direction because of the percolation phenomenon,which results in a decrease of the resistance coefficient and an increase of the gas flow rate from the furnace wall toward the furnace center.

带式焙烧机操作参数对球团强度影响研究及源头减排NOx措施

基于SPSS统计分析软件,对带式焙烧机球团矿抗压强度与各工艺参数进行相关性分析,并使用线性回归功能建立回归模型,根据模型计算结果,通过降低焙烧温度,源头治理带式焙烧机脱硫脱硝入口烟气NOX浓度,同时确保球团矿抗压强度不下降。

虾饲料颗粒对自动饲喂系统提升管管壁的磨损研究

实验针对虾饲料颗粒对气力输送自动饲喂系统管道的磨损开展研究。基于气固两相流理论,建立计算流体模型与离散元模型,通过计算流体力学与离散单元法耦合求解,探究气力输送自动饲喂系统提升管角度与入口风速对弯管内法向与切向磨损的影响。结果表明:提升管角度对法向和切向累积接触能影响不大,较大提升管角度可显著减小管道切向磨损面积;入口风速对法向和切向累积接触能影响较大,且较小入口风速可显著降低管道法向磨损面积。研究结果可为虾饲料自动饲喂系统的设计优化提供理论指导。

锌对球团矿还原反应的影响

利用浸泡法制得富锌球团矿,测定不同温度下球团矿和富锌球团矿还原失重量随时间变化,建立了球团矿气-固反应的未反应核模型,研究了锌对球团矿还原动力学的影响。结果表明,本实验中,球团矿还原反应控速环节为界面化学反应;球团矿和富锌球团矿的化学反应活化能分别为54.34、54.38 kJ/mol,表明富锌对球团矿还原的阻碍作用十分有限;锌对球团矿还原的影响主要表现在:①表面形成的ZnO壳阻碍球团矿还原,②内部锌蒸气发生循环反应起到催化作用。当温度较低(900℃)时,表面富集的ZnO壳影响大,阻碍球团矿的还原;温度在950~1000℃,锌蒸气催化作用显著,削弱或抵消了ZnO壳的阻碍作用;随着温度继续升高,由于锌蒸气还原FeO反应是放热反应,锌蒸气催化作用降低甚至可忽略不计。

基于COMSOL的全陶瓷微封装燃料元件建模与传热分析

采用COMSOL软件构建了全三维全陶瓷微封装(FCM)燃料元件模型,提出了一种FCM燃料元件内TRISO颗粒随机分布的高效建模方法,可以实现较高填充率的颗粒弥散填充。分析了不同颗粒填充率(35%、40%和45%)下以及不同颗粒随机分布下FCM燃料元件的温度分布特性。结果表明:FCM燃料元件中心区域温度高,沿径向温度降低;TRISO燃料颗粒特别是燃料核芯的温度明显高于周围基体的温度,温差可达130 K甚至更高,其中最大的温度梯度出现在Buffer层;在相同线功率下,随着颗粒填充率的增加,燃料芯块的最高温度降低,平均温度略有升高;受到颗粒分布随机性的影响,当颗粒填充率减小时,平均温度和最高温度分布的离散程度均增加,但总体上颗粒随机分布对燃料芯块平均温度的影响较小。

球团焙烧过程工艺模拟研究及应用——链箅机—回转窑与带式焙烧机工艺模拟

工艺设计的合理性与先进性是球团厂达产达效的根本,而工艺模拟可让设计者对工艺系统中的质量流与能量流以及两者间的相互影响关系的认识更加清晰明了。基于球团料层热质传输模型开发了链箅机—回转窑和带式焙烧机两种工艺模拟流程,并详细阐述了两种工艺模拟流程的步骤、控制策略以及应用方向,同时给出了实例流程的模拟结果以及与球团试验结果的对比。对比结果说明,模拟工艺可以使工艺设计从经验化转变到数字化,可为工艺优化和生产操作提供指导。

预热竖窑气固传热与水分蒸发数值模拟

通过对一种新型预热竖窑的预热脱水研究,建立了气固两相传热和水分蒸发收缩核模型.在气体速度分别为10,15和20 m/s与993 K的温度条件下,针对预热竖窑的气体温度分布,以铬铁球团为主的固体混合物料温度分布和水分蒸发情况进行模拟分析.结果表明,该预热竖窑在20 m/s与993 K的条件下,固体物料温度达到850 K以上并实现球团干燥,可以满足物料预热的温度和含水量要求.通过合理的预热工序,防止了冶炼过程中因含水率过高导致球团出现爆裂影响生产安全的问题,也满足了企业对冶炼过程中产生的高温尾气的余热利用的目标.

环模制粒挤压过程力学建模及影响因素分析

该文旨在通过研究环模制粒机挤压过程受力状况为其节能降耗及优化设计提供一定的参考。根据环模制粒机制粒成形过程与机理的分析和对环模系统受力状况的研究,建立了环模扭矩力学模型,推导出最大物料挤压高度及最大环模扭矩的计算公式;以力学模型为基础,分析了泊松比、摩擦系数等物料特性及环模、压辊系统的结构参数对环模扭矩的影响规律。研究结果表明,物料特性对制粒能耗影响很大;在一定范围内减小模孔长径比、减小压辊直径有利于降低能耗;而采用大尺寸的环模与压辊不仅可以提高产量,同时还可以降低能耗。该研究对于降低环模制粒机的能耗具有重要意义,并可为相关的试验提供理论依据。