A Model for Predicting the Erosion Rate Induced by the Use of a Selective Catalytic Reduction Denitrification Technology in Cement Kilns Flue Gas

Selective catalytic reduction(SCR)is a technology by which nitrogen oxides are converted with the aid of a catalyst into diatomic nitrogen and water.It is known that the catalyst can be easily eroded if a cement kiln with a high-dust content is considered.To understand this process,numerical simulations have been carried out considering a single catalyst channel in order to study the collision and erosion of fly ash and catalysts at meso scale.Based on a response surface methodology,the effects of five factors on the erosion rate have been studied,namely,the catalyst particle velocity,the particle size,the particle concentration,the incidence angle and the catalyst porosity.The results show that the influence of particle velocity,particle size and particle concentration is statistically significant and the particle size and incidence angle have a significant effect on the erosion rate.A quadratic polynomial prediction model for the erosion rate of honeycomb catalysts in cement kiln SCR reactors is finally proposed to support the future optimization of these systems.

An Experimental and Numerical Study on the Cleaning of Pleated Bag Filters Using Low-Pressure Pulsed-Jets

Pulsed-jet cleaning is recognized as the most efficient method to regenerate bag dust collectors traditionally used in industrial processes to control the emission of particulates.In this study,non-woven needle felt filter bags with and without a film coating material have been analyzed considering different geometries(different number N of pairs of pleated filter bag sides)in the frame of dedicated low-pressure pulsed-jet cleaning experiments.The flow structure inside the bag and the response characteristics of its wall have also been analyzed numerically through a computational fluid-dynamics/structural-dynamics(CFD-CSD)unidirectional fluid-solid coupling method.As shown by the experiments,the peak pressure(P_(0))on the wall of the filter bag with N=8 and 12 is higher,which indicates dust can be removed more effectively in these cases.The peak pressure on the wall increases first and then decreases along the direction of the bag length,while the peak pressure of the pleated filter bag with nonwoven needled felt film coating is greater than that without film coating.A comprehensive analysis of the time variation of acceleration,deformation,strain,stress and other factors,has led to the conclusion that the pleated filter bag with N=12 would be the optimal choice.

Y型褶式洁净滤袋多元结构参数对其过滤阻力影响的CFD模拟研究

为研究褶式滤袋褶数增加引起的褶间距变化对滤袋过滤性能的影响,提出一种新型Y型褶式滤袋,研究了多元几何特性对过滤压降的影响。利用GeoDict软件构建聚酯纤维滤料三维过滤介质模型,用于Y型褶式滤袋的宏观数值模拟研究,基于响应曲面法探究Y型结构下褶式滤袋多元结构参数对其过滤性能的影响。研究结果表明,Y型褶式滤袋相较于常规8,16褶滤袋过滤压降均有所降低。Y型褶式滤袋(褶数NY=8,开口角α=30°,内凹直径d=228 mm)的过滤面积相较于常规8褶滤袋增加58.04%,出口速度分布均匀性提高21.23%;其出口速度分布均匀性相较于常规16褶滤袋提高28.51%。Y型褶式滤袋的最优结构参数为NY=12,α=20.17°,d=240.18 mm,过滤压降达到最小值136.67 Pa。

CFD–DEM simulation of particle deposition characteristics of pleated air filter media based on porous media model

In this study, the three-dimensional physical model of pleated air filtration media was simplified to porous media model, and the calculation parameters of porous media were obtained based on experimental data. The model of V-shaped pleated air filter media is constructed, the height of the media pleat is 50 mm and the pleat thickness is 4 mm, the pleat angle is 3.7°. The Hertz-Mindlin contact model was modified by Johnson Kendall Roberts (JKR) adhesion contact model. The deposition process of particles in media was simulated based on computational fluid dynamics (CFD) theory and discrete element method (DEM). Results show that the CFD–DEM coupling method can be effectively applied to the macro research of pleated air filter media. The particles will form dust layer and dendrite structure on the fiber surface, and the dust layer will affect the subsequent air flow organization, and the dendrite structure will eventually form a “particle wall”. The formation of the “particle wall” will prevent the particles from moving further in the fluid domain, which makes area of pleated angle become the “low efficiency” part about the particle deposition. Compared with area of pleated angle, the particles are concentrated in the opening area and the middle area of the pleated to agglomerate and deposit.

Numerical investigation of non-spherical particle deposition characteristics on filter media

In the building environment,PM2.5 seriously affects people’s health and quality of life,so it is necessary to study the particle deposition characteristics.In addition,it is essential for a thorough investigation of the dust removal mechanism to understand the non-spherical particles deposition characteristics.The stacking angle experiment was used to calibrate the discrete element simulation parameters.And four simulation methods(CFD-DPM,CFD-DEM,API interface loading drag model based on EDEM software and EDEM simulation)were used to numerically simulate the non-spherical particles deposition characteristics.The optimal simulation method EDEM was applied to study the non-spherical particles deposition characteristics in filter media,which saves the calculation time obviously.On this basis,the particle parameters on the particle deposition characteristics of filter media were investigated.The results show that the deposition rate of non-spherical(special shape)particles with the same volume is basically consistent on the filter media,hence it is more realistic that the dust actual shape is simplified into the triangular-shaped particles.As the particle size increases,the number of deposited particles on the filter media decreases.And the larger the particle size,the more dispersed the distribution.It has a significant impact on the number of particles deposited on the filter media when the particle velocity is 0.1 m/s.The particle deposits to the lower part of the filter media in the form of a parabola and deviates from the outlet seriously at 0.1 m/s.Moreover,it has little effect on the number of particle deposition at the other velocities,and most particles are deposited on the upper part of the filter media with the increase of particle velocity.

Effect of Refresh Time on XeF2 Gas-assisted FIB Milling of GaAs

Focused ion beam (FIB) machining can be used to fabricate gallium arsenide-based devices, which have a surface fnish of several nanometers, and the FIB machining speed and surface fnish can be greatly improved using xenon difuoride (XeF2) gas-assisted etching. Although the refresh time is one of the most important parameters in the gas-assisted etching process, its efect on the machining quality of the surface fnish has rarely been studied. Therefore, in this work, we investigated the efect of the refresh time on the etching process, including the dissociation process of XeF2, the refresh time dependency of the sputter in yield under diferent incident angles, and the surface fnish under diferent refresh times. The results revealed that a selective etching mechanism occurred at diferent refresh times. At an incidence angle of 0°, the sputtering yield increased with the refresh time and reached its maximum value at 500 ms;at an incidence angle of 30°, the sputtering yield reached its minimum value at a refresh time of 500 ms. For surface roughness, the incident angle played a more important role than the refresh time. The surface fnish was slightly better at an incidence angle of 30° than at 0°. In addition, both F and Xe elements were detected in the processed area: Xe elements were evenly distributed throughout the processing area, while F elements tended to accumulate in the whole processing area. The results suggest that the optimum surface can be obtained when a larger refresh time is employed.

烧结烟气活性炭脱硝机制

烧结烟气氮氧化物(NO_(x))排放占钢铁行业NO_(x)排放总量的50%以上,随着环保法规的日益严格,现有及新建烧结机只有装设烟气脱硝装置才能满足排放法规的NO_(x)排放要求。而活性炭微孔丰富、比表面积大、吸附能力强,低温时即可同时脱除烟气中的SO_(2)、NO_(x)、粉尘及其他有害气体。因此,低温烧结烟气活性炭脱硝具有显著的特点及技术优势,但活性炭脱硝易受烟气中SO_(2)和H_(2)O的影响。本工作综述了低温烟气活性炭脱硝机理,主要包括物理吸附、化学吸附及选择性催化还原反应。烟气中氧气的存在起氧化作用,能有效提高活性炭的脱硝率;而SO_(2), H_(2)O和NO存在竞争吸附作用会降低活性炭的脱硝性能,详述了SO_(2)和H_(2)O对活性炭脱硝的抑制作用及影响。阐述了活性炭负载过渡金属、稀土金属等金属氧化物化学改性对脱硝性能的促进作用及其脱硝机理,并对多元金属的负载进行了介绍;最后对烧结烟气活性炭低温脱硝技术进行了展望。要点:(1)综述了活性炭脱硝机理。(2)阐述了活性炭脱硝的影响因素。(3)详述了活性炭负载过渡金属(稀土金属)氧化物对脱硝的提高作用及机理。(4)总结并展望了低温烧结烟气活性炭脱硝技术的研发,并提出了建议。

铁矿石尾矿粉催化还原NO的实验研究

以马鞍山钢铁集团南山矿铁矿石尾矿为主要原料制备无载体催化剂,对其进行了XRF,BET和XRD表征,并于电加热石英玻璃管固定床中实验研究了催化剂对NH3还原NO的催化活性.结果表明,用铁尾矿所制催化剂在反应温度500-600℃下具有良好的催化活性,600℃时催化还原率达97.5%,且粒径越小催化还原率越高;氧含量对催化还原率有较大影响,350℃时增加氧含量可提高催化还原率,500℃时增加氧含量会降低催化还原率;氧化铁作为主要活性组分,在催化剂中含量越高催化还原率越高,但氧化铁高温时易烧结,会降低催化还原率.

活性炭混合钢渣烧结烟气脱硫脱硝实验研究

采用混合法用钢渣与活性炭制备混合钢渣活性炭吸附剂,对其进行XRF, BET, SEM和FT-IR等表征,于可编程电加热固定床反应器中进行模拟烧结烟气脱硫脱硝实验,考察反应温度、SO_2浓度及[NH_3]/[NO]浓度比、O_2含量等因素对混合钢渣活性炭的吸附及催化性能的影响。结果表明,模拟烧结烟气中SO_2初始浓度0.06vol%, NO初始浓度0.04vol%, O_2含量15vol%及反应温度120℃条件下,最高脱硫脱硝率分别为79%和34%。按浓度比[NH_3]/[NO]=1通入还原剂NH_3时,脱硫脱硝率均升高,表明钢渣具有一定催化还原作用。脱硝率随反应温度升高而下降,O_2含量提高有利于混合钢渣活性炭对SO_2和NO的吸附。掺混钢渣降低了吸附剂的比表面积,但钢渣中含一定量Fe2O3,具有一定催化还原作用,有利于NO吸附。同时,加入钢渣也是对固废资源的合理利用,达到"以废制污"的目的。

无纺针刺毡滤料褶式滤袋的阻力特性分析

以滤袋褶形结构的高宽比ɑ为优化对象,建立不同褶数下的褶式滤袋结构的三维几何模型,采用多孔介质及标准k-e双方程湍流模型对褶数N=8, 12, 16, 20, 24、袋长L=2.5, 3.0, 3.5 m的褶式滤袋进行气相流场的数值模拟。结果表明,相同进口风速下,褶数N=12 (ɑ=1.12)的褶式滤袋的过滤阻力最小,过滤阻力随进口风速的增长率明显小于其它4种褶数,袋室内的流场分布更均匀,对不同处理风量的工况适应性较好。不同袋长的褶式滤袋除尘器的过滤阻力均随进口风速增加呈二次曲线式增长,处理风量较小时,褶式滤袋越长系统压损越小,但褶式滤袋过短或过长时因系统压损较大均不适宜在高风量下运行,其中L=3.0 m的滤袋其垂直方向的压差梯度较小,袋室内的压力及速度分布更均匀,有利于保护滤袋,降低运行能耗。

高湿黏性颗粒在聚四氟乙烯微孔膜滤料表面沉积特性的数值模拟

基于聚四氟乙烯(PTFE)微孔膜滤料扫描电镜(SEM)图像,建立PTFE微孔膜滤料微观结构模型,采用计算流体力学和离散单元法(CFD-DEM)耦合的方法对黏性颗粒在微孔膜滤料表面沉积特性进行模拟,引入液桥力模型,忽略范德华力的作用,统计计算域内颗粒的受力情况,分析了不同表面能条件下3~6μm粒径颗粒在微孔膜滤料表面的沉积特性,将模拟结果与黏附效率的经验公式进行对比。结果表明,黏附效率与经验值、颗粒受力与液桥力模型的相对误差均在6%以内,CFD-DEM耦合计算方法可用于模拟不同环境湿度条件下的颗粒沉积;过滤风速、粒径与黏性是影响沉积形态的重要因素,提高过滤风速及增大颗粒粒径与黏性,颗粒更易在滤料表面形成稳定的树突结构,黏附效率及含尘压降增加。环境相对湿度影响两物体间液桥体积,接触力影响颗粒沉积,当增加表面能与液桥体积时,接触力及液桥力均相应增加,根据受力平衡原理,环境相对湿度对颗粒沉积影响很大。

新型结构微孔膜滤板清灰性能的数值模拟

为探究不同影响因素对旋转脉冲清灰微孔膜除尘器所使用的新型结构微孔膜滤板清灰性能的影响,采用CFD方法对其脉冲清灰流场进行了数值模拟,通过与文献实验数据比较,验证了数值计算模型的准确性,考察了喷吹压力、喷吹高度、喷吹管末端与入口端直径比、喷孔直径及滤板长度对新型结构微孔膜滤板壁面平均峰值压力的影响,并对滤板侧壁压力分布随喷吹时间变化的规律进行了研究。设计了五因素三水平正交试验,以滤板平均峰值压力为设计指标,分析获得最佳的清灰系统参数。结果表明,增大喷吹压力、喷孔直径及减小喷吹管末端与入口端直径比均可以提高滤板壁面平均峰值压力,有利于提高新型结构微孔膜滤板的清灰性能;喷吹高度对滤板壁面平均峰值压力的影响较小,但提高喷吹高度可有效减小滤板顶部的负压,顶部负压减小有利于提高微孔膜滤板的使用寿命;滤板侧壁压力会随喷吹时间变化而不断变化,使不同时刻下滤板侧壁的压力分布不同;滤板长度逐渐增加会对新型结构微孔膜滤板中下部的清灰效果产生不利影响。

Effect of interaction between different CeO_(2)plane and platinum nanoparticles on catalytic activity of Pt/CeO_(2)in toluene oxidation

The plane exposure of support vitally affects the catalytic performance of the catalyst.In this work,CeO_(2)nanorods((110)plane exposure),nano-octahedrons((111)plane exposure)and nano-cubes((100)plane exposure)were prepared as the supports of Pt/CeO_(2)samples to investigate the effect of CeO_(2)plane exposure on total toluene oxidation.Characterizations reveal that the(110)plane of CeO_(2)is more helpful to the dispersion of Pt species,followed by(111)face.The improved dispersion of Pt species can enhance the metal-supports interaction,which promotes the electron transfer of CeO_(2)carrier to Pt nanoparticles and the adsorption-activation of O_(2),thereby facilitating the total oxidation of toluene via the Langmuir-Hinshelwood(L-H)mechanism.Therefore,Pt/CeO_(2)-r(nanorods)sample expresses excellent catalytic performance of toluene oxidation.Finally,the procedure of toluene total oxidation was studied by in-situ diffuse reflectance infrared Fourier transform(DRIFT)spectroscopy.We expect that this work can contribute to the development of an effective sample for the decomposition of volatile organic compounds(VOCs).

褶型纤维过滤介质压力损失的多尺寸模拟

统筹考虑纤维结构特性、纤维排布及纤维层数等因素,基于MATLAB编写控制程序,建立褶型纤维过滤介质微观尺寸模型,并计算过滤介质固体体积分数α,采用数值模拟方法获取微观尺寸下过滤风速v与压力损失Δp之间的数学关联式,进而获取介质的粘性阻力系数C1。在此基础上,建立褶型纤维过滤介质宏观尺寸模型,基于微观尺寸模拟得到的α及C1,采用数值模拟的方法得到宏观尺寸下迎面风速μ与Δp之间的数学关联式,并将数学关联式与多个经验公式进行对比。结果表明,褶型纤维过滤介质内纤维排列方式及介质厚度对Δp有影响,但对C1等性质参数影响不大;微观尺寸研究得到的参数可以为宏观尺寸研究提供指导,微观结构与宏观结构性质参数可以沿用。本研究结果对拓展纤维过滤介质的研究方法及优化其结构具有重要理论及实际意义。