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.

空气过滤用静电纺纳米纤维膜的制备及性能研究

为了开发高效低阻的空气过滤用纤维膜,采用静电纺丝的方法制备了聚丙烯腈(PAN)静电纺纳米纤维膜。通过改变PAN浓度及静电纺丝时长,得到了不同形貌及过滤性能的静电纺纳米纤维膜。结合场发射扫描电子显微镜等表征方式和过滤性能测试台对静电纺纳米纤维膜形貌及过滤性能进行测试与分析,获得性能最优的PAN静电纺纳米纤维膜的制备参数如下:PAN浓度为9wt%,静电纺丝时长为5.0 h。此条件下制备的静电纺纳米纤维膜厚度为0.0240 mm,平均纤维直径为396 nm,PM2.5过滤效率为99.99%,过滤压降为67 Pa,品质因子最高,为0.137 Pa^(-1)。

高湿黏性颗粒在PTFE滤料表面的沉积规律研究

过滤过程中颗粒物在滤料上的沉积形貌对除尘器过滤性能及清灰频率的确定至关重要。为深入了解颗粒物在聚四氟乙烯(PTFE)滤料表面的沉积规律,搭建了一套过滤实验系统,基于该实验系统对比了过滤时间、粉尘浓度、过滤风速和含水率对颗粒单位面积沉积质量及粉尘层平均厚度的影响,探究了两种沉积速率的适用性及高湿黏性颗粒的黏附效率,并推导了不同含水率粉尘层的厚度分布模型。通过建立沉积粉尘层内部颗粒间的受力模型,对颗粒的受力运动情况进行分析,后续沉积颗粒自身重力对先前沉积颗粒的压缩作用不可忽略,颗粒的运动趋势由上层粉尘层重力、气流对颗粒的曳力及颗粒间黏附力共同决定。实验结果表明,高湿粉尘较干燥粉尘单位面积沉积质量有所降低,随着粉尘含水率增大,粉尘层平均厚度和单位面积沉积质量呈先减小后增大的趋势;高湿粉尘的沉积受颗粒间黏附力大小的影响,粉尘含水率为10%时质量沉积速率和黏附效率最小;粉尘含水率为9%和13%时粉尘层均匀性较干燥粉尘层下降,当高湿颗粒间的黏附力可以抵抗上层重力的压缩作用时颗粒滑动减少,粉尘层结构均匀。含水率为10%~12%时粉尘层均匀性稳定,且含水率为10%时最佳。

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.

ftr82 is necessary for hair cell morphogenesis and auditory function during zebrafish development

Damages of sensory hair cells(HCs)are mainly responsible for sensorineural hearing loss,while the pathological mechanism remains not fully understood due to the many potential deafness genes unidentified.ftr82,a member of the largely TRIMs family in fish,has been found specifically expressed in the otic vesicle while its function is still unclear.Here,we investigate the roles of ftr82 in HC development and hearing function utilizing the zebrafish model.The results of in situ hybridization illustrate that ftr82 is always restricted to localize in otic vesicles at different stages.The defects of HCs are observed both in ftr82 morphants and mutants,including significantly decreased crista HCs,shortened cilia as well as remarkably reduced functional HCs in neuromasts,which could be successfully rescued by co-injection of exogenous ftr82 mRNA.The behavior assay of startle response indicates that larvae lacking of ftr82 exhibits lower sensitivity to external sound stimuli.Further research reveals that the loss of HCs is mainly caused by cell apoptosis mediated by caspase-3 activation.Our study demonstrates that ftr82 is a crucial hearing-related gene that regulates the HC morphogenesis and auditory function performing,which provides new insight into the rapid identification of the deafness gene.

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.

转炉一次除尘新OG系统高效喷淋塔喷嘴雾化特性的模拟

利用离散相模型对转炉一次除尘新OG系统高效喷淋塔内喷嘴的雾化特性进行模拟,分析了喷射角度、喷射压力、喷射流量及喷嘴水平间距等因素对雾化场索太尔平均直径（SMD）和蒸发效率的影响.结果表明,在一定范围内随喷射角度增加,液滴在雾化场中的覆盖面增大,液滴驻留时间变长,蒸发效率增加,雾化场SMD减小,喷射角度大于60°时,SMD值减小缓慢.随喷射压力增大,液滴蒸发效率增加,雾化场SMD减小,压力大于1.0 MPa时对SMD的影响较小.随喷射流量增加,液滴蒸发效率减小,雾化场SMD增加,流量小于0.15 kg/s时,SMD增加幅度偏小.两喷嘴水平间距越大,液滴分布面积越大,但对雾化场SMD影响较小.在一定条件下,喷嘴间距约为800 mm时,截面速度分布较均匀.

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.

转炉一次除尘新OG系统高效喷淋塔喷嘴布置方式对喷淋特性的影响

采用离散相模型对新OG系统高效喷淋塔入口段及主体段喷嘴的布置方式进行数值模拟,考察了喷嘴喷射方向和喷淋层数对雾化场气流分布和降温效果的影响。结果表明,喷嘴的喷射方向和塔内的喷淋层数对雾化场的气流分布和降温效果影响较大;喷淋塔入口段采用逆流喷射时,出口截面的速度分布最均匀且降温效果最好;高效喷淋塔的主体段的喷淋层数为5时,塔内烟气的速度流场较均匀,且中心区域的气流速度为2~4 m/s,有助于延长气体与液滴的作用时间;随喷淋层数增加,塔内温度梯度变化增大,水蒸气质量分数分布与温度分布对应,塔内的平均湍动能逐渐增高。

基于空泡系数法的小型CO2跨临界热泵热水器最佳充注量计算及实验

自然工质CO2具有良好的环境和热力学性能,在小型系统中得到了越来越广泛的应用。小型系统的充注量决定系统性能优劣,存在着一个最佳值。基于一套小型CO2水源热泵热水器实验台,选用6种典型的空泡系数模型,运用空泡系数法对其最佳充注量进行计算,通过实验研究不同充注量对系统性能的影响,并利用实验结果对各种模型的计算结果进行验证,判断其计算准确度。结果表明,6种模型计算结果均具有较高的准确度,最大误差为9.80%;本系统中,Hughmark模型对于最佳充注量的计算结果误差为2.59%,且这个误差对于系统制热性能系数EERheat几乎没有影响。

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。

蜂窝状空气滤清器的流场分析及结构优化

基于多孔介质理论,采用标准k-?湍流模型对不同结构的宏观蜂窝状空气滤清器的内部流场和阻力特性进行数值模拟,从而进行结构优化,提高其性能。采用的模型为相同滤芯(褶高h=5mm),壳体进出口形状分别为圆形与圆形(方案1)、圆形与椭圆形(方案2)、椭圆形与圆形(方案3)和椭圆形与椭圆形(方案4)的组合;优化得到的壳体结构与褶高分别为5, 10, 15 mm的蜂窝状滤芯组合,研究其过滤性能。结果表明,方案2的流场分布更均匀;压降随流量变大近似呈线性增长,当流量小于额定流量的60%时,4种方案的压降大致相等,大于额定流量的60%时,方案2的压降比方案1, 3和4小,方案2的壳体结构较合理。方案2滤芯褶高对空气滤清器流场分布有一定影响,且在研究的褶高范围内压降先降低后增加,存在最佳褶高使空气滤清器的压降最小。

选择性催化还原蜂窝状催化剂内流动特性的多尺度模拟

为提高选择性催化还原(SCR)脱硝反应器内催化剂的脱硝效率和使用寿命,从细观和宏观两个角度对SCR脱硝反应器的流动特性多尺度数值进行研究。在细观层面研究了不同高度的催化剂层产生的阻力随进口速度的变化,并计算得到阻力关系式。宏观层面,基于阻力关系式,计算出催化剂宏观结构数值模拟所需的粘性阻力系数和惯性阻力系数,对反应器内的流动特性进行数值模拟,并将其结果与实验数据对比,最大误差为8.6%。将关系式应用于具有不同结构(蜂窝状和斜板状)催化剂的脱硝反应器中,计算结果与文献值趋势基本一致,最大误差为12.9%。

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).