Applicability Assessment of Subcritical Flux Operation in Crossflow Microfiltration with a Concentration Polarization Model

In the process of crossflow microfiltration, a deposit of cake layer tends to form on the membrane, which usually controls the performance of filtration. However it is found that there exists a condition under which no deposit of cake layer is made. This condition is called the subcritical flux condition and the maximum flux in the condition here is called the critical flux. Which means, it is a flux below which a decline of flux with time due to the deposit of cake layer does not occur. This study develops a concentration polarization model to predict the critical flux condition and to study about its characteristics. The model is verified with experimental results. For the model, the concept of effective particle diameter is introduced to find a representative size of various particles in relation to diffusive properties of particles. The modeling and the experimental results include that the critical flux condition can be determined by the use of effective particle diameter and the ratio of initial permeate flux to crossflow velocity. This study also finds that the (sub)critical flux operation is limited for the real world application because of the limitation to increasing crossflow velocity and its sensitivity to the change of feed composition.     

Pressure-Dependent Elasticity and Energy Conservation in Elastoplastic Models for Soils

This paper presents a study on the consequences of combining energy conservative or non-conservative elasticity within a plasticity framework. Toward this end, a versatile energy potential function is first presented and examined. It is shown to cover a wide range of existing empirical relations for pressure-dependent stiffness of soils. Utilization of these functions within hyperplastic constitutive framework allows for the resulting models to satisfy the Law of Energy Conservation for both elastic and plastic components of soil behavior. Apart from the theoretical rigor, a very important result of this approach is that it automatically implies stress-induced cross-anisotropy of the elastic component of soil behavior and dilatancy term occurs due to shear modulus dependency on pressure. Proper modeling of these phenomena, normally neglected by conventional hypoelastic-plastic models, has been shown to have a significant effect on the accuracy of the model predictions of undrained behavior of overconsolidated clays both in laboratory tests and in tunnel excavation problem.     

Reaggregation of Flocs in Coagulation-Cross-Flow Microfiltration

Cake layer in cross-flow microfiltration can be reduced by coagulation of particles. This is because enlarging particle size by coagulation increases shear induced diffusivity and the back transport of rejected particles. In addition, it is known that flocs can be broken when they are passing through a pump. In light of these facts, this study aims to experimentally look at the floc-breaking phenomenon being related to cake layer reduction. Kaolin is used as particles and aluminum sulfate as a coagulant for the experiment. The results of particle size analyses show that the aggregated particles in feed are completely disaggregated by the pump but reaggregated in the membrane module. This suggests that the reaggregation of particles is critical to cake reduction and flux enhancement. This study proves that most of it occurs around the movable cake layer on membrane where G value is small. Charge neutralization of particles is also proven a dominant coagulation mechanism for reaggregation around the movable cake layer over sweep flocculation. These results suggest that rapid mixing and charge neutralization of particles are more important in reducing cake layer than flocculation. In this reason, in-line mixer is expected to work better with coagulation-cross-flow microfiltration than conventional coagulation tank and this study proved it.     

微滤+反渗透技术在污水处理中的应用

长期以来,各种废水的深度处理一直是废水处理过程中的一大技术难题,对此环保处理工作人员对该问题进行了大量的研究,并在此基础上取得了许多优异的成果。但是不同的技术方法所对应的废水处理条件各有不同。膜分离技术以其高效、节能以及清洁生产等特点广泛用于各种污水处理中。其中微滤+反渗透技术尤为突出,并受到广泛关注。文章对近年来膜分离技术的最新研究和进展进行了概述,并对未来的发展进行了展望。     

超细铁粉的制备和应用

文章对近年来超细铁粉的制备方法作了较为全面的阐述,并介绍了超细铁粉主要的应用领域.     

HEDP和渗透剂T协同阻垢性能的研究

静态阻垢法研究了1-羟基乙叉-1，1-二膦酸(HEDP)的阻垢性能，考查了几个主要因素对HEDP阻垢性能的影响。结果表明HEDP的加入量为12．0mg／L．渗透剂T的浓度为0．6mg／L时阻垢率最大，为75．6％；渗透剂T的加入明显地改善了HEDP的阻垢性能．阻垢性能随Ca^2 浓度的增加而增加，在pH值为6到9时药剂的阻垢性能稳定。     

氮对超细晶奥氏体不锈钢组织和性能的影响

研究了在304不锈钢粉末中添加不同含量的氮化物,通过机械合金化和放电等离子烧结技术制备出不同N含量的超细晶奥氏体不锈钢,并分析了其组织和性能的变化.XRD图谱显示未添加N的烧结样由马氏体和奥氏体共同组成,而添加了N的烧结样由单一的奥氏体组成,TEM形貌观察发现烧结试样的晶粒尺寸都在纳米级别,而添加N的烧结试样比未添加N的烧结试样晶粒尺寸更加细小.力学性能测试结果显示烧结试样的硬度、耐磨性都随N含量的增加而增加,抗拉强度随N含量的增加先增后减.极化曲线的测量结果显示烧结试样的耐腐蚀性能随着N含量的增加而增加.     

光催化和微滤处理有机磷农药废水

[目的]针对光催化处理有机磷农药废水工艺中,有机磷降解生成无机磷,无机磷会导致水体富营养化以及催化剂分离难问题,将陶瓷膜微滤与光催化相结合采处理有机磷农药废水.[方法]将膜微滤过程引进光催化降解有机磷废水处理工艺中,通过膜的截留特性回收催化剂、降低PO<,4><'3->含量,同时对微滤过程的操作参数进行了优化.[结果]微滤促进了除磷效果,消除了二次污染,改善了出水水质,有利于催化剂的分离回收.光催化和微滤处理有机磷废水,PO<,4><'3->去除率达99.1%.COD<,cr>,去除率达91.8%,远高于单独光催化或单独微滤的结果.当操作压差为0.10MPa,流速为5 m/s,膜通量达230L/(m<'2>·h).[结论]采用光催化-微滤组合工艺处理有机磷农药废水是一个行之有效的方法.     

Use of Iron Oxides to Enhance Metal Removal in Crossflow Microfiltration

This research investigated whether iron oxyhydroxides used in conjunction with microfiltration could improve the removal of metals from a waste while maintaining adequate flux. Filtration of individual metals, a mixture of metals, and the mixture with two iron oxides were investigated. The research indicated that use of a coagulant (an iron-containing salt) might not be as important in microfiltration systems as in conventional gravity separation systems, because of the small pore size of microfilters. In some cases, filtration efficiency was relatively poor at the beginning of a treatment cycle, but in almost all cases it became excellent once a layer had built up on the membrane surface. The greatest benefit provided by iron oxides might be to reduce membrane fouling. A crystalline iron oxide such as goethite is more attractive than ferrihydrite. The flux improvement with goethite is greatest if a thin layer is deposited on the membrane surface before the contaminant metals are injected into the system, so that the goethite can trap the potentially foulant metal hydroxide particles away from the membrane surface.     

氟离子对保护渣传热和渣膜矿相结构的影响

连铸过程中保护渣的渣膜结构及结晶器传热情况对铸坯质量有重要影响,试验采用高温导热系数测定装置及结晶器渣膜黏度和热流模拟测试仪,研究不同F~-配加量渣膜的高温导热系数和矿相结构。结果表明:随F~-含量(4.22%~13.33%)的增加,渣膜的导热系数逐渐减小,对应的渣膜结晶率逐渐增大,且试验渣膜结晶率均较高,达75%以上。不同F~-含量的保护渣所对应渣膜的结晶矿物种类相同,主要为枪晶石和硅灰石。随F~-含量的增加,枪晶石析出量不断增多,晶形逐渐变大;硅灰石生成量不断减少,晶形逐渐变小。该研究成果对改善低氟保护渣浇铸的铸坯质量具有重要指导意义。     

Pilot-Scale Evaluation of Chemical Cleaning Protocols for Organic and Biologically Fouled Microfiltration Membranes

The Edward C Little Water Recycling Facility (ECLWRF) is the largest high-purity water recycling facility in the United States. Here, microfiltration (MF) membranes play a critical role in treating the secondary effluent and serving as pretreatment to the downstream reverse osmosis systems. New chemical clean-in-place (CIP) formulations were evaluated through pilot-scale tests for their ability to improve the performance restoration for the Phase III continuous MF (CMF) membranes at the ECLWRF. Membrane autopsies found that the primary fouling mechanisms for the CMF membranes were biological and organic in origin. It was also determined that the current CIP protocol provided an incomplete removal of the biological and organic foulants. The cleaning test results found that the current CIP regime for the Phase III system performed better than the four commercially available cleaning solutions evaluated here. However, improved results were obtained when hydrogen peroxide was added to the current CIP regime consisting of caustic soda and the commercially available Memclean C cleaning solution. The effects of the addition of hydrogen peroxide to the standard cleaning procedure shows some promise; however, further research is needed to understand the cleaning mechanisms and long-term effects of using hydrogen peroxide as a cleaning additive.     

Existence of Critical Recovery and Impacts of Operational Mode on Potable Water Microfiltration

Results from a potable water microfiltration (MF) pilot study employing untreated surface water are reported. The effects of filtrate flux and recovery on direct flow, outside-inside, hollow fiber MF fouling rates, and backwash effectiveness are presented. Constant flux experiments suggested the existence of a critical recovery below which MF fouling rates were low and effectiveness of backwashes was high and relatively independent of the recovery. However, in the range of experimental conditions investigated, fouling rates increased dramatically and backwash effectiveness decreased steeply when this critical recovery was exceeded regardless of the flux. In general, for a fixed recovery, specific flux profiles analyzed on the basis of volume filtered per unit membrane area were insensitive to filtrate flux. Fouling was accelerated by operating membranes at constant flux rather than at constant pressure, in part, because of membrane compaction and cake compression. Changing the mode of filtration between constant flux and constant pressure is shown to have no effect on MF filtrate water quality. For any given capacity, membrane area requirements are decreased, and power requirements are increased when membranes are operated at constant flux rather than at constant pressure.     

唐钢超薄热轧带钢生产线的质量控制技术

介绍了唐钢FTSR超薄热轧带钢生产线的工艺流程,以及代表其技术特色的H^2结晶器、动态液芯压下、动态PC控制、半无头轧制、铁素体轧制等新技术。认为：H^2结晶器与普通漏斗型结晶器相比,坯壳所受的应力大大降低,不易产生裂纹;优化的辊列设计及动态液芯压下技术确保了铸坯的内部质量;半无头轧制解决了超薄带钢直接穿带和甩尾困难的难题;动态PC和工作辊弯辊技术相互配合,保证了产品质量的稳定;而三点除鳞,尤其是粗轧和精轧之间设中间冷却装置,不仅可以改善板带表面质量,也为实现精轧在铁素体状态下轧制提供了条件。     

Effect of Soda Ash on Properties of Mold Flux and Mineralogical Structures of Flux Film

During continuous casting,properties of mold flux and mineralogical structures of flux film play important roles in controlling steel quality.The effect of soda ash on the physical properties and crystallization characteristics of mold flux was investigated using process mineralogy,including polarizing microscopy,X-ray diffraction,and electron microprobe,etc.Mold flux was mainly prepared using cement clinker and industrial mineral materials under laboratory conditions,and the mineralogical structures of the flux film were systematically identified and quantitatively analyzed.The results showed that,by increasing the soda ash content from 10mass% to 18mass%,the crystallization temperature,critical cooling rate and crystallization ratio of the flux film decreased,but the crystallization ratio still reached 75% after adding soda ash,and the mineral compositions and microstructures of the flux film changed slightly.When the soda ash content exceeded 14mass%,the critical cooling rate and the crystallization ratio decreased slightly,whereas the mineral content of the flux film changed evidently,with a large amount of cuspidine precipitation and a significant decrease in the wollastonite content until it reached zero,which resulted in deterioration of the lubrication of the flux film.     

Flow Resistance and Momentum Flux in Compound Open Channels

New formulations are presented for flow resistance and momentum flux in compound open channels. As implemented in the St. Venant equations, these formulations facilitate a physically enhanced approach to evaluating conveyance, roughness, stage-discharge relationship, and unsteady flood routing in compound open channels. An analysis using steady flow data from the well-controlled experiments at the large-scale Flood Channel Facility, HR Wallingford, demonstrates the ability of the present approach to properly resolve the discontinuity of overall roughness across the main-channel bankfull level. Also, the proposed formulations are shown to be conducive to obviating the long-standing computational difficulty in unsteady flood routing due to small flow depths over flat and wide floodplains. The present work should find general applications in one-dimensional computation of river flows.