陶瓷膜过滤性能的影响因素

研究了氯化钠盐水温度、盐水中固含量和陶瓷膜孔径对陶瓷膜过滤器过滤性能的影响,结果显示:盐水中含固质量分数在2％～22％变化时,陶瓷膜通量无明显变化;盐水温度升高,膜通量增大,但对颗粒物截留效果无明显影响;10 nm孔径的陶瓷膜通量较40、50 nm孔径的陶瓷膜通量小,陶瓷膜对颗粒物A(粒径5～40 μm)和B(粒径0....     

气升式陶瓷膜装置过滤钛硅分子筛悬浮液

为克服膜污染,提高膜通量,文章将曝气引入到陶瓷膜过滤过程中,计算了曝气量对液相循环流速、气含率以及膜面剪切力的影响。采用气升式陶瓷膜过滤装置,以平均孔径为200 nm的ZrO2陶瓷膜为分离介质,考察了固含量(质量浓度)、曝气量、跨膜压差对钛硅分子筛悬浮液固液分离性能的影响。结果表明:曝气量增大,液相循环流速和气含率随之增大;曝气量在416—2 333 mL/min内,气液二相流流型为弹状流,气弹区膜面剪切力是液弹区的3—10倍。陶瓷膜对钛硅分子筛的截留率为100%;当固含量为1%时,曝气量由100 mL/min增大至850 mL/min,膜稳定通量增大了33%,进一步增大曝气量,通量开始下降。膜的稳定通量随着固含量的增大而降低。当曝气量为850 mL/min,固含量为1%时,跨膜压差由0.1 MPa增大至0.2 MPa,稳定通量降低了41%,但进一步增大跨膜压差到0.3 MPa时,稳定通量又表现出增大趋势。对膜过滤阻力的计算分析结果表明:曝气作用能减轻浓差极化,但不能消除滤饼与膜孔堵塞污染。     

气升式陶瓷膜过滤装置处理油田含聚采出水

采用新型的气升式陶瓷膜过滤系统处理油田含聚采出水,通过气液两相流替代单一的液相流动,降低了陶瓷膜处理油田含聚采出水过程的能耗,系统考察了曝气孔大小、曝气量和跨膜压差对膜渗透通量的影响。结果表明,采用孔径为微米级的曝气头曝气使高压气体在多通道膜管内的分布更为均匀,进而有效抑制膜污染和浓差极化,延缓通量衰减。当曝气孔径为1μm时,渗透通量达到最大,且曝气量从300 L·h~(-1)增加到600 L·h~(-1)时,通量显著增加。此外,跨膜压差对膜的渗透通量影响显著,当跨膜压差为0.4 MPa时,渗透通量最佳。陶瓷膜处理油田采出水的出水水质各方面指标数据较为稳定,达到5.1.1回注水标准。最后,计算讨论了气升式陶瓷膜过滤装置的吨水能耗。     

气升式陶瓷膜过滤装置处理油田含聚采出水

采用新型的气升式陶瓷膜过滤系统处理油田含聚采出水,通过气液两相流替代单一的液相流动,降低了陶瓷膜处理油田含聚采出水过程的能耗,系统考察了曝气孔大小、曝气量和跨膜压差对膜渗透通量的影响。结果表明,采用孔径为微米级的曝气头曝气使高压气体在多通道膜管内的分布更为均匀,进而有效抑制膜污染和浓差极化,延缓通量衰减。当曝气孔径为1 μm时,渗透通量达到最大,且曝气量从300 L·h^-1增加到600 L·h^-1时,通量显著增加。此外,跨膜压差对膜的渗透通量影响显著,当跨膜压差为0.4 MPa时,渗透通量最佳。陶瓷膜处理油田采出水的出水水质各方面指标数据较为稳定,达到5.1.1回注水标准。最后,计算讨论了气升式陶瓷膜过滤装置的吨水能耗。     

陶瓷膜分离钛硅分子筛的实验与模型计算

在面向过程的陶瓷膜材料设计理论模型的基础上,以TS-1钛硅分子筛悬浮液固液分离为应用体系,计算了陶瓷膜分离过程的操作条件与渗透性能的关系,与实验结果有良好的一致性.计算表明,对于平均粒径为290 nm的钛硅分子筛体系,陶瓷膜存在最优孔径区间(200~300 nm),使膜保持高渗透通量.孔径小于200 nm时膜通量随孔径增大而增大,孔径大于300 nm时膜通量随孔径增大而减小;采用孔径为200 nm的陶瓷膜过滤钛硅分子筛,渗透通量随时间的变化关系与模型预测结果一致,稳定通量达到800 L/(m2.h).     

PP/Al(OH)_3/Mg(OH)_2/ZB复合材料阻燃性能的研究

测试了PP/Al(OH)3/Mg(OH)2/ZB、PP/Al(OH)3/Mg(OH)2/ZB/CaCO3和PP/Al(OH)3/Mg(OH)2/ZB/CaCO3/POE复合材料的阻燃性能。结果表明:随着阻燃剂用量的增加,氧指数升高,而燃烧速率和烟密度下降,且阻燃剂的加入对延缓燃烧速率的作用效果十分显著;相同配方下试件越厚燃烧速度越慢,且随阻燃剂用量的增加,试件越厚燃烧速率下降的幅度越慢;纳米CaCO3及POE的加入可以增大氧指数,降低烟密度,有利于阻燃,但同时也会使水平燃烧速率略微增大。     

阳极氧化铝膜过滤BSA溶液过程中的污染分析

采用阳极氧化铝膜过滤牛血清蛋白溶液,考察了孔径20、100、200 nm 3种膜的过滤通量随时间的变化关系,在相同的操作条件下孔径20 nm的膜具有较高的渗透通量(400 L/(m2.h))和较小的过滤阻力(8.3×1011/m)。还考察了蛋白质浓度、泵送时间及清洗对膜污染情况的影响。结果表明,在实验的范围和条件下,随蛋白质浓度的增大,膜污染加重,稳定通量增大;泵送时间增长,膜污染速度加快,通量增大;通过纯水清洗加超声清洗的方法去除可逆污染,清洗后膜与新膜过滤通量相当。     

弹状流对陶瓷膜超滤葡聚糖水溶液的影响

为降低膜污染和浓差极化需维持较高膜面流速,能耗较高。将气升式外循环引入膜过程,可有效降低浓差极化和能耗。实验考察了曝气量对渗透通量的影响,当曝气量为400 L·h^-1时,与相同液速条件下单相流错流过滤相比较,膜通量提升87%;进一步增大曝气量,膜通量增加趋势变缓。对气升式膜过滤过程的水力学特性进行了研究,在弹状流条件下,气液两相流可有效提高膜面剪切力,增强膜面传质。在较低流速下,曝气可有效降低膜污染阻力,提高膜通量。结合气液两相流理论和膜过滤阻力模型,分析了弹状流提升膜通量的机理。     

加压碳化体系对纳米碳酸钙粒度和分散性的影响

利用加压碳化体系制备粒径均一、高分散性纳米碳酸钙材料。考察氢氧化钙浓度、表面活性剂添加量、反应温度、CO2压力对制备纳米CaCO3粒子尺寸和分散程度的影响,采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、Zeta电位和傅立叶变换红外光谱(FT-IR)对制备的纳米碳酸钙粒子进行表征。结果表明,最优加压碳化反应条件是Ca(OH)2质量浓度为2%、表面活性剂添加量为3%(占碳酸钙理论产量的百分比)、反应温度为40℃、CO2压力为6 MPa,所得立方形碳酸钙平均粒径为117 nm,晶型为方解石型碳酸钙。碳化反应加入表面活性剂十六烷基三甲基溴化铵(CTAB)使CaCO3表面形成的正电荷增大至+37.7 mV并高于标准值30 mV,表明制备的CaCO3产品具有良好的分散性且稳定。通过FT-IR和Zeta电位对CTAB改性前后CaCO3纳米粒子进行表征,探讨了CTAB对合成纳米CaCO3分散性的影响机理,为纳米碳酸钙制备提供了一种新的方法。     

苛化麸皮液的配制和投加试验

一、概述原盐溶解后的粗盐水中含有一定量的Ca~( )、Mg~( ),为了使Ca~( )、Mg~( )变成沉淀物而除去,必须加入适当的精制剂,如加入NaOH及Na_2CO_3,则发生如下反应: Ca~( ) Na_2CO_3=CaCO_3↓ 2Na~ Mg~( ) 2 NaOH=Mg(OH)_2↑ 2 Na~ 反应所生成的沉淀最初是粒径极小的胶体颗粒,由于盐水中存在大量的电解质、泥砂等使CaCO_3、Mg(OH)_2胶体颗粒得以迅速压缩双电层脱离稳定状态并和泥砂等接触凝聚,形成细小的颗粒。如将此悬浮液静     

Unsteady-State Permeate Flux of Crossflow Microfiltration

Abstract

In this study a membrane filtration cell was installed to investigate the variation of permeate flux with filtration time under various operating conditions including crossflow velocity, pressure drop, particle concentration, membrane pore size, particle size, pH, and electrolyte concentration. The dimensions of the filtration channel in the CFMF cell were 6 cm x 0.6 cm x 0.036 cm, and the flow of the suspension in the channel was controlled under the laminar flow region. Spherical polystyrene latex particles of 0.303, 0.606, and 1.020 μm were used as the suspension particles in the experiments. The density of the particles was 1.05 g/cm³. It was found that the unsteady-state permeate flux increased with an increase in particle size, membrane pore size, or crossflow velocity, but decreased with an increase in particle concentration or electrolyte concentration in the suspension. A mathematical model based on mass balance and hydrodynamic theory was developed in this study. In addition, the effect of cake growth and particle concentration decline during experiments on the permeate flux were also considered in this model. This model predicts satisfactorily the unsteady-state permeate flux of CFMF under various operating conditions.     

低膜面流速下曝气对管式膜水力特性及膜污染影响

采用曝气强化管式膜超滤高岭土混合液,考察了低膜面流速下曝气对强化膜分离过程影响,探讨了曝气对膜面水力特征及膜污染过程影响,并对过滤介质影响及膜污染阻力构成进行了研究。结果表明,在低膜面流速下,通过向管式膜引入曝气使膜表面形成气液两相流,可实现膜通量稳定保持在15L/(m²·h)以上。不仅如此,曝气的引入使膜表面雷诺数由1800~2500增至3300~4500,显著增强了膜表面湍流程度,并且实现了低膜面流速下使膜污染指数控制在较低水平,节省了运行能耗。此外,曝气的引入主要减轻了膜表面滤饼污染,使膜过滤总阻力减小且对高岭土截留效率影响不大,但强烈的膜面传质使高岭土粒径有减小趋势,并且膜表面形成污染阻力以不可逆污染层为主,不利于膜污染长周期控制。     

Modeling of Particle Fouling and Membrane Blocking in Submerged Membrane Filtration

Abstract

The models of particle fouling and membrane blocking in a submerged membrane filtration are developed in this study. The effects of operating conditions, such as aeration intensity (air flow rate) and filtration pressure, on the filtration flux, membrane blocking, and cake formation are discussed thoroughly. The experimental results show that the filtration resistances due to cake formation and membrane blocking play significant roles in determining the overall filtration resistance, but the latter one is more dominant. An increase in aeration intensity leads the filtration flux to increase due to the reduction of cake formation on the membrane surface. However, a higher filtration pressure causes more severe membrane internal blocking and then to lower filtration flux. The cake properties and the filtration resistance due to membrane blocking are analyzed and can be regressed to empirical functions of filtration pressure. A force balance model for particle deposition on the membrane surface is also derived. In order to estimate the shear stress acting on the membrane surface, the diameter, shape, and rising velocity of air bubbles are analyzed based on hydrodynamics. Once the model coefficients are obtained, the pseudo‐steady filtration flux under various conditions can be estimated by the proposed model and the basic filtration equation. The calculated results agree fairly well with the available experimental data.     

Unsteady-State Permeate Flux of Crossflow Microfiltration: Effect of Particle Size Distribution

Abstract

A mathematical model based on a hydrodynamic theory and mass balance was developed for the prediction of the unsteady-state permeate flux in crossflow microfiltration under the influence of particle size distribution. Experiments were also conducted in a membrane filtration cell to verify this model. Spherical polystyrene latex particles of 0.303, 0.606, and 1.020 μm were used to make suspensions of various particle size distributions. The flow of the suspension in the channel of the filtration cell was controlled under the laminar flow region. It was found that the unsteady-state permeate flux increased as the mean particle size of the suspension was increased. Moreover, the model predicted satisfactorily the unsteady-state permeate flux under the effect of particle size distribution.     

Tubular Membrane Filtration with A Side Stream and its Intermittent Backwash Operation

The tubular membrane filtration system is widely applied to solid-liquid separation processes. Any improvements to the filtration module would increase separation efficiency, thus reducing operating costs. In this experiment, PMMA powder with an average particle diameter of 0.8 µm was filtered by a ceramic tubular membrane with an average pore size of 0.2 µm, and the impacts of the operating variables, such as suspension concentration, the filtration pressure, and the crossflow velocity on the permeate flux were discussed. In order to understand the increased permeate flux, the proposed module is comparable to the tubular membrane filtration module, but with an additional side stream under the same filtration mass flow rate. In addition, variations of shear force on the membrane surface are analyzed by CFD simulation, and the influence of backwash operations on the permeate flux is discussed. The results show that the side stream membrane filtration increased the shear force on the membrane surface, reduced fouling on the membrane surface, and increased the permeate flux. Furthermore, a backwash operation with a side stream flow channel could effectively clean the particles deposited in the module, thus, increasing the permeate flux.     

A comparison of hydrodynamic methods for mitigating particle fouling in submerged membrane filtration

Hydrodynamic methods are used for mitigating particle fouling and for enhancing the filtrate flux in submerged membrane filtration. In the comparison membrane blocking-cake formation filtration system, the effects of filtration pressure, aeration intensity, backwash duration and stepwise increasing pressure on the filtration resistances and filtration flux are measured and discussed. Aeration is helpful for reducing particle deposition on the membrane surface, while stepwise increasing pressure can mainly mitigate internal fouling of the membrane. Periodic backwash can significantly reduce both the resistance caused by the membrane internal fouling and by cake formation; consequently, it can effectively recover the filtrate flux. In contrast, increasing the pressure in constant pressure filtration leads the flux to be decreased due to more severe membrane blockage. According to the comparison of the long-term flux and the received filtrate volume, among these hydrodynamic methods, the periodic backwash with longer duration is the optimal strategy for the filtration.     

Migration and Deposition of Submicron Particles in Crossflow Microfiltration

Abstract

The migration and deposition of submicron particles in laminar crossflow microfiltration is simulated by integrating the Langevin equation. The effects of operating conditions on the particle trajectories are discussed. It is found that the Brownian motion of particles plays an important role in particle migration under a smaller crossflow velocity of suspension or a smaller filtration rate. Based on the simulated trajectories of particles, the transported flux of particles arriving at the membrane surface can be estimated. The particle flux increases with an increase of filtration rate and with a decrease of particle diameter; however, the effect of crossflow velocity on the particle flux is not obvious. The forces exerted on particles are analyzed to estimate the probability of particle deposition on the membrane surface. The probability of particle deposition increases with an increase of filtration rate, with a decrease of crossflow velocity, with a decrease of particle diameter, or with an increase of zeta potential on the particle surfaces. The simulated results of packing structures of particles on the membrane surface at the initial stage of filtration show that a looser packing can be found under a larger crossflow velocity, a smaller filtration rate, or a smaller diameter of filtered particles. Crossflow micro-filtration experiments are carried out to demonstrate the reliability of the proposed theory. The deviation between the predicted and experimental data of filtration rate at the initial period of filtration is less than 10% when the Reynolds number of the suspension flow ranges from 100 to 500.     

Permeate flux decline in cross-flow microfiltration at constant pressure

Microfiltration processes are frequently used to separate solids from aqueous suspensions. The rejection of suspended matter is facilitated by means of a size exclusion mechanism and is affected by membrane properties, characteristics of the suspension and operating conditions. Therefore, the filtration performance of a single polymeric hollow-fibre membrane was investigated by monitoring the permeate flux decline for a filtration at constant transmembrane pressure (TMP). For these bench-scale experiments, a model suspension consisting of silica particles in xanthan gum solutions was used in order to represent the characteristics of biological suspensions such as activated sludge properly. In the framework of this study, it was confirmed that the permeate flux declines rapidly during the first stage of filtration until an equilibrium of particle deposition and entrainment is reached. The steady-state permeate flux was found to increase with an increase in cross-flow velocity, a decrease in solid concentration, a decrease in particle size (for this ratio of particle to pore diameter) and a decrease in apparent viscosity of the suspension. However, the equilibrium permeate flux was not affected by variations in TMP, which is in agreement with the limiting flux theory.     

Flux enhancement and cake formation in air-sparged cross-flow microfiltration

The flux enhancement in cross-flow microfiltration of submicron particles by sparged air-bubble is studied. The effects of operating conditions, such as air-bubble velocity, suspension velocity and filtration pressure, on the cake properties and filtration flux are discussed thoroughly. The results show that the pseudo-steady filtration flux increases as the air-bubble velocity and filtration pressure increase. The sparged air-bubble can significantly improve filtration flux, but the flux enhancement is more remarkable in the lower air-bubble velocity region. A gas–liquid two-phase flow model is adopted for estimating the shear stress acting on the membrane surface under various operating conditions. The cake mass can be significantly reduced by increasing the shear stress acting on the membrane surface. However, the SEM analysis illustrates that the particle packing structure becomes more compact as the air-bubble velocity increases. This results in a slightly higher average specific cake filtration resistance under higher air-bubble velocity. Consequently, a minimum flux occurs at the critical shear stress, e.g., τ_w = 1.1 N/m² in this study, when these effects are both taken into consideration. As the shear stress increases by increasing the suspension or gas-bubble velocity, the filtration flux decreases in the low shear stress region but, on the contrary, quickly increases in the high shear stress region. Furthermore, a force balance model is derived for understanding the particle deposition on the membrane surface. The relationship among filtration flux, shear stress and overall filtration resistance is obtained and verified by experimental data.     

Influence of Water Compositions and Conditioning on Flux Enhancement in an Immersed Membrane System

Abstract

The objective was to quantify the importance of operational conditions, aeration, and physico‐chemical conditioning on membrane fouling intensity. The suspension filterability was also analysed by using frontal filtration and a cake filtration model. Results pointed out the moderated role of aeration to reduce compound accumulation on the membrane surface. It did not appear as a determining criterion to prevent membrane fouling. In contrast, the physico‐chemical conditioning appeared as a determining criterion to increase critical flux. According to the experimental conditions 200 l/m²/h/bar membrane permeability could be maintained transmembrane pressure (TMP) when filtering stored rainwater. This permeability value was 2–3 times higher than the values obtained without conditioning. Moreover, according to the low turbidity of such stored rainwater and because of the high selectivity of the membrane, the coagulation step, a very low amount of 10 mg/l FeCl₃, was sufficient to intensify the filtration step. This conditioning interest appeared less significant when filtering salted water in immersed membrane systems, but a 20 mg/l FeCl₃ addition appeared sufficient to double the value of critical flux. Nevertheless filtration in frontal mode pointed out the significant impact of physico‐chemical conditioning in reducing the cake deposit hydraulic resistance.