Analysis of Feed Effects on a Single-Stage Gas Centrifuge Cascade

Abstract

The Onsager pancake model for the fluid dynamics of the countercurrent flow of gas in a centrifuge is used to study the separation performance of a single-stage gas centrifuge cascade. Based on the fluid dynamic solutions, Cohen-Onsager theory is used to calculate the separative performance. The separation considered is the enrichment of natural ²³⁵U to 3%. The effects of the introduction of the feed gas on the separation performance are studied, and this work is compared to similar work by Rätz who used a much simpler model. The present work agrees well with the simpler model on predictions of separative performance but not on parameters such as the axial location of the feed stream.     

浅析一步法二甲醚生产工艺中原料气的利用率

介绍并对比了一步法、二步法生产二甲醚工艺技术,并以Texaco、Shell煤气化技术生产的典型合成气成分为基准进行具体实例计算,计算结果表明一步法二甲醚生产工艺原料气利用率高于二步法二甲醚生产工艺原料气利用率。     

Effect of Recycling of Feed Solution on the Efficiency of Supported Liquid Membrane Module

Abstract

The effect of recycling of a feed solution from the outlet to the inlet of the feed channel of a plate-and-frame type supported liquid membrane module on the recovery of zinc was investigated under the condition that the feed side mass transfer resistance is predominant. Di(2-ethylhexyl)phosphoric acid was used as the carrier. It was found that at a given feed flow rate, recycling of the feed solution is effective for improving the recovery of zinc since recycling brings about an increase of the flow rate in the feed channel and also the mass transfer coefficient in the feed side. The experimental data could be satisfactorily simulated by a proposed theoretical model.     

流道结构对膜分离性能的影响

基于CFD技术对不同流道结构的平板式纳滤膜分离器内的流动进行了数值模拟,以考察流道结构对膜分离性能的影响。分析了在平板膜器中加设螺旋形隔板和蛇形隔板后截面流体的次流状况。模拟结果表明在无绕流板流道中加设隔板后存在次流现象,螺旋形流道中流体流动存在二次流漩涡,蛇形流道拐角附近的流体也存在较强的二次流动,对减轻膜污染和浓差极化均有作用。     

Effect of Support Material Properties on Dynamic Membrane Filtration Performance

A dynamic membrane is defined as a cake layer which forms on a support material, for example, filter cloth or mesh when the liquid to be filtered includes suspended particles. Formation of an effective dynamic cake layer is highly related with the retention of particles on the support material surface. Therefore, support material properties are considered to be of prime importance in the performance of dynamic membrane treatment systems. This study investigates the effect of support material properties including pore size and structure of the material on dynamic membrane formation and performance. In this concept, a comparative evaluation was made between support materials which have different yarn types. The results showed that high total suspended solids removal efficiency (>98%) could be achieved by using dynamic membrane filtration technology. Mono-monofilament and staple filter cloths were determined as the most appropriate materials in terms of the critical fluxes which were 9.2 L/m² · h and 17–19 L/m² · h for mono-mono filament and staple materials, respectively. However, considering the results of more long-term experiments, mono-monofilament filter cloth was found more suitable for cake layer accumulation. Therefore, we postulate that mono-monofilament cloth can be used in dynamic membrane filtration systems as an alternative to traditional membranes in anaerobic membrane bioreactors.     

有机废水中盐含量对膜蒸馏处理性能的影响

采用真空膜蒸馏技术对高盐有机废水进行浓缩回收。考察了废水进料温度、真空度、进料流速、废水盐度、废水的进料方式等因素对膜通量和截留率的影响。结果表明,在常压循环方式进料,透过侧真空度0.04～0.095 MPa,进料温度为30～80℃,进料流量为40～160 L/h的条件下,通过实验设计的膜蒸馏过程,可以将质量分数为10%盐度的有机废水,COD〉7 500×10^-6,浓缩至质量分数为30%盐度的有机废水,透过水的盐度〈0.01%,COD〈20×10^-6,通过盐结晶方法去除相应有机物后,可获得纯度较高的工业盐。     

Effect of External Recycle and Double-Pass Barrier Location on Membrane Extraction in Cross-Flow Modules

Abstract

The dispersion free membrane extraction through a cross-flow rectangular membrane module with arbitrary location of an impermeable plate placed for double-pass and external-recycle operations in raffinate phase, has been investigated. Theoretical treatment was analogous to the heat transfer in heat exchangers for the mass transfer in mass exchangers. An experiment was carried out in a cross-flow conduit of stainless steel inserted with a membrane sheet made of microporous polypropylene to extract acetic acid from aqueous solution by methyl iso-butyl ketone. Theoretical predictions are in agreement with the experimental results. Considerable improvement in mass-transfer performance is obtainable if the width of the first-pass subchannel, ΔB decreases, as well as the width of the second-pass subchannel, (1?Δ)B increases. The mass-transfer rate increases also when the reflux ratio increases. Based on the economic point of view, the suitable value of Δ (B is the width of a membrane sheet) may be 0.2.     

Membrane Filtration with Reversible Adsorption: The Effect of Transmembrane Pressure,Feed Flow Rate,and the Geometry of Hollow Fiber Filters on Their Performance

The effect of transmembrane pressure, feed flow rate, and the geometry of hollow-fiber filters on their performance is studied for depth membrane filtration with reversible adsorption. Mathematical models for rectangular and radial filters are used to find the maximal operation times with a filter retention of not less than 0.9 at constant product (permeate plus filtrate) flow rates for the treatment of a latex suspension in continuous-flow and batch operations. It is shown that the maximal operation time and, hence, product volume is achieved when the feed flow rate approaches the initial permeate flow rate. It is also found that several filters with a lower initial permeate flow rate allow one to achieve a much longer operation time than one filter with the same total initial permeate flow rate.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 4, 2005, pp. 426–431.Original Russian Text Copyright © 2005 by Polyakov, Kazenin.     

氯化锂对聚醚砜膜过滤性能和污染行为的影响

向聚醚砜(PES)铸膜液中添加无机氯化锂(LiCl)颗粒,通过相转化法制备PES膜,考察LiCl含量对PES膜过滤性能和污染行为的影响,分析污染物过滤堵塞模型.结果表明,LiCl的添加质量分数为5％时,PES膜孔径增大80％,水通量增加了3倍;LiCl并没有削弱PES膜对牛血清蛋白的截留效果,其截留率高达97％.而且,...     

Effect of Feed Composition on the Gas Separation Performance of Binary and Ternary Mixed Matrix Membranes

Binary and ternary component mixed matrix membranes comprised of zeolite 4A and p-nitroaniline (pNA) in the polycarbonate (PC) matrix were prepared and appraised in gas separation. For comparison, homogenous membranes of PC and PC/pNA membranes were also investigated. The membranes were utilized to separate binary mixtures of CO₂/CH₄, H₂/CH₄, and CO₂/N₂. The effect of feed composition on the separation performance of membranes was investigated. Separation factors and ideal selectivities were similar for the PC membrane. A similar trend was also observed with the PC/pNA membrane. The separation factors of the PC/pNA membrane for CO₂/CH₄ were almost twice as high as those of the PC membrane regardless of the feed composition. The ideal selectivities were, however, higher than separation factors for PC/zeolite 4A and PC/pNA/zeolite 4A membranes. The PC/ pNA/zeolite 4A membrane has separation factors of 18 for 77% CO₂/ 23% CH₄ mixture, and 40 for 20% CO₂/ 80% CH₄ mixture, respectively. The separation factors of the mixed matrix membranes depended on the feed composition strongly. The PC/ pNA/zeolite 4A membrane had higher separation factors and lower permeabilities than the PC/zeolite 4A membrane. pNA assisted to eradicate partly the detrimental effects of interfacial voids and improved the molecular sieving effect of zeolite 4A dispersed in the PC.     

The Effect of Polyethersulfone Concentration on Flat and Hollow Fiber Membrane Performance

Abstract

Flat and hollow fiber (HF) membranes are made in order to determine the effect of the polyethersulfone (PES) concentration in the precursor film-casting solution on resultant flat and hollow fiber membrane performance. The additive polyvinyl-pyrrolidone (PVP) is included in the film-casting solution to ensure that membranes can be made over wide variations in the PES polymer concentration. In general, membrane permeability decreases and solute separation ability increases as the PES concentration increases. However, for both flat and HF membranes, performance is strongly dependent on whether the PES concentration is above or below the critical value. Flux greatly decreases and solute-separation ability increases when the critical PES concentration is surpassed. Membrane performance is generally optimized when the PES concentration is at the critical value.     

进水水质对EDI产水电阻率的影响分析

分别讨论了电导率、总有机碳（TOC）、可溶性硅、硬度及游离CO2等进水水质指标短时间恶化对于EDI膜堆产水电阻率的影响,给出了EDI膜堆相关性能的恢复能力,为EDI系统的运行提供相关依据。     

Effect of Pharmaceuticals on the Performance of a Novel Osmotic Membrane Bioreactor (OMBR)

The integration of forward osmosis (FO) and biological process, known as the osmotic membrane bioreactor (OMBR), may be viewed as beyond the state of the art for used water treatment and water reclamation. While it is known that the OMBR is able to produce good product water quality in terms of total organic carbon (TOC) removal, limited information is available on the removal of organic micro-pollutants in relation to process performance under the concentrated environment. In this study, a novel OMBR system was continuously operated over 73 days, during which pharmaceuticals were dosed on two occasions into the system. It was found that while pharmaceutical removal was high (>96%), other process parameters in the form of TOC, mixed liquor suspended solids (MLSS) and extracellular polymeric substances (EPS) were unmistakably affected. The major portion of TOC that permeated the FO membrane was found to be low-molecular weight neutral compounds which were associated with the impaired biological process. Microbiological analysis confirmed shifts in microbial populations occurred due to the increased salinity and dosage of the pharmaceuticals. The study demonstrated the importance of the biological process for optimal OMBR system performance, and paves the way for further research in this direction.     

渗透模式影响纳米涂层修饰陶瓷微滤膜分离性能的研究

研究了膜分离技术处理含油废水存在因油滴变形引起的膜堵塞问题.为减少膜污染,使用在市场上销售氧化铝微滤膜孔道表面制备纳米ZrO2涂层,利用纳米涂层改变微滤膜的表面亲水憎油性,具有良好的效果.考虑其工业应用条件,重点研究了循环模式(模拟大量废水处理)和浓缩模式(模拟少量废水处理)对膜渗透通量的影响.结果表明:循环模式下料液的油浓度为恒定的,纳米涂层能有效提高微滤膜的渗透通量.膜面流速的增加在一定程度上能提高膜渗透通量,但超过一定程度后,增加不明显.当膜面流速为7 m/s时,修饰陶瓷膜的最大渗透通量为280 L/(m2·h),油截留率为96.4％.在浓缩模式下,料液的油浓度随渗透液的排出呈指数性增加,随着油浓度的增加,渗透通量持续衰减,油截留率持续上升.当油浓度达到一定程度后,修饰陶瓷微滤膜不能有效地实现稳定含油废水的油水分离.     

渗透模式影响纳米涂层修饰陶瓷微滤膜分离性能的研究

研究了膜分离技术处理含油废水存在因油滴变形引起的膜堵塞问题。为减少膜污染,使用在市场上销售氧化铝微滤膜孔道表面制备纳米ZrO2涂层,利用纳米涂层改变微滤膜的表面亲水憎油性,具有良好的效果。考虑其工业应用条件,重点研究了循环模式（模拟大量废水处理）和浓缩模式（模拟少量废水处理）对膜渗透通量的影响。结果表明：循环模式下料液的油浓度为恒定的,纳米涂层能有效提高微滤膜的渗透通量。膜面流速的增加在一定程度上能提高膜渗透通量,但超过一定程度后,增加不明显。当膜面流速为7m／s时,修饰陶瓷膜的最大渗透通量为280L／（m^2·h）,油截留率为96．4％。在浓缩模式下,料液的油浓度随渗透液的排出呈指数性增加,随着油浓度的增加,渗透通量持续衰减,油截留率持续上升。当油浓度达到一定程度后,修饰陶瓷微滤膜不能有效地实现稳定含油废水的油水分离。     

微波辐照对废地膜混杂增强复合材料力学性能的影响

采用自行改造的微波辐照装置对PE-g-MA增容废地膜混杂增强复合材料进行微波辐照处理,研究了微波辐照对混杂增强废地膜材料力学性能的影响.研究结果表明:经微波辐照后,共混材料的界面相容性得到改善、力学性能得到提高.当微波功率为200 W,辐照时间为240 s时,共混体系的拉伸强度和冲击强度达到最大值,分别提高了13.16%和23.93%;衰减全反射(ATR)分析表明:微波辐照可以改善废地膜混杂复合材料的界面相容性、提高其力学性能,主要是物理浸润作用的结果.     

磺化聚砜对聚砜中空纤维膜结构与性能的影响

以聚乙二醇(PEG)为添加剂,二甲基乙酰胺(DMAc)为溶剂,采用浸没沉淀法制备了磺化聚砜(SPSF)/聚砜(PSF)中空纤维膜,考察了SPSF对聚砜中空纤维膜结构及性能的影响。实验结果表明:添加SPSF后,因其在分子链中产生的极性磺酸基团,使聚砜膜的表面接触角从94.7°降低到75°,平均孔径增加15.8%,其纯水通量较之未加入SPSF大幅提高,纯水通量从未添加SPSF时的129.2 L/(m~2·h)增加到了312.4 L/(m~2·h)。当SPSF质量分数为1.5%,PEG/DMAc为35/45,空气间隙为5 cm时,膜的综合性能最好。此时,纯水通量为302.6 L/(m~2·h),对牛血清蛋白溶液(BSA)的截留率为93.1%,孔隙率为76.1%,平均孔径55.2 nm,拉伸强度为4.89 MPa。     

多孔中空纤维膜制备及后处理对膜性能的影响

采用干-湿法纺丝工艺,以N,N-二甲基乙酰胺为溶剂,聚乙烯吡咯烷酮(PVP)为添加剂,制备聚偏氟乙烯/聚氯乙烯/聚甲基丙烯酸甲酯共混五孔中空纤维膜,研究了纺丝工艺参数以及后处理对膜性能的影响.结果表明,当干纺程为20 cm,芯液中DMAC质量分数为40%,芯液流量为13 mL/min时,制备的纤维膜综合性能最好.该中空纤维膜最大水通最为612 L/(m2·h),截留率为83%.