Systematic analysis and optimization of power generation in pressure retarded osmosis: Effect of multistage design

This work presents a systematic method for analysis and optimization of specific energy production (SEP) of pressure retarded osmosis (PRO) systems employing single‐stage configuration as well as multistage design with interstage hydro‐turbines. It is shown that the SEP normalized by the draw solution feed osmotic pressure increases with the number of stages as well as a dimensionless parameter . As compared to the single‐stage PRO, the multistage arrangement not only increases flux and volume gain, but also allows a stage‐dependent, progressively decreasing hydraulic pressure, both of which contribute to enhanced SEP and power density. At the thermodynamic limit where γ_tot goes to infinity, the theoretical maximum SEP by an N‐stage PRO system is , where q_tot is the ratio of the draw solution flow rate at the outlet to the inlet on the system level. For single‐stage PRO, it is no more than π₀. For infinite number of stages, the theoretical limit becomes . SEP under realistic conditions and practical constraints on multistage design are discussed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 144–152, 2018     

Robust and high performance pressure retarded osmosis hollow fiber membranes for osmotic power generation

Novel fabrication perspectives have been demonstrated to molecularly construct robust hollow fiber membrane supports for high performance thin‐film composite (TFC) pressure retarded osmosis (PRO) membranes. For the first time, we found that the desirable hollow fiber supports should possess high stretch resistance and acceptable ductility. The microstructure strength of the hollow fiber support may have more weights on overall robustness of the TFC PRO membranes than the apparent cross‐section morphology. Effectively manipulating the kinetics of phase inversion during spinning by maneuvering bore fluid chemistry, and polymer solution composition is a promising method to tailor the strength of hollow fiber supports. Prestabilization of the TFC membranes at elevated lumen pressures can significantly improve their PRO performance. The newly developed TFC PRO hollow fiber membranes exhibit a power density as high as 16.5 W/m² and a very low specific reverse salt flux (J_s/J_w) of 0.015 mol/L at a hydraulic pressure of 15 bar using synthetic seawater brine (1.0 M NaCl) as the draw solution. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1107–1119, 2014     

压力延滞渗透膜的研究进展

压力延滞渗透(pressure retarded osmosis,PRO)是一种利用不同浓度溶液间渗透压差进行产能的新型膜技术。膜是PRO过程的核心元件,对其产能效果有巨大影响。PRO膜需要有良好的水渗透性和较高的截留率,并具有足够的强度承受高压。首先阐述了PRO过程对膜性能的要求,然后从活性层、支撑层及物理/化学预处理3个方面归纳了当前广泛使用的非对称膜的研究进展,总结了膜材料、制备过程和预处理等对膜性能的影响。同时,归纳了对称膜及准对称膜方面的研究状况,两者可有效降低膜的内部浓差极化现象(ICP),是未来PRO膜研究的一个重要方向。     

Progress in pressure retarded osmosis (PRO) membranes for osmotic power generation

The rapid increases in global energy consumption and greenhouse gas emissions have stimulated the exploration of renewable energy sources as alternative fuels. Osmotic pressure gradient energy released from the mixing of water streams with different salinities is an unexploited resource of renewable energy. By employing a semipermeable membrane to control the mixing process, the osmotic pressure gradient energy can be harvested in terms of electrical power via pressure retarded osmosis (PRO) without causing adverse environmental impacts. The ideal of harvesting osmotic power via PRO was proposed in the early seventies; however, the absence of effective membranes with desirable structure and performance hindered further advancement of the PRO technology. During the last few years, a significant progress in PRO technology has been achieved. Novel flat-sheet and hollow fiber polymeric membranes with desired structure, mechanical robustness and permeation characteristics have been developed for PRO applications. Membranes with a target power density of 5 W/m² to produce commercially viable PRO processes have been achieved. At this point of time, a comprehensive review is imperative in order to summarize what we have accomplished and provide insights for the development of next generation PRO membranes. After a brief introduction of the PRO process and the early PRO development using the existing RO/NF and FO membranes, this review focuses primarily on novel and the state-of-the-art PRO membranes. Furthermore, the requirements for fabricating effective PRO membranes will be discussed and future perspectives will be presented.     

反渗透和压力延迟渗透耦合脱盐系统的能效优化研究

针对开环和闭环两类结构的反渗透-压力延迟渗透耦合脱盐系统进行了模型构建与系统优化分析。首先，以标准化比能耗为目标函数，构建了开环结构和闭环结构耦合系统的非线性约束优化模型。在优化模型中，引入包括半透膜性能、操作状态及设计变量的无量纲参数组，建立反渗透和压力延迟渗透单元过程的特征方程以简化模型。同时，为了保证比较的公平性，开环结构的总体能耗中额外包含了预处理和后处理能耗。通过求解上述优化模型，系统地比较和分析了无量纲半透膜总面积和水回收率同时变化导致的最优标准化比能耗、膜面积分配和操作压力的变化规律。结果表明，在水回收率处于正常水平(≤ 0.55)且系统总面积充足(≥0.9)时，闭环结构在节能及减少预处理费用方面比开环结构具有更明显优势。     

隔网对压力延迟渗透过程性能的影响

建立了一个将局部跨膜渗透过程和全尺寸通道内流动过程相结合的多尺度理论模型,通过计算各物理参数沿膜组件的分布来确定全尺寸应用下压力延迟渗透过程的工作性能。通过数值计算,重点研究了隔网的孔隙率、厚度以及层数对全尺寸应用下压力延迟渗透过程性能的影响,发现提高原料液和提取液隔网的孔隙率可以提高压力延迟渗透过程的功率密度,但是同时会降低该过程的比能。降低原料液隔网的厚度和提高提取液隔网的厚度可以提高该过程的功率密度,而原料液和提取液隔网厚度的降低均可以提高该过程的比能。多层隔网会对压力延迟渗透过程的能量密度和比能均产生负面影响。本文研究结果可以为膜组件的设计提供参考：原料液隔网应当具有相对较小的孔隙率和厚度,而提取液隔网应当具有相对较大的孔隙率和厚度,尽量不要使用多层隔网。     

正渗透原理及分离传质过程浅析

正渗透是一种新兴的膜分离技术,因其低能耗、抗污染、对污染物截留能力广等的潜力,在脱盐、废水处理、农业和电力等领域的应用前景备受瞩目。本文介绍了正渗透概念和原理,通过正渗透传递过程的现象学模型,对浓差极差极化与质量传递的关系作出分析,提出了强化正渗透传质过程的一些建议。     

Pressure retarded osmosis: From the vision of Sidney Loeb to the first prototype installation — Review

The energy released from the mixing of freshwater with saltwater is a source of renewable energy that can be harvested using pressure retarded osmosis (PRO). In PRO, water from a low salinity solution permeates through a membrane into a pressurized, high salinity solution; power is obtained by depressurizing the permeate through a hydroturbine. The combination of increased interest in renewable and sustainable sources of power production and recent progress in membrane science has led to a spike in PRO interest in the last decade. This interest culminated in the first prototype installation of PRO which opened in Norway in late 2009. Although many investigators would suggest there is still lack of theoretical and experimental investigations to ensure the success of scaled-up PRO, the Norway installation has evoked several specialized and main-stream press news articles. Whether the installation and the press it has received will also boost competitive commercialization of membranes and modules for PRO applications remains to be seen. This state-of-the-art review paper tells the unusual journey of PRO, from the pioneering days in the middle of the 20th century to the first experimental installation.     

界面聚合中空纤维正渗透膜的制备和表征

以聚砜为原料,通过浸没沉淀法制备中空纤维基膜,然后采用界面聚合法制备出中空纤维正渗透膜。考察了制膜参数、基膜结构和FO性能三者之间的关系。结果表明基膜的厚度为影响FO性能的主要因素之一。基膜的厚度越厚,FO过程中渗透效率越低。制得PSF中空纤维正渗透膜的厚度为0.129 mm,断裂拉伸力为2.48 N,FO通量为10.3 L·m^-2·h^-1,逆向盐扩散性能为0.15 g·L^-1。     

Osmotic power — power production based on the osmotic pressure difference between waters with varying salt gradients

Statkraft engaged in the development of osmotic power technology in 1997, and is today the most prominent developer of the osmotic power technology in a global context. The commercialisation of osmotic power is dependent on large volumes of sufficiently efficient semi-permeable membranes with high flux and salt retention. In addition to developing the technological concept and critical parts of the system, such as the membrane technology, Statkraft has also identified the energy potential, the financial aspects and the environmental implications of the technology. Osmotic power stands out as a promising and yet unexploited, new renewable energy sources. Throughout the last years, Statkraft has been successful in its furtherance of the necessary membrane technology and has recently started the detailed planning and design of the first osmotic power prototype plant in which it will further verify and test the technology.     

Effects of free volume in thin‐film composite membranes on osmotic power generation

For the first time, the effects of free volume in thin‐film composite (TFC) membranes on membrane performance for forward osmosis and pressure retarded osmosis (PRO) processes were studied in this work. To manipulate the free volume in the TFC layer, a bulky monomer (i.e., p‐xylylenediamine) was blended into the interfacial polymerization and methanol immersion was conducted to swell up the TFC layer. Results from positron annihilation lifetime spectroscopy (PALS) show that p‐xylylenediamine blending and methanol induced swelling enlarge and broaden the free volume cavity. In addition, the performance of TFC membranes consisting of different free volumes were examined in terms of water flux, reverse salt flux, and power density under high pressure PRO operations. The TFC‐B‐5 membrane (i.e., a TFC membrane made of blending monomers) with a moderate free volume shows the highest power density of 6.0 W/m² at 9 bar in comparison of TFC membranes with other free volumes. After PRO operations, it is found that the free volume of TFC layers decreases due to high pressure compression, but membrane transport properties in terms of water and salt permeability increase. Interestingly, the membrane performance in terms of resistance against high pressures and power density stay the same. A slow positron beam was used to investigate the microstructure changes of the TFC layer after PRO operations. Compaction in free volume occurs and the TFC layer becomes thinner under PRO tests but no visible defects can be observed by both scanning electronic microscopy and PALS. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4749–4761, 2013     

反渗透系统中浓差极化的影响

以实测数据为依据,论证了反渗透膜系统中浓差极化的影响,测定了保证系统稳定运行时浓差极化系数的临界值。由此为反渗透膜系统的稳定运行与优化设计提供了一个重要依据。     

影响反渗透制备脱离子水的运行因素

介绍了影响反渗透装置制备脱离子水的运行因素并进行了有针对性的分析,提出了相应的预防措施。     

反渗透系统中难溶盐极限回收率的解析分析

基于反渗透系统给水三类难溶盐饱和度的解析计算,计及了温度、pH、回收率、阻垢剂及浓差极化等因素的影响,导出了用系统给水参数解析表达的反渗透系统浓水难溶盐饱和度,得出了反渗透系统给水参数决定的系统难溶盐极限回收率．从而为反渗透系统的极限收率指标提供一个简捷而清晰的求取方式。     

Osmotic power production from seawater brine by hollow fiber membrane modules: Net power output and optimum operating conditions

This study analyzes the net energy output and optimum operating conditions for osmotic power generation from seawater brine based on the currently available hollow fiber membranes in the module scale. Factors that are influential on membrane performances, such as external concentration polarization, internal concentration polarization, salt reverse diffusion, and dilution have been taken into account. Net power density is defined and applied to characterize the efficiency of the PRO system, in terms of power production minus pumping energy, pretreatment cost and energy consumption by pressure drop in the membranes. When using 1 M NaCl as the draw solution and 10 mM NaCl as the feed, it is found that up to 7 W m^?2 net power density can be harvested by the PRO system depending on the water sources. Coupling with the existing RO plant is highly beneficial in terms of readily available high pressure source, high salinity and less or negligible pretreatment costs for the draw solution. Sources with higher salt concentrations are preferred. The optimum hydraulic pressure, module length, flow rate to membrane area ratio and feed to draw flow rate ratio have also been analyzed to maximize the net power output. In addition, implications on hollow fiber development are discussed. Fibers with high water permeability, lower structural parameter, good mechanical stability, better fouling resistance, and outer‐selective configurations are recommended for further studies. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1216–1225, 2016     

A novel ammonia—carbon dioxide forward (direct) osmosis desalination process

A novel forward (direct) osmosis (FO) desalination process is presented. The process uses an ammonium bicarbonate draw solution to extract water from a saline feed water across a semi-permeable polymeric membrane. Very large osmotic pressures generated by the highly soluble ammonium bicarbonate draw solution yield high water fluxes and can result in very high feed water recoveries. Upon moderate heating, ammonium bicarbonate decomposes into ammonia and carbon dioxide gases that can be separated and recycled as draw solutes, leaving the fresh product water. Experiments with a laboratory-scale FO unit utilizing a flat sheet cellulose tri-acetate membrane demonstrated high product water flux and relatively high salt rejection. The results further revealed that reverse osmosis (RO) membranes are not suitable for the FO process because of relatively low product water fluxes attributed to severe internal concentration polarization in the porous support and fabric layers of the RO membrane.     

正渗透膜材料的研究进展

正渗透技术因其低能耗、耐污染等优势受到国际和国内众多学者的关注,尤其近几年来,取得了迅速发展。本文对正渗透过程中的影响因素以及浓差极化现象作了简要分析,结果表明,内浓差极化是影响正渗透技术效率低下的重要因素,而制备适当的膜材料是有效改善内浓差极化的关键技术。回顾了正渗透分离技术在国内外的发展历程,通过不懈的探索和研发,先后成功制备得到不同材料和结构的正渗透膜。重点讲述膜材料在正渗透领域所取得的最新研究进展,最后指出众多正渗透膜材料由于条件限制难以推广应用,希望在未来的研究过程中突破这项技术难题,缩短科研理论与实际应用之间的差距,在膜材料的实际应用方面取得创新性成果。     

反渗透技术在纯水制备中的应用

主要介绍了反渗透制备纯水的生产工艺技术,以及生产操作中影响反渗透膜性能的主要因素。     

A trimethylamine–carbon dioxide draw solution for osmotic engines

This study evaluates the pressure retarded osmosis performance of TMA–CO₂ for potential use in osmotic heat engines. Power densities up to 18.6 W m^?2 were achievable at relatively low pressure (10 bar) using 5 M TMA–CO₂ draw solutions. Compared to NaCl control tests, the TMA–CO₂ exhibited 20% lower water flux due in large part to its larger molecular size and associated higher solution viscosity and lower diffusion coefficient. Compared to the ammonia‐carbon dioxide draw solution, water flux was comparable but reverse solute flux of TMA–CO₂ was nearly one order of magnitude lower. Larger solute size was found to create a performance tradeoff as reduced reverse solute flux improved water flux while higher viscosity and lower diffusion coefficient worsened water flux. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3369–3375, 2018     

热电厂反渗透系统污堵原因解析及处理

某热电厂保安过滤器滤芯更换频繁,一级反渗透系统污堵较快.通过检查及分析,系统预处理未进行有效杀菌导致水体内微生物滋生是系统污堵的主要原因.现场采取调节杀菌剂加药量、增设分段杀菌装置及系统整体灭活等处理措施,取得了较好的效果.