Spiral-wound Modules Research Articles

Quantitative estimation of internal concentration polarization in a spiral wound forward osmosis membrane module compared to a flat sheet membrane module

Internal concentration polarization (ICP) within the forward osmosis (FO) membrane affects the reduction of driving force. The magnitude of ICP in the FO membrane was investigated experimentally by measuring water flux in both spiral wound (SW) and flat-sheet (FS) modules with different draw solutions (sodium chloride, sodium sulfate, and disodium phosphate). The FO SW module always shows inferior water flux performance to the FO FS module. The water flux in the FO SW module can be easily estimated by just changing structure parameter. The estimated structure parameter in the FO SW module is 9.1325×10−4 m, which is quite higher than 4.2×10−4 m in the FO FS module. The increase of the structure parameter is attributed to the bending of the FO membrane in the SW module. It can be concluded that a module design such like SW type is not suitable for the FO process.

Full-scale direct contact membrane distillation (DCMD) model including membrane compaction effects

While many models exist in the literature for description of lab-scale direct contact membrane distillation (DCMD) performance, only a handful of modelling attempts at full-scale have been described. In this article a method is presented for the simulation of the flux and energy efficiency of a full-scale, counter-currently operated, spiral-wound DCMD module. The model is based on a previously calibrated lab-scale model. The geometry of the full-scale, spiral-wound module is discretized into small sections and the lab-scale model is applied in each section. It was found that the membrane used in this module compacts significantly under the operational conditions. This effect cannot be neglected, therefore the model had to be extended to account for it. It is noteworthy that, apart from this extension, no additional model calibration at full-scale was needed. Given its validity at full-scale the model can be safely used for extended scenario analysis with regard to the optimization of the module design. The developed model and method are powerful tools to decide on system design and operation.

The effect of backing layer for pro membranes and modules

There has been increasing global interest in the environmental pollution problems produced by fossil fuel consumption and greenhouse gas emissions. In order to tackle these issues, new renewable energy such as solar, wind, bio gas, fuel cell and pressure retarded osmosis(PRO) have been developed extensively. Among these energy sources, PRO is one of the salinity gradient power generation methods. In PRO, energy is obtained by the osmotic pressure generated from the concentration difference between high and low concentration solutions separated by a semipermeable membrane. The development for high power density PRO membranes is imperative with the purpose of commercialization. This study investigates development of thin film composite PRO membrane and spiral wound module for high power density. Also, the influence of membrane backing layer on power density was identified, and the characteristic factors of PRO membranes was determined. Different backing layers were used to improve power density. As expected, the PRO membrane with more porous backing layer showed higher power density.

Wastewater treatment by spiral wound reverse osmosis: Development and validation of a two dimensional process model

Reverse osmosis (RO) has become a significant method for removing salts and organic compounds from seawater and wastewater in recent decades. Spiral-wound module has been widely used due to a number of special features such as high packing density, premium separation and low operating cost. In this paper, a two-dimensional mathematical model is developed for the transport of dilute aqueous solutions through a spiral-wound RO module and the operational characteristics of the process under steady state conditions are analysed. The model is based on the solution-diffusion model coupled with the concentration polarization mechanism. This model yields a set of Differential and Algebraic Equations (DAEs), which are solved using the gPROMS software. The model is validated using experimental data from the literature for the rejection of dimethylphenol as solute in aqueous solutions. The model is then used to simulate the process under steady state conditions to gain deeper insight of the process.

Characterization of feed channel spacer performance using geometries obtained by X-ray computed tomography

Spiral-wound membrane modules used in water treatment for water reuse and desalination make use of spacer meshes for keeping the membrane leaves apart and for enhancing the mass transfer. Computational fluid dynamics (CFD) has gained importance in the design of new spacers with optimized hydrodynamic characteristics, but this requires a precise description of the spacer geometry. This study developed a method to obtain accurate three-dimensional (3-D) geometry representations for any given spacer design from X-ray computed tomography (CT) scans. The method revealed that the filaments of industrial spacers have a highly variable cross-section size and shape, which impact the flow characteristics in the feed channel. The pressure drop and friction factors were calculated from numerical simulations on five commercially available feed spacers used in practice. Model solutions compared well to experimental data measured using a flow cell for average velocities up to 0.2m/s, as used in industrial reverse osmosis and nanofiltration membrane operations. A newly-proposed spacer geometry with alternating strand thickness was tested, which was found to yield a lower pressure drop while being highly efficient in converting the pumping power into membrane shear. Numerical model solutions using CFD with geometries from CT scans were closer to measurements than those obtained using the traditional circular cross-section strand simplification, indicating that CT scans are very well suitable to approximate real feed spacer geometries. By providing detailed insight on the spacer filament shape, CT scans allow better quantification of local distribution of velocity and shear, possibly leading to more accurate estimations of fouling and concentration polarization.

Spatial heterogeneity of biofouling under different cross-flow velocities in reverse osmosis membrane systems

The spatially heterogeneous distribution of biofouling in spiral wound membrane systems restricts (i) the water distribution over the membrane surface and therefore (ii) the membrane-based water treatment. The objective of the study was to assess the spatial heterogeneity of biofilm development over the membrane fouling simulator (MFS) length (inlet and outlet part) at three different cross-flow velocities (0.08, 0.12 and 0.16m/s). The MFS contained sheets of membrane and feed spacer and simulated the first 0.20m of spiral-wound membrane modules where biofouling accumulates the most in practice. In-situ non-destructive oxygen imaging using planar optodes was applied to determine the biofilm spatially resolved activity and heterogeneity.Comparison of the inlet and outlet position of the MFS showed a more (i) heterogeneous biofilm distribution and a (ii) higher biological activity at the inlet side (first 2.5cm) for all cross-flow velocities. The lowest cross-flow velocity had the highest biomass activity particularly at the inlet side. A better characterization of biofilm development, including the factors that influence the biofilm spatial heterogeneity in membrane systems with time, may help to develop effective strategies for biofouling control in membrane systems.

A predictive model for spiral wound reverse osmosis membrane modules: The effect of winding geometry and accurate geometric details

Abstract A new one-dimensional predictive model for spiral wound modules (SWMs) applied to reverse osmosis membrane systems is developed by incorporating a detailed description of the geometric features of SWMs and considering flow in two directions. The proposed model is found to capture existing experimental data well, with similar accuracy to the widely-used plate model in which the SWM is assumed to consist of multiple thin rectangular channels. However, physical parameters that should in principle be model-independent, such as membrane permeability, are found to differ significantly depending on which model is used, when the same data sets are used for parameter estimation. Conversely, when using the same physical parameter values in both models, the water recovery predicted by the plate-like model is 12–20% higher than that predicted by the spiral model. This discrepancy is due to differences in the description of geometric features, in particular the active membrane area and the variable channel heights through the module, which impact on predicted performance and energy consumption. A number of design variables – the number of membrane leaves, membrane dimensions, centre pipe radius and the height of feed and permeate channels – are varied and their effects on performance, energy consumption and calculated module size are analysed. The proposed spiral model provides valuable insights into the effects of complex geometry on the performance of the SWM as well as of the overall system, at a low computational cost.

Development of a mathematical model for apple juice compounds rejection in a spiral-wound reverse osmosis process

The use of Reverse Osmosis (RO) membrane processes for the clarification and the concentration of apple juice is proposed as an alternative to the conventional concentration technique, which is based on evaporation and freezing. Several models have been published on RO process models relying on different assumptions that predict the permeate flux and aroma compounds rejections for aqueous solutions apple juice. The solution-diffusion model (Lumped model) has been applied for the previous models. The main instrument of this study is the use of the gPROMS software to develop a new distributed steady state model that will relax a number of earlier assumptions.The model has been validated with an observational data of apple juice filtration derived from the literature by analysing the permeate flux and the performance of membrane rejection at different concentrations, temperatures and pressures for a laboratory scale of spiral-wound RO module. Simulated results corroborate with experimental and model predictions.

Modeling, control, and dynamic performance analysis of a reverse osmosis desalination plant integrated within hybrid energy systems

An RO (reverse osmosis) desalination plant is proposed as an effective, FLR (flexible load resource) to be integrated into HES (hybrid energy systems) to support various types of ancillary services to the electric grid, under variable operating conditions. To study the dynamic analysis of such system, special attention is given here to the detailed dynamic modeling and control design of RO desalination process that employs a spiral-wound membrane module. In particular, the solution-diffusion model modified with the concentration polarization theory is applied to predict RO performance over a large range of operating conditions. Simulation results involving several case studies suggest that an RO desalination plant can provide operational flexibility to participate in energy management at the utility scale by dynamically optimizing the use of excess electrical energy. The incorporation of additional commodity (fresh water) produced from a FLR allows a broader range of HES operations for maximizing overall system performance and profitability.

Mini-review: novel non-destructive in situ biofilm characterization techniques in membrane systems

Membrane systems are commonly used in the water industry to produce potable water and for advanced wastewater treatment. One of the major drawbacks of membrane systems is biofilm formation (biofouling), which results in an unacceptable decline in membrane performance. Three novel in situ biofouling characterization techniques were assessed: (i) optical coherence tomography (OCT), (ii) planar optodes, and (iii) nuclear magnetic resonance (NMR). The first two techniques were assessed using a biofilm grown on the surface of nanofiltration (NF) membranes using a transparent membrane fouling simulator that accurately simulates spiral wound modules, modified for in situ biofilm imaging. For the NMR study, a spiral wound reverse osmosis membrane module was used. Results show that these techniques can provide information to reconstruct the biofilm accurately, either with 2-D (OCT, planar optodes and NMR), or 3-D (OCT and NMR) scans. These non-destructive tools can elucidate the interaction of hydrodynamics and mass transport on biofilm accumulation in membrane systems. Oxygen distribution in the biofilm can be mapped and linked to water flow and substrate characteristics; insights on the effect of crossflow velocity, flow stagnation, and feed spacer presence can be obtained, and in situ information on biofilm structure, thickness, and spatial distribution can be quantitatively assessed. The combination of these novel non-destructive in situ biofilm characterization techniques can provide real-time observation of biofilm formation at the mesoscale. The information obtained with these tools could potentially be used for further improvement in the design of membrane systems and operational parameters to reduce impact of biofouling on membrane performance.

Modeling of a forward osmosis and a pressure-retarded osmosis spiral wound module using the Spiegler-Kedem model and experimental validation

Abstract A mathematical model is developed for a spiral wound module for both forward osmosis (FO) and pressure-retarded osmosis (PRO) applications. This model is obtained by combining the membrane transport, external concentration polarization, and internal concentration polarization models with the pressure drop and mass balance equations for both the feed as well as the draw solutions. The Spiegler-Kedem (SK) model is used for describing the local mass transport in the active layer of the membrane. In addition, a new expression is established for determining the internal concentration polarization in the support layer of the membrane. A nonlinear constrained optimization technique is then applied, along with the experimental data for FO and PRO, to predict the unknown parameters of the mathematical model for the spiral wound module. To ensure the validity of the proposed model and predicted parameters, the model is again used to predict and compare the performance of the module at a variety of operating conditions. Apart from this, the product recovery and the energy extraction efficiency of the module at a variety of operating conditions are also analyzed. Lastly, we have tried to answer the question, whether the Solution Diffusion (SD) based model or the SK based model is better for design and analysis, and for obtaining the optimal operating conditions for both FO as well as PRO applications.

Multi-scale modelling of OSN batch concentration with spiral-wound membrane modules using OSN Designer

Three commercial spiral-wound membrane modules of different sizes, from 1.8″×12″ to 4.0″×40″, are used to concentrate a solution of sucrose octaacetate in ethyl acetate under different operating conditions. A mathematical model to describe the batch concentration process is developed, based on a combination of the classical solution diffusion membrane transport model and the film theory, to account for the mass transfer effects. The model was implemented using the “OSN Designer” software tool. The membrane transport model parameters as well as all parameters in the pressure drop and mass transfer correlations for the spiral-wound modules were obtained from regression on a limited number of experimental data at steady state conditions. Excellent agreement was found between the experimental and multi-scale modelling performance data under various operating conditions. The results illustrate that the performance of a large scale batch concentration process with spiral-wound membrane modules can be predicted based on laboratory crossflow flat sheet test data when the fluid dynamics and mass transfer characteristics in the module, and the necessary channel geometry are known. In addition, the effects of concentration polarisation, pressure drop through feed and permeate channels, and thermodynamic non-ideality of the solution at large scale batch concentration are also investigated.

Influence of hydrocarbon species on the removal of thiophene from FCC gasoline by using a spiral wound pervaporation module

Pervaporation is an emerging technology in the field of thiophene removal from the Fluid Catalytic Cracker (FCC) gasoline. The performance of pervaporation process for thiophene removal depends on different types of hydrocarbon species present in the FCC gasoline due to their distinctive transport properties in the membrane, as well as due to their distinct physical and thermal properties. In membrane modules, the presence of different hydrocarbon species may also affect the variations in flow variables such as the temperature and concentrations in the feed and permeate channels. This in turn may further influence the performance of the module. The present study shows how different hydrocarbon species present in the gasoline influence the performance of a spiral wound module. First, the experimental data for a number of binary mixtures are obtained for a variety of hydrocarbons and thiophene. This data is then analysed by using a mathematical model for the spiral wound module. The membrane transport parameters are determined by using a parameter estimation technique. The results indicate that the thiophene (C4H4S) removal from different binary mixtures may be sorted out based on the type of hydrocarbon species present in the binary mixtures as linear alkane>alkene>branched alkane>aromatic compounds. Results for a ternary mixture show that the same mathematical model may also be used for predictions of the module performance by assuming the ternary mixture to be equivalent to a binary mixture of two species: first is thiophene, and second species is a pseudo-species, having the average physical properties of two other hydrocarbons present in the ternary mixture. The same approach may be extended to a multicomponent feed of a real FCC gasoline, containing a variety of hydrocarbons and sulphur containing compounds. This approach may provide sufficiently accurate predictions with much lesser efforts in comparison to more rigorous, and much more tedious, multicomponent modelling.

A pilot-scale forward osmosis membrane system for concentrating low-strength municipal wastewater: performance and implications.

Recovery of nutrients and energy from municipal wastewater has attracted much attention in recent years; however, its efficiency is significantly limited by the low-strength properties of municipal wastewater. Herein, we report a pilot-scale forward osmosis (FO) system using a spiral-wound membrane module to concentrate real municipal wastewater. Under active layer facing feed solution mode, the critical concentration factor (CCF) of this FO system was determined to be 8 with 0.5 M NaCl as draw solution. During long-term operation at a concentration factor of 5, (99.8 ± 0.6)% of chemical oxygen demand and (99.7 ± 0.5)% of total phosphorus rejection rates could be achieved at a flux of 6 L/(m2 h) on average. In comparison, only (48.1 ± 10.5)% and (67.8 ± 7.3)% rejection of ammonium and total nitrogen were observed. Cake enhanced concentration polarization is a major contributor to the decrease of water fluxes. The fouling also led to the occurrence of a cake reduced concentration polarization effect, improving ammonium rejection rate with the increase of operation time in each cycle. This work demonstrates the applicability of using FO process for wastewater concentrating and also limitations in ammonium recovery that need further improvement in future.

Process engineering optimization of nanofiltration unit for the treatment of textile plant effluent in view of solution diffusion model

A nanofiltration (NF) based separation process is used to treat the effluent from a textile plant to allow for water reuse and fulfill environmental standards. The wastewater effluent contains reactive black (RB5)- and disperse (DR60) dyes. A NF-unit model E2 series with HL 2521 TF spiral wound module was used to carry out experiments. 90 & 93% color removal and COD reduction for RB5 and 98 & 95% for DR60 were achieved. A parametric study of the separation process is undertaken to characterize the effects of the operating variables, e.g., trans-membrane pressure, dye/salt concentration in the feed, temperature, and cross flow velocity. The solution diffusion model was used to develop power correlations to calculate the permeate side solute mass transfer coefficient as a function of effective cross-flow Reynolds number. In contrast to the commonly assumed constant hydraulic solvent permeability, a non-linear relationship was developed over the applied trans-membrane net driving pressure. The latter correlates exponentially with salt permeability for both dyes. The effects of feed salt-content on solute mass transfer coefficient, water and salt permeability, concentration polarization, dye hydrophobicity and ionic strength were studied. Results were used to assess engineering specifications of a commercial size NF-plant (500m3/d capacity).

Membrane technologies in the solution of environmental problems

The currently available reverse osmosis, nanofiltration, and ultrafiltration membrane technologies can be used in the solution of different problems related to the treatment of strongly polluted waters of different origin and the reuse of effluents. Nevertheless, experience in the operation of membrane facilities shows the existence of specific problems due to membrane fouling and measures for its averting. As a result of the extensive studies of the mechanisms of scaling, a new approach was proposed to decrease the fouling of membranes, which consists in the improvement of the construction of a membrane channel and in the selection of membrane characteristics. The developed design of open-channel spiral-wound modules makes it possible to exploit membrane units almost without the danger of scaling and to create new effective water treatment technologies on this basis. Long-term studies and pilot tests made it possible to develop a procedure for the optimization of membrane unit operations with minimum expenditures on electric power, maintenance, and effluent discharge.

Experimental and numerical characterization of the water flow in spacer-filled channels of spiral-wound membranes

Micro-scale flow distribution in spacer-filled flow channels of spiral-wound membrane modules was determined with a particle image velocimetry system (PIV), aiming to elucidate the flow behaviour in spacer-filled flow channels. Two-dimensional water velocity fields were measured in a flow cell (representing the feed spacer-filled flow channel of a spiral wound reverse osmosis membrane module without permeate production) at several planes throughout the channel height. At linear flow velocities (volumetric flow rate per cross-section of the flow channel considering the channel porosity, also described as crossflow velocities) used in practice (0.074 and 0.163 m·s−1) the recorded flow was laminar with only slight unsteadiness in the upper velocity limit. At higher linear flow velocity (0.3 m·s−1) the flow was observed to be unsteady and with recirculation zones. Measurements made at different locations in the flow cell exhibited very similar flow patterns within all feed spacer mesh elements, thus revealing the same hydrodynamic conditions along the length of the flow channel. Three-dimensional (3-D) computational fluid dynamics simulations were performed using the same geometries and flow parameters as the experiments, based on steady laminar flow assumption. The numerical results were in good agreement (0.85–0.95 Bray–Curtis similarity) with the measured flow fields at linear velocities of 0.074 and 0.163 m·s−1, thus supporting the use of model-based studies in the optimization of feed spacer geometries and operational conditions of spiral wound membrane systems.

Characterization of membrane fouling distribution in a spiral wound module using high-frequency ultrasound image analysis

The fouling phenomenon in spiral wound membrane modules was investigated using ultrasonic time domain reflectometry (UTDR) and computational fluid dynamic (CFD) simulations. This study utilized a high-frequency 50-MHz ultrasound system to measure the fouling distribution in the spiral wound ultrafiltration and reserve osmosis membrane modules. The results show that for a porous membrane, the voltage decreases as the fouling increases while the opposite is true for a dense membrane. The effects of gravity and module orientation on fouling were also investigated. It is clear from the results that gravity and membrane curvature play a role in the deposition of foulants on the membrane surface. This finding is supported by CFD simulations revealing that the inner membrane experiences higher axial velocities as the fluid flows through the spacers, thus generating a higher wall shear stress in the interior, which can aid in reducing membrane fouling. This study demonstrated that UTDR with a high-frequency transducer can be used to analyze the fouling phenomenon in spiral wound membrane modules.

Extended flue gas trials with a membrane-based pilot plant at a one-ton-per-day carbon capture rate

A membrane-based pilot plant for carbon dioxide capture from the flue gas of a coal-fired power plant has been installed and operated at the National Carbon Capture Center in Wilsonville, Alabama, USA. The membrane system is sized to treat flue gas containing one ton per day of carbon dioxide. Stable operations for three extended runs conducted over a period of two years have been achieved with both pulverized coal and simulated natural gas flue gas. Carbon capture rates up to and over 90% were achieved with full-scale Polaris™ modules in individual trials that ran up to 1800h. Both cross-flow and countercurrent sweep spiral-wound modules demonstrated effective and stable carbon capture performance. This paper describes the experimental correlations that were developed, and summarizes the observed performance envelopes resulting from the combination of selected operating process conditions, equipment, and modules.

High concentration of skim milk proteins by ultrafiltration: Characterisation of a dynamic membrane system with a rotating membrane in comparison with a spiral wound membrane

The purpose of this work was to characterise the ultrafiltration of skim milk with a dynamic system with a rotating membrane regarding flux in milk protein concentration. The flux of the dynamic system showed a maximum at medium rotational speeds, probably due to the permeate backpressure or a shift in the deposited particle size range to smaller particles above a critical rotational speed. The flux increased almost linearly up to a transmembrane pressure (TMP) of 100 kPa. At higher TMP, the curves levelled off, especially at higher protein concentrations. The dynamic system was less limited by the increasing retentate viscosity and reached significantly higher volume reduction ratios (VRR) as compared with a spiral wound module (SWM). SWM are suitable to achieve VRR <5–6 before a dynamic system, possibly in combination with tubular ceramic membranes, could be used to achieve higher VRR >8.