2INTRODUCTION  feed module retentate permeate In order to apply membranes on a technical scale, large membrane areas are normally required. The smallest unit into which the membrane area is packed is called a module.The module is the central part of a membrane installation. The simplest design is one in which single module is used.feedmoduleretentatepermeateFig 1. Schematic drawing single module design:Permeate : the fraction of the feed passedRetentate: the fraction of the feed retained
3INTRODUCTION A number of module design are possible and all are based on two types of membrane configuration:[a] Flat[b] Tubular- Plate and frame- Spiral woundTubularCapillaryHollow fiberThe difference between the latter type as is shown in Table 1.ConfigurationDiameter (mm)TubularCapillaryHollow fiber10.00.5 – 10.0< 0.5
4Surface area per volume (m2/m3) INTRODUCTION The membrane surface area per volume is only a function of the dimensions of the tube.Tube radius (mm)Surface area per volume (m2/m3)50.50.05360360036000The choice of module configuration, is based on :Economic considerationOthers :Ease of cleaning, maintenance, and operationCompactness of the systemsScaleThe possibility of membrane replacement
5PLATE-AND-FRAME MODULE  PermeateMembraneSpacerRetentateFeedFig 2. Schematic drawing of a plate-and-frame module.Sets of two membranes are placed in a sandwich-like fashion with their feed sides facing each other. In each feed and permeate compartment thus obtained a suitable spacer is placed. The number of sets needed for a given membrane area furnished with sealing rings and two end plates then builds up to a plate-and-frame stack.
6PLATE-AND-FRAME MODULE  Fig 3. Schematic flow path in plate-and-frame module.MembraneSpacerFeedPermeateRetentateSpacer material is used to improve mass transfer and to reduce concentration polarization.
7Fig 4. Schematic flow path of SPIRAL-WOUND MODULEThis module in fact a plate-and-frame systems wrapped around a central collection pipe. The packing density of this module ( m2/m3)Membrane and permeate-side spacer material are then glued along three edges to build a membrane envelope. The feed-side spacer separating the top layer of the two flat to build a membrane envelope.The feed flows axial through the cylindrical module parallel along the central pipe whereas the permeate flows radially towards the central pipeFig 4. Schematic flow path ofa spiral-wound module.
8TUBULAR MODULESIn contrast to capillaries and hollow fibers, tubular membranes are not self-supporting.Such membranes are placing inside a porous stainless steel, ceramic or plastic tube with the diameter of tube being, in general, more than 10 mm. The number of tubes put together in the module may vary.Fig 5. Schematic drawing of tubular module.The feed solution always flows through the centre of the tubes , while the permeate flows through the porous supporting tube into the module housing.
9CAPILLARY MODULES  INSIDE-OUT OUTSIDE-IN The capillary module consist of a large number of capillaries assembled together in a module. The free ends of the fibers are potted with agents such as epoxy resin, polyurethanes, or silicone rubber.Two types of module arrangement can be distinguish :INSIDE-OUTThe feed solution passes through the bore of the capillary (lumen) whereas the permeate is collected on the outside of the capillariesOUTSIDE-INThe feed solution enters the module on the shell side of the capillarioes (external) and the permeate passes into the fiber bore
10CAPILLARY MODULES The choice between the two concepts is mainly based on the application where parameters such as pressure, pressure drop, type of membrane available, etc are important.A packing density of about 600 – 1200 m2/m3 is obtained with modules containing capillaries.FeedPermeateRetentateFeedPermeateRetentate(a)(b)Fig 6. Schematic drawing of capillary module (a) inside-out, (b) outside-in
11HOLLOW FIBERS MODULES  The difference between the capillary module and the hollow fiber module is simply a matter of dimensions since the module concepts are the same. In this concept the fiber modules are arranged in a loop and are potted on one side, the permeate side.The hollow fiber module is the configuration with the highest packing density m2/m3WHEN is used ?The feed stream is relatively cleanFig 7. Schematic drawing of hollow fiber moduleSeawater desalination, but very effective pretreatment is required
12HOLLOW FIBERS MODULES  Outside-inInside-outGas separationPervaporationTo avoid high pressure losses inside the fiber and to attain high membrane areaTo avoid increase in permeate pressure within the fibersHOLLOW FIBERS MODULES Fig 8. membrane for separation gas
14COMPARISON OF MODULE CONFIGURATIONS TubularPlate-and-frameSpiral-woundCapillaryHollow fiberPacking densityLowVery highInvestmentHighFouling tendencyCleaningGoodPoorMembrane replacementYes/noYesNo
15SYSTEMS DESIGN – CROSS FLOW FILTRATION  To reduce concentration polarization and fouling as far as possible, the membrane process is generally operated in a cross flow mode.Various cross-flow operations can be distinguished :FeedPermeateRetentate(a)(b)(c)(d)Co-currentCounter-currentCross-flowPerfect mixing
16SYSTEMS DESIGN – CROSS FLOW FILTRATION  Co current flowCross flowCounter currentflowPerfect mixing flowThe worstThe bestTwo basic methods can be used in a single stage or a multi stage, are:Feed pump(a)Single pass systemRecirculation pump(b)Recirculation system
17SYSTEMS DESIGN – HYBRID DEAD-END/CROSS FLOW SYSTEM  PermeateFeedABDead-end systemThe high recovery, the feed is completely passing the membrane.A tremendous flux decline is obtained.Cross flow systemThe recovery is much lower.Better fouling control.The hybrid dead-end/cross flow process may combine the advantages of both processes and this concept is very beneficial in microfiltration and ultrafiltration where back-flushing is possible and essential.
18SYSTEMS DESIGN – CASCADE Often the single-stage design does not results in the desired product quality and for this reason the retentate or permeate must be treated in a second stage.A combination of stages is called a CASCADEPermeateFeedRetentate(a)PermeateFeedRetentateTwo-stage membrane process
19SYSTEMS DESIGN – CASCADE PermeateFeedRetentatePermeateFeedRetentate(b)Three-stage membrane process
20EXAMPLES of SYSTEMS DESIGN : ULTRAPURE WATER  In the ultrapure water production system, ions, bacteria, organics, and other colloidal impurities have to be removed. A single membrane process does not give a high quality product and a combination of separation processes (hybrid processing) is necessary.UVWell water tapActivated carbonRODrainMixed-bedIon exchangeMicrofiltratinultrafiltrationPermeateStorageFig 9. flow diagram for an ultrapure water production system
21EXAMPLES of SYSTEMS DESIGN : ULTRAPURE WATER  Pretreatment is also necessary and depends on the quality of the source water.Specifications for ultrapure waterElectrical resistance (MΩ.cm)>18Number of particles (/ml)< 10Bacteria count (/ml)< 0,01TOC (ppb)< 20
22EXAMPLES of SYSTEMS DESIGN : DESALINATION OF SEAWATER  Feed(seawater)PretreatmentRO systemsHigh-performance RO membranes exhibit a salt rejection > 99%.To improve the quality further, a two-stage (or multi-stage) system is often used.PURE WATER
23EXAMPLES of SYSTEMS DESIGN : DESALINATION OF SEAWATER 
25ECONOMICS Installation cost The capital cost The operating cost Whether or not a membrane process or another separation process is used for a given separation is based entirely on economic considerations. In fact, the costs have to be calculated for every specific separation problem and for this reason the economics will only be considered very general.Installation costThe capital costThe operating costMembrane modulesCost of piping, pumps, electronics, vesselPretreatment and post-treatmentPower requirementMembrane replacementLabour and maintenance
26Membrane performance characterized by PROCESS PARAMETER RetentionMembrane performance characterized byPermeationSchematic drawing of a membrane system :feedmoduleretentatepermeatecf qfcr qrcp qpWhere:cf : feed concentration qf : feed flow ratecr : retentate concentration qr : retentae flow ratecp : permeate concentration qp : permeate flow rate
27PROCESS PARAMETER  Recovery Is define as the fraction of the feed flow which pass through membrane.The recovery ranges from 0 to 1 and is a parameter of economic importance.Commercial membrane process are often designed with a recovery value as high as possible. Increasing recovery, the performance declines because the concentration of the less permeable component increases.In laboratory set up, the recovery usually approaches zero, which implies maximum separation performance.
28PROCESS PARAMETER  Volume Reduction In batch operation, the volume reduction is defined :RetentionWhich is solute is retained by the membrane