MEMBRANE TECHNOLOGY INTRODUCTION 1 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 ID: 618529
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Slide1
MODULE MEMBRANE
MEMBRANE
TECHNOLOGYSlide2
INTRODUCTION [1]
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.
Fig 1
.
Schematic drawing single module design:
feed
module
retentate
permeate
Permeate : the fraction of the feed passed
Retentate: the fraction of the feed retainedSlide3
INTRODUCTION [2]
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 wound
Tubular
Capillary
Hollow fiber
The difference between the latter type as is shown in Table 1.
Configuration
Diameter (mm)
Tubular
Capillary
Hollow fiber
10.0
0.5 – 10.0
< 0.5Slide4
INTRODUCTION [3]
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)
5
0.5
0.05
360
3600
36000
The choice of module configuration, is based on :
[1]
Economic consideration
[2]
Others :
Ease of cleaning, maintenance, and operation
Compactness of the systems
Scale
The possibility of membrane replacementSlide5
PLATE-AND-FRAME MODULE [1]
Permeate
Membrane
Spacer
Retentate
Membrane
Permeate
Feed
Fig 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.Slide6
PLATE-AND-FRAME MODULE [2]
Membrane
Spacer
Feed
Permeate
Retentate
Fig 3
.
Schematic flow path in plate-and-frame module.
Spacer material is used to improve mass transfer and to reduce concentration polarization.Slide7
SPIRAL-WOUND MODULE
This module in fact a plate-and-frame systems wrapped around a central collection pipe. The packing density of this module (300-1000 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 pipe
Fig 4
.
Schematic flow path of
a spiral-wound module.Slide8
TUBULAR MODULES
In 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. Slide9
CAPILLARY MODULES [1]
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-OUT
The feed solution passes through the bore of the capillary (lumen) whereas the permeate is collected on the outside of the capillaries
OUTSIDE-IN
The feed solution enters the module on the shell side of the capillarioes (external) and the permeate passes into the fiber boreSlide10
CAPILLARY MODULES [2]
Feed
Permeate
Retentate
Feed
Permeate
Retentate
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.
Fig 6
.
Schematic drawing of capillary module (a) inside-out, (b) outside-in
(a)
(b)Slide11
HOLLOW FIBERS MODULES [1]
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 30.000 m2/m3
WHEN is used ?
The feed stream is relatively clean
Seawater desalination, but very effective pretreatment is required
Fig 7
.
Schematic drawing of hollow fiber moduleSlide12
HOLLOW FIBERS MODULES [2]
HOLLOW FIBER
Outside-in
Inside-out
Gas separation
Pervaporation
To avoid high pressure losses inside the fiber and to attain high membrane area
To avoid increase in permeate pressure within the fibers
Fig 8.
membrane for separation gasSlide13
HOLLOW FIBERS MODULES [3]Slide14
COMPARISON OF MODULE CONFIGURATIONS
Tubular
Plate-and-frameSpiral-wound
Capillary
Hollow
fiber
Packing density
Low
Very high
Investment
High
Low
Fouling
tendency
Low
Very highCleaningGood
PoorMembrane replacementYes/noYesNo
NoNoSlide15
SYSTEMS DESIGN –
CROSS FLOW FILTRATION [1]
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 :
Feed
Permeate
Retentate
Permeate
Feed
Permeate
Retentate
Feed
Permeate
Feed
Permeate
Feed
Permeate
Feed
Permeate
(a)
(b)
(c)
(d)
Co-current
Counter-current
Cross-flow
Perfect mixingSlide16
SYSTEMS DESIGN –
CROSS FLOW FILTRATION [2]
Co current flow
Cross flow
Counter current
flow
Perfect mixing flow
The worst
The best
Two basic methods can be used in a single stage or a multi stage, are:
Feed pump
(a)
Single pass system
Feed pump
Recirculation pump
(b)
Recirculation systemSlide17
SYSTEMS DESIGN –
HYBRID DEAD-END/CROSS FLOW SYSTEM [1]
Dead-end systemCross flow system
The high recovery, the feed is completely passing the membrane.
A tremendous flux decline is obtained.
The
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.
Permeate
Feed
A
BSlide18
SYSTEMS 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
CASCADE
Permeate
Feed
Retentate
Two-stage membrane process
(a)
Permeate
Feed
RetentateSlide19
SYSTEMS DESIGN –
CASCADE
Permeate
Feed
Retentate
(b)
Three-stage membrane process
Permeate
Feed
RetentateSlide20
EXAMPLES of SYSTEMS DESIGN :
ULTRAPURE WATER [1]
UV
Well water tap
Activated carbon
RO
Drain
Mixed-bed
Ion exchange
Microfiltratin
ultrafiltration
Permeate
Storage
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.
Fig 9
.
flow diagram for an ultrapure water production systemSlide21
Pretreatment is also necessary and depends on the quality of the source water.
EXAMPLES of SYSTEMS DESIGN :
ULTRAPURE WATER [2]
Specifications for ultrapure water
Electrical resistance (M
Ω
.cm)
>18
Number of particles (/ml)
< 10
Bacteria count
(/ml)
<
0,01
TOC (ppb)< 20Slide22
EXAMPLES of SYSTEMS DESIGN :
DESALINATION OF SEAWATER [1]
High-performance RO membranes exhibit a salt rejection > 99%.
To improve the quality further, a two-stage (or multi-stage) system is often used.
Feed
(seawater)
Pretreatment
RO systems
PURE WATERSlide23
EXAMPLES of SYSTEMS DESIGN :
DESALINATION OF SEAWATER [2] Slide24
EXAMPLES of SYSTEMS DESIGN :
OTHERSSlide25
ECONOMICS
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 cost
The capital cost
The operating cost
Membrane modules
Cost of piping, pumps, electronics, vessel
Pretreatment and post-treatment
Power requirement
Membrane replacement
Labour and maintenanceSlide26
PROCESS PARAMETER [1]
feed
module
retentate
permeate
c
f
q
f
c
r
q
r
c
p
q
p
Membrane performance characterized by
Retention
Permeation
Schematic drawing of a membrane system :
Where:
c
f
: feed concentration qf : feed flow rate
cr : retentate concentration qr : retentae flow rate
cp : permeate concentration qp : permeate flow rateSlide27
Recovery
PROCESS PARAMETER [1]
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.Slide28
Volume Reduction
In batch operation, the volume reduction is defined :
Retention
Which is solute is retained by the membrane
PROCESS PARAMETER [2]Slide29
TERIMA KASIH