Filtration (1)

Contents
 Introduction about Filtration
 What is Filtration
 Difference between Filtration & Sieving
 Objectives of Filtration
 Type of collections
 Comparative Filtration Efficiencies
 Fibers used in Filtration
 Fabrics used for filtration
 Filter fabric requirement
 Dust Filtration
 Manufacturing Methods
 Classification of filtration
 Methods of filtration
 Designing for filtration
 Application of Textile filter
 Operating problems
 Comparison of woven & Non-woven filter fabric
 Testing of filters
 conclusion

Filtra ti o n
i on a bout
Intro duct

Google Images.com

 Filtration plays a critical role in our day-to-day
life by providing healthier and cleaner products
and environment.
 Textile materials are used in the filtration of air,
liquids, in food particles and in industrial
production.
 Filtration fabrics are used widely in vacuum
cleaners, power stations, petrochemical plants,
sewage disposal, etc.
 Textile materials, particularly woven and
nonwoven, are suitable for filtration because of
their complicated structure and thickness. Dust
particles have to follow a tortuous path around
textile fibres.

IJFTR,Aug .1992

What is Filtration ?
 Filtration is a mechanical or physical operation,
which is used for the separation of solids from
fluids (liquids or gases) by interposing a
medium through which only the fluid can pass.
examples:
1. Filtration, as a physical operation is very
important in chemistry for the separation of
materials of different chemical composition.
2. Filtration is also important and widely used as
one of the unit operations of chemical
engineering.

Difference between Filtration &
Sieving

Objective of Filtration

 To eliminate the contaminant particles so as
to recover dispersing fluid.
 To recover solid particles by eliminating the
dispersing fluid

Type of collections
There are four main types of equipments
like :
 Cyclones
 wet scrubbers
 Fabric filter
 Electrostatic Precipitators
are used to remove solid particles from
air or gas stream.

Textile Trends Januarary 1989

Comparative Filtration Efficiencies
Collector type Efficiency on Particle size of
10 Um 5Um 1Um
High efficiency 85.0% 67.0% 10.0%
cyclone
Fabric filter 99.9% 99.9% 99.0%
Wet scrubber 99.8% 99.6% 94.0%
Electrostatic 99.0% 98.0% 92.0%
precipitators


Fibres used in Filtration
 Many grades of cellulose and most natural and
synthetic fibers at one time or another.
 The most popular fibers used being polyester,
polypropylene and glass.
 Following are acrylics, rayon, nylon, cotton, fluoro
polymers and a host of others that fill niche
applications because of their special material
compatibility for particular applications.
 Most people associate glass fibers with air and
synthetics with liquid filtration, but there are plenty
of exceptions, especially with synthetics in the form
of melt blown nonwoven fabrics that are increasing
popular in air filtration.

The Indian Textile Journal

Dust Filtration
Filtration efficiency of a filter fabric is
greatly influenced by three factors:
 Type of fibres
 Yarn characteristic
 Weave of filter fabric


Types of fibres
key: *poor, **Average, ***Good, ****Very good,
****Excellent
Fibre Worki Acid Alkaline Abrasion Water Price
ng resista resistan resistanc resita
Temp. nce ce e nce
Cotton 90 * **** **** **** Average
wool 100 **** * ** *** Average
Nylon66 110 * **** **** **** Average
Polyester 150 *** ** **** ** Average
Acrylic 130 **** ** **** **** Average
Polypropyle 100 ***** ***** **** ***** Average
ne
Nomex 200 ** **** ***** *** High
Teflon 250 ***** ***** ** ***** Very
high
Glass 290 ** ** * ***** Low

Yarn characteristics

Yarn characteristics which greatly affects
the filtration efficiency are:

 Thread count
 Yarn size
 Twist of yarns
 Napping


Type of yarns also affect the filtration
efficiency of filter fabrics :
 Staple fibre yarn;
Efficient particle retention, poor cake
release properties,& can be easily blended.
 Multi-filament yarn;
Retaining extremely fine particles & good
cake release properties.
 Mono-filament yarn;
poorest retention of solids but higher flow
rate.
Textile Trends January 1989

Fabrics used for filtration
 In filtration, nonwoven fabrics can be generally
described as a random fibrous web, formed by
either mechanical, wet or air laid means and having
interconnecting open area throughout the cross-
section and able to remove a percentage of
particulate from liquid or gaseous fluids streams
flowing through it.
 Needle felt fabrics for bag house filtration represent
the heaviest weight and most costly,
 whereas spun bonded fabrics, especially from
polypropylene polymer for use in coolant filtration
used in automotive and aircraft machining are the
lowest weight and least expensive.

 Air-laid and air bonding are popular because
of its high-loft, bulk and large dirt holding
capability in air filtration, including pre filters
capable of capturing larger particles.
 Melt blown nonwoven fabric continues to
be the rising star with rapid penetration into
many liquid and air filtration applications.
 Resin bonded nonwovens are popular in air
filtration and point-bonded fabrics provide
an alternative to overall bonded fabrics
which commonly are used to fibers
consisting dissimilar melt or softening points


Filter fabric requirement
 The necessary efficiency to retain the
particulate matter & control the emission.
 A good dust release property to effect a
uniform pressure drop throughout the bag
life .
 Physical characteristic to withstand the
mechanical stresses for continued
performances.
 The necessary physical & chemical
properties to withstand the conditions at
the collection point.

Man Made Textile in India April 92

Performance of various weaves used
for filtration fabrics
 Initial flow rate was excellent with sateen,
good with twill & plain woven fabric was
poor .
 Retention efficiency was excellent with
plain, satisfactory with twill, was poor with
sateen woven fabric.
 Excellent resistance to blinding was
performed by twill & sateen woven fabrics
but poor for plain fabrics.
 Also the sateen weave gives best cake
release then plain weave & poor with twill
weave.

Manufacturing Methods:

 Ist method:
First is direct melt, where polymer chip
is loaded into process equipment; fiber
is extruded while simultaneously forming
a porous web. This is usually the
least expensive method, because webs
are formed in single-step from polymer
to roll stock.

© 2003 Edward C. Gregor &
Associates,

 Second method:
 There are other desirable constructions,
with special characteristics, which cannot be
made in a single step.
 Such nonwoven forms include air laid,
wet-laid needle felt, spun laced and resin
bonded.
 These fabrics require a pre-formed
fiber, often referred to as either staple or
staple carded fiber. Staple fiber is typically
carded and formed into a web
© 2003 Edward C. Gregor &
Associates,

Classification of
filtration filtration
1) Particle
Particle filtration is the separation of
particles having size above 10 microns.
These can be filtered out easily without any
usage of micro porous membrane.

2) Microfiltration
A typical microfiltration membrane pore size
range is 0.1 to 10 microns (µm).

The Indian Textile Journa,98l

3) Ultra filtration
 Ultra filtration (UF) is a variety of membrane
filtration in which hydrostatic pressure forces a
liquid against a semi permeable membrane.

4) Nano-filtration
 Nano-filtration is a relatively recent membrane
filtration process used most often with low total
dissolved solids water such as surface water
and fresh groundwater, with the purpose of
softening (polyvalent cation removal) and
removal of disinfection by-product precursors
such as natural organic matter and synthetic
organic matter.

5) Reverse osmosis
 Reverse osmosis is similar to the membrane
filtration treatment process. This is the
reverse of the normal osmosis process,
which is the natural movement of solvent
from an area of low solute concentration,
through a membrane, to an area of high
solute concentration when no external
pressure is applied.

The Indian Textile Journal,98
,

Methods of filtration
 There are many different methods of
filtration; all aim to attain the separation of
substances.
 Separation is achieved by some form of
interaction between the substance or
objects to be removed and the filter.
 The substance that is to pass through the
filter must be a fluid, ie, a liquid or gas.
Methods vary depending on the location of
the targeted material, ie, whether it is in the
fluid phase or not.
The Indian Textile Journal oct.2011

Solid Gas separation
Eg, Filters used in cigars, filters used in AC systems.

The Indian Textile Journal oct.2011

Solid Liquid separation
Eg, Filters used in sewage disposal plants, filters in
chemical industries, water purifiers, etc.

Designing for filtration

While designing a filter for the end use, below
factors have to be considered:
 1. Flow velocity.
2. Pressure inside filtering system.
3. Size and concentration of particles to be
filtered out.
4. Nature and component of the suspension
filtered.

Selection of the fibres should be according to
their nature which can withstand the harsh
environmental conditions such as
temperature, abrasion chemical conditions etc.

Generally, for filtrations, synthetic
fibres are used because:
1) They have reduced fabric weight
2) They are having higher strength
3) Easier handling and replacement
4) Easier separation of filter cakes
5) Resistance to rot
6) Higher filtration rate
7) Higher fatigue resistance
8) Good dimensional stability
9) High temperature resistance
10) Better abrasion, corrosion and
chemical resistance

The Indian Textile Journal,oct.2011

Advantages of nonwoven filter over the
woven filters are:
 1) High permeability
2) High filtration efficiency
3) Less blinding tendency
4) No yarn slippage as in woven media
5) Good gasketing characteristics
6) Good cake discharge

 As fibre diameter increases, filtration efficiency
decreases.
 Also, void volume, which is required to reduce the
pressure drop is more in case of nonwoven (98%)
than that of woven or knitted (70%), thus nonwoven
are advantageous to use.

The Indian Textile Journal,oct .2011

Application of Textile filter
 Metallurgical industry
 Foundries
 Cement industries
 Chalk & lime plants
 Brick works
 Ceramic industries
 Flour mills
 Medical
 Pharmaceutical
 Acoustics
 Screen printing

Man Made textile in India december1991

Operating problems
 Cleaning
 Rupture of cloth
 Temperature
 Bleeding
 Humidity
 Chemical attack

Man Made textile in india december1991

Comparison of woven & Non-woven filter
fabric

Woven filter fabric Non-woven filter fabric

Man-Made Textile in India,May.2003

Testing of filters

 It is done to measure the filtering capacity of
the fabrics, for intended suspension in liquid
filtration.
 Other factors, which need to be considered
include the rate of filter choking, service life of
the filter cloth, filtrate purity and cake removal.
 Efficiency of filter is directly related with the
particle size. As the particle size is increased,
the efficiency of the filter increases, and vice
versa. It is also increased by selection of
proper size of fibre, orientation and packing.


Conclusion

 Each filter fabric is intended for a
specific use in the specific climate under
the specific conditions for its optimum
output and enhanced efficiency. For
coming decades, filter fabric filtration will
play a very critical role in our day-to-day
life; there is not a single type of fabric
used in all the applications. The usage
of the filter fabrics varies according to
their end use.


Filtration (1)

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