Filtration Fabric
Filtration is the process of separation of one material
from another that is solids from liquids or gases.
The objective of filtration is as follows:
- To get purity of product
- It improves the process efficiency
- It saves the energy
- Ensures recovery of precious metals
- Improves in pollution control
- There are two filter mechanisms
- Solid-liquid filter
- Solid-gas filter (dust collection)
Requirement:
- Maybe expected to operate for quite lengthy periods
- It should sustain difficult physical and chemical conditions
- May be woven or non- woven
- Dust collection efficiency : 25 to 99.9% depending upon the fabric type
- Structures of textile fabrics to help to give high filtration efficiencies
- Woven fabrics: pores of filtration formed at yarn interstices
- Non- woven fabrics : pores formed by small spaces that occur between the individual fibers
- Porosity: Ratio of volume of air in fabric to total fabric volume
- Permeability: capacity of porous media to transmit fluids
- Air permeability: measure of ease with which air can flow under pressure difference across an area of the material
Examples of Filtration:
- Purification of domestic and industrial effluents to get cleaner environment
- Dye stuff and pigments( used for clothing, furnishing and paints)
- Filtration of edible product E.g. sugar, flour, oils, fats etc
Application / Uses:
- Water filtration in paper manufacture
- Air filters in air conditioning system and automobile engines
- Vacuum cleaners, power stations, chemical plants, sewage disposal etc.
Filtration Mechanism:
Filters are classified as per cleaning mechanism
- Dry filters
- Wet filters
Dry filters there are different types of dry filter
mechanism such as interception, inertial deposition, random diffusion,
electrostatic deposition, Gravitational forces. And the filters used in Air
conditioning like HVAC, HEPA and ULPA.
Fabrics and fibers for Dry filtration:
- Polyester is widely used due to its strength, relatively high temperature resistance up to 150 degrees Celsius.
- Cotton fabrics were used in older shaker type system
- Polyphylenesulphide (PPS) for temperature up to 190 degrees
- Micro glass blanket- is used for removal of impurities in utilities and high efficiency extended surface filter in HVAC
Filters in Air Conditioning:
- ULPA (ultra low penetration air filter) : It provides efficiency up to 99.9999%, removes dust, carbon black, smoke, seed particles etc
- HEPA (High efficiency particulate air filter) : Provide efficiency up to 99.95%, it is sued in hospitals operation rooms for air free from harmful bacteria and other impurities
- HVAC (Heating, Ventilation and Air conditioning): used in forced air heating and cooling system. It reduces indoor concentration of hazardous air particles.
Wet Filtration Mechanism:
It is a basic mechanism for particle removal from fluid
(solid / liquid filtration mechanism).
Surface screening, depth straining and cake filtration are some
examples. Filters bags, filter press, belt filters are some equipments used in
wet mechanism.
Filtration requirements for wet filtration mechanism:
- Cotton swells when wet and hence highly efficient as filter fabrics, synthetic fibers are highly stable but have some limitation.
- Nylon 6,6 and polypropylene can be used as it offers filtrate clarity
- It should be resistant to blinding and abrasive forces
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