EQUIPMENT FOR FILTRATION OFAIR

PRESENTED BYSWAPNA.MM. Pharm

2nd semester

Department of pharmaceuticsUniversity College of Pharmaceutical Sciences,

Kakatiya University, Warangal-506009.

CONTENTS

INTRODUCTION PRINCIPLES OF AIR FILTRATION AIR FILTERS CONCLUSION REFERENCES

INTRODUCTION

The purpose of air filtration is to remove

contaminants from the air.

The removal of airborne particulate from an airstream is called air filtration and is accomplishedthrough mechanical, and electrostaticphenomenon.

The first step in selecting an air filtration systemis to understand the contamination – what it isand how it is harmful.

PRINCIPLES OF AIR FILTRATION

There are four basic principles of operationwhich apply to the various types of air filtrationsystems.

Inertial Separation Impingement Diffusion Electrostatic

Inertial Separation: In inertial separators, particles are collected

by centrifugal forces arising from a rapiddeflection of the airflow such that the dustparticles, having mass and kinetic energy, areunable to follow the path of the gasmolecules and, proceed in a different path tothe main air stream.

Viscous Impingement: The term “viscous” is in front of the impingement

principle of operation because the air filter media isoiled with a sticky adhesive and, therefore, operatesas a “viscous” filter.

Viscous impingement filter media is made up ofsynthetic fibers, glass fibers, or expanded metal foilmesh in a pad, or mat, in multi layers or pleatedforms.

DIFFUSION: In the case of aerosols moving through a filter, Brownian

motion causes erratic motion of the particles about thesteady aerodynamic path.

This motion would not of itself result in additional collectionof particles by fibers if the particle concentration wereeverywhere identical.

But since the motion is totally random, the transfer ofparticles across any surface near a fiber will be proportionalto the concentration on opposite sides of that surface.

It can be shown that there is a net transfer of particles acrossa surface and that this transfer is in the direction of the fibersurface itself. The rate at which such transfer takes place isproportional to a diffusion coefficient

Electrostatic filtration: Electrostatic filtration is an extremely effective

method for removing dust, smoke, and other smallparticles from air over a particle size range fromabout 10 to 0.01 microns.

The principle involved is that of passing the airthrough an ionizer screen where electrons collidingwith air molecules generate positive ions whichadhere to dust and other small particles present,giving them a positive charge.

AIR FILTERS

Historically, packed towers were the first airfilters used by the industry for air purification. Different air filters include Packed towers Membrane filter cartridges Bag filters HEPA filters

DESCRIPTION OF PACKED TOWERS: Packed towers used to filter fermentation air are

comprised of beds which can be constructed of padof paper, cotton wool, glass wool.

The diameter of fibrous material is typically between0.5 and 15 micro meters and the space between thefibers can be many times this range.

The filter consists of a steel container or housingfilled with loose fibrous packing.

The air inlet is on the bottom and the outlet is on thetop of the filter.

MEMBRANE FILTER CARTRIDGES: Cartridge filters are easily handled, and

consists of high surface area and tight particlecapture specifications.

Membrane filters can have absolute ornormal ratings.

A normal rating is an arbitary micron valueassigned by the manufacturer, based up onthe removal of some percentage of allparticles of a given size or larger.

An absolute pore rating can be defined as thediameter of the largest spherical particle that willpass through a filter under specified conditions. It isan indication of the largest available pore opening inthe filter elements.

Membrane filter cartridges are available as either prefilter or sterilizing filter configurations.

Pre filters are used for particulate removal andsterilizing filters are used for removal of bacterialcontaminates.

BAG FILTERS:

Recovery of particulate matter from exhaust gas is vital for anyindustry from two aspects

To avoid pollution problems Recovery of finished product-increasing the plant yield

For recovering particulate matter different options available are –Cyclones, Venturi, scrubbers, bag filters, electrostatic precipitatorsetc. Out of these bag filter becomes the best choice if following aredominant selection criteria’s:

Material is expensive and hence high collection efficiency is desired. Particulate size is very fine. Material recovery in powder form is desirable & not in solution form.

WORKING PRINCIPLE OF BAG FILTER:

The dust-laden air enters the bag filter bustle. The air is uniformly distributed avoiding channeling. Initially a coat of material forms on the bags. Subsequently,

the coat acts as the filtering medium. The dust is accumulated on filter elements while the air

passes thorough the filter bags from outside to inside. The accumulated powder is dislodged from the bags by

reverse pulse-jet air intermittently. The dislodged powder falls on bottom cone and is

discharged through powder discharge valves. The dust free air is sucked by induced draft fan and is

exhausted to atmosphere. Knockers are provided on conical portion especially for

sticky/hygroscopic materials

FEATURES OF BAG FILTERS

Better performance. Easy in maintenance and long life.

HEPA FILTERS: HEPA filters, by definition, remove at least 99.97% of

airborne particles 0.3 micrometers (µm) in diameter. HEPA filters are composed of a mat of randomly arranged

fibres. The fibres are typical composed of fiberglass andpossess diameters between 0.5 and 2.0 micron. Key metricsaffecting function are fibre diameter, filter thickness, and facevelocity.

The common assumption is that, a HEPA filter acts like asieve where particles smaller than the largest opening can passthrough is incorrect. Unlike membrane filters, where particlesas wide as the largest opening or distance between fibrescannot pass in between them at all, HEPA filters are designedto target much smaller pollutants and particles.

These particles are trapped (they stick to a fibre)through a combination of the following threemechanisms:

Interception, where particles following a line of flow in the airstream come within one radius of a fibre and adhere to it.

Impaction, where larger particles are unable to avoid fibres byfollowing the curving contours of the air stream and areforced to embed in one of them directly; this effect increaseswith diminishing fibre separation and higher air flow velocity.

Diffusion, an enhancing mechanism is a result of the collisionwith gas molecules by the smallest particles, especially thosebelow 0.1 µm in diameter, which are thereby impeded anddelayed in their path through the filter.

Conclusion

The level of sophistication of air filtrationequipment is dependent on the service of the airand the environment conditions of the rotatingmachinery`s locatiion.

Thus, we can ensure that filtration equipmentsfor air is very necessary in the pharmaceuticalindustry.

References James Swarbrick , Encyclopedia of

Pharmaceutical Technology , vol-6 ,pg no 51 Theodore H. Meltzer , Maik W. Jornitz ,

Filtration in the Bio pharmaceutical Industry Sarfaraz Niazi , Handbook of Pharmaceutical

Manufacturing Formulations:Sterile….,vol-6 James Swarbrick , Encyclopedia of

Pharmaceutical Technology , vol-3 ,pg no-1748 www.wikipedia.org www.thomasnet.com

Thank You