EQUIPMENT FOR FILTRATION OFAIR PRESENTED BY SWAPNA.M M. Pharm 2 nd semester Department of pharmaceutics University 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 air stream is called air filtration and is accomplished through mechanical, and electrostatic phenomenon. The first step in selecting an air filtration system is to understand the contamination what it is and how it is harmful.
PRINCIPLES OF AIR FILTRATION There are four basic principles of operation which apply to the various types of air filtration systems. Inertial Separation Impingement Diffusion Electrostatic
Inertial Separation: In inertial separators, particles are collected by centrifugal forces arising from a rapid deflection of the airflow such that the dust particles, having mass and kinetic energy, are unable to follow the path of the gas molecules and, proceed in a different path to the main air stream.
Viscous Impingement: The term viscous is in front of the impingement principle of operation because the air filter media is oiled with a sticky adhesive and, therefore, operates as a viscous filter. Viscous impingement filter media is made up of synthetic fibers, glass fibers, or expanded metal foil mesh in a pad, or mat, in multi layers or pleated forms.
DIFFUSION: In the case of aerosols moving through a filter, Brownian motion causes erratic motion of the particles about the steady aerodynamic path. This motion would not of itself result in additional collection of particles by fibers if the particle concentration were everywhere identical. But since the motion is totally random, the transfer of particles across any surface near a fiber will be proportional to the concentration on opposite sides of that surface. It can be shown that there is a net transfer of particles across a surface and that this transfer is in the direction of the fiber surface itself. The rate at which such transfer takes place is proportional to a diffusion coefficient
Electrostatic filtration: Electrostatic filtration is an extremely effective method for removing dust, smoke, and other small particles from air over a particle size range from about 10 to 0.01 microns. The principle involved is that of passing the air through an ionizer screen where electrons colliding with air molecules generate positive ions which adhere to dust and other small particles present, giving them a positive charge.
AIR FILTERS Historically, packed towers were the first air filters 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 pad of paper, cotton wool, glass wool. The diameter of fibrous material is typically between 0.5 and 15 micro meters and the space between the fibers can be many times this range. The filter consists of a steel container or housing filled with loose fibrous packing. The air inlet is on the bottom and the outlet is on the top of the filter.
MEMBRANE FILTER CARTRIDGES: Cartridge filters are easily handled, and consists of high surface area and tight particle capture specifications. Membrane filters can have absolute or normal ratings. A normal rating is an arbitary micron value assigned by the manufacturer, based up on the removal of some percentage of all particles of a given size or larger.
An absolute pore rating can be defined as the diameter of the largest spherical particle that will pass through a filter under specified conditions. It is an indication of the largest available pore opening in the filter elements. Membrane filter cartridges are available as either pre filter or sterilizing filter configurations. Pre filters are used for particulate removal and sterilizing filters are used for removal of bacterial contaminates.
BAG FILTERS: Recovery of particulate matter from exhaust gas is vital for any industry 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 precipitators etc. Out of these bag filter becomes the best choice if following are dominant 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 and possess diameters between 0.5 and 2.0 micron. Key metrics affecting function are fibre diameter, filter thickness, and face velocity. The common assumption is that, a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect. Unlike membrane filters, where particles as wide as the largest opening or distance between fibres cannot pass in between them at all, HEPA filters are designed to target much smaller pollutants and particles.
These particles are trapped (they stick to a fibre) through a combination of the following three mechanisms: Interception, where particles following a line of flow in the air stream come within one radius of a fibre and adhere to it. Impaction, where larger particles are unable to avoid fibres by following the curving contours of the air stream and are forced to embed in one of them directly; this effect increases with diminishing fibre separation and higher air flow velocity. Diffusion, an enhancing mechanism is a result of the collision with gas molecules by the smallest particles, especially those below 0.1 µm in diameter, which are thereby impeded and delayed in their path through the filter.
Conclusion The level of sophistication of air filtration equipment is dependent on the service of the air and the environment conditions of the rotating machinery`s locatiion. Thus, we can ensure that filtration equipments for air is very necessary in the pharmaceutical industry.
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
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