Filtration is the removal of a suspended particle from a fluid, liquid or gas, by passing the fluid through a porous or semi permeable medium.A dirty fluid in a manufacturing process in any industry can decrease productivity and effect the product also which lead to high rejection rates. The removal of contaminants from a process fluid makes that fluid more valuable and increases product yields. In any manufacturing process the end product is the culmination of many steps, each potentially creating difficulties. A properly designed filter system can eliminate many costly problems. A filter placed in a strategic location can eliminate such problems and also act as a monitor for the whole process. For example, a filter that clogged prematurely for no apparent reason suggests that there are improper conditions somewhere in the process.
Dust Collector collects dust from heavy dust loads and provides clean air. Dust collector consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system (distinguished from air cleaners which utilize disposable filters to remove the dust). Industrial Dust Collector offer very high performance and are fault resistant. These are of four types:
1. Cartridge Dust Collector
Cartridge Dust Collector employs perforated metal cartridges that contain a pleated, nonwoven filtering media. Due to its pleated design, the total filtering surface area is greater than in a conventional bag of the same diameter, resulting in reduced air to media ratio, pressure drop, and overall collector size.Dust laden air is drawn into Dust Collector through inlet due to suction created by exhaust fan and passes through filter cartridge elements. The dust gets deposited on outer surface of cartridges and clean air flows through the center passage of cartridge into clean air plenum. Clean air further exit into atmosphere. Cartridges are periodically and automatically get cleaned through air purging. Dust released from cartridges slides downward into the hopper for further collection into the dust bin.Cartridge filters can be used to protect critical orifices located in a manufacturing process (i.e. an extruder) so that the openings do not become clogged and cause downtime. If the fluid in question is re-circulating, reclaim value can also be increased by placing a cartridge filter in line. Properly dispersing a mixture, such as pigment / resin mixture, is an example of this. The compressed air is used for filter cartridge cleaning. The air filter cartridge is washable and reusable. The space required for a cartridge filter system is about one eighth the volume required by a bag filter system. The typical life span of the cartridge filters is two to two and half times the bag filters. It makes the cartridge filter systems far more economical too.
Its Special Features:
· Down Flow Principle
· Assures high collection efficiency.
· Modular Design with no moving Parts
· Low maintenance and replacement of cartridge element is easy and quick
· Fair Air to Filter Ratio
· Assures longer life of cartridges
· Variety of Fabric Material: Cartridges are normally of synthetic webbed material.
· Quality & Reliability
Cartridge Filter Systems have several applications -
- Dust collection, pneumatic conveying, central vacuum cleaning systems, etc. It provides exceptionally high degree of filtration so particularly used where toxic materials, or materials of high value (e.g. gold dust) are handled.
- In the industries where cleanliness of high order is expected (e.g. clean room applications),
- In the tissue culture, aquaculture, pharmaceutical, chemical, pesticide, premium sugar, decorative laminates, printed circuit boards, diffusion labs, etc. the dust has to be eliminated.
- For powder coating paints - in their manufacturing or painting process - After pulverizing in a mill the powder paint has to be removed and collected pneumatically, at the end of which a CFS can collect all the paint. Similarly, paint can be recovered efficiently in the painting process. Its benefit is in quick change-over when the colour is to be changed.
- In the pesticides industry, toxic materials are pulverized to prevent pollution of environment and exposure of the workers with the toxic materials.
- In the coated paper industry, where high quality paper is manufactured, presence of dust in the environment can be detrimental to the quality of the end product. Collection of dust from the buff rolls (cotton bowls) with cartridge filter systems prevents re-entrainment of the dust into the atmosphere
- Ready made bags/pads for cements, ceramics, chemicals, drugs, food & beverages pharmaceuticals, paints, powders, paper mills, electroplating, floor mills, oil mills, pollution control equipments, fertilizer industries, cosmetics, Pharmaceutical , Power generation, Reverse Osmosis System etc
- Engineering industries in any type of liquid etc.
- Finally, since gases are fluids, the removal of aerosols or mists can be achieved with cartridge filters known as coalescers.
2 Fabric Bag Dust Collector
These are commonly known as Bag House. Fabric collectors use filtration to separate dust particulates from dusty gases. Dust-laden gases enter the baghouse and pass through fabric bags that act as filters. The Dust laden air is drawn into dust collector through inlet due to suction created by exhaust fan and passes through fabric bags. Heavier dust particles fall into hopper due to loss of momentum. Finer dust gets deposited on inner surface of fabric bags and clean air passes across outer surface of filter bags and then exit into atmosphere through outlet. Bags are cleaned through motorised shaking arrangement. Dust released from filter bags slides downward into hopper which collects into dust bin. Fabric bags are normally of cotton woven satin cloth.Fabric filters are generally comprised of following parts 1.clean plenum 2.dusty pleanum 3.bag, cage, ventury assembly 4.tubeplate 5.RAV/SCREW 6.compressed air header 7.blow pipe 8.housing and hopper.
The high efficiency of these collectors is due to the dust cake formed on the surfaces of the bags. The fabric primarily provides a surface on which dust particulates collect through Inertial collection , Interception , Electrostatic forces mechanisms A combination of these mechanisms results in formation of the dust cake on the filter, which eventually increases the resistance to gas flow. The filter must be cleaned periodically.
· Modular Design with no Moving Parts
· Low maintenance and replacement of fabric bags is easy and quick.
· Fair Air to Filter Ratio
· Assures longer life of bags
· Variety of Fabric Material
They are one of the most efficient and cost effective types of dust collectors, having collection efficiency of more than 99% for very fine particulates. These dust collector bags are offered with coatings and finishes on both the sides of collector bags. These coatings help in enhancing cleaning and efficiencies.
Types of baghouses
As classified by cleaning method, three common types of baghouses are:
1 Mechanical shaker
In mechanical-shaker baghouses, tubular filter bags are fastened onto a cell plate at the bottom of the baghouse and suspended from horizontal beams at the top. Dirty gas enters the bottom of the baghouse and passes through the filter, and the dust collects on the inside surface of the bags.
Cleaning a mechanical-shaker baghouse is accomplished by shaking the top horizontal bar from which the bags are suspended. Vibration produced by a motor-driven shaft and cam creates waves in the bags to shake off the dust cake. The air to cloth ratio for shaker baghouses is relatively low, hence the space requirements are quite high. They are popular in the minerals processing industry.
In reverse-air baghouses, the bags are attached onto a cell plate at the bottom of the baghouse and suspended from an adjustable hanger frame at the top. Dirty gas enters the baghouse and passes through the bag from the inside, and the dust collects on the inside of the bags.
Reverse-air baghouses are compartmentalized to allow continuous operation. Before a cleaning cycle begins filtration is stopped. Bags are cleaned by injecting clean air into the dust collector in a reverse direction, which pressurizes the compartment. The pressure makes the bags collapse partially, causing the dust cake to crack and fall into the hopper below. At the end of the cleaning cycle, reverse airflow is discontinued, and the compartment is returned to the main stream. However to prevent total collapse and fabric chafing during the cleaning cycle, rigid rings are sewn into the bags at intervals. In this maintenance needs are somewhat greater.
In reverse - pulse - jet baghouses, individual bags are supported by a metal cage, which is fastened onto a cell plate at the top of the baghouse. Dirty gas enters from the bottom of the baghouse and flows from outside to inside the bags. The metal cage prevents collapse of the bag.
Reverse-pulse-jet dust collectors can be operated continuously and cleaned without interruption of flow because the burst of compressed air is very small compared with the total volume of dusty air through the collector. Because of this continuous-cleaning feature, reverse-jet dust collectors are usually not compartmentalized. The short cleaning cycle of reverse-jet collectors reduces recirculation and redeposit of dust. These collectors provide more complete cleaning and reconditioning of bags than shaker or reverse-air cleaning methods. Also, the continuous-cleaning feature allows them to operate at higher air-to-cloth ratios, so the space requirements are lower.
This cleaning system works with the help of digital sequential timer attached to the fabric filter. This timer indicates the solenoid valve to inject the air to the blow pipe.
3 Pleated Bag Dust Collector
Dusty air is drawn into dust collector through inlet due to suction created by exhaust fan and passes through Pleated Bag elements. The abrasive resistant inlet promotes dropping out high particulate which allows uniform air flow, thus increases filter life. The dust gets deposited on outer surface of Pleated Bag and clean air flows through the center passage of Pleated Bag into clean air plenum. Clean air further exit into atmosphere through outlet duct. Pleated Bags are periodically and automatically get cleaned through air purging. Dust released from Pleated Bags slides downward into the hopper for further collection into the dust bin.
· Fair Air to Filter Ratio
· Assures longer life of cartridges
· Variety of Material
· Cartridges are normally of synthetic webbed material
· Modular Design: With no Moving Parts.
4 Wet Scrubber
Dust collectors that use liquid are commonly known as wet scrubbers. In these systems, the scrubbing liquid (usually water) comes into contact with a gas stream containing dust particles. The greater the contact of the gas and liquid streams, the higher the dust removal efficiency.
The Wet Scrubber consisting of single stage Scrubbing Filters which is located at the bottom of Multi Nozzles.
All types of wet scrubber have one of three basic operations:
· Gas-humidification - The gas-humidification process conditions fine particles to increase their size so they can be collected more easily.
- Gas-liquid contact – In this process the particle and droplet come into contact by four primary mechanisms:
o Inertial impaction - When water droplets placed in the path of a dust-laden gas stream, the stream separates and flows around them. Due to inertia, the larger dust particles will continue on in a straight path, hit the droplets, and become encapsulated.
o Interception - Finer particles moving within a gas stream do not hit droplets directly but brush against them and adhere to them.
o Diffusion - When liquid droplets are scattered among dust particles, the particles are deposited on the droplet surfaces by Brownian movement, or diffusion. This is the principal mechanism in the collection of submicrometre dust particles.
o Condensation nucleation - If a gas passing through a scrubber is cooled below the dewpoint, condensation of moisture occurs on the dust particles. This increase in particle size makes collection easier.
- Gas-liquid separation - Once contact is made, dust particulates and water droplets combine to form agglomerates. As the agglomerates grow larger, they settle into a collector.
The "cleaned" gases passed through a mist eliminator (demister pads) to remove water droplets from the gas stream. The dirty water from the scrubber system is either cleaned and discharged or recycled to the scrubber. Dust is removed from the scrubber in a clarification unit or adrag chain tank. A drag chain system removes the dirt and deposits ii into a dumpster.
Spray-tower scrubber wet scrubbers may be categorized by pressure drop as follows:
· Low-energy scrubbers: Gravity-spray-tower scrubber, liquid droplets formed by liquid atomized in spray nozzles fall through rising exhaust gases. Dirty water is drained at the bottom. Its efficiency is poor below 10 µm. However, they are capable of treating relatively high dust concentrations without becoming plugged.
· Low- to medium-energy scrubber: Packed-bed scrubbers consist of beds of packing elements, such as coke, broken rock, rings, saddles, or other manufactured elements. The packing breaks down the liquid so that the dusty gases streams passing through the bed and get deposited on the surfaces of the packing elements. These scrubbers have good collection efficiency of 5 μm particles and above.
- Medium- to high-energy scrubbers: It is of three types -Cross-flow scrubbers, Co-current flow scrubbers and Counter-current flow scrubbers. Its efficiency can be increased by minimizing target size, ie., using 0.003 in.
· High-energy scrubbers: Venturi scrubber depends on pressure drop. Venturi scrubbers consist of a venturi-shaped inlet and separator. It achieves very high collection efficiencies for respirable dust. Venturi scrubbers can maintain pressure drop with varying gas flows.
Liquid Filtration is the passing of flow of liquid containing suspended solids, through porous medium, the element. Oil is vital for any machinery’s moving parts. Liquid filters remove the contaminants from the oil or any fluid and clean it by capturing contaminants that can cause damage. For Increased emissions control and tighter tolerances it requires high efficiency filters. When an application requires higher efficiency filtration than cellulose filter media are used. Synthetic media captures more and smaller contaminant than cellulose media.
For liquid filtration, Cartridge Filtration is preferred. Cartridge filtration is typically pressure driven. Other types of filtration and separation devices may employ alternative driving forces: gravitational settling, centrifugal force, a vacuum, etc. There are several advantages associated with using pressure as the driving force in a cartridge filtration system:
- Greater output per unit area
- Smaller equipment than when using other driving forces (consider settling ponds and deep bed filters)
- Ease of handing volatile liquids.
Many chemical processes require the use of catalysts in order to be functional. Cartridge filtration can recover the unused portions of the catalyst so that it can be used over again. If the catalyst is a precious metal, or if a precious metal is used in the actual reaction, cartridge filtration can recover unused portions and thus reduce operating costs. Cartridge filter can be surface or depth-type filter depth-type filters capture particles and contaminant through the total thickness of the medium, while in surface filters (papers, woven wire and cloths) particles are blocked on the surface of the filter.
Surface filters are used for filtering sediment of similar-sized particles. A pleated 5-micron filter works best because it has more surface area than other filters. Depth filters have a limited surface area, but they have the advantage of depth. So if the size of filter surface is increased, higher flows are possible, the filter last longer, and the dirt holding capacity increases. Cartridge filters are normally designed disposable.
In the case of pollution control, contaminants need to be recovered from waste effluents before the fluid is released into the environment, and thus can be accomplished by cartridge filtration.
Applications of liquid filtration by cartridge filtration are in bulk chemicals, control of sub micron, petrochemicals ,water purification, hydraulic fluids, cosmetics, sterilization of pharmaceuticals fluids, reagent grade chemicals, paints, varnishes, semiconductors, sugars, electric utilities and often used as final filtration after other filters.
The other method which can be used for Liquid filtration is Bag Filtration. In this process the flow can be from the outside to the inside of the filter (that means the separation of particles happens on the external surface of the filter) or viceversa. The particles are normally captured on the internal surface of the bag filter.
Bag filters are in general not designed for replacement when they are clogged. Bag filters are mostly surface-type filters.
Applications of liquid filtration by Bag Filtration are in food industry (vegetable oils, vinegar), semiconductors, coolants, cleaning fluids, waxes, paints, plastisols etc.