This article takes an in depth look at jet dust collectors.
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A jet dust collector is a suction filtration unit that pulls dust ladened air into a filtration system that collects particulate matter and releases clean air. The filters of jet dust collectors are cleaned by compressed air that uses a reverse pulse controlled by a diaphragm valve or differential pressure sensor. The filtration system can be either vertical or horizontal. With the horizontal configuration, filters lay on top of one another. In a vertical system, the filters hang from the top of the collector.
The efficiency of jet dust collectors has made them the most widely used type of dust collection system. They require little maintenance, can clean high density dust filled air, and have excellent filtration systems. The uses for jet dust collectors include product recovery, dust capturing, filtering explosive media, metalworking chip capturing, central vacuum cleaning systems, and pneumatic conveying.
Jet dust collectors are a special type of baghouse dust collecting system. The term jet dust collector refers to the method that the dust collector uses to clean its filters, which is a reverse jet of air that forces the dust off the fabric of the dust caked filters. With some types of jet dust collectors, the determination of when to clean the filters is triggered by the differential pressure between the clean side of the filters and their dirty dirty side, which is registered by a differential pressure sensor.
An essential part of a safe work environment is to keep the air clean and free of contaminants. Jet dust collectors are an ideal method for cleaning the air to capture particles as small as two microns (µ).
Air box pulse jet dust collectors are the typical baghouse form of dust collector that pulls air into the system where a baffle at the inlet collects large particles. One method for cleaning filters is backflushing that uses air, chemicals, or water to clean filters. Select air box pulse jet dust collectors combine the cleaning processes of backflushing and pulse jet to create a more efficient filter cleaning system.
The combined processes of backflushing and jet pulse cleaning increases the efficiency of the dust collector and extends the useful life of the filter bags. Air box pulse jet dust collectors are exceptionally reliable and can be adapted and configured to fit the needs of a wide range of dust gas properties.
With a bin vent pulse jet dust collector, dust filled air enters from the bottom of the collector and accumulates on the surface of the bag filters. A blast of air from venturi tubes hits the bag filters caked debris, which falls through the open bottom. Bin vent dust collectors operate with a constant pressure that is controlled by an electronic timer. They are capable of handling grain loads of 100 grains per cubic foot.
Bin vent pulse jet dust collectors are low maintenance due to their limited number of moving parts. When bulk materials are discharged into a silo, heavy particles fall to the bottom. Fine dust particles float upwards toward the vent of the bin. To meet Environmental Protection Agency (EPA) standards, the particles in the dust have to be removed before the air can be released. This is the function of bin vent jet pulse dust collectors.
Cartridge pulse jet dust collectors are a horizontal style dust collector that has a smaller footprint and compact design. The cartridge style pulse jet dust collector has superior filtration efficiency with filters that can remove 0.5 microns at 99.99% efficiency. Filters are pulse cleaned while the system is in operation. Cartridge systems are used for dry, free flowing powders, dust, and fumes.
Cylindrical pulse jet dust collectors are designed to endure internal or external static pressure, making them ideal for explosion protection. The types of dust they filter are sander dust, fine lint, grain, and cellulose. They can handle media at speeds of up to 20 feet per minute (FPM) or 6 m per minute. A tangential inlet acts as a cyclone causing the air to spin, moving the heavy particles to the wall and into a collection bag.
Fume pulse jet dust collectors are engineered for handling fine and light dust applications. The particulate matter collected by fume jet dust collectors are sub micrometer size or measured in nanometers, which is 1000th of a micrometer. The precision of fume jet dust collectors eliminates particulate matter from gas streams.
The nature of fume jet dust collectors requires that the system have a spark baffle. It is a cartridge style jet dust collector where the fume inlet is at the bottom of the collector.
Modular jet dust collectors make it possible to add units as the need arises and increase filtering capacity or have several units connected. They have a hopper inlet that has a deflector plate or baffle to trap heavier particles that drop directly into a hopper or bag. This design reduces the amount of dust that comes in contact with the filter bags reducing abrasion, which decreases pressure drop and prolongs the life of the filter bags.
A unique form of jet dust collector is the offline system, where the inlets and outlets for the system are closed to stop the flow of dirty air. Once closed, a pulse valve with a supply of compressed air is released into blowpipes above the vertical bags. A pneumatic damper system placed at the inlet and outlet is used to stop the air flow.
The pulses of air are released at 0.1 of a second intervals to supply a burst of air to clean the filter bags. The complete process takes approximately 30 seconds, after which the pneumatic dampers reopen. The offline cleaning system is used for coal fired boilers and municipal waste incinerators. It allows for thorough and continuous cleaning of the bag filters to achieve low emissions.
The filter of a pulse jet dust collector is the essential piece that completes the dust collection process. They are made of a variety of materials depending on the type of mechanism and the media being filtered. When dust comes in contact with the filter, it is collected on the outside of the bag as the air passes through.
The cleaning process for pulse jet dust collector filters can be online as the filtration mechanism is still filtering or offline when there is a pause in the filtering process. Filter bags for jet dust collectors can be made of paper or fabric.
In a pulse jet dust collector cartridge system, filters are round and pleated, compacting a large surface area into a smaller filter. The material used to make the filters is paper made of cellulose, polyester, or a combination of the two.
Bag filters for pulse jet dust collectors are the most common filter found in pulse jet dust collectors. They are designed to collect the dust on the exterior surface of the bag and be cleaned by a pulse of compressed air that knocks the cake dust off and into a hopper. The pulse of air can be on a timed mechanism or applied when there is a pressure drop.
For the pressure drop system to be activated, the thickness of the caked dust has to reach a particular resistance to activate the controller. The application of the pulse of air creates a shock wave and ripple effect on the surface of the filter bag that further enhances the impact of the pulsed compressed air from the venturi nozzle.
High temperature pulse jet dust collector filters are used in applications where the temperature reaches 204o C or 400o F. They are used in industries that produce dust that has excessive heat. In normal high temperature applications, it is necessary to cool the dust before entering the dust collector. By using high temperature filters, it is possible to eliminate the cooling process.
The properties of the media that are being filtered determines the material from which the filter is made since each type of material is designed to meet the needs of different air streams. Filters can be woven or non-woven, which is another factor in the selection process.
Fiberglass pulse jet bag filters can be used in applications where the temperature may reach 260o C and with corrosive gases. They have exceptional resistance to all forms of chemicals. Fiberglass bag filters are non-absorbent, noncombustible, and have excellent dimensional stability.
PTFE filters can withstand temperatures up to 260o C. They have excellent resistance to oxidation, chemicals, and degradation by ultraviolet rays or mildew. The major drawback to using PTFE filters is their expense.
PPS felt is a high temperature type filter. It performs well in applications where alkaline is present and has exceptional chemical resistance. It is a strong abrasion resistant fabric that is good for applications up to 190o C. PPS filters are used with coal fired boilers, incinerators, fluidized bed systems, cement mills, and smelting industries.
Aramid is used in high temperature applications due to its resistance to abrasion and ability to perform at temperatures of 205o C. It is resistant to flames and has excellent thermal stability. Aramid is produced in felted and woven fabrics as a filament or staple fiber.
The main quality of polypropylene that makes it ideal for jet dust collectors is its smooth surface that easily releases caked dust. The material is resistant to abrasion and static buildup and has a low operating temperature of 90°C.
Polyester filters have a temperature range of 130° C to 150°C with good resistance to oxidation and limited resistance to acids and alkalis. They do not perform well where there is hydrolysis at high temperatures. Polyester filters have exceptional resistance to the effects of solvents but will be degraded by water and nitric, Sulphuric, and carbonic acids.
Homopolymer acrylic filter bags are made of needle felt acrylic with good abrasion resistance, energy absorption, and moisture heat hydrolysis properties at temperatures ranging from 127°C to 135°C. In some cases, they are coated with calcium carbonate or a thin layer of Teflon membrane that increases the life of the filter. The main use of homopolymer acrylic filters is for the filtration of processes that involve ferrous and nonferrous metals.
Filter bags are held in place by a wire cage with 10, 12, or 20 vertical wires. The cages can be top loading or bottom loading. The collar of the cage is what holds the bag securely in place. The diameters of cages vary between 4” and 7” with wire thicknesses ranging between 9 gauge and 11 gauge. Bottom loading cages have a split collar in the same diameters and metal gauges as top loading ones.
The main parts of a pulse jet bag dust collecting mechanism are the filter bag assembly, blow pipe, and hopper. All dust collecting systems have a method of separating particulate matter from air to produce cleansed or clean air. Filtration systems are one of the many methods.
When dust is collected in a filtration system, it cakes and builds up on the exterior of the filters. This requires the filters to be cleaned of particulate matter to continue the efficient operation of the system. Jet dust collectors use compressed air to discharge the caked dust and keep the filtration system in full operation.
Dust ladened air enters the dust collector through the inlet, which can be seen on the left of the diagram. As the air enters the collector, its velocity decreases because of the expansion of the volume of air. As the velocity decreases, the larger particles fall into the hopper below the dust collector. In some jet dust collectors, a baffle plate inside the inlet forces the larger particles to fall into the hopper.
The remaining dust filled air, with the large particles removed, moves through the filter bags that capture particulate matter on their exterior.
As the dust filled air flows upward into the filters, dust particles are captured on the outside of the bags releasing cleaned air. The grey portion of the diagram below is a representation of the bags of the filtration system.
As the air flows upward, the bag filters collect the small dust particles releasing clean or cleansed air. The flow of the air forces the cleaned air out the outlet of the dust collector.
Pulse jet valves are indirect solenoid valves that get energized when air is trapped in their diaphragm, causing a pressure difference in the diaphragm that forces it to suddenly open. When the valve de-energizes, air passes through to the chamber that creates a balance of air pressure and closes the valve. The opening and closing of the diaphragm happens very quickly in pulses for the cleaning of the filter bags.
Differential pressure is a data metric used to determine the operation of a pulse jet dust collector. In jet dust collectors, the resistance in the filter builds up as dust cakes on the sides of the filter, making it more difficult for air to move through. The vacuum pressure is lower on the dirty side than it is on the clean side. A differential pressure reading is taken between these two points to determine the amount of resistance.
When the pressure becomes too high, in a jet dust collector, compressed air is released through the venturi valve. In timed systems, the differential pressure sensor alerts operators to malfunctions in the cleaning system.
As the dust laden air is filtered, heavy layers of caked dust particles build up on the outside of the filter bags, which increases their resistance and hampers their efficiency. The consequence of the condition is the need to remove the caked dust particles. Included in the need to clean the clogged bag filters is the preservation of the integrity of the filters and prolonging their life.
The compressed jets of air method for cleaning bag filters is one of a variety of bag filter cleaning methods. The execution of the process can be by a manually operated button, a pressure sensor, or a timer. In either case, a solenoid valve and a compressed air header releases air pulses that cause shock waves through the filter bags in the opposite direction of the air flow pattern. As the short pulses, that last a few seconds, strike the bags, the caked dust is released and falls into the hopper.
The component through which the bursts of air are released is a venturi valve that is a cone shaped device located at the top of the tubular filters. At the top of the venturi, negative pressure pulls additional air down into the walls of the filter bags during the pulsing.
In the diagram below, the venturi sets inside the bag cage to release the pulse of air to remove the caked on dust particles.
With the increasing regulations regarding air quality, manufacturer’s concerns, and society’s focus on the environment, jet dust collectors have gained greater interest and use. Of their many benefits, the one that is admired the most is their ability to continuously run as the filter bags are being cleaned.
Jet dust collectors make up approximately 50% of the dust collectors in use today. In all dust collectors, the cleaning of the filters is a necessity for the good of air quality and the efficiency of the collector. The precision cleaning provided by a jet dust collector makes it stand out as the most effective method.
The simplified design of jet dust collectors maximizes performance, minimizes maintenance, and creates longer usage. Fast valve opening and closing leads to effective bag filter cleaning while minimizing the use of compressed air. Certain varieties of valves have an operating life of one million cycles.
Keeping a work area clear of contaminants and potential dangers is a key component for a company’s success. Such conditions make workers feel safe and ensure their continued good health. The dust collecting process of a jet dust collector rapidly cleanses the air to keep workers, equipment, and the work environment clean and secure.
A cluttered, dirty workplace makes it difficult for the successful completion of projects. Dust and debris slow down machinery, workers, and production. Dust, dirt, and debris spread quickly and get into every crevice, crack, opening, and space. The tiniest build up of dust can cause heavy processing equipment to malfunction and break down. All of these factors are eliminated by jet dust collectors that constantly remove dust and circulate clean air.
Manufacturing operations produce air pollutants required to be controlled by the Environmental Protection Agency (EPA), which has specified five major air pollutants.
Jet dust collectors are designed to collect and remove these pollutants from the air at manufacturing and production facilities.
The chart below provides information regarding air quality using a numerical index from zero to 500. The higher the index value, the greater is the health concerns, with an index of 300 or higher being hazardous air quality.
Jet dust collector manufacturers are fully aware of air quality standards and are constantly refining, designing, and configuring their products to meet the EPA’s specifications.
As much of a hindrance as dust is to employees and machinery, it is just as harmful and detrimental to products where it can significantly influence a product's quality. This factor is especially true in the case of electronics and technical devices. Keeping air quality at exceptionally high standards improves the quality of products and ensures that what is being delivered complies with the manufacturer’s standards.
Jet dust collectors and filters can be customized to precisely fit the special requirements of a manufacturing environment. Every production and manufacturing facility has a unique set of needs depending on its location, type of dust produced, and the regulations of the area. The versatility and adaptability of jet dust collectors allow them to be configured to meet the needs of any set of conditions.
Some systems may require fire suppression capabilities, while others may have greater concern for the volume of air being processed. Regardless of the conditions and stipulations, jet dust collectors can be customized and shaped to meet the demands.
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