This article takes an in-depth look at jet dust collectors.
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A pulse jet dust collector is a suction filtration unit that pulls dust-laden air into a filtration system that collects particulate matter and releases clean air. The filters of pulse 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 pulse 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 pulse jet dust collectors include product recovery, dust capturing, filtering explosive media, metalworking chip capturing, central vacuum cleaning systems, and pneumatic conveying.
Pulse jet dust collectors are a special type of baghouse dust collecting system. The term pulse 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 pulse jet dust collectors, the determination of when to clean the filters is triggered by the differential pressure between the clean and dirty sides of the filters, which is registered by a differential pressure sensor.
An essential part of a safe work environment is keeping the air clean and contaminant-free. Pulse jet dust collectors are ideal for cleaning the air to capture particles as small as two microns (µ).
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 include 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.
A unique form of pulse 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. Next, 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-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.
Modular pulse jet dust collectors make it possible to add or connect several units as the need arises to increase filtering capacity. They have a hopper inlet with 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.
Air box pulse jet dust collectors are a typical baghouse dust collector that pulls air into the system, where a baffle at the inlet collects large particles. One method for cleaning filters is backflushing, which 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 pulse jet cleaning increase the dust collector's efficiency and extend the filter bags' useful life. 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 and gas properties.
Cartridge pulse jet dust collectors are horizontal-style dust collectors with a smaller footprint and compact design. A 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.
In 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 a Venturi tube hits the caked debris, which falls through the open bottom. Bin vent dust collectors operate with a constant pressure 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.
A fume pulse jet dust collector is a cartridge-style pulse jet dust collector where the fume inlet is at the bottom of the collector. They are engineered for handling fine and light dust applications. The particulate matter collected by fume pulse jet dust collectors is sub-micrometer and measured in nanometers (1/1000th of a micrometer). The precision of fume pulse jet dust collectors eliminates particulate matter from gas streams.
The nature of fume pulse jet dust collectors requires that the system have a spark baffle.
The filter of a pulse jet dust collector is the essential piece that completes the dust collection process. They are made of various 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 pulse 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 caked dust off and into a hopper. The air pulse can be on a timed mechanism or applied when pressure drops occur.
For the pressure drop system to be activated, the thickness of the caked dust has to reach a particular resistance to activate the controller. In addition, the application of the pulse of air creates a shock wave and ripple effect on the surface of the filter bag, further enhancing 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 400 °F (204 °C). They are used in industries that produce excessively hot dust. In normal applications with high temperatures, it is necessary to cool the dust before it enters the collector. By using high-temperature filters, it is possible to eliminate the cooling process.
The properties of the filtered media determine the filter material since each material is designed for different air streams. In addition, 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 with corrosive gasses or high temperatures reaching 500 °F (260 °C). 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 500 °F (260 °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 type of high-temperature filter. It performs well in applications containing alkaline and has exceptional chemical resistance. It is a strong, abrasion-resistant fabric that is good for applications up to 374 °F (190 °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 up to 400 °F (205 °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 pulse jet dust collectors is its smooth surface that easily releases caked dust. The material is resistant to abrasion and static buildup but has a low operating temperature of 194 °F (90 °C).
Polyester filters have a temperature range of 266 °F to 302 °F (130-150 °C), with good resistance to oxidation and limited resistance to acids and alkalis. However, they do not perform well with 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 260 °F to 275 °F (127 °C to 135 °C). In some cases, they are coated with calcium carbonate or a thin layer of Teflon membrane that prolongs the filter’s life. 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 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 split collars with 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, such as filtration, of separating particulate matter from air to produce cleansed or clean air.
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. Pulse jet dust collectors use compressed air to discharge the caked dust and keep the filtration system in full operation.
Dust-laden air enters the dust collector through the inlet, as seen on the below diagram’s left side. 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 pulse jet dust collectors, a baffle plate inside the inlet forces the larger particles to fall into the hopper.
With the large particles removed, the remaining dust-filled air moves through the filter bags, which capture particulate matter on their exteriors.
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 represents the bags of the filtration system.
As the air flows upward, the bag filters collect the small dust particles and release clean air. Finally, the airflow forces the cleaned air out of the outlet of the dust collector.
Pulse jet valves are indirect solenoid valves that are energized when air is trapped in their diaphragm, causing a pressure difference that forces the diaphragm to suddenly open. When air passes back into the chamber, the new air pressure balance de-energizes and closes the valve. The opening and closing of the diaphragm happen in quick pulses during bag filter cleaning.
Differential pressure is a data metric used to determine the operation of a pulse jet dust collector. 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. A differential pressure reading is taken between the dirty and clean sides to determine the amount of resistance; the pressure is always lower on the dirty side.
Compressed air is released through the Venturi valve when the pressure becomes too high. 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, increasing their resistance and hampering their efficiency. Therefore, the clogged bag filters must be cleaned to preserve their integrity and prolong their lifespan.
Compressed jets of air are one of many methods for cleaning bag filters. The process can be executed by a manually operated button, a pressure sensor, or a timer. In either case, a solenoid valve and a compressed air header release air pulses that cause shock waves through the filter bags in the opposite direction of the air flow pattern. As the short pulses, lasting 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, 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 inside the bag cage releases pulses of air to remove the caked-on dust particles.
With the increasing regulations regarding air quality, manufacturers’ concerns, and society’s focus on the environment, pulse 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.
Pulse jet dust collectors make up approximately 50% of the dust collectors in use today. In all dust collectors, cleaning the filters is necessary for good air quality and the efficiency of the collector. The precise cleaning provided by a pulse jet dust collector makes it stand out as the most effective method.
The simplified design of a pulse jet dust collector maximizes performance, minimizes maintenance, and creates longer usage. Fast valve opening and closing lead 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 of a company’s success. Such conditions make workers feel safe and ensure their continued good health. The dust-collecting process of a pulse 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 to complete projects successfully. Dust and debris slow production, spread quickly, and penetrate every crevice, crack, opening, and space. In addition, the tiniest buildup of dust can cause heavy processing equipment to malfunction and break down. All of these factors are eliminated by pulse jet dust collectors, which 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.
Pulse jet dust collectors are designed to collect and remove these pollutants from the air in manufacturing and production facilities.
The chart below provides information regarding air quality using a numerical index from 0 to 500. The higher the index value, the greater the health concerns, with an index of 300 or higher representing hazardous air quality.
| Air Quality Index for Ozone Levels and Particulate Pollution | |||
|---|---|---|---|
| Daily AQI Color | Level of Concern | Values of Index | Description of Air Quality |
| Green | Good | 0 to 50 | Air quality is satisfactory, and air pollution poses little or no risk. |
| Yellow | Moderate | 51 to 100 | Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution. |
| Orange | Unhealthy for Sensitive Groups | 100 to 150 | Members of sensitive groups may experience health effects. The general public is less likely to be affected. Some members of the general public may experience health affects; members of sensitive groups may experience more serious health effects. |
| Red | Unhealthy | 151 to 200 | Some members of the general public may experience health affects; members of sensitive groups may experience more serious health effects. |
| Purple | Very Unhealthy | 201 to 300 | Health alert: The risk of health effects is increased for everyone. |
| Maroon | Hazardous | 301 and higher | Health warning of emergency conditions: everyone is more likely to be affected. |
Pulse 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 and can significantly influence their 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.
Pulse 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, the type of dust produced, and the area’s regulations. The versatility and adaptability of pulse jet dust collectors allow them to fulfill any 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, pulse jet dust collectors can be customized and shaped to meet their demands.
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