For indoor dry dust collector installations, cartridge dust collectors are often the best option for applications where the dust is dry and can flow freely, such as in chemical processing, minerals, blasting, welding, plasma cutting, dry powder handling, and metal finishing. But cartridge filters, just like baghouse filters, demand regular maintenance to provide continuing filtration efficiency.
In early dust collection systems, filters inside a collector gradually built up a layer of dust; over time, the pressure drop across the filter media rose until the resistance to airflow through the system reached an unacceptable level. The dirty filters had to be removed and replaced with clean filters to return the system to a lower pressure drop condition.
Today, discarding and replacing filter cartridges when they get dirty rather than cleaning them is the exception rather than the rule. In those exceptional cases, the filter cartridges are typically made of inexpensive cellulose fibers and intended for lighter-duty applications like filtering light fumes or small amounts of airborne dust, such as in paint booths, plasma-welding booths or shop-venting applications.
Cartridge filters can be manufactured with a variety of filter media, including cellulose, cellulose/polyester blends, flame retardant cellulose or cellulose/polyester, carbon impregnated, spun-bonded hydrophobic or oleophobic fibers, or filters with polytetrafluoroethylene (PTFE) (Teflon) surface treatments.
Sly offers both horizontal and vertical cartridge dust collection systems, each equipped with its own built-in cartridge cleaning system designed to minimize the consumption of compressed air.
Vertical collector cartridge cleaning
PleatJet vertical dust collectors are designed for on-demand pulsed filter cleaning. Their downflow design and built-in classifier used in vertical collectors separates out heavier dust particles, reducing dust loading. Their cellular construction allows for automatic on-line pulse cleaning without dust becoming re-entrained in the filter. A cleaning cycle reverses the usual direction of airflow within a cartridge. Instead of dirty air flowing through the filter, leaving dust behind on the outside, a blow pipe inside the filter sends a 100-millisecond pulse of compressed air down the center of each cartridge, which releases the dust cake clinging to the outside of the cartridge.
Horizontal collector cartridge cleaning
PleatJet II™ PLUS horizontal cartridge collectors use the Opti-Pulse cartridge cleaning system, which is designed to provide even distribution of the cleaning air pressure in the cartridge to enhance cleaning effectiveness. In a standard venturi cleaning system for baghouse filters, the cleaning air enters the filter at a high velocity with entrained secondary air. This jet pulse travels to the end of the bag and rebounds up the filter, flexing the material and dislodging the dust cake.
In contrast, cartridge filters are much shorter than baghouse filters and their rigid design doesn’t allow them to flex. Instead, a 100-millisecond pulse of compressed air is used to dislodge the dust on the filter. A specially designed cone in the Opti-Pulse system reduces the velocity of the cleaning air, converting this energy to a more uniformly distributed cleaning pressure. Uniform cleaning ensures that the greatest possible filter surface area is available for dust collection. Cleaning the cartridges only when necessary and not continuously translates into energy savings (by reducing the consumption of compressed air) and extended cartridge life.
The Opti-Pulse cleaning system uses a MP-494 timer with a “clean-on-demand” module to trigger cleaning cycles automatically, based on the pressure loss across the dust collector. Let’s consider setting up the system to trigger a cleaning cycle at 4-1/2 inches of differential pressure, then to stop cleaning when the pressure is reduced by a half-inch water column. Over a cartridge’s first year of use, it might be necessary to clean the filers only once every few hours to maintain this desired level of differential pressure. However, by the end of the cartridge’s second year of use, although it might still be possible to maintain 4-1/2 inches of pressure while cleaning on demand, it might require pulse the cartridges with cleaning energy three times as often.
This clean-on-demand practice minimizes the number of cleaning cycles the filter cartridge will undergo, reducing mechanical wear on the filter media. It also makes it easy for maintenance personnel to track the number of cleaning cycles being performed, and helps them determine when a filter is nearing the end of its useful life.
Common cartridge cleaning mistakes
Although pulse clean-on-demand systems take most of the guesswork out of cartridge cleaning, mistakes can happen. Here are some of the most common ones we’ve encountered:
- Using a cartridge with inadequate filtration area for the type and amount of dust involved. Applications in which a high level of dust loading is anticipated can overload the filter media, filling the filter pleats with dust that is difficult for the cleaning system to dislodge.
- Extending the pulse duration in an attempt to control differential pressure across the unit. Changing the length of the cleaning pulse from 100 milliseconds to 500 milliseconds won’t deliver any more cleaning energy to a filter cartridge. It can only consume more compressed air (and more energy) and increase the amount of recovery time needed before the next cleaning cycle. Instead of delivering longer pulses, reduce the time between cleaning cycles.
- Neglecting to check the integrity of the dust collector’s seals or gaskets. Old, cracked seals and can allow cool, moist ambient air to leak into the collector, where it can mix with the warmer air in the gas stream and create condensation. That condensation can cause the collected dust to become more agglomerative, less permeable and more difficult to dislodge during a cleaning cycle.
- Failing to anticipate the dust being collected could carry a high static charge. Dust with a high static charge will remain stuck in a filter’s pleats far longer than it will in a more traditional round filter. Choose static-dissipating filter media and grounded filters to combat this problem.
To learn more about how to maximize the filtration efficiency of your cartridge dust collector system and dust collector filter cleaning process, contact the Sly sales representative nearest you.