Custom fan designs, such as spark safe fans for explosive dusts, and turnkey projects for environmental control systems are also available. We have experienced engineers who can assist clients with fan selection and sizing.

About Reverse Pulse Filters

Many industries require dust collectors to remove harmful or irritating particulates and ensure compliance with local air pollution control legislation. In the past, cleaning dust collectors could be difficult and involve production downtime, but maintaining and cleaning a baghouse has become much easier with reverse pulse jet filter technology. This principle, which is also called pressure-jet cleaning, is a widespread technique which uses a high-pressure air jet to clean the filter bag or cartridge. Air is cleaned by drawing it through filter bags with a high-efficiency exhaust fan. Periodically, a burst of air interrupts the flow of polluted air into the bag and causes a shock wave to travel through it. The bag flexes and dust cake (“filter cake”) is broken up and dislodged to fall into storage hoppers or trays. The cleaning cycle normally occurs at intervals of about ten minutes.

The use of reverse pulse filter units can be recommended:

• For dusts that standard self-cleaning baghouses with shaker systems cannot deal with.
• Where constant airflow volumes must be filtered without any downtime to clean the baghouse.

Reverse pulse jet bag houses are commonly used in many industries, from cutting processes such as plasma cutting and welding, to powder and bulk material handling applications such as conveying.

There are two main kinds of units using this operating principle: top load (also called top entry or walk-in plenum) and bottom load (bottom entry, frequently used in bin vents) units. The difference is simply the point at which the baghouse is normally entered to change the filters.

A variety of filter media can be used with this system. Because gas has to flow from the outside to the inside, bags generally require some kind of support structure so they will not collapse. Bags can be placed on a wire cage attached to a plate at the top of the unit. Air then flows from the bottom of the unit to the top, where it is discharged.

Polyester needlefelt fabric with a wire cage, or polypropylene media contained in pleated cartridges are two of the types in use. It should be noted that the filtration velocities that can be achieved depend on the medium used. With very high velocities, dust can be blown onto nearby fabric surfaces. This effect tends to be greater with cartridge media.

Anti-static materials and media treated to be more robust are also offered.

This technology offers the operator several benefits:

• Continuous operation is possible because the pulse takes less than a second.
• Wear on bags is low, reducing maintenance costs.
• Allows for more robust woven bags to be used.
• High cloth to air ratios can be obtained.
• Compact systems with fewer bags are possible because of the aforementioned improved bag characteristics. This can save valuable floor space.
• Some designs allow for bags to be changed without entering the baghouse.
• High collection efficiencies for respirable dust. HEPA filters can be included in many cases.
• High operating efficiency thanks to reduced build-ups of residual dust.
• Low pressure drops relative to the dust collection efficiencies obtained.
• Cleaning is managed and controlled automatically.

Gas exhaust streams with high moisture contents or high temperatures are not usually suitable for reverse pulse filter baghouses. Dry compressed air is typically needed for cleaning, and the blasts produced must be strong enough to cause a strong shock wave across the whole bag (i.e. the airflow capacity of the equipment should be high enough). The pulse duration should usually be set to 0.1 seconds for proper operation and a sufficiently high air to cloth ratio should be maintained. For dangerous dusts, dust handling can be minimized by using sealed disposable bags in which to store the dust in a reverse pulse hopper (RPH) design.