Dust Collector Filter Bags and Baghouse Socks by BCE

One of the most important facets of air pollution control is the use of filter bags for dust collection.  BCE designs and manufactures a variety of filter bags engineered to fit nearly any situation.  

BCE also offers same day shipping on most standard sizes of replacement filter bags.  If BCE doesn’t have your bag in stock, we’ll custom configure your baghouse socks according to your specifications!

The bags used in fabric filter baghouses can be manufactured for several different processes, depending on such factors as the type of fiber and the design temperature.

Most filter bags commonly encountered in pulse-jet filters are of the “needle-felt” variety.  This is a textile technology where batts of short fibers are interlocked onto a backing.  The traditional backing for the bag is a woven scrim.  Recent technological advancements, however, have allowed some fibers to be made into “scrimless” bags, where the backing is a batt of the same fiber as the bag itself.  There are some distinct advantages to having a scrimless (fiber supported) bag compared to one with a scrim:

  • Since the scrim does not aid in the filtering process, not all of the weight of a scrim-supported bag contributes to filtering. In a scrimless bag, all fibers, including the backing, are available for filtration.
  • Fiber-supported bags are stronger than those with scrims, since stitching weakens scrims, but strengthens fibers.
  • Fiber-supported bags are usually less expensive, since scrims typically cost more to produce than the fiber backing.
  • Scrims can blind if dust completely penetrates the fiber mat.
  • Fiber-supported bags flex better than those with scrims, providing for better pulse cleaning.

As dust-laden air passes through a bag, entrained particulates are forced into the randomly interlaced fibers in the mat and are collected when they impact on the fibers.  The efficiency of a brand-new bag is low; however it increases rapidly once dust becomes trapped in the fibers, reducing permeability.  In that state, a stable operating differential pressure is reached, and the actual filtration is accomplished by the dust cake, not the bag.  To increase efficiency when filtering small particles, some bags are made with fine denier (i.e. smaller diameter) fibers, which provide more surface to catch particulates for a given bag weight.

Woven bags are typically used in filter types that use gentler bag cleaning than pulse-jets, such as shakers or reverse air.  Woven fabrics are not as efficient as felted fabrics.  Fiberglass is most commonly used as a woven, rather than felted fabric, but this material is fragile.  If used in a pulse-jet filter, reduced air pressure is needed in addition to a cage with double the normal number of vertical wires, to reduce the stress on the bag from the differential pressure.  Off-line cleaning is also recommended for these bags.

A number of surface treatments are available for filter fabrics.  The following are descriptions of some of the more common bag finishes:

• Glazing
The bag is heat treated with pressure to melt the outer fibers to form a smooth finish.  Glazing is also called an eggshell finish.  This treatment is used for sanitary applications and product recovery when the fibers of an untreated bag could contaminate the product.  It’s also used to handle dusts that are slightly oily or sticky.

• Singeing
The fabric is exposed to an open flame, which burns off the outer strands of the fibers.  Recommended for those dusts that tend to attach to the outer fibers and are not easily removed when the bag is pulsed.  Bag efficiency can be reduced by this process.

• Static dissipating
Static electricity buildup on a filter bag can inhibit cake release as well as create the potential of an electrical discharge which can cause an explosion with certain dusts.  Static can be dissipated in several ways.  The least expensive is to have a full length grounding wire sewn into the seam of the bag, which is connected to a grounded tubesheet.  A disadvantage of this system is that static is discharged local to the wire and may not be discharged if it builds up on the opposite side of the bag to the wire.  Another method is to blend conducting fibers of carbon or stainless steel throughout the bag to 5% of the total bag weight.

• Oleophobic
This is a water and oil repellent treatment where a fluorocarbon-based resin is impregnated into the fiber mat to allow wet, oily or sticky dusts to be released when the bag is cleaned.  It also imparts some chemical resistance to degradation of the bag by hydrolysis.

• Siliconizing
The fabric is given a silicone treatment to improve cake release in high moisture applications and during equipment start-up.  It should not be used when collecting food products.

• PTFE Laminate
PTFE (polytetrafluoroethylene) laminate is a micro-porous high-temperature membrane which can be thermally bonded onto most woven and non-woven filter media.  This material is extremely slick and has found applications in non-stick cookware and making outdoor clothing and equipment waterproof.

When applied to a filter bag, the membrane forms a network of microscopically thin fibers.  The usual pore size is 0.2-0.5 microns, but a mean pore size of 0.08 microns with 70% porosity has been reported.  The membrane transforms the bag from an in-depth filter to a surface filter with near zero emissions.  Since the membrane serves the role as the initial dust cake, there is no need to pre-coat the bags prior to or during operation.

Bags with PTFE membranes operate at lower pressure drops than conventional bags because of the nearly total elimination of fine particle penetration into the fibers of the bag.  This also allows a higher air-to-cloth ratio and less pulse energy required for bag cleaning.

Bags with PTFE membranes need to be handled carefully to avoid damage to the membrane.  They should not be used in the presence of hydrocarbons.