Filtration and Vacuum Specialists since 1976

www.jbii.com

The Micron
JB Systems Little Newspaper
110 Corporate Plaza East Dr.
LaGrange, GA 30241
1-706-884-3006

Filtration and Vacuum Specialists since 1976

www.vacuumpumpusa.com




A Scientific Review of Dust Collection - Part 9

Using Pleated Bags In Dust Collectors

Reference material by: Scientific Dust Collectors

Because our newsletters are a service to our valued customers we have decided to share some important and educational information on Scientific Dust Collection. Over the next several months we will be focusing on the use of Dust Collectors. We felt that the extensive information and it's importance in the industry would be very useful in helping our customers make an informed decision on their needs for dust collectors in their businesses. Because the information is extensive we will be spreading it over several months.


A pleated bag consists of a length of multiple folds of filter media that are formed into the shape of a cylinder. In general, the outside diameter of the pleats typically matches the outside diameter of a standard cylindrically shaped filter bag that it sometimes replaces. The filter media is encapsulated between the bottom end cap and the top sleeve arrangement which allows for the attachment to the bag cup. It then is fastened to the tube sheet. The pleat depth varies with the outside diameter of the filter element. Typically for the family of sizes of pleated bags, the smallest outside diameter has the shortest pleat depth. The spacing of the pleats can vary so that two to three times the standard circumferential media area is achieved when comparing it to the standard cylindrical shaped bag. The inside diameter of the pleated bag is less than the standard felted polyester bag due to the pleat depth. Generally, for most collector designs, the smaller inside diameter of the pleated bag has a negligible effect on the filtering or cleaning of the bag. This is especially true if the manufacturer continues to use a venturi in the cough of the pleated bag.

Pleated Bag

History

Pleated bag elements were originally used in retrofitting existing bughouses where existing fabric bag media was unacceptable. As the manufacturing prices reduced due to volume production and competition, the dust collection industry has seen an increase in the use of these types of bags.

Benefits / Advantages

Some of the key benefits are listed below.

  1. Able to retrofit pleated bag into an existing baghouse
  2. Able to triple the amount of filter media in each bag due to the pleating process, but each type of filter media has its unique Frasier Permeability rating which has an effect on the pressure drop through the filter media. For instance , a lower Frasier Permeability in the filter media (reference media A) than the original filter media (reference media B) indicated that less CFM fan air is able to pass through a one square of filter media at the given 1/2" WG. Therefore, to retain the 1/2" WG and the original CFM (reference media A) more area of the filter media B will be needed in order to compensate for the reduction of CFM @ 1/2" WG. The following example will help clarify the principle.
  3. Able to diffuse the cleaning air due to the pleating arrangement. Therefore, the cleaning velocity is less direct and c causes less dust cake compression on the neighboring pleated bags which helps the pulse cleaning system to clean at a lower differential pressure. It should be noted that in a typical retrofit application, the cleaning capacity is fixed in the original design of the collector. Therefore, a large addition of more pleated filter media will not be cleaned and will eventually become plugged.
  4. May be able to reduce the operating pressure differential if the available cleaning air can clean the additional area of the pleated filter media.
  5. Able to reduce the size of a new collector as compared with a standard baghouse due to the increase in filter media area per unit length of the pleated bag.

For clean filter media B to pass 24 CFM through the filter media and to have a maximum limit of 1/2" WG pressure rise, than an area factor needs to be calculated and applied to the reference media B as shown below:

Step 1
original filter media CFM/ft2
= area factor
replacement filter media CFM/ft2

Step 2
multiply (area factor) times (1 ft2 area of media B) =

2 ft2 is the area required of media "B" to be equivalent to media "A" at (24 CFM at 1/2" WG.)

Clean filter media "A" passes 24 CFM fan air per square foot and causes a 1/2" WG pressure rise.
Clean filter media "B" passes 12 CFM
fan air per square foot and causes
a 1/2" WG pressure rise.

Disadvantages of Pleated Bags

Some disadvantages are listed below:
  1. The present cost of pleated bag media is significantly more expensive per square foot than the standard bag media.
  2. The pleated bag collector is not practical to convert to standard bags since the air flow and cleaning design is adapted to the larger filter media areas. The reduction in filter media area could be from 1/2 to 2/3.
  3. A fixed cleaning system is a limitation in a retrofitted baghouse where straight bags are replaced by pleated bags. The cleaning system is designed to clean a given area of media. The extra media will not be cleaned and it will eventually plug.
  4. The pleated media may have a lower Frasier Permeability number which in this case requires more filter media area in order to have equivalent fan air CFM at the same pressure rise in inches of WG.

Figure 9-1
Figure 9-2

Physical Characteristics

The pleated bags are manufactured in both top and bottom removal styles. See Figures 9-1 and 9-2, respectively. There is generally an inner core that gives rigidity and strength to the pleated bag. Also, various manufacturers supply bands that are placed circumferential to prevent ballooning of the media during the cleaning pulse. Multiple pleat depths are manufactured which typically range from .6 inches to 1.875 inches in correlation with bag outside diameters that range from 41/2 inches to 8 inches in diameter. Also, a wide range of overall bag heights are manufactured from 24 inches to 90 inches.

Various media options are also available in pleated bags. In addition to standard spun bonded polyester material, specialty material options can be obtained. Some of these are hydro and oleophobic finishes which help to repel water and oil; static dissipating membranes; and PTFE membranes for higher efficiency and release.

Some design features of pleated bags are:

  • Molded urethane top and bottom.
  • Positive interlocking seal.
  • Integrated internal pleat retainers.
  • High chemical tolerance.
  • Shallow pleats with open spacing.
  • 200 F operating temperature.
  • Positive sonic welded searing.

The installation of the bottom removal pleated bags is very similar to the mounting of standard fabric bags. The mounting of the bottom removal pleated bags require a compatible bag cup that is mounted onto the tube sheet and a band clamp.

The band clamp is loosely placed over the urethane neck of the pleated bag, and then the pleated bag is located on the bag cup. When the pleated bag is in place, the bag is secured to the bag cup by tightening the band clamp.

For the installation of the top removal pleated bag, a bag cup is not required. Instead, the pleated bag manufacturer provides a snap band that secures the pleated bag to the tube sheet.

A good retro fit application is when the baghouse air jet cleaning system has ample capacity to clean more filter media, but the present amount of media is insufficient to prevent the operating pressure from rising significantly. A high differential pressure at the magnehelic gage indicates a compaction of the dust cake, loss of fan air flow for the process application, reduced bag life, and higher fan energy costs. In this case, a pleated bag with two to three times more filter media allows the process air to flow at a lower operating pressure since it has the capacity to clean more media. The lower pressure flow equates to more fan air flow as predicted by the manufacturer's fan curve.



Request Information Home Contact Us


Visit our other sites: jbii.com, jbsystemsusa.com
solventrecoveryusa.com, vacuumpumpusa.com, jbii.com
water-filtersystems.com, wastewater-filtration.com,
liquidfiltration-products.com, oilandfuel-filtration.com, jbiit.com


© 2011 JB Systems, Inc. | 110 Corporate Park East Drive | LaGrange, GA 30241
(706) 884-3006 | Fax: (706) 884-3067 | Toll Free: 1-800-868-6204
E-Mail: sales@jbsystemsusa.com