Filters and Fabrics
At the center of the Dust Collection System is the baghouse filter. Shocking announcement, I’m sure. Big deal. The filter is there to collect the nuisance dust and prevent air pollution. Just choose the right filter and all is good. “The right filter” is the key phrase.
What can be so difficult about choosing “the right filter”? In the industry, there is the matter of “filter media,” which takes into consideration depth and surface filtration. Depth filtration uses the depth of the filter media to collect particulate matter and leverages the dust cake formed to increase filter life and efficiency. On the other hand, surface filtration keeps particulate matter at the filter media’s surface by augmenting its surface to collect fine particle, ultimately minimizing reliance on the dust cake for filtration efficiency.
BWF offers more than 1,700 different filter media. See Figure 1. What, you ask, can make choosing so complicated? Remember, we are talking “system,” and everything about the system must be included in the filter media selected―from the type of industry and process conditions to the filter’s fabric media and construction.
The following considerations are just a few samples of what to incorporate into your Dust Collection System.
Influencing Industry Factors. The following are influencing factors, with examples, for selecting the optimum filter medium:
- Dust: Composition, Concentration, Amount, and Physical/Chemical Characteristics
- Gas Composition: Chemical makeup of the gas in contact with the filter media
- Temperature: Temperature Range, Average, Peaks, Standard Deviation
- Cleaning Process: Periodic shaking, Low/High Pressure Pulse Jet, etc.
- Operation: Time between Change Outs, Time System is Offline, etc.
- Static Charge: Static Charge Formation Potential – Creating Explosion Risk
Best Practice: Each industry’s unique aspects drive filter and filter media selection.
Fabric Considerations. There are a host of fabric types and heat treatment finishes (See Figure 2 and Table 1). For instance: Aramid (Nomex, Conex), Cotton/Rayon, Fiberglass, Homopolymer Acrylic (Dolanit, Ricem), Nylon, PPS (Torcon, Procon), PTFE (Teflon, Profilen), Polyester, Polyimid (P-84), Polypropylene/ High-Temp Polypropylene. The chart below (see Table 1) identifies some other characteristics to consider when choosing the right filter media/material type for your system such as chemical properties.
Once the fabric has been chosen, surface finish decisions are required.
- Felt Finishes include: mechanical (singe or glaze), chemical (bath treatments, Teflon, acrylic, fluorocarbon, silicone), lamination (PMTec Membrane)
- Fiberglass Finishes include: silicone, graphite Teflon (SGT) (protects glass yarns from abrasion, adds lubricity); chemical (silicone, graphite, Teflon), lamination (PMTec Membrane)
|Table 1 – Filter Material Types
Filter Material Type
|Polypropylene||195||205||90||95||* * * *||* * * *||* * * *||*|
|Polyamide||230||240||110||115||*||* *||* * *||* *|
|Polyacrylonitrile Copolymer||240||250||115||120||* * *||* *||* *||* * *|
|Temperature Resistant Olefin||255||275||125||135||* * * *||* * * *||* * * *||*|
|Polyacrylonitrile Homopolymer||255||285||125||140||* * *||* * *||* *||* * *|
|Polyester||275||300||135||150||*||* *||*||* * *|
|PPS-Polyphenylene Sulfide||375||400||190||200||* * * *||* * * *||* * * *||* *|
|m-Aramid||400||425||200||220||* *||* *||* *||* *|
|Aromatic Polyamide-imide||400||425||200||220||*||* *||*||* * *|
|Polyimide||465||500||240||260||* * *||* *||* *||* * *|
|PTFE-Polytetrafluorethylene||500||535||250||280||* * * *||* * * *||* * * *||* * * *|
|Fiberglass||500||550||260||285||* * *||* * *||*||* * * *|
|*Resistance Ratings:||Restricted = *||Moderate = * *||Good = * * *||Excellent = * * * *|
Filter Construction. Filter construction must match that of the cages constructed of rigid wire, which support the filters and prevent collapse.
Filter Construction Considerations depend on the type of system. For instance, the Pulse Jet Cleaning System considerations include: Top or Bottom Load, Top Cuff Construction (how bag is attached to tubesheet), Bottom Disc, Wear Strip, Middle Wear Strip, Static Charge Dissipation, Grounding Wire, Seam (Sewn or Thermal Bond). The Reverse Air System needs include: Woven fiberglass, Seam (Vertical), Mild Steel, Stainless Steel, Galvanized Anti-Collapse Ring.
Cage Construction Considerations for the Pulse Jet System include:
- Filter’s Top Cuff Construction
- Tubesheet Design
- Top or Bottom Load Filter
- Vertical Wire Count for Bag Support
- External, Internal, or No Venturi
Then consideration must be given to stitching, seams, overlaps, tensioning, anti-collapsing features, beaded cords, wear strips, filter bag bottoms, etc.
Well, you can see now, how we quickly get to 1,700 media choices. While it seems overwhelming, experts who understand your industry, your business, your operations, and baghouse systems can simplify the entire filter media choice process.
If you would like to discuss your Baghouse Dust Collection System, please contact Matt Devitt at firstname.lastname@example.org.
Part 7 will discuss Pleated Filters. However, if you would like advice before it is published, please contact Matt Devitt at email@example.com.