Filter bags can be made from a variety of materials (also known as filter media), depending on the specific application, operating conditions of a baghouse, and the type of contaminants or particles they are designed to capture. The following aspects must be considered when it comes to filter media design and selection:
- Efficiency: Filtration efficiency, measured as the percentage of contaminants removed from the gas stream, is a crucial performance factor. Filter media captures particles through size exclusion, using their porous structure to physically block particles, or through adsorption and attraction mechanisms. Achieving high efficiency requires optimizing pore size, surface area, compatibility with the gas stream, and other filter media characteristics.
- Longevity and Durability: The operational lifespan of filter media depends on its resistance to factors causing degradation over time, including temperature, chemical exposure, moisture, and mechanical forces during cleaning/backwashing.
- Flexibility and Adaptability: The ability to adapt filter media to different applications through tailored pore sizes, compatibility with various chemistries, and configurations (depth vs surface filtration) expands its usefulness across industries. Media flexibility minimizes the need for custom media for specific applications, improving cost-effectiveness.
Overall, balancing these parameters can optimize filter operation, reduce operating costs over time, and minimize ecological impact – the core goals of high-performance and high-efficiency filtration. Careful media design and selection are key to achieving efficient, reliable, and environmentally sound dust emission controls. The filtration function of filter media is mainly determined by:
- Filter Media Material
- Filter Media Construction
- Filter Media Treatment
Filter Media Material
Each material has its own unique filtration characteristics. Choosing the right material with its corresponding characteristics that are best suited for the specific application can help boost the performance and longevity of the dust filtration system.
Material Comparison
The table below is a filtration characteristics comparison across some of the most common filter media materials:
| Filter Media | Temperature Resistance | Chemical Compatibility | Abrasion Resistance | Moisture Resistance | Particle Size Range | Application |
|---|---|---|---|---|---|---|
| Polyester | Up to 275°F (135°C) | Good | Moderate | Good | General | General industrial dust collection |
| Acrylic | Up to 275°F (135°C) | Good | Moderate | Good | Fine to Coarse | General industrial applications |
| PPS (Ryton) | Up to 375°F (190°C) | Excellent | Excellent | Good | Fine to Medium | Coal-fired boilers, chemical plants |
| Aramid (Nomex) | Up to 400°F (204°C) | Good | Good | Good | Fine to Medium | Asphalt production, metal smelting |
| P84 (Polyimide) | Up to 500°F (260°C) | Excellent | Excellent | Good | Fine to Medium | Incineration, cement production |
| Fiberglass | Up to 500°F (260°C) | Good | Excellent | Excellent | Fine to Coarse | High-temperature applications, metals |
| PTFE | Up to 500°F (260°C) | Excellent | Excellent | Excellent | Fine to Ultrafine | Chemical processing, pharmaceuticals |
Note: The information provided in the table is general and may vary based on specific formulations and manufacturers. It’s important to consult with filter media suppliers and manufacturers for detailed specifications and recommendations based on particular requirements.
Material Selection Considerations
Selecting the right filter media for a baghouse is crucial for the effective and efficient operation of the dust collection system. Several factors should be considered when choosing filter media for a baghouse:
- Particle Size and Characteristics: Identify the size and nature of the particles you need to capture. Different filter media are designed to handle specific particle sizes and types. For example, fine particulate matter may require a different filter media than larger, heavier particles.
- Filtration Efficiency: Filtration efficiency is a measure of how well a baghouse filter bag can capture dust particles from a gas stream. It is usually expressed as a percentage of the inlet dust concentration that is removed by the filter bag.
- Temperature: Consider the operating temperature of the process. Some filter media can withstand higher temperatures than others. If the process involves elevated temperatures, choose a filter media that can handle the heat without compromising performance.
- Chemical Compatibility: Understand the chemical composition of the dust or particulate matter. Choose a filter media that is chemically compatible with the contaminants to prevent degradation or breakdown of the filter material.
- Moisture Levels: Assess the moisture content in the gas stream. Some filter media may be prone to clogging or degradation when exposed to high levels of moisture. Select a filter media that can handle the moisture conditions of the application.
- Abrasion Resistance: Consider the potential for abrasion in the gas stream. If the dust particles are abrasive, choose a filter media that is resistant to wear and tear to ensure a longer lifespan for the filter bags.
- Cleaning Mechanism: Consider the cleaning method used in the baghouse (e.g., pulse jet cleaning, reverse air cleaning, shaker cleaning). Different filter media may respond differently to cleaning mechanisms, so choose a media that is compatible with the cleaning process.
- Regulatory Compliance: Ensure that the selected filter media comply with any applicable regulatory standards and environmental requirements. Certain industries may have specific regulations regarding emissions and air quality, and using compliant filter media is essential.
- Cost Considerations: Evaluate the initial cost and lifecycle cost of the filter media. While certain materials may be more expensive upfront, they could provide cost savings over the long term by offering better durability, performance, and lower maintenance costs.
Filter Media Construction
Filter media construction refers to the way that filter media are constructed. It is commonly categorized as woven and nonwoven. To further enhance filtration efficiency and filter bag durability, a dual-density felt structure is often used to construct filter media.
Nonwoven
Nonwoven fabrics are made using a process that involves first joining the fibers together in ordered or random patterns, and then coupling the layers of nonwoven with a polymer to give life to a porous material suitable for filtration. The most commonly used filtration nonwoven raw materials include polyester, acrylic, PPS, aramid, polymide, PTFE, fiberglass, and mixed fiber blends. Generally, they are used with higher energy cleaning systems such as pulse-jet dust collectors. The four most widely used nonwoven fabrication processes are:
- Needlefelting
- Spunlace (Hydro-entangling)
- Spunbond
- Meltblown
Within the needlefelting category, a dual-density felt structure is often used to construct filter media. In a genuine dual-density filter media, two media of different densities are separated by a scrim in the middle that provides dimensional stability and a densified central core which improves filtration efficiency by minimizing dust migration through the felt. The scrim structure offers a clear advantage over unsupported felts (without scrim) which are produced in a single process with a homogeneous fiber blend and filtration characteristics only.
Woven
Woven fabrics are made by weaving single strands of materials such as monofilament or fibrillated yarns on a loom with a definite repeated pattern. The most commonly used filtration woven raw materials include polyester and fiberglass. Generally, they are used with low energy cleaning systems such as shaker or reverse air baghouses.
Filter Media Treatment
Different fibers provide each media with different dust filtration characteristics. Filter media can be further treated to improve their filtration efficiency and performance, such as lengthened filter media life cycle, better dust cake release, reduced valve pulsing, more consistent airflow, reduced differential pressure, and reduced downtime and maintenance.
Singeing
Singeing is done by passing the filter material over an open flame. This removes any straggly surface fibers and results in a more uniform filter bag surface. You can typically see this process done on polyester, polypropylene, acrylic, aramid, aramid, and P84 felts.
Calendering (Glazing)
Calendering, also known as Glazing, is the high-pressure pressing of the fabric by rollers to flatten or smooth the material. Calendering pushes the surface fibers down onto the body of the filter media. Calendering can be applied to various media such as polyester, polypropylene, and aramid. This is done to increase and uniform surface life, improve stability and reduce shrinkage.
Napping
This process is the scraping of the filter surface across metal points or burrs on a revolving cylinder. Napping raises the surface fibers, creating a “fuzz”, that provides a large number of sites for particle collection by interception and diffusion. Fabrics used for collecting sticky or oily dust are sometimes napped so they can provide better collection and an easier cleaning process.
Coating
Coating, also known as resin treatment, involves immersing the filter media in natural or synthetic resin. This process helps lubricate the fibers, helps the fibers to shed water and oils (hydrophobic & oleaphobic), and provides high-temperature durability.
ePTFE Membrane
ePTFE stands for expanded polytetrafluoroethylene, and it is a microporous membrane that is laminated to the filtration side of the filter media to enhance the filtration performance. The performance improvements include enhanced emissions control, easy dust cake release during the cleaning cycle, reduced cleaning energy cost, and higher collection efficiency due to its surface filtration characteristics.
For More Information
Aokai is enthusiastic about helping customers achieve high and long-lasting filtration efficiency. This is exactly why we insist on manufacturing filter media in-house. As a leading filter media manufacturer and supplier in China, we custom design and manufacture dust filter media that best suits customers’ unique dust collection requirements. Aokai provides filter media solutions for abrasive, corrosive, high-temperature, and explosive dust filtration, and specializes in dust collection processes in asphalt mixing, chemicals, cement, metals, power generation, waste-to-energy, renewable energy, woodworking, and many other demanding industries. Contact Aokai for more information about our Filter Media manufacturing process and product offerings.
