Choosing the Right Bag Filter Bag for Your Application
Bag filters are used in industrial dust collecting areas to capture particulate laden air, turning it into clean air. There are a variety of filter bags available to suit different applications and requirements.
Woven bags consist of a mesh or needle felt filter media. Nonwoven filter bags consist of various forms of carded or spun-bonded webs or meltblown. These are often combined with a PTFE membrane for added performance.
Flow Rates
Bag filter systems are designed to handle a variety of flow rates. However, many factors impact how fast a system can move water through it. These factors include the water source’s turbidity, temperature, and viscosity. It’s important to consider these variables when evaluating the best filtration options for your building’s needs.
When selecting a filter, you should be aware of how quickly a system can process water and how much head loss it experiences at maximum flow rate. Flow rate testing should be conducted under the actual conditions found in the filter bag production process. This includes assessing the fluid’s turbidity, temperature, viscosity, and particle size distribution.
To avoid prematurely damaging a filter, it’s recommended to select one that can accommodate fluctuations in your water’s flow rate. Flow rates that are too high can create a strain on the filters and impede filtration efficiency. Likewise, low flow rates can result in the accumulation of debris and reduced water filtration capacity.
Liquid bag filters offer user friendly, cost effective filtration solutions for a wide range of applications. They are available in a variety of materials, including polyester, polypropylene, nylon, porous PTFE film and other fluoropolymers, nomex, and woven felts. They are typically sewn together using a ring to form an opening that allows the liquid to pass through, and can be sealed with either a zinc plated steel ring or a sanitary snap (also known as a “snap-ring”). They can be used for pressure or suction filtration.
Capacity
There are many factors to consider when selecting the proper filter bag for your system. The type of fluid to be filtered, the size of particles, the nominally rated efficiency and chemical and temperature compatibility with the liquid are all important to determine the proper filter bag for your application.
Filter bags are available in a wide range of sizes, material and micron ratings. They can be used in a variety of types of filter housings. They are made of a variety of woven and nonwoven materials, such as needle felts, various forms of carded nonwovens, meltblown fibers, spun bonded webs, and composite structures.
The conventional needle felt filter bags are primarily sewn together with a mesh grid pattern and have nominally rated retentions based on their construction. These are the least expensive of all filter bag designs. They are often referred to as snap-ring or SNAP bag filter bags. A variant of these, called SENTINEL bag filter bags have a modified crush seal ring welded to the bag, providing higher efficiencies and dirt-holding capacities than standard needle felt bags.
Woven glass fiber bag filters are constructed of a series of woven layers with coarser materials that remove larger particles and then finer materials that trap smaller particulates. These have well documented efficiencies and capacities and are used for industrial dust control, air pollution prevention and valuable mineral dust collection.
Ease of Cleaning
The system uses a Fan or Blower to either pressure (push) or vacuum (suck) the air across the filter bag’s media. This creates contact with the dirty side of the filter media and allows clean air to flow from the opposite end. The bag’s media is designed with a dirty and clean side to capture the dust.
The fabric material used for the bag is also important to note. Some materials are easier to clean for re-use, such as melt-blown polypropylene. Other materials Underground garage drainage membrane are more difficult to clean and re-use, such as the standard woven polyester (30 micron) or needle felt. The latter offers much higher permeability for reduced interstitial velocity and enhanced fine filtration spec.
Other features and options are also available to enhance certain filtration applications. For example, a displacement balloon variation moves the dirty gases closer to the filter bags’ inside surface area, reducing product loss during bag changes. Displacement balloons also reduce pressure spikes within the piping system and increase worker safety.
The bag itself is easily cleaned by simply washing it in a bucket with high-pressure water. It’s easy to see why these bags are so popular! Make sure to rinse the filters well to avoid damaging the fabric. Hang them up to dry afterward, as a fully-filled bag may attract rodents if left sitting in the elements for too long.
Maintenance
Regardless of the filter type or design, there are certain maintenance requirements that must be met to ensure optimal filtration performance. This includes consistent monitoring, cleaning, inspection, and troubleshooting. It is important to be proactive in this process and understand the underlying causes of issues such as dust emissions, pressure drop, and airflow calculations.
Keeping track of daily pressure drop readings is crucial to detect and address any issues that may arise (e.g., visible particulate emissions exceeding permitted limits, excessive clogging of the bag house, reduced ventilation at the baghouse pick-up points). It is also essential to conduct regular inspections and perform periodic cleaning to check for signs of wear and tear or any damage to the bags or cages. These inspections should be documented for future reference.
The snap-ring is a plastic or metal ring that is sewn within the filter bag opening and aligns with a groove in the support basket to provide a seal. This system is effective in holding the filter bag firmly in place yet easily removed for cleaning. It is commonly incorporated with the crush-seal ring, which creates an outward force on the top of the ring to improve sealing by reducing the gap between the ring and the groove.
Lastly, it is important to have a properly working cleaning system in order to dislodge the accumulated dust cake from the filter media. Failure to do so could result in increased pressure drop, lowered airflow at pick-up points, or shortened filter life.