Filter Bag Clogging: Causes, Signs & Prevention

As one component of filters, liquid filter bags are undoubtedly a key part of the filtration process and are known as the heart of filters. This is because they determine the filtration effect for customers to a certain extent. Filter bags are manufactured from various materials and specifications, suitable for a wide range of industries.

The product life cycle is short. Why do products with the same rated precision perform differently?

It is important to bear in mind that the service life of a filtration system is closely related to the water permeability of the material. If a material has low water permeability, the product has a low initial pressure drop and slow pressure build-up. Naturally, it will last longer, and vice versa. In addition, the process control of surface treatment also affects its service life. The surface of liquid felt undergoes rigorous folding and calendering. If excessive pursuit of surface gloss leads to overheating of fused fibers, the filtration channels will be blocked. This will inevitably reduce liquid permeability, raise the pressure drop of the filter medium, and shorten the service life of liquid filter bags. Therefore, a smooth fabric surface alone does not guarantee better performance.

How is the precision of needle felt microporous filter materials determined?

For surface filter materials, the diameter can be measured directly, which represents the precision of the filtration system. However, precise values cannot be obtained by measurement for needle felt microporous filter materials. Therefore, the traditional calibration method is to calibrate a material with corresponding weight, thickness and permeability to a certain rated precision. Each material supplier adopts different standards, but every batch of materials should have strict industry properties and complete test data. Hence, when the filter bag provided by your supplier is calibrated to 5μm, this precision is only a relative filtration precision, and it does not mean the filter bag can capture particles with a diameter of 5μm.

The standard rating is the same, but why are the filtration results different?

Strictly speaking, the standard rating only refers to the material’s standard accuracy, which is different from the specific accuracy and serves merely as a reference for classification. When selecting liquid filter bags, it is critical to inquire about the filtration efficiency under the nominal rating, a point overlooked by most customers. Therefore, filtration efficiency can vary greatly for materials with the same 1μm standard rating, which will definitely lead to vastly different user experiences.

Filter bags are key components for measuring the filtration efficiency of bag filters. The cost of replacing filter bags constitutes the primary maintenance expense for bag filters. Hence, the service life of a filter bag is related to its filtration performance and operating cost.

Four factors affect the service life of filter bags:

Select an appropriate filtration system based on water temperature, humidity and chemical properties, and fully consider factors such as filtration velocity, cleaning methods and discharge concentration. Filter bags are generally used in bag filters, while woven fabrics are applied to indoor reverse-blow bag filters or vibration-analysis bag filters.
Reasonable structural design: The filter bag structure shall meet the requirements of the matched bag filter, featuring easy installation and reliable sealing. It should achieve a suitable filtration area and good filtration performance, and avoid conditions that facilitate clogging and damage.
Superior sewing technology: Adopt advanced processes and sewing specifications that meet design requirements. Thermal shrinkage allowances are reserved according to the type of filter media and operating temperature. Equipped with complete machinery, the stitching pitch is reasonable with no skipped stitches or broken threads, complying with relevant standards. High-quality accessories are properly fitted; filter bags have no raw edges or damage. The entire filter bag shall be free of defects such as pinholes, slack yarns and dirt, and be properly packaged to prevent damage and moisture during storage and transportation. Fiberglass filter bags cannot be stored under high pressure for a long time, otherwise their service life will be affected.

Correct installation method for inner and outer filter bags: The sealed bags and perforated plates shall be sealed and fixed reliably. The filter bags are hung vertically under the perforated plates. Adjacent filter bags must not collide with each other. Filter bags and frames shall be installed correctly; the frames shall be flat and free of burrs.Installation method for inner filter bags: The top of the filter bag is equipped with a bag cover. The bag cover is hung on the main filter beam via the hanging device, and the bottom end is reliably sealed and fixed with the lower bag. When installing filter bags, adjust the tension to the standard value to prevent the filter bags from loosening or falling off during filtration and backblowing. Readjust the tension after the first week and the first month of operation. All fittings inside the filter bags (anti-shrink rings) shall be properly matched, free of burrs and cracks.
During the use of filter bags for reliable and efficient liquid filtration, the contaminated area gradually increases and the pressure differential rises. Contamination protection shall be performed based on effective filtration to keep the pressure differential between the inside and outside of the filter bag within the set range.

During the operation of the bag filter, abnormal conditions shall be avoided, such as sudden rise of gas temperature, ingress of corrosive substances due to temperature, humidity and chemical corrosion, or sudden drop of gas temperature below the dew point. Factors including mechanical wear or impact shall not exceed the tolerance of the filter bags.

If filter bag damage is found during equipment maintenance, detect and replace it in a timely manner. Frequently monitor the pressure differential change of the bag filter upon filtration failure, and promptly check whether the filter device works normally. When the process conditions of the filter device change, adjust the filtration cycle or the working system of the bag filter in a timely manner.