The hardening of the multi disc filter bag results from the combined effects of deterioration in filter bag fiber properties and pore clogging.
The core reasons can be categorized into four main areas, including slurry properties, operating parameters, equipment selection, and maintenance. These four causes are related, so if they persist over time, they may lead to issues with the multi disc filter bag, such as stiffness, reduced air permeability, and difficulty with filter cake release.
Four Major Factors Affecting Multi Disc Filter Bag Performance
Slurry Properties
Over time, various impurities in the slurry adhere to and accumulate on the surface of the multi disc filter bag, which is the primary cause of pore blockage and fiber hardening.
Blockage Caused by Fine Particle Deposition
If the content of fine particles in the slurry is excessively high, they tend to become embedded in the pores of the multi disc filter bag during filtration. They cannot be removed by conventional washing.
The long-term accumulation of these fine particles within the multi disc filter bag forms a dense layer, causing the filter bag pores to clog and the fabric to become stiff.
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Sticky Substances and Grease Deposits
During filtration, organic compounds and metal ions present in some slurry materials may react with oxygen or undergo polymerization due to air exposure and temperature changes. As a result, insoluble and difficult-to-clean hard deposits can form and attach to the surface of the multi disc filter bag, causing the filter bag to gradually become hardened and reducing its filtration performance.
Operating Parameters
Improper operating parameters can disrupt the normal functioning of the multi disc filter bag, accelerating impurity deposition and fiber damage.
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High Filtration Pressure
When the feeding pressure of the multi disc filter exceeds the designed operating range, fine particles can be pressed deep into the pores of the multi disc filter bag rather than forming a uniform filter cake on the filter bag surface.
This accelerates pore clogging and makes cleaning more difficult. In addition, continuous high pressure compresses the filter bag fibers, reducing their resilience and gradually causing the multi disc filter bag to harden.
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Improper Operation of the Spray Nozzle System
If the spray nozzle system in the multi disc filter has a long cleaning cycle, or if the cleaning water pressure or flow rate is insufficient, the filter cake on the multi disc filter bag surface cannot be removed in time. This will cause the filter cake to accumulate and gradually become compacted and hardened. Once the accumulated contaminants exceed the cleaning capacity of the spray system, impurities remain adhered to the multi disc filter bag surface, accelerating the clogging and hardening of the bag.
In addition, if the nozzle becomes clogged or the spray angle deviates, some areas of the multi disc filter bag may not be effectively cleaned, causing impurities to accumulate locally in the filter bag and eventually harden.
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Improper Temperature Control
When the temperature of the slurry in the multi-disc filter is too low, viscous substances tend to solidify and congeal, thereby adhering to the multi disc filter bags.
However, when the temperature is too high, it accelerates the aging of the fibers in the multi-disc filter bag and simultaneously causes the impurities in the slurry to oxidize and polymerize, forming hard lumps that accelerate the hardening of the filter bag.
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Unstable Feed
If the feed concentration and flow rate of the multi disc filter fluctuate excessively, it can result in an uneven filter cake thickness.
This can cause localized areas of the filter cake to become compacted, allowing impurities to enter the multi disc filter bag.
This, in turn, leads to localized hardening of the filter bag. Over time, this can cause the entire filter bag to harden, reducing the filtration efficiency of the filter cloth.
Equipment Status and Multi Disc Filter Bag Selection
Abnormal operating conditions of the multi disc filter, or a mismatch between the selected multi disc filter bag and actual operating conditions, increase the risk of filter bag hardening.
Improper Selection of Multi Disc Filter Bag
If the selected multi disc filter bag is incompatible with the slurry characteristics, the filter bag will harden.
For example, using a multi disc filter bag with larger pore sizes to handle pulp containing a high concentration of fine particles may allow these particles to penetrate and accumulate within the filter bag pores.
On the other hand, using a multi disc filter bag with excessively small pore sizes for pulp containing coarse particles can cause excessive filter cake compaction, leading to rapid pore clogging and reduced filtration performance.
Furthermore, if the multi disc filter bag material cannot adapt to the actual operating environment, such as when the chemical composition of the slurry, temperature, or mechanical action exceeds the material’s tolerance, the multi disc filter bag fibers will gradually degrade, resulting in reduced elasticity and eventual hardening.
Abnormal Multi Disc Filter Status
If the spray nozzle system of the multi disc filter malfunctions, contaminants on the surface of the multi disc filter bag cannot be removed in a timely and effective manner. Consequently, after prolonged operation, scale tends to form on the surfaces of the multi disc filter bags and multi disc filter plates, roughening the filtration area and accelerating the adhesion of impurities and the clogging of pores. This causes the filter bags to gradually lose their permeability and flexibility, ultimately leading to hardening.
Furthermore, if the multi disc filter’s sealing performance is inadequate, external air, dust, or other impurities may enter the filtration system and adhere to the multi disc filter bags’ surfaces, accelerating contamination, clogging, and hardening.