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The dewatering process of the belt filter press is a multi-stage, multi-factor synergistic physical process. Its core lies in the combined design of the filter cloth tension and roller pressure system to gradually apply pressure and shear force to the sludge, thereby achieving efficient separation of water.
1. Working principle: synergistic effect of tension and roller pressure
The dewatering power of the belt filter press comes from the continuous clamping of the sludge by the two tensioned filter belts and the pressure gradient formed by the roller system layout. The specific mechanism of action is as follows:
Filter cloth tension effect
The filter belt maintains constant tension through a pneumatic tensioning device. The tension makes the filter belt close to the surface of the roller to avoid wrinkles or slipping, and at the same time provides basic pressure for subsequent roller pressure. The greater the tension, the closer the contact between the filter belt and the sludge, and the higher the efficiency of the squeezing force transmission.
Roller pressure and pressure gradient
The rollers are arranged in a decreasing diameter manner to form an S-shaped or spiral path. When the sludge passes through the roller with the filter belt, the bending angle of the filter belt gradually increases due to the change in roller diameter, and the squeezing force and shear force on the sludge layer gradually increase, thereby realizing the progressive separation of water from gravity dehydration to high-pressure dehydration.
2. The role of key components in dehydration
Filter belt
Material characteristics: It must have high strength, acid and alkali resistance, air permeability and other characteristics to ensure that sludge particles are intercepted under high pressure and allow water to seep out quickly.
Tension control: The tensioning device dynamically adjusts the tightness of the filter belt through the pneumatic system to avoid tension imbalance caused by feed fluctuations or sludge adhesion.
Roller system layout
Gravity dehydration area: The horizontally arranged rollers allow the sludge to drain naturally under the action of gravity, removing 40%-50% of the free water.
Wedge-shaped squeezing area: The upper and lower filter belts gradually narrow to form a wedge-shaped space, which applies pre-pressure to the sludge, causing it to lose fluidity and initially form a mud cake.
High-pressure roller pressure zone: rollers with decreasing diameters apply increasing linear pressure to the sludge, destroy the sludge floc structure through shearing, and release bound water.
Auxiliary system
Correction device: automatically correct the filter belt deviation through pneumatic or mechanical feedback to ensure uniform pressure distribution.
Cleaning system: high-pressure spraying removes sludge residues in the pores of the filter belt to maintain water permeability and filtration efficiency
3. Influencing factors
Adjustment of filter cloth tension
Too high tension may cause increased wear of the filter belt, while too low tension will reduce the pressing efficiency. It needs to be dynamically adjusted according to the properties of the sludge (such as viscosity and solid content). Municipal sludge is usually controlled at around 0.5 MPa.
Roller layout and material
Roller coating rubber: enhance friction and reduce filter belt wear.
Roller diameter decreasing design: optimize pressure gradient to avoid local overload or insufficient dehydration.
Sludge conditioning
It is necessary to add high molecular flocculants to make the sludge form stable flocs and reduce the risk of filter belt blockage. The dosage is usually 0.2%-0.5% of the dry weight of the sludge.
Operation parameter matching
Filter belt speed: Too fast speed will shorten the dehydration time and affect the solid content of the mud cake. It is generally controlled at 1-7 m/min.
Mud layer thickness: The amount of mud fed is controlled by the limiting device. Too thick will easily lead to incomplete squeezing.
