Structure and Selection of Belt Filter Press for Sludge Dewatering

The belt filter press for sludge dewatering consists of a filter belt, pressure rollers, a belt tensioning system, a belt alignment system, a belt washing system, and a belt drive system.

Belt filter presses for sludge dewatering are classified into four types: general-purpose belt filter presses, heavy-duty belt filter presses, super-heavy-duty belt filter presses, and heavy-duty belt filter presses for industrial production.

1. Working Principle of the Belt Sludge Dewatering Machine

The sludge containing water is separated and pumped into the sludge mixing tank, where a coagulant is added for thorough mixing. The flocculant is a polymer that functions by bridging, net capturing, and neutralizing the electrostatic properties during the mixing of the sludge.

The mixed sludge then flows into the sludge filter press’ sludge distribution device, where the sludge is evenly distributed over the gravity dewatering area. Under the dual guidance of the sludge rake and gravity, the free water in the sludge is rapidly removed as the dewatering filter belt moves.

Due to the design of the gravity dewatering zone being relatively long, it achieves maximum gravity dewatering. The flipped sludge enters the ultra-long wedge-shaped pre-press dewatering zone, where the sludge removed from the gravity zone is gently squeezed, forming a sandwich-like layer. This layer undergoes sequential, slow pre-pressure filtration to reduce the remaining free water to a minimum. As the two filter belts slowly advance, the gap between the belts gradually decreases, and the sludge layer becomes harder.

Through pre-press dewatering, a large diameter filter roller removes a substantial amount of free water, allowing the sludge cake to smoothly enter the extrusion dewatering zone, which is in an "S" shape. In this "S" shaped squeezing section, the sludge is trapped between the upper and lower layers of filter cloth and is repeatedly squeezed by several compression rollers.

As the two filter belts pass through the wave-like path formed by alternating rollers, the up-and-down positioning of the belts generates shear forces on the trapped sludge cake, removing the majority of the remaining water. This results in further dewatering of the sludge cake. Finally, the dry sludge cake is scraped off by a fiber scraper and transported to the sludge storage area via a conveyor or a shaftless screw conveyor.

2. Structure and Selection of the Belt Sludge Dewatering Machine

The belt filter press is composed of the filter belt, pressure rollers, belt tensioning system, belt alignment system, belt washing system, and belt drive system. When selecting the machine type, the following factors should be considered:

2.1 Filter Belt

The filter belt should have high tensile strength, resistance to bending, resistance to acid and alkali, and resistance to temperature changes. The specific nature of the sludge should also be considered to select the appropriate weave texture, ensuring good air permeability and excellent sludge particle interception performance.

2.2 Roller Pressure Adjustment System

This is typically completed by a pneumatic device.

2.3 Belt Tensioning System

This is usually controlled by a pneumatic system. The belt tension is generally controlled between 0.3–0.7 MPa, with a common value of 0.3 MPa.

2.4 Belt Speed Control

Different types of sludge require different belt speeds. For any specific type of sludge, there is an optimal belt speed range. Within this range, the dewatering system can ensure a certain treatment capacity while obtaining high-quality sludge cakes.

3. Advantages of the Belt Sludge Dewatering Machine

The belt filter press is less affected by fluctuations in sludge load. It also features low moisture content in the discharged sludge, stable operation, low energy consumption, simple management and control, and relatively low requirements for the operational staff’s skill levels.

4. Applications of the Belt Sludge Dewatering Machine

The belt filter press is widely used in municipal sewage treatment plants, organic sludge from industrial wastewater, and industrial wastewater treatment. It is especially effective in treating industrial wastewater.