What Is A Screw Press Dewatering Machine?

A screw press sludge dewatering machine is a solid-liquid separation device that utilizes the screw extrusion principle. It uses the powerful extrusion force generated by changes in screw diameter and pitch, along with the small gaps between the moving and fixed rings, to extrude and dewater sludge.

(1) Screw Press Body: The screw press body consists of fixed rings, moving rings, a screw shaft, screws, gaskets, and several connecting plates. The fixed rings are connected by six screws. Gaskets and moving rings are installed between the fixed rings. Both the fixed and moving rings are made from wear-resistant materials, ensuring a long service life. The screw shaft passes between the fixed and moving rings, with the moving rings loosely fitted onto the screw shaft.

(2) Screw Shaft: The screw shaft consists of a shaft and screw blades. The shaft itself is welded from a solid shaft and a hollow shaft. The assembly process involves first welding the solid shaft and hollow shaft together, followed by rough machining to ensure coaxiality at both ends. Then, the spiral blades are fully welded onto the shaft.

(3) Drive Unit: The drive unit is the power source for the equipment, and its performance directly affects the overall performance. Therefore, a high-performance motor is generally selected, with an IP54 protection rating and an F-class insulation rating.

(4) Filtration Tank: The filtration tank is constructed from welded plates and is used to collect the filtrate filtered by the screw press. The tank is connected to the frame with screws on all sides, and flanges are provided on the sides for connection to external equipment.

(5) Mixing System: The mixing system is mainly used to fully mix sludge and chemicals to form flocs, which are then fed into the screw press for dewatering.

After gravity thickening in the thickening section, the sludge is transported to the dewatering section by the screw press. As it moves forward, the filter gaps and screw pitch gradually decrease, and under the obstruction of the back pressure plate, a large internal pressure is generated. The volume continuously shrinks, achieving thorough dewatering.

(1) Thickening: When the screw drive shaft rotates, the multiple solid and movable plates surrounding the drive shaft move relative to each other. Under gravity, water is filtered out from the gaps between the relatively moving plates, achieving rapid thickening.

(2) Dewatering: The thickened sludge moves forward continuously with the rotation of the screw shaft. Along the direction of the sludge cake outlet, the screw pitch gradually decreases, and the gap between the rings also gradually decreases, causing the volume of the screw cavity to shrink continuously. Under the action of the back pressure plate at the outlet, the internal pressure gradually increases. Driven by the continuous rotation of the screw drive shaft, the water in the sludge is squeezed out, and the solid content of the filter cake continuously increases, ultimately achieving continuous dewatering of the sludge.

(3) Self-Cleaning: The rotation of the spiral shaft drives the moving ring to rotate continuously. The equipment relies on the movement between the fixed ring and the moving ring to achieve a continuous self-cleaning process, thus cleverly avoiding the clogging problem that is common in traditional dewatering machines.

Ten minutes before startup, turn on the spray system. Sludge enters through the inlet. If the flow rate is too high, excess sludge will flow back through the overflow outlet to prevent overflow.

The sludge then flows into the flocculation mixing tank, where it mixes with the flocculant to form flocs. These flocs are then fed into the dewatering unit for concentration and dewatering. Clean water flows out through the gaps between the rotating and stationary rings into the collection tank. The sludge is compressed along the conveying direction of the screw press, resulting in increasingly smaller spaces and greater internal pressure, causing the sludge to become increasingly dry before finally being discharged from the outlet.

Half an hour before shutdown, turn on the spray system again to clean the sludge and debris from the screw shaft and rotating and stationary rings. The entire operation of the screw press is automated, saving costs.

(1) Wide Applicability: Suitable for sludge from municipal wastewater, food, beverage, chemical, leather, welding materials, papermaking, printing and dyeing, and pharmaceutical industries. It is suitable for dewatering both high and low concentration sludge. When dewatering low concentration (2000 mg/L~) sludge, there is no need to build a thickening tank or storage tank, reducing construction costs and minimizing phosphorus release and anaerobic odor generation.

(2) Compact Design: The dewatering machine contains an electrical control cabinet, metering tank, flocculation mixing tank, and the main body of the dewatering machine. It occupies little space, facilitating maintenance and replacement. It is lightweight and easy to transport.

(3) Self-Cleaning: The machine has a self-cleaning function. No cleaning is required to prevent filter clogging, reducing flushing water consumption and internal circulation burden. It excels at dewatering oily sludge.

(4) Low-Speed Operation: The screw shaft rotates at approximately 2~3 rpm, resulting in extremely low power consumption. It has few malfunctions, low noise and vibration, and safe operation.

(1) Sludge Blockage in the Dewatering Unit

Reasons:

Equipment Quality Issues: Especially the flatness of the screw shaft and ring plates. The screw shaft and ring plates are the main dewatering components of the screw press. If there is no leveling process for the shaft and ring plate surfaces, sludge blockage is likely to occur during use.

Nature of the Sludge: Sludge is divided into organic and inorganic types. Organic sludge is characterized by high organic content, easy decay and odor, fine particles, low specific gravity, high water content, and difficulty in dewatering. It is a hydrophilic substance with a colloidal structure, making it easy to transport via pipelines. Inorganic sludge, on the other hand, has the opposite characteristics. When using a screw press to treat sludge with a high inorganic content, or because the sludge particles are coarse, have a high specific gravity, and separate quickly from the water, the water content may already be very low by the time it exits the screw shaft filter chamber. This results in poor sludge flowability and blockage in the dewatering section.

Improper Operation: Different models of screw presses have different processing capacities. If the amount of sludge entering the screw press is much greater than its processing capacity, the screw press will be overloaded. If the screw press is not cleaned and emptied before and after use, the remaining sludge will adhere to the spiral blades, leading to equipment blockage.

Before use, allow the screw press to idle for about 10 minutes, supplemented by a spray system. After use, turn off the feed and allow the screw press to idle for about 30 minutes to completely drain any remaining sludge. Simultaneously, clean the screw blades with clean water.

For minor blockages, try reversing the screw press (there is a "Variable Frequency Reverse" button on the control interface), or turn on the spray system.

For severe blockages, stop operation immediately, inspect the equipment, flush with plenty of clean water, and, if necessary, remove the screw shaft to clean the attached sludge.

Reasons:

Flocculation Problem: Due to the special operating principle of the screw press, wastewater treated by the screw press must undergo pre-treatment with chemicals. After the wastewater flocculates and settles, it is then pumped into the equipment for dewatering. The compatibility between the chemicals and the wastewater, the proportion of chemicals added, and the solubility of the chemicals all affect the size of the flocs in the wastewater.

Inadequate Equipment Debugging: Debugging involves adjusting the flocculation effect of the wastewater, the rotational speed and frequency of the main shaft, and the gap of the back pressure plate to match the wastewater flow rate at the sludge inlet.

Solutions:
Chemical debugging is very important. First, match the appropriate chemicals according to the characteristics of the wastewater being treated. Then, adjust the proportion of chemicals added according to the speed and size of the flocs to ensure that the wastewater reaches a good flocculation state before entering the reaction tank.