What is a Screw Press (I)

  1. What is a Screw Press?

    The screw press is a novel solid-liquid separation device that utilizes the principle of screw extrusion. It employs a powerful extrusion force generated by the change in screw diameter and pitch, along with tiny clearances between the moving and fixed rings, to achieve the extrusion dehydration of sludge.

  2. Components of the Screw Press:

    a. Screw Body:

    • Comprises fixed rings, moving rings, screw shaft, screw, gaskets, and several connecting plates. Fixed rings are connected using six screws, with gaskets and moving rings placed between them. Both fixed and moving rings are made of wear-resistant materials for an extended machine life. The screw shaft passes through the middle of the fixed and moving rings, with the moving ring freely rotating on the screw shaft.

    b. Screw Shaft:

    • Consists of a shaft and helical blades. The shaft is welded by joining a solid shaft and a hollow shaft. During assembly, the solid and hollow shafts are first welded, followed by rough machining to ensure coaxiality at both ends. The helical blades are then fully welded to the shaft using a seam welding method.

    c. Drive Unit:

    • The drive unit serves as the power source for the equipment, and its performance directly impacts the overall machine performance. Generally, a high-performance motor with IP54 protection and F-class insulation is selected.

    d. Filtrate Trough:

    • Welded from plate pieces, it collects the filtrate pressed out by the screw press. The filtrate trough is connected to the frame via screws around its perimeter, and a flange is provided on the side for external equipment connections.

    e. Mixing System:

    • Primarily used to thoroughly mix sludge with chemicals to form flocs before entering the screw press for pressing and dewatering.
  3. Dewatering Principle of the Screw Press:

    After sludge undergoes gravity thickening in the concentration section, it is transported to the dewatering section of the screw press. As the sludge advances, the gradually decreasing clearance between the filter gaps and the helical pitch, along with the blocking effect of the back pressure plate, generates substantial internal pressure, continually reducing the volume and achieving thorough dehydration.

    a. Concentration:

    • When the screw drive shaft rotates, multiple fixed and movable overlapping pieces around the drive shaft move relative to each other. Under the action of gravity, water is quickly filtered out through the gaps between the moving overlapping pieces, achieving rapid concentration.

    b. Dewatering:

    • The sludge, concentrated through the screw drive's rotation, continuously moves forward. Along the direction of the mud cake outlet, the helical pitch of the screw drive gradually decreases, and the gap between rings gradually narrows. The volume of the screw chamber continually shrinks. Under the action of the back pressure plate at the outlet, internal pressure gradually increases. With continuous rotation of the screw drive, water in the sludge is squeezed out, and the solid content in the filter cake keeps rising, ultimately achieving continuous sludge dewatering.

    c. Self-Cleaning:

    • The rotation of the screw drive continuously moves the moving ring, achieving a continuous self-cleaning process by moving between the fixed and moving rings, cleverly avoiding the clogging issues commonly found in traditional dewatering machines.
  4. Operation and Maintenance of the Screw Press:

    • Ten minutes before starting, turn on the spray device. If the sludge flow is too high, excess slurry will return from the overflow outlet to prevent spillage.
    • Flow into the flocculation mixing tank, where sludge is thoroughly mixed with flocculants to form flocs for concentration and dehydration in the screw press.
    • Continuous operation of the entire process is automated, saving costs.
    • Half an hour before shutting down, open the spray device to clean the screw shaft and the moving and fixed rings of sludge and debris.
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