Belt Press

WSI has been designing and building Belt Filter Presses for over 12 years. Our belt press uses industry standards as well as proprietary technology. All of our presses have five major components; a headbox for optimal sludge flocculation, a gravity section to thicken the sludge, an adjustable wedge section to allow for maximum dewatering, an “S” section to permit a gradual increase in pressure and a cake doctoring section to remove the sludge from the belt. Each section is custom designed to meet or exceed the demands of the project.

WSI Belt Press Designs

Electrical & Controls

The system is provided with a main control panel that houses the Variable Frequency Drives (VFDs), motor starters, relays, Programmable Logic Controller (PLC) and Human Machine Interface (HMI). The VFDs are configured for the torque share operation mode. The panel enclosure is NEMA 4X with a side mount air conditioning unit to protect the control components in a wet, washdown environment. The HMI provides the press operational information in a graphical format to the operator and allows the adjustment of set points and parameters. The panel is provided with physical Hand-Off-Auto switches for all motors, enabling the system to be operated in an automatic mode as well as manually and overriding the logic controller.

When in automatic mode, the logic controller will flow pace the polymer injection rate to meet the operators desired dosage per feedback from the sludge magnetic flow meter.

Pneumatic Tracking System

Automatic air actuated tracking systems are employed for both the upper and lower belts. Each system consists of a rubberized tracking roller mounted in pillow block housings, automatic proportional servo-regulator unit with tracking finger, and a belt over track detector (limit switch) to automatically shut the unit down in the event of a failure in the tracking system. The proportional valve is connected to a guide paddle, which rides on the belt at a 35-45 degree angle. As the belt moves to one side or the other the paddle assembly follows this movement. The paddle turns the regulator; air is then sent to the airbag guiding the necessary direction of roller shift. At the same time, air on the opposite airbag is exhausted until shift point is reached. As the belt is tracked back, the air pressure between the two airbags is equalized and the roll returns to the center operating position.

Extended Gravity Section

The Extended Gravity Section allows the flocculated sludge to drain. The belt in this area is supported by 6” diameter rolls in lieu of a traditional UHWM deck. The rolls on the gravity deck offer three major advantages over UHMW wear bars. First, the rolls wick water from the belt and speed drainage. Second, the friction between the belt and the gravity deck is significantly reduced, extending the life of the belt. Third, the downtime associated with replacing the UHMW wear bars is eliminated. Arrays of chicanes are positioned along the length of the gravity section. The chicanes clear belt area and corn row the thickened sludge allowing further thickening and drainage. An adjustable leveling plate smooths the tops of the corn rows into a sheet prior to entering the wedge section of the press.

Flocculation and Distribution

Polymer is injected on the discharge side of the sludge feed pump through a four-port ring injector with adjustable mixing intensity. The ring injector provides for rapid mixing of the polymer and thickened sludge. Flocculation begins to occur in the sludge pipe and further develops in the up-flow flocculation box located on the front end of the press. The flocculation box has a conical bottom that slows the velocity of the incoming sludge. A distribution paddle continuously moves thickened floc from the top of the floc box and down the distribution chute to the gravity section ensuring equal distribution across the width of the machine.

S-Roll Section

In the S-Roll section, the two belts wrap around the rollers in an “S” pattern, moving from rolls of greater diameter to lesser diameter. As the diameter of the roll’s decreases, increasing pressure is applied to the sludge cake expelling more water with each roll wrap. This follows the same principles throughout the entire machine of ever-increasing pressure and increasing cake dryness. By the time the cake reaches the end of the machine, it has developed into a dry cake devoid of free water that is scraped from the belt by the UHMW doctor blades.

Frame Construction

The frame is constructed from 6”x6”x3/’8” structural steel tubing that is capped and sealed. Drilled and tapped machined plates are welded onto the frame structure to eliminate penetrations into the structure. All cross members are flanged and bolted. Steel channel, angle and I-Beams are never used in the frame construction of a WSI press. Channel and angle have poor torsion characteristics, and all are prone to the accumulation of water and sludge which accelerates corrosion of the structure.

Rack and Pinion Tensioning System

Automatic pneumatic belt tensioning is accomplished with Firestone airbags similar to the airbags used on tractor trailer suspension systems. Airbags are provided on both sides of the tensioning roll and are tied together with a heavy-duty rack and pinion system and shaft thrust tube to ensure parallel alignment of the roll. Airbags are a dependable and low maintenance option over hydraulically or pneumatically operated cylinders. The thrust tube provides additional rigidity and precision that is unmatched by the sag of an extended cylinder. Proper alignment of the tensioning roll is critical to proper tracking of the belt.

Dual Motor Drive

Drive motors are provided for both the upper and lower belts for heavy mud applications. Conventional press designs utilize a single drive motor in which power is delivered to the other drive roller through a bull gear on the far side of the main drive roll shaft. There is no play in the bull gear and the two drive rolls are locked firmly in time. When dewatering heavy mud, bull gear press designs cause dewatering belts to either wrinkle or loop (fold over) to take up the uneven stresses. A wrinkle or a fold in the belt causes critical deformation of the belt thread and creates a weakness that significantly reduces the operation life of the belt.

WSI’s dual drive motor system allows the two drives to communicate on a VFD network. The master drive operates under advanced magnetic flux vector control and the slave drive operates under real sensorless vector control. Together, this is known as a torque control method that allows play between the two drives to alleviate binding in the belt that would otherwise cause belt wrinkling or looping. Once a belt has wrinkled, it will crease and fail at the point of weakening. The dual drive motor control is standard on all WSI dewatering belt presses.