Eliminating Intermediate Bearings Saves Downtime and Maintenance Costs at Columbia Wastewater Treatment Plant

General Description

The City of Columbia, SC provides water treatment services to approximately 63,000 homes and businesses in the area, resulting in 35 million gallons per day of sewage. Wastewater arrives at the plant via 1,000 miles of pipe, where it is treated before discharging into the Congaree River. Dewatered biosolids are a byproduct of wastewater treatment and transferred to a landfill outside the city.

With so many people depending on reliable water treatment, unplanned downtime can be devastating. Three existing screw conveyors at the wastewater treatment plant were causing downtime and excessive maintenance. Intermediate bearings were a recurring failure point on all three conveyors in the process due to the abrasiveness of dewatered biosolids. KWS provided a site evalutation of the existing screw conveyors and replaced the conveyors on an expedited timeline. With over 50 years in the bulk material handling industry, KWS has the experience to solve problems and eliminate unnecessary downtime.

Design Parameters

1. Product Type: Dewatered Biosolids
2. Material Density: 45 to 55 Lbs. per Cubic Foot
3. Capacity: 400 Cubic Feet per Hour
4. Duty: 24 Hours per Day, 7 Days per Week

KWS Advantages

KWS evaluated and recommended improvements to prevent recurring bearing failures. Detailed measurements were taken of the existing screw conveyors by KWS engineers. While KWS could have provided new units with superior heavy-duty intermediate bearings, KWS recommended to design out the hazard. By utilizing oversized pipe, KWS spanned the full length of each conveyor while staying well within CEMA recommended deflection allowances. Removing the intermediate bearings removes the primary failure point, and also eliminates the need for preventative maintenance checks, freeing up maintenance personnel to spend that time in other areas of the plant.

KWS Special Features

Two screw conveyors receive dewatered biosolids from centrifuges and transfer the material to a gathering screw conveyor. KWS eliminated the need for intermediate hanger bearings by mounting the screws flights on larger-than-standard pipe. After fabrication, all screws were straightened in a lathe to a maximum of 0.015-inch TIR at the bearing locations. The screw conveyors were constructed from 304 stainless steel to prevent corrosion due to the high moisture content of the application. Pedestal and bulkhead trough ends were located on each end with flanged gland seals and pillow block roller bearings. Flanged gland seals prevent leakage of biosolids from the conveyors. Pillow block roller bearings provide support for the weight of the screws.

Each screw conveyor was equipped with an emergency stop pull switch. Motion sensors monitor screw conveyor rotation. Hinged covers with safety bolts permit inspection of the full length of each conveyor only by trained maintenance personnel.

Two KWS heavy-duty flat rack and pinion slide gates were located on the inlets of the gather screw conveyors and can be closed during maintenance of downstream equipment. All KWS gates utilize bronze-bushed rollers that are self-lubricating and require no maintenance.