Southern Alberta Liquid Waste Facility: WAS Centrifuge Case Study
A HAUS DDE 3532 decanter centrifuge removes solids from waste activated sludge (WAS) for a liquid waste services company in Southern Alberta.
The application
A water treatment technology company approached us to assist with the removal of solids from waste activated sludge (WAS) for a liquid waste services company in Southern Alberta.
The feed is thickened waste activated sludge from biological treatment, at 0.8 % to 2.0 % total suspended solids and 65 % to 70 % volatile solids. One duty centrifuge was specified, running about 7 hours a day, 5 days a week.
The challenge
The sludge is thin and light. At 0.8 % solids the centrifuge has to take 7.4 m³/h on average and up to 12 m³/h; at 2.0 % solids, up to 9 m³/h. The maximum solids load is 340 kg/h. Design polymer use was below 9 kg of active polymer per dry tonne, to be confirmed by bench testing and polymer screening once sludge was available.
The cake had to reach at least 18 % total solids with at least 95 % solids capture, and the centrifuge had to work with the plant’s own sludge feed pump and polymer system.
What Archer supplied
- HAUS DDE 3532 dual-drive decanter centrifuge
- Duplex stainless steel 2205 bowl, AISI 316 scroll, flame-sprayed tungsten carbide on the scroll flights and feed zone
- Cake and centrate discharge chutes, with a motorized sludge diverter gate on the cake outlet
- Stainless steel NEMA 4X control panel, CSA certified, with an Allen-Bradley CompactLogix PLC, 10-inch PanelView touch screen and VFDs for both drives
- Vibration transmitter, Pt100 RTDs on both main bearings, and cake and centrate sampling ports
- PLC and HMI programming, general arrangement and foundation drawings, O&M manuals, special tools and a two-year rebuild spare parts kit
- Commissioning and start-up support
How it works
The PLC sets the scroll differential speed through the back-drive. Operators can hold a fixed differential speed, or run in torque mode, where the PLC raises or lowers the differential speed to keep scroll torque at set point and so follows changes in the feed. The panel also runs the plant’s sludge feed pump on a PID loop from the feed flow meter and interlocks the feed pump and polymer system with the centrifuge.
The scroll has a baffle disc, so liquid can leave the cake end during start-up. The diverter gate sends this to drain until scroll torque shows dry cake, then switches to cake discharge. On stop, feed and polymer shut off and the bowl is flushed with plant water as it coasts down, while the scroll keeps conveying solids out. A pause mode keeps the bowl turning while the cake truck is changed.
High torque, vibration or bearing temperature stops the feed and starts a flush; high-high values trigger a controlled shutdown.
Results
Performance was guaranteed at a feed of 8 m³/h, including polymer:
| Solids removal | 95 % minimum |
|---|---|
| Cake dryness | 18 % minimum |
The centrifuge shipped from the HAUS factory in early 2018 and was commissioned on site in November 2018. It has been in service at the facility since then.
Equipment
| Centrifuge | HAUS DDE 3532, dual drive |
|---|---|
| Bowl | 353 mm inside diameter, duplex stainless steel 2205 |
| Hydraulic capacity | 19 m³/h |
| Processing capacity | 7.4 – 9 m³/h average, 12 m³/h maximum |
| Maximum solids load | 340 kg/h |
| Main drive | 15 kW, VFD |
| Back-drive | 5.5 kW, VFD, 87:1 Sumitomo Cyclo gearbox |
| Controls | Allen-Bradley CompactLogix PLC, 10-inch PanelView touch screen |
| Power supply | 575/600 V, 3-phase, 60 Hz |
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