Effluent Plant Upgrade

The Challenge

A DAF is only as good as what feeds it. The existing centrifugal pumps had poor suction performance and could not cope with the solids load in the effluent — blockages, lost prime, and a feed rate that surged instead of holding steady.

That is not just a pump problem. Flotation depends on consistent hydraulic and solids loading: when the feed swings, the air-to-solids ratio moves off design, the float layer breaks up, and separated material carries through to the downstream plant. Fix the DAF chemistry all you like – if the feed is erratic, the results will be too.

The Solution

• Pumps Selected For Suction And Solids
  260 m³/hr each at 50 Hz — specified on suction conditions and solids passage, not on the duty point alone. That is where the old pumps failed.
  
• Duty And Standby
  One running, one available. Either can be isolated and serviced without taking the DAF, or the plant behind it, out of service.
  
• VSD Speed Control
  Feed rate matched to actual plant flow instead of throttled at a valve – steady loading to the DAF, soft starting, and no hydraulic shock on the lines.
  
• New Pipework And Gate Valves
  Suction and delivery replaced and resized for the new duty, with new gate valves so isolation is positive and maintenance does not mean draining the plant.

A duty point is not a pump specification.

The replaced pumps could deliver the flow on paper. What they could not do was pull it, or pass what was in it. Suction conditions and solids handling are what decide whether an effluent pump survives the application.