Sludge mixing pumps_VSD or Fixed speed

[Sam1390]

Hi all,
I am working on a wastewater plant and there are a few mixing pumps e.g. primary sludge tank mixing pump , digested sludge tank mixing pump and Anaerobic digester mixing pumps.
some vendor offered Fixed speed while the preference is VSD.
Can you please let me know for these specific applications which one is better and why?

 

[bimr]

If you are just transferring sludge, the fixed speed is fine. You can operate the pump on a time clock and you can keep the velocity up so the sludge doesn't settle out. If you are transferring sludge to another process such as a dewatering unit, you would want VSD so the pumping rate can be matched to the processing rate.

 

[Sam1390]

Thanks bimr for your response .
the pumps I was taking about is the recirculation pumps not a transfer pump.

 

[bimr]

Mixing pumps may be fixed speed as there is little benefit to adjusting speed. These are generally low HP pumps and little energy savings with VFD's.