VFD Retrofit on Aeration Blowers

Does the machine have a manufacturer to direct this question to?

There is maybe more than one and not all are the same so while the crystal ball is broken it might be a good idea to give some more information.

If in doubt buy a VFD and report back here how it went!

Yes, and no.

There are some very knowledgeable people here who can and will help you with your problem.

IF YOU WANT SOME HELP, HERE IS WHAT YOU NEED TO DO:

1. Register with CR4.
2. Spend more than a few minutes explaining the situation. Try imagining someone explaining the situation to you and see if what information they gave you would enable you to understand the situation enough to help.
3. Check back here regularly to see if someone has posted to your thread.

For a start, what is a dual vane aeration blower? Most types of blower can be driven via VFD, often installed that way as original equipment. I'm sure VFDs have been retrofitted, whether it's common is a matter of opinion.

Any fixed pitch blade and rotary vane will have an optimum efficiency at corresponding design speed. Their design is fixated to operate at that speed with peak efficiency, now, efficiency will decrease consequently at some other speed other done design speed.

Employing a VFD is almost parallel to quantity of stuff you want to have, example for aeration, it is the quantity of air you want to deliver in the tank to neutralize COD and BOD.

Quantity and efficiency is a different thing, I should say

Your question kind of misses the mark.

In Waste water treatment, you need to keep a certain D.O. (Dissolved Oxygen) set-point.

Efficiency means less when you are trying to achieve certain parameters!

That's correct, but the air flow needed to maintain setpoint DO varies with the load on the plant. Could easily be 5:1, depending on the size of works (big installations usually show smaller variation). I've worked on plants where air flow control is by

- Roots blower with VFD

- high-speed centrif with inlet guide vane control

- multi-stage motor speed centrif with inlet valve throttling

and switching machines on/off in a multi-blower system.

Also there's an Aerzen centrif, design bought from Sarlin I believe, direct drive via VFD at about 20000 rpm, with only 1 moving part, uses aerodymanic bearings. Sounds great, but I've not seen one, don't know how good it is in practice.

Exactly!

There's more to motor efficiency than just attaching a VFD to it. There are so many variables that must be met or designed for!

Fans and blowers normally do not benefit from having a VFD installed unless variable speed/flow is required by the process or the unit is very large and requires starting torque reduction to avoid mechanical shock to the assembly.

An in-depth energy/power study should be done to identify what the investment return period length is that will return 100% of investment dollars back to the owner.

The possibility of lowering overall maintenance costs through avoidance of mechanical shock to the motor and fan components should considered and included.

Also; Keep in mind that a VFD will add significant maintenance costs to the process and these costs also need to be included in the justification study.

It is Not be nice to an ANON week......call the manufacturer of your equip

Turbo blowers used in modern WWTP aeration systems are far too complicated for a simplistic answer. However, people actually IN that industry have in fact studied this exact issue.

http://www.premier-water.com/files/aerationSystem.pdf

The conclusion at the end of this White paper leans toward having a VFD, but the company that wrote this, Turblex, is now part of Siemens who makes and sells VFDs, so take that for what it's worth. Still, they make a compelling argument backed up with data.

Most NEW installations I have seen are now using this concept: Dual-Point control, but using variable diffuser vanes to control flow and variable speed to control head. You asked to compare this with dual VANE control, where instead of the VFD for head control, you use outlet dampers. This paper shows that to be significantly less efficient.