PD Blower Manufacturers?

[sjohns4]

Anyone have any expirence with blower manufacturers?
I'm looking to put a couple PD's in a clients wastewater plant. The packages from Aerzen, Kaeser, and Roots "looked" like well built stuff at their WefTech displays.

Does anybody have any expirences with these or any other manufacturers they would be willing to share?

Thanks

Mike

 

[bimr]

Aerzen and Kaeser both make good blowers. I just installed some Kaeser and the client was extremely pleased with the lack of noise.

 

[sjohns4]

Do you know what the life expectancy of PD's are? I've got PD guys in one ear and turbo compressor folks in the other and I'm trying to do a fair evaluation to see which one will truly have the lowest O&M cost over the 20 year planning period.

Thanks,

Mike

 

[bimr]

A quality blower (pd and centrifugal) is going to last 30 years. If you buy the inexpensive pd blowers, maybe 10-15 years.

 

[Darrel624]

Some subtle differences but both Aerzen and Kaeser make quality blowers with 20 year design life.

 

[SteveWag]

The one really big advantage PD blowers have is the ability to be controlled (the motors) by VFD’s. This can save a huge amount in power costs. Be aware of the need for mixing, sometimes just using DO or ORP control you will end up with solids on the bottom. Be sure to evaluate the manufacturers minim air flow, this is used for cooling. And, remember that some blowers supply aeration as well as air lifts. Slowing these down a little may cause lifts to stop. Be-are of sales men selling Power Factor Devices and VFD’s/DO Probes to your clients.
Steve

 

[sjohns4]

That's a very good point Steve. The plant has no on-line DO monitoring and is currently operating multistage centrifiguals in a manual mode. By my calcs we'll need a lot more air for mixing then we do to meet biological demand. Once we get the DO control system operational if we find we are operating at minimium air flow with high DO levels the next phase will be to install a mixing system in the aerobic cells.

Curious - what are your concerns with the DO probes & VFD's?

The PD guys and turbo-compressor guys have gotten prety ugly, to the extend of each calling the other flat out liars.

I'm heading towards bidding both, using the turbo-compressor efficiency numbers, assessing a 20-year cost of power per HP for every factored HP over what is in the specs, and requiring either a ASME PTC-10 or ASME PTC-9 certified test during submittals to verify efficiencies. If everyone is telling me the truth the power factor penalty for the PD guys should bring their bid cost to equal with the TC guys.

Anyone care to play devil's advocate and critique my logic?

Thanks,

Mike

 

[bimr]

SteveWag is telling you the same thing that I did.

1. Centrifugal blowers are not a good application for flow throttling. As you throttle the centrifugal blower back, you also change the blower discharge pressure.

2. If you throttle back the centrifugal too much, the blower will go into "surge" and you have to shut down. Surge is internal recycling within the blower. Centrifugals have a limited operating range in which the blowers can be operated.

3. If you have multiple blowers, then the complications of throttling the blowers increase. How do propose to throttle multiple centrifugal blowers at the same time? What you end up doing is taking individual blowers off line. Then you have to readjust all the other blowers.

4. DO probes foul over time giving maintenance headaches. You have to plan for a probe cleaning program. The new models of probes from Endress + Hausers are much better in this regard.

5. You also can not throttle the low pressure aeration flows using valves. Valves will not work. Trying to control the flow of a low pressure compressible fluid is very difficult.

6. PD blowers will work for your application simply because they are positive displacement.