3 Phase Energy System-Exhaust Regeneration

[Rob S.]

In "Green Manufacturer Magazine" I seen a company in Washington State that uses exhaust from a dust collector to turn a low rpm generator to produce electricity.The unit sets
on top of a Donaldson Dust Collector and uses the 73 mph exhaust to rotate the generator.
Have any of you seen or heard of this system.They claim
it can produce and supply 25% of the customer's demand.

Thanks,

http://www.3pesi.com

 

[glenncovington]

This is very interesting. I wonder if any studies have been done to show the effects on the original supply fan load to determine if it is consuming more energy to supply the generator. I would think that the static pressure would have to of gone up some in the collector causing the motor load to increase.

 

[Rob S.]

That is a good point. I am going to look into it a little more and I will post the answers that I get. If you think of any more questions I
will ask and post the answers when I get them also.

Thanks,

 

[kamenges]

Originally posted by glenncovington:

I would think that the static pressure would have to of gone up some in the collector causing the motor load to increase.

Probably not as much as one would think. The kinetic energy in that airstream is going someplace already. It is simply going into heating the surrounding air. All they are doing is pulling some of that energy out before it gets to the atmosphere.

Keith

 

[milldrone]

I would think that the static pressure would have to of gone up some in the collector causing the motor load to increase.

Actually the motor loading (and amp draw of course) drop as the static pressure increases. Presuming the fan is centrifugal. The other thing that does happen is there is less air moving in the system. Less air movement = less dust pickup.

If you do not believe me you can test this yourself. Take an ammeter and clamp on a vacuum cleaner, centrifugal pump or centrifugal fan block the outlet and watch the amps drop.

In my thinking the only way this can work is if the dust collection system was over sized to begin with (inefficient)

 

[glenncovington]

You are correct about the pressure. I guess what I should have said is that the increased load on the system might require an adjustment to the supply fan to maintain the same amount of airflow, therefore possible requiring additional energy. We have multiple baghouses with 200hp fans on them. The pressure drop across the filter is 2-4 in of H2O. In a dust system certain velocities (airflow) must be maintained to keep the particles from falling out.

If the pressure increase was small, then the system would probably still move enough air without any changes. I think there probably is a lot of inefficiency in the system that a chance to recover some of it would be great.

 

[Badger]

Actually the motor loading (and amp draw of course) drop as the static pressure increases. Presuming the fan is centrifugal. The other thing that does happen is there is less air moving in the system. Less air movement = less dust pickup.

If you do not believe me you can test this yourself. Take an ammeter and clamp on a vacuum cleaner, centrifugal pump or centrifugal fan block the outlet and watch the amps drop.

In my thinking the only way this can work is if the dust collection system was over sized to begin with (inefficient)

Correct. Same applies to a rotary vane/screw air compressor, when it goes off-load. All that happens is the air inlet is closed and as it cannot draw any more air in thus creating a partial vacuum in the stator and the motor runs at much reduced power consumption.

 

[jrwb4gbm]

Just my opinion, probably not worth 2 cents.
Picture this: The air providing the coupling between the motor and generator, or, a direct belt providing the coupling. Seems like to me that there is no real difference. Maybe one coupling method is more efficent than the other, maybe not. It seems to me just more load added to the motor instead of a way to recover energy.
Maybe this is just way too much of a simplistic approach.

 

[kamenges]

The energy is already in the air stream. It has to ultimately go somewhere. Now that energy is just turning into heat as the air stream hits something (filter, bag, stationary air molecules) and slows down. The recovery device is just taking some of the energy out of the air stream before the air stream blows all it's energy up as heat. The air stream on the 'downstream' side of the device is just moving more slowly than it was before it got to the device.

Keith

 

[leitmotif]

Well I think my Industrial Exhaust Ventilation instructor should be proud of me. My first thought was why bother recapture at the separator bag house end just slow the fan. Then I remembered that to convey sawdust or any other particulate adequate transport velocity must be maintained to prevent plugging duct work. So in effect the system is operated at a high and inefficient / energy wasting level to ensure adequate conveying thus no (less) plugging of ducts. Given this it makes sense to take advantage of the energy left in the airstream after separator and baghouse. Sort of like a turbocharger on a gas or diesel engine but at lower levels of enthalpy.

Dan Bentler

 

[jraef]

Well I think my Industrial Exhaust Ventilation instructor should be proud of me. My first thought was why bother recapture at the separator bag house end just slow the fan. Then I remembered that to convey sawdust or any other particulate adequate transport velocity must be maintained to prevent plugging duct work. So in effect the system is operated at a high and inefficient / energy wasting level to ensure adequate conveying thus no (less) plugging of ducts. Given this it makes sense to take advantage of the energy left in the airstream after separator and baghouse. Sort of like a turbocharger on a gas or diesel engine but at lower levels of enthalpy.

Dan Bentler

I think that's the key and that's likely why they don't claim this can be used on ANY fan. The concept of air stream exhaust energy recovery is generally well disproven. Any change to the air stream on the exhaust side is normally going to correspond to a pressure differential that affects the intake power curve in an equal manner. But in THIS SPECIFIC CASE, you do have to maintain that velocity of air movement in the ducts leading TO the baghouse. Once through the bags, that energy to maintain the velocity becomes wasted energy and in fact gets turned into noise that must be muffled. This looks as though it can recover a portion of the waste by replacing the muffler with a low speed turbine. To their credit, they are not marketing this as a panacea for all fan applications; their brochure says "The Exhaust Regenerator TM is a simple retrofit to the muffler of qualifying equipment" (emphasis added). So they are saying up-front that there are specific applications where this will work.

 

[milldrone]

This looks as though it can recover a portion of the waste by replacing the muffler with a low speed turbine. To their credit, they are not marketing this as a panacea for all fan applications; their brochure says "The Exhaust Regenerator TM is a simple retrofit to the muffler of qualifying equipment" (emphasis added). So they are saying up-front that there are specific applications where this will work.

I read the same brochure and agree, Its the muffler that they are replacing. So if your system has no muffler, you probably wont qualify. Also there is a large emphasis on the rebate. No rebate = very long payback.

By the way I searched the laboratory site they listed as an approval of their product (searched for 30 minutes) and could not find any mention of this product. There were however many hits for heat recovery from exhaust.

 

[jdbrandt]

If this is a Reverse Pulse Fabric Filter (RPFF) baghouse, also remember that the 'reverse pulse' part blows air in the opposite direction of the flow, and, when the bags are being cleaned, the flow will be minimal (hopefully) for a short time.