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Pressure Booster selection considerations

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Pressure Booster selection considerations

Pressure Booster selection considerations

BLogsdon

(Civil/Environmental)

(OP)

31 Oct 16 14:56

Our lab scientists are looking to replace the N2 bottles they use for their HPLC equipment with a N2 generator. Our manufacturing air pressure is maintained at 100 psi which is closer to 90 psi by the time it makes it to the lab. They need, at most, about 2 CFM at 110 psi of N2.

I am debating between a small dedicated compressor and a pressure booster (Festo DPA-40 or similar); however, I am not familiar with pressure boosters.

Does anyone have experience with the reliability of pressure boosters? One of the local compressor salesmen told me they last no more than a year with regular use, but I would imagine his opinion is pretty biased.

Also, are there any design considerations with regard to a booster that would be different than an air compressor?

Thanks!
Ben

Replies continue below

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RE: Pressure Booster selection considerations

zdas04

(Mechanical)

31 Oct 16 16:06

Quote (Festo)

Pressure boosters are intended for the occasional relieving of compressed air. They are not suitable as a replacement for compressors, as wear on seals and drive pistons increases significantly during continuous operation without breaks.

seems to say that this technology (basically a diaphragm pump for gas) is unlikely to be the most efficient delivery system. At your delivery volume (I'll assume that the "CFM" you are talking about is "SCFM", precision helps here since 2 aCFM at 100 psig at sea level is is 15.8 SCFM) efficiency may not be a huge issue.

With nitrogen generators you also have to be really concerned about purity. The output purity of units this small range from 95-98% nitrogen with no less than about 1% argon (which seems to be a tough problem to separate from nitrogen).

Not being familiar with Festo, I did a search and found Festo DPA and the note that saysseems to say that this technology (basically a diaphragm pump for gas) is unlikely to be the most efficient delivery system. At your delivery volume (I'll assume that the "CFM" you are talking about is "SCFM", precision helps here since 2 aCFM at 100 psig at sea level is is 15.8 SCFM) efficiency may not be a huge issue.With nitrogen generators you also have to be really concerned about purity. The output purity of units this small range from 95-98% nitrogen with no less than about 1% argon (which seems to be a tough problem to separate from nitrogen).

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Pressure Booster selection considerations

BLogsdon

(Civil/Environmental)

(OP)

31 Oct 16 17:28

The literature for these lab devices is pretty vague. The spec for the largest user requiring "A nitrogen generator with a minimum capacity of L per day with 100 psi at the side panel. Maximum consumption of nitrogen gas is 21 L/min." I'm assuming they are referring to volume at room temperature and 100 psi as measured through one of those rising ball-type flow meters.

The volume of air is very small for the majority of use (closer to 14 l/min)--so even though the pressure booster will be operating continuously, it should be very slow operation...unless I'm misunderstanding the concept of operation.
I'm getting some more info from the Festo distributor to find out how it will perform at low flow rates.

RE: Pressure Booster selection considerations

georgeverghese

(Chemical)

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What is the most efficient compressor type? 31 Oct 16 23:19

I'd hesitate to use inert gas from an N2 generator (which gets its feed from a crappy oilflooded air compressor) for something as delicate as a GC.

RE: Pressure Booster selection considerations

israelkk

(Aerospace)

1 Nov 16 08:34

Try http://www.haskel.com/ they have excellent pneumatic driven boosters.

RE: Pressure Booster selection considerations

BLogsdon

(Civil/Environmental)

(OP)

1 Nov 16 13:30

I'm not worried about air quality. We're a pharmaceutical company and only have oil-free compressors, desiccant dryers, and (depending on the application) filter down to 0.02 um.

The problem is our entire process and compressed air system has been validated at the 100 psi pressure so I am unable to bump pressure up for this lab application.

Those Haskel units are really slick!

RE: Pressure Booster selection considerations

georgeverghese

(Chemical)

2 Nov 16 00:15

If you've got good quality air, then I'd give these Haskel units a try - installing a buffer vessel between the Haskel unit and the GCs' could help to reduce run time for these boosters (assume the Haskel unit is downstream of the N2 generator) to extend operating life.

For example, the Haskel booster could kick in at 110psig and stops at 150psig to feed the buffer vessel. If you want, add a forward sensing pressure regulator on the N2 supply buffer vessel set at 100psig to feed the GCs'.

Check with Haskel if there is a risk of drive air getting into N2, or if there could be N2 leakage loss into the LP side of the drive mechanism.

RE: Pressure Booster selection considerations

BLogsdon

(Civil/Environmental)

(OP)

2 Nov 16 14:14

George, running the pressure to full compression of the booster, storing it in a receiver, and regulating it down to the desired N2 pressure is EXACTLY what the rep from Haskel suggested. Then I'll come off the regulator to a membrane N2 generator.

I'm leaning toward the Haskel unit because of their robustness.

Thanks for everyone's suggestions! I'll post an update after the project is complete.

RE: Pressure Booster selection considerations

georgeverghese

(Chemical)

3 Nov 16 01:39

Guess you must be leaning in the direction of the N2 gen unit on the LP side ( rather than immediately d/s of the Haskel booster) due to design pressure limitations on the N2 gen unit - okay.
If not, a membrane type unit may work better on the HP side and you'd use less compressed air per unit volume of N2 generated ( ie reject-waste gas flow is less when feed air pressure is higher).
Another option may be to use an impregnated carbon bed type pressure swing adsorption unit for N2 generation.

RE: Pressure Booster selection considerations

BLogsdon

(Civil/Environmental)

(OP)

12 Dec 16 15:57

House air supplied by oil-free compressors at about 90 PSI
Boost pressure to about 175 PSI with a 2:1 pressure booster
Store air in receiver and reduce to approximately 115 PSI
Pass air through membrane-type N2 generator (outlet approx 110 PSI)
Distribute in poly tubing to end users with point-of-use regulator

The pressure booster I chose was from Midwest Pressure Systems. Fantastic support, high quality product, and made in the USA. I calculated, that at the flow rate I am expecting, it should last at least 3 years before requiring a rebuild.

I'll post another update once equipment is installed and tested.

Final design:The pressure booster I chose was from Midwest Pressure Systems. Fantastic support, high quality product, and made in the USA. I calculated, that at the flow rate I am expecting, it should last at least 3 years before requiring a rebuild.I'll post another update once equipment is installed and tested.

RE: Pressure Booster selection considerations

georgeverghese

(Chemical)

13 Dec 16 01:41

With this arrangement, there is a risk of off spec inert gas quality if total instantaneous consumption at lab users is more than the design case flow. How will you then insulate or buffer the membrane unit from erratic flow profile at the user end? An intermediate buffer vessel to store this inert gas will help. Ideally a high set FIC loop with FCV on the exit ( or a cruder version of this may be a backpressure PCV) on the outlet of the inert gas buffer vessel.

RE: Pressure Booster selection considerations

BLogsdon

(Civil/Environmental)

(OP)

13 Dec 16 13:39

I considered that but feel the risk is low since the N2 demand will be steady and well within the capacity for the N2 generator. In fact, this system is more regulated than is commonly done for these lab gas systems--typical lab units have a N2 membrane generator immediately downstream of a small scroll compressor with no significant storage.

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News

Thank you RayfromTX, and thank you once again TrimixToo for your courteous, insightful and informative response. Thank you as well for opening the files that I could not access on my Mac. I am truly appreciative of your going the extra mile to assist a compatriot who also happens to be a total stranger.

My next step may well be to contact the folks at Haskel or Nuvair. (I have a friend who used to work for Nuvair, but he left that position several years ago.)

There are several reasons why I&#;d prefer not to have a compressor. The only place where I could put and use it would be in our garage, and my wife has this inexplicable desire to occasionally put her car inside, especially when she returns home during one of our frequent torrential rain storms. Who could have imagined that?

Most of the units that have the capacity to run the Haskel are very loud. I&#;ll be doing fills well into the night and have no desire to disrupt the neighborhood with noise pollution. Things are bad enough around here with the infernal whine and bellowing of the local leaf blowers, barking dogs, ambulance sirens, and heliport.

Our garage&#;s wiring may not be able to support the amperage that a suitable compressor requires. Putting a 15 amp load on an already busy 120 circuit may not be tenable. We&#;ve got a 220 line which we use for our clothes dryer, but any compressor that runs off of 220 will most likely be very loud and probably be overkill for its&#; intended purpose.

A compressor is yet another bit of equipment that will require my attention and maintenance. I&#;ve owned one in the past, and this is not a major obstacle, but one that I&#;d prefer to avoid. A preliminary search yielded a pair of compressors that may suit my needs, but I&#;ve never actually seen either of them, an Eagle EA-, and Campbell Hausfeld DC both seem to be quiet enough for my domestic situation, and pull low enough amperage to suit the available circuit. I do not know however if they have the capacity to efficiently run the booster.

I&#;ve got well over a dozen SCUBA cylinders, a pair of which I&#;d use for supply O2, and another pair for trimix dil; leaving me with plenty to use for my OC dives, air dil, and drive gas. Getting good, affordable, fast EANx and air fills locally is not an issue, just O2 and mix, for which I&#;ll have to drive and wait a few hours when necessary. I can deal with that a couple of times a month. I&#;ve also got several reliable regulators, one of which I can designate for use of the drive gas supply.

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