compressor sizing 1

[swoosh172]

I posted this in the pipes forum and they directed me here..

It I have a compressed air continuous plant demand of 15,000 scfm at 30 psig, can I serve this with an IR compressor rated for 3,000 cfm free air delivery at 150 psig with a pressure regulator to 30 psig? I am confused as to what the free air delivery is? Does this mean it can supply 3,000 cfm at 150 psi which would be 15,000 cfm at 30 psig? I used the equation P1V1=P2V2. My location is pretty much at standard conditions. Thanks in advance.

 

[Latexman]

Free air is the volume of air at 14.7 psia and 60_o. So when you say "3,000 cfm free air delivery at 150 psig", that does not make total sense to me. Is it supplied 3,000 cfm free air and then compressed to 150 psig? What do you mean? State a volumetric flow at a temperature and a pressure. That's how a gas flow is specified.

Good luck,
Latexman

 

[Latexman]

60^o F.

Good luck,
Latexman

 

[swoosh172]

I think it is the vendor literature that is confusing. It states 3,000 cfm free air delivery and 150psi working pressure. It is a 800HP compressor, so I think they mean 3,000 cfm of 150psi air. If it were standard conditons then it would only be 294 cfm at 150 psi.

 

[Latexman]

So 3,000 cfm x 164.7 psia / 44.7 psia = 11,000 cfm @ 30 psig. So, it's not big enough.

Good luck,
Latexman

 

[DRWeig]

Hi swoosh,

If you're still uncertain, here's what I would do. I bet the vendor's literature includes a phone number or e-mail address.

Use it, and tell them that their marketing department has made confusing literature that may cost them a sale. Tell them you need an engineer calculate for much air will be available on the 30 psig side of a regulator, and you need it quickly.

The engineers LOVE hearing that stuff, and they might even offer to design the rest of your system for you at no charge. You'll forever have a technical support friend, at the very least.

Good on ya,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[TD2K]

If it's an 800 Hp driver, I think your compressor is rated to compress 3000 inlet cubic feet per minute to 150 psig. That sounds about right for a compressor I installed a few years ago but the actual information is at the office to confirm it.

15000 scfm at 30 psig is 'about' 5000 actual cfm. Your compressor isn't going to do it if it's only compressing 3000 cfm at atmospheric pressure.

 

[TD2K]

The 3000 cfm is at inlet conditions. The compressor I installed was rated for 2700 scfm from 11.5 psi (absolute) to 115 psi (gauge). Compressor Hp requirements was about 670 Hp, installed motor was 800 Hp.

 

[Latexman]

TD2K,

I have not seen you on ET since about 2009. Big project over? Welcome back!

Good luck,
Latexman

 

[swoosh172]

Just to close the loop on this. I called the compressor manufacturer and they informed me that SCFM to them means standard conditions at their test criteria. Their standard conditions is 100 psi. No wonder it is confusing when we have different companies having different terminology for SCFM!

 

[Latexman]

It is worth repeating, "State a volumetric flow at a temperature and a pressure. That's how a gas flow is specified." Anything else leads to confusion and errors.

Good luck,
Latexman

 

[TD2K]

scfm is at 100 psi (and no A or G)?

I'm confused now

Hi Latexman

 

[Latexman]

In my little world, if it's not specified, "standard" means 14.7 psia and 60 F. Fwiw.

Good luck,
Latexman

 

[Montemayor]

This interesting and practical topic is in capable hands if it receives comments and recommendations from the likes of Latexman and TD2K.

It could really heat up if we could get David's (zdas04) to pitch in with his valued views and recommendations.

As Latex said, WELCOME BACK TO THE FORUMS TD2K .

 

[zdas04]

TD2K,
"psi" without a qualifier is simply lazy and it has no meaning. In school in means "psia". In some people's mind in industry, "of course it is psig". It is horrible.

I have the same problem with Bar and kPa. I often get grief for writing bar(a), but I don't care. When I was an undergraduate no one would ever consider reporting "bar" as other than referenced to absolute zero, today bar(g) is almost more common that bar(a) even though it is difficult to get agreement on how to convert (it used to be that zero bar was absolute zero, and atmospheric pressure usually occured at 0.8-0.95 bar, now absolute zero is -0.8 to -0.95 bar(g)).

Latexman,
You must not work much with contracts. Before I retired I had 4 contracts that I had to live under and every damn one of them had a different "standard". "Standard" is absolutely whatever two parties agree it is.

David

 

[TD2K]

Zdas, I know you've been beating this dead horse for a while but keep on giving it a whack.

I recently finished up a job where the client handed us their design basis memorandum. I asked whether a concentration they had provided was ppmv or ppmw. Talk about deer in the headlight look from them. How do you expect someone to provide you a design when you don't really know what you are asking them to provide?

I also use bar(a). Maybe people don't like it but they can't claim they don't know what I mean.

 

[Montemayor]

Thank you David!

That's music to my ears....

 

[zdas04]

I figure I can't really change anything, but if I'm as consistent as humanly possible (i.e., not very) then with as much as I write maybe a few people will be shamed into being more careful.

David