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Compressor selection
2

Compressor selection

Compressor selection

(OP)
Hi all, We have an application to boost/compress commercial nitrogen from ~580 psi inlet pressure to ~590 psi(10psi boost)in a closed circuit for heat transfer application. Operating Temp is ~150-210 deg F. The inlet volume is 800 ICFM at 580psi Can any one suggest what are the options and who makes and which will be most durable and maintenance free units?
 
Also can I have an approx idea of theoretical BHP need in this application? (I had way off conflicting figures given by some vendors) Thanks in advance ....Raj
 

RE: Compressor selection

What is ICFM?  Is it CFM at inlet conditions or something else? When I googled it the first response was "International Convention of Faith Ministries" and I didn't think that was right.

OK, assuming it is inlet conditions then that converts to 37.4 MMSCF/day.  Your lift is only 1.017 compression ratios, but the job is still 1500 hp.

I think I would look at an axial compressor to do this since you can't get a blower with that kind of pressure rating.

David

 

RE: Compressor selection

perhaps there are alternatives to the process such that the end result can be achieved.  however, the description of the process, process conditions (i.e. flow & inlet/outlet P & T), and the desired results are needed for any assistance to be provided.

a compressor for an application so described is rare, rare indeed.

btw, icfm is inlet cubic feet per minute at the compressor inlet.

an axial flow compressor may not be applicable at these pressures.

good luck!
-pmover

RE: Compressor selection

pmover,
What the heck are you talking about?  He provided inlet pressure and temperature (range), outlet pressure, gas being compressed, and a way to calculate mass flow rate.  I don't know what might have been missing.  I'm usually the first to complain when someone asks a question without providing enough information and I think RMSINT did a reasonable job of stating his problem.  

Also, I've seen axial machines with ANSI 600 discharge flanges so I don't think 580 psig is a stretch.  At the low ratios and big volume I would look at a dynamic machine instead of a PD machine.  If you could find a dynamic blower that would work at 580 psig that would be ideal, but I'm not familiar with any of those.

David

RE: Compressor selection

ACFM (Actual CFM) unit be more correct.
Could you give some precisions about the application in itself? (type of HX, purpose of application, description of the loop etc)

Thks
Rgds
Wimple

 

RE: Compressor selection

(OP)
As mentioned by David I had just enough info for selection and calculating HP.
Thanks David for the valuable answers.
ICFM stands for  Inlet Cubic Feet/ Minute
Regards
Raj

RE: Compressor selection

Since David answered the question I'll just add comment on ACFM vs ICFM...

My understanding has always been that compressor manufacturers use ICFM as conditions upstream of equipment in front of the compressor inlet.  So, in an air compressor ICFM is at the air inlet of the unit, or skid boundary, and ACFM is at the compressor flange after inlet piping, inlet filter, inlet valve, etc....  The difference in value is due to pressure drop and temperature rise across that equipment.

RE: Compressor selection

djv,
My confusion was that in the case of air compresors, ICFM is reasonably close to SCFM and most of the time you can safely ignore the difference.  I've never seen that term applied to a 570 psig compressor inlet and wanted to clarify.  For communication, mostly I see SCF or nm3 for elevated pressures.  If a particular calc requires ACF (like compressor hp) then the coversion is done at that time from SCF. It doesn't matter generally as long as there is clarity.

David

RE: Compressor selection

David,
I agree ICFM is not appropriate in this case and understand the confusion.  I wrote that, but must have deleted it when editing my response before posting.  I don't agree that ICFM is close to SCFM in air compressors (except if you're at STP) - did you mean ICFM is reasonably close to ACFM?  I agree you can often ignore the difference there.

RE: Compressor selection

ICFM is the same as ACFM at inlet conditions.  I guess I'm not getting your distinction.

David

RE: Compressor selection

I guess I confused things by taking about an air compressor taking atmospheric air.  This is different with the pressurized suction and I, like you, mostly see scf in this case.  To answer your question...

I guess there is no distinction in this case.  In the case of the air compressor the distinction is two different inlet points with different conditions - skid boundary (upstream of filter, inlet valve,...) and compressor flange (downstream of that equipment).  P&T will be different, although it may be negligible in terms of cfm.  This is the way air compressor mfrs often distinguish between ICFM and ACFM.



 

RE: Compressor selection

by the way, its 50 HP compressor.  It's a fan blower. if the polytropic efficency goes form 70% to 25%, the enrgy goes up to 140 HP.  look up blowers.

RE: Compressor selection

(OP)
Hi dcasto
David's estimation (pl see the reply on 8/3/09) is ~ 1500 HP.
You have indicated 50HP. How can be so different?
By the way can you please recommend some  blower companies who make it for such high pressure inlet conditions?
Raj

RE: Compressor selection

Gas power is about 40-50 HP.
Rgds
Wimple
 

RE: Compressor selection

been awhile since visiting the site . . .

David,
my purpose for for stating "alternatives to the process such that the end result can be achieved" expand beyond just the compressor boundaries and conditions stated by OP.  there are many applications & situations in which rotating machinery selection and the process conditions are modified/changed (slightly in this case ?) to be the best fit and perhaps avoid additional equipment/machinery.  since reading the posting again, the OP notes a closed loop and a heat transfer application.  whether or not the overall process can be changed, we do not know; hence, my question.

for the compression ratio and HP initially stated, it is rare for an IFC (likely a 1 or 2 stage AFC) at the stated conditions.  yes, a dynamic machine is likely more appropriate.

hope this clarifies my initial posting . . .

good luck!
-pmover

RE: Compressor selection

(OP)
Thanks to  Dcasto for the input on this and suggestion. I will be in touch with Spenser for application assistance
I am not still clear abut the HP need being so different in two responses David and dcasto.
Is there review from David on this?

RE: Compressor selection

consider the answer HP I submitted is the correct one
Dcasto is correct as well.
thats it

rgds
wimple

RE: Compressor selection

Dcasto,
I went to the Spencer Web site and on the custom applications I found:

Quote:

Spencer solves air and gas handling challenges that are so difficult, sometimes the only alternative to our involvement is to change the process. When you don't have that option, Spencer capabilities and our Engineering Edge are your best resources. High-performance blowers and gas boosters can be built to handle corrosive and toxic sulfides, halogens, acids, flue and stack gases, cyanides and ammonia. Maximum parameters include temperatures to 1100°F, housing design pressures to 1000 PSIG, operating pressures to 300 PSIG
I think they stop well below the 580 psig this application requires.

I'm really curious about what parameter we are looking at differently.  800 ACFM at 570 psig and 200F is 37 MMSCF/day.  Even at 1.017 ratios, the masses involved in moving that many molecules takes more than 50 hp.  What are you seeing that I'm not.

David

RE: Compressor selection

(OP)
With my limited know how tells me there can be only one theoritical BHP for this needs ,w/o considering efficiency.
I wonder if I had stated the same N2,  is equivalent to
 ~ 26000 cfm at 1 Bar (SCFM), or ~120,000 lbs of N2 per hour would it make any difference?
Since this become too custom project the parameters been looked into to get modified to be within  more of common standard ranges available in compressor/blower industry.

RE: Compressor selection

Of course 50 HP we are talking about "Gas power".
No Mechanical losses included.

Rgds
Wimple
 

RE: Compressor selection

If you run the ariel program with VMG thermo gata, it calculates 229 HP on a JGR 4 frame.  Using a JGE2 with pipeline cylinders you get 116 HP.

I ran a 70% polytropic eff and got 50HP.  I assume a custom unit could get that efficency.  Sundyne would be another good choice

http://www.sundyne.com/cda/ind/pr/spec/0,10516,CLI1_DIV92_ETI7223_IMD2_MDI41,00.html

Sundynes typically run in the 50% range of eff, so it could be a 70 HP unit.

RE: Compressor selection

I put the data into Ariel and on the Service/Stage screen (where it does a hp calc without knowing the compressor) it calls it a 477 hp application.  This was with 100% nitrogen, dehydrated.

I went ahead an put in the JGR/4 (the program picked 7-3/8R cylinders with a 7-inch bore) and got 286 hp.  I'm not sure that Ariel can really handle sub 1.1 ratios.

I tried it in Coolware and Rotosize, but no screw is going to work with that suction pressure.

The Sundyne looks like a good machine, too bad they don't have a calculator but I don't know of any centrifugal machines that do.  My experience says that if a PD machine is between 200 and 500 hp then a dynamic machine will be a lot higher hp than 70 hp.  I'd love to see RMSINT submit this application to a centrifugal compressor vendor and see what driver they recommend.

David

RE: Compressor selection

We use sundynes all the time on regen gas flow where dried gas is compressed through a heater, sent through the mole sieve bed to remove water, cooled to condense water and sent back into the inlet gas.  The largest system I've run with a Sundyne is a 500 psi in, 550 psi out on about 25 MMSCFD.  It had a 300HP motor on one and a 300HP steam turbine on the spare.

Most typical systems run about 25 psi differential and 2 MMSCFD.  They have a 25HP driver.

Sundyne will size them up.

The oldest system I used a Swearingen as in Swearingen of RotoFlow and Unranium Centrifuge (multi-stage compresssor).

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