CR4 - The Engineer's Place for News and Discussion ®


Previous in Forum: Pipe Jointing Through Socket - Pipe Welding of GI (Galvanized Iron) Pipe  
Close
Close
Close
10 comments
Member

Join Date: May 2016
Posts: 8

How Much Condensate Water for a Given SCFM of Compressed Air

08/31/2017 1:05 PM

I have a turbo air compressor making 3200 SCFM at 110 psi in 100% humidity. How do I compute the volume of water it will condensate out?

Register to Reply
User-tagged by 1 user
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
2
Guru
Hobbies - DIY Welding - Don't Know What Made The Old Title Attractive... Popular Science - Weaponology - New Member United States - US - Statue of Liberty - 58 Year Member

Join Date: Apr 2009
Location: Across the street from Glacier National Park
Posts: 6329
Good Answers: 262
#1

Re: How much condensate water for a given SCFM of compressed air

08/31/2017 1:24 PM

With a little bit more information this calculator will calculate for you:

Can the intake not be located somewhere else? That's a lot of water, perhaps consider a move of the compressor itself? That humid an environ can be unfriendly on equipment.

__________________
Semper Ubi Sub Ubi
Register to Reply Good Answer (Score 2)
Member

Join Date: May 2016
Posts: 8
#2
In reply to #1

Re: How much condensate water for a given SCFM of compressed air

08/31/2017 1:41 PM

I'm calculating a worst case scenario. We are located in Asheville, NC and frequently have very high humidity and lots of rain (I feel sort of petty saying that today while gulf coast is drowning). This will hopefully help convince bosses that condensate removal is a substantial and important job.

Register to Reply
Guru
Hobbies - DIY Welding - Don't Know What Made The Old Title Attractive... Popular Science - Weaponology - New Member United States - US - Statue of Liberty - 58 Year Member

Join Date: Apr 2009
Location: Across the street from Glacier National Park
Posts: 6329
Good Answers: 262
#3
In reply to #2

Re: How much condensate water for a given SCFM of compressed air

08/31/2017 1:51 PM

"... condensate removal is a substantial and important job."

Well, yeah... The equipment isn't really intended to be a water pump.

__________________
Semper Ubi Sub Ubi
Register to Reply
2
Guru
Engineering Fields - Mechanical Engineering - New Member Fans of Old Computers - TRS-80 - New Member Popular Science - Weaponology - New Member Safety - Hazmat - New Member Hobbies - Fishing - New Member United States - Member - New Member

Join Date: Apr 2012
Location: Detroit MI, USA
Posts: 1918
Good Answers: 200
#5
In reply to #2

Re: How much condensate water for a given SCFM of compressed air

08/31/2017 2:41 PM

I don't care how many scfm you are making, condensate removal is absolutely necessary. Water in the airlines will destroy much of your air powered equipment.

I know this from experience, when our air dryer went down, Management thought we could hold off on a new one. I nickeled and dimed them to death with failed MAC valves, air motors, air brakes, cylinders, defective parts from water contaminating paint guns, etc.

I won, and got an entire new air system from Kaeser, with 2 new compressors, air drier, condensate filters and removal valves, plus a new tank and all new piping because old tank and piping could not be used from the corrosion on the inside. There is a lot of piping in a 50,000 square foot coating facility.

New dryer at the time in went down - $15k

Cost of equipment replaced because of water contamination over a 2 year period - $25k to 35k.

Cost of complete new compressed air system with piping and tanks - $220k

__________________
How we deal with death is at least as important as how we deal with life. --CAPTAIN KIRK, Star Trek II: The Wrath of Khan
Register to Reply Good Answer (Score 2)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26567
Good Answers: 697
#7
In reply to #2

Re: How much condensate water for a given SCFM of compressed air

09/01/2017 3:34 AM

<...condensate removal is a substantial and important job...> More than that, it is actually "unavoidable".

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 12208
Good Answers: 143
#10
In reply to #2

Re: How much condensate water for a given SCFM of compressed air

09/01/2017 11:12 AM

It goes back to the purpose of this air. If instrument air, or air that is for operating automated valves, it needs to be dry, free of condensate, or you will have serious unreliability issues going forward.

If service air, placing moisture and particle traps inline at several points may be all that is needed.

It all depends on how the air will be used. For example, if this happened to be auxiliary air into the bypass line on a gas turbine (just upstream of the hot section), then removing the moisture is totally unnecessary, a waste of effort and money. You will still gain virtually all the mass flow input to the turbine you could get with dry air.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that, still doing it. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 12076
Good Answers: 765
#4

Re: How much condensate water for a given SCFM of compressed air

08/31/2017 2:38 PM

At 25°C and 1 ATM of pressure with 100% humidity there is 23 gm/m3 of water in air. I doubt you'll need to remove all of that moisture but you now have some number.

I suspect your turbo compressor manufacturer has a maximum inlet humidity recommendation. Depending on the design of the turbo air compressor it may accept saturated inlet air. When this compressed air cools back to room temperature condensation may happen. The humidity limitations of the equipment downstream of the turbo is the next concern.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26567
Good Answers: 697
#6

Re: How much condensate water for a given SCFM of compressed air

09/01/2017 3:01 AM

Using a set of tables for humidity/temperature/pressure for air, and a mass balance calculation. Locate the point at which the air is 100% saturated at the higher pressure and whatever temperature, which gives the mass of water vapour per unit of air in the outgoing stream. Given the mass of water per unit of air in the incoming stream and the flowrate, the condensate is leaving as a side stream as water, thereby balancing the mass flow. A rigorous calculation is inherently complex and a simpler way is described below.

Compressed air at 100% relative humidity is going to do some serious mischief in downstream equipment, as the water will condense and potentially freeze as the air expands in the equipment that is being serviced. Industrial "Instrument air" is typically dried using supplementary equipment to -40degC dewpoint for that purpose.

A liquid sidestream is unavoidable so why there is curiosity about it from other regions of the organisation is abstruse. After all, water comes out of air conditioning equipment as well, and there is little concern there, usually. So why not simplify things and assume that the dryer is working effectively, all of the water that is going in comes out in this sidestream, and work backwards from there (rhetorical question - NNTR)? It makes calculation much simpler and there is already a figure that can be used for that purpose given in #4⇑.

Another way of determining this figure is to discuss matters with the equipment supplier over the telephone, as individuals there will be doing this sort of calculation routinely and may even be able to give an answer during the call.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
3
Guru

Join Date: Jan 2006
Location: Tamworth, UK.
Posts: 1519
Good Answers: 35
#8

Re: How much condensate water for a given SCFM of compressed air

09/01/2017 7:42 AM

A lot of useful replies, especially about the economic benefits of installing a dryer.

Nobody in their right mind runs a modern compressed system without a dryer.

I say this because over the years manufacturers of products using compressed air to function have relied on 'dry' air to work - often to the extent of using 'wet' air as grounds for invalidating their warranties.

No complex arguments are needed. "Premature failure of our products? Yes!" - "Have you got a dryer?" - "No! - well tough,not our problem."

Anyway back to answer you question about the quantity of water it would help to look at the volume off air sucked in (the volume at atmospheric pressure). Where in your case SCFM means Standard Cu Ft per Minute. The 'standard' refers to atmospheric volume, and 3200 cu.ft should be used in calculations.

All you need is a chart or graph giving saturated water vapour content at various temperatures. For the purpose of keeping it within the realms of mental arithmetic using 25C as the atmospheric temperature it will be 23g/m3. Convert cu.ft to m3 by dividing by 35. that is 92m3. Now multiply both = 2103 grams - and that is 2.1kg per minute sucked into your system.

Now look at the pressure. At 110 psig the volume of the atmospheric air will have been reduced by a factor of 8.5 when it is in the system.

Which comes from the pressure ratio. ie. (110 + 14.7)/(14.7)=8.5. Your air volume is now 10.8 m3. Now the interesting bit - the air volume has reduced but the 'grams', not reacting to pressure, remain exactly the same, ie. 2.1kg in all - where in theory if spread evenly throughout the air would be 195g/m3.

Now because the ambient air is 25C, that is the temperature of your system to which the compressed air will cool to, and when it does the final maximum water the air at any pressure at 25C is still the same = 23g/m3 - and this figure can only be achieved when at 110 psig by 172 g/m3 condensing to liquid.

The problem is the air cools to ambient through every inch of the pipework and the condensate appears everywhere. Any equipment using compressed air will cool as air expands rapidly so further condensation occurs.

A fridge dryer will create a pressure dewpoint below ambient. The condensate drops out at one point, is separated and dumped - the warms up above dewpoint and remains dry as it passes through the system.

Keep to basics when explaining it to 'management' they will not appreciate being blinded with science - as is the complex subject of water vapour in air - the met office with experts and £millions of computers still get it wrong.

__________________
When arguing, remember mud-slinging = lost ground.
Register to Reply Good Answer (Score 3)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26567
Good Answers: 697
#9

Re: How much condensate water for a given SCFM of compressed air

09/01/2017 8:14 AM

...so if there is <...2.1kg per minute...> [tips hat to #8⇑] going into the system, one may take a <...worst-case scenario...> of 2.1kg, or "a -full", per minute coming out of it in the side stream. A 20mm diameter pipe will route that by gravity to drain easily. So why is there any great concern from the upper echelons of the organisation? Do tell!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Register to Reply 10 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Copy to Clipboard

Users who posted comments:

Doorman (2); horace40 (1); James Stewart (1); JPool (1); Marcus delecti (1); PWSlack (3); redfred (1)

Previous in Forum: Pipe Jointing Through Socket - Pipe Welding of GI (Galvanized Iron) Pipe  

Advertisement