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# 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?

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#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.

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#2

### 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.

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#3

### 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.

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#5

### 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

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#7

### 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".

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#10

### 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.

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#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.

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#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.

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#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.

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#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!

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