moisture separator

[honche725]

how do you know that a moisture separator is undersized?

our problem is that when two air compressors are running, we have liquid water carry over along our pipelines. at this condition, air pressure is varying as opposed to a stable pressure when only 1 compressor is running. does this mean that a moisture separator works well only under stable pressure conditions?

lastly, the only way we cool our air is thru a heat exchanger with water as the cooling medium. the exit temperature of air is way below the dew point of air at 3 barg (our compressor discharge). does this mean that all of the water will condense?

thanks

 

[ash9144]

The liquid carry over is a function of velocity, not equilibrium T, P. You probably need some type of separator after the condensers.

I've seen designs before with vac pump discharges going to coolers then atmosphere with no separator and they always have liquid carry over.

 

[dcasto]

Water will continue to condense as the temperature drops. You problem is the water cooler works well with 1 unit. the second compressor requires more water circulation so the air is cooling some more after your separator.

 

[honche725]

thanks for the replies. our system is designed in such a way that after the compressors, there is a heat exchanger which cools the compressed air and after it is a moisture separator.

ash9144 may be right that because of the increase in velocity (due to 2 compressors running) some of the liquid water did not have the opportunity to be separated in the separator.

dcasto, what do you mean when you say "the 2nd compressor requires more water circulation so the air is cooling some more after the separator"? in our case, the exit temperature of the compressed air after the cooler/condenser is the same when either 1 or 2 compressors are running. both at about 37 deg C. dew point for air at 3 barg is 51 deg C. so this means that almost all of the moisture in the compressed air is condensed.

thanks again and hoping for your early reply.

 

[dcasto]

Do you individual exchangers and seperators?
I'm saying that your water cooling system needs more cooling water with 2 units running than 1.

If you outside air temperature or ground temperature is lower than 37 C, then you WILL condense water downstream of the seperator.

 

[honche725]

thanks again guys for the replies. further questions.

for the water cooling system, the exit temperature of the compressed is 37 deg C for both cases, when 1 and/or 2 compressors are running. i suppose the amount of cooling water is enough. is this correct?

dew point for compressed air (3 barg) is 50+ deg C. is it correct to assume that at 37 deg C, all of water vapor in the air has condensed - meaning that after the heat exchanger, no more water will condense even if the temperature of air goes down?

thanks again.

 

[dcasto]

Dew point means, if you cool the gas below that temperature, liquids will form. The dew point out of you compressors may be 50 C, which means if you cool the air below 50 C, which you have, then water will form as a liquid. If the air is cooled below 37 C, then more water will form.

 

[djack77494]

Your dew point does not make sense to me. With your ambient temperature less than 50C, water vapor will condense out of your air system. Downstream of the final compressed air condenser, additional cooling just due to heat losses to ambient is likely. Thus, even if you've done a great job of separating water droplets from the compressed air, you will get additional cooling and therefore additional condensation. Also, remember that if you have some significant pressure drops somewhere downstream, you will get Joule-Thompson cooling and further droplet formation. Sounds like this compressed air won't be good for much more than blowing dust off the shop floor.