I'm a relatively new engineer working at a manufacturing facility. I'm trying to analyze our current air drying system as we have reoccurring dew point problems, but I haven't seen a lot of information on the internet and there aren't people in my department that can help.

What I'm trying to determine is the total water load that the dryer should be designed for.

Info: 2x 5500 SCFM three stage centrifugal compressors rated at 125 psia discharge. There are two intercoolers and one aftercooler prior to the air dryer with the downstream temperature of the air at 100F. The air dryers are supposed to provide a pressure dew point of -40F. Design weather would be 95F db/ 50%RH and 14.7 psia.

I was trying to follow this website's process:

I don't know where they get the "humidity" values in g/m3. ASHRAE tables use lb_w/lb_da and I've tried converting that into lb_w/ft^3, but the numbers don't seem to agree with the table they use. They also just divide SCFM by the pressure ratio to get ACFM, but I don't believe that is the correct conversion.

Some of the calcs I tried to do:

1) Take inlet conditions and use Ashrae psychrometric table to get humidity ratio. W = Ws*RH.

2) Multiply W by air density to get Lb_w/ft^3. Multiply by ICFM to get inlet water rate. lb_w/min

3) THis is where I run into trouble: with discharge conditions of P=125 psia and T=100F (post- aftercooler), what is the saturation humidity? My idea is calculated the saturation humidity at discharge conditions and the difference between that and our inlet would be the condensation rate of the intercoolers and aftercoolers.

4) The leftover water in the air would be the load on the what the desiccant would need to adsorb. so using BASF-200, 100%RH adsorbs 42% wt H20. so if the dryer load is 1 lb_w/min and the dryer has a 4 hour adsorbing time, I would need around 600 pounds of desiccant?

Sorry for the long winded post. I've had a lot of time to think about this. Thanks in advance if anyone can help or point me to some good resources.