Relative Humidity and Dew Point after compression

[bhasker2]

Hello all,

Would appreciate some guidance here.

I have an air compressor compressing ambient air to 3000 psi into a 425cu-in tank. I have the volumetric flow rate at the exit. If I was looking for relative humidity, dew point, and moisture content/accumulation at the exit, how would I go about doing so.

The air would then be expanded from 3000 psi to 600 psi, how would I get the same information again?

I'm trying to evaluate the size of the moisture separator and heat exchanger needed to keep the system out of moisture by getting those values.

Thank you in advance.

 

[crshears]

Hello bhasker,

What type of compressor? If required, what type of oil scavenging equipment?

How many stages of compression? Intercooling/aftercooling? If so, air-to-air or air-to-water/glycol?

Average ambient climatic conditions?

What type if any of post-compression drying equipment? Cyclonic only, dessicant only, or a combination?

Have you no supplier's / manufacturer's / consultant's data for any of this?

CR

 

[bhasker2]

crshears,

I'm working with an oil-free breathing air compressor. It's a five stage oil-free compression. The information I do have is the outlet pressure and temperature, which is 3000 psi and 225degC. With this information I should be able to determine the relative humidity, dew point, and moisture content at the exit, no?

Post-compression heat exchanger is something I will be looking into, but I need to know how much moisture I'll be working with. No dessicant.

Am I simplifying the problem?

 

[zdas04]

Your mass of water vapor cannot increase within the process. You can find the 100% RH mass of water vapor at each point in your process. You'll find numbers like 1600 lbm/MMSCF at the suction, 28,000 lbm/MMSCF at the first stage discharge (pre-cooler), 1400 lbm/MMSCF at the cooler outlet (so 200 lbm/MMSCF must condense), and so forth until cooler outlet at 100F and 3000 psia would be something like 20 lbm/MMSCF. You can get the 100% RH point from a psychometric chart.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[chicopee]

I am not sure if there is a good way to find the amount of water at the exit because a good portion of the moisture entrained in the air intake will condense into water once in the tank. How much moisture will condense, I don't known so I guess that you would have to test for RH at the exit point.

 

[bhasker2]

I really should have been clearer. So, after the intercooling within the five stage compressor, the exit temperature is at around 250F. I had misread the compressor specs. Considering ambient as intake and the exit at 3000psi. The saturation temperature at 3000 psi is 340F, so condensate will surely appear at the exit, and RH should surely be 100%, since T_exit < T_saturation.

Hence, I want to calculate how much condensate, so that I know what size moisture separator I would need after the compressor. The tank would arrive after the moisture separator, which then would be expanded to 600 psi. A heat exchanger is going to be introduced in between the expansion; and once again, I want to know what size heat exchanger from the condensate I calculate.

Am I going about this the right way? First time tackling a system such as this. Would appreciate any guidance.