Compressed Air System - To identify dew point and suitable dryer

[chendian]

Hi,

I'm working to identify and design of medium pressure compressed air system.
I need to define the air quality requirement for the air compressor especially for the dew-point value and suitable dryer to be considered.
I don't have any consumer requirement for air quality dew-point, thus i think i need to identify the most stringent condition but im not sure where to start.

At the moment the available parameters are as follows:
1. System line pressure is 50 bar
2. Environment temperature (inlet) is 25 degreeC with relative humidity 85%
2. What other parameters that i need to consider?
3. What is the equation or engineering tool that i need to use to identify the value.

Thanks.

 

[zeusfaber]

Receivers and the like last much longer if you fill them with air at a pressure dewpoint comfortably lower than the lowest ambient temperature you're likely to see. It's often no more complicated than that.

A.

 

[georgeverghese]

Depends on the users for this compressed air. Generally, spec should be a water dewpoint ( at max op press) some 10degC lower than the lowest expected daily average atmospheric temp. In most cases, PSA or TSA mole sieves dryers can give you a water dewpoint of -40degC or so.
If you are generating inert gas with this air, then you must insist on oil free air compressors, else the air dryer and the inert gas generation unit will get fouled / poisoned with lube oil vapor, even when lube oil vapor adsorber units are installed.
Why do you need compressed air at 50barg?

 

[chendian]

To zeusfaber,

Thanks for the feedback.
Yes it should be lower than the ambient temp, but i unable to justify the most lowest limit i can go for as i need to consider the compression of 50 bar of the air, right?


To georgeverghese,

Thanks for the feedback.
Noted but how can i get the characteristic/info of compressed air condition at 50bar.
Is there any specific psychometric chart or calculators that can identify the dew point at pressure 50 bar?

No inert gas, just ambient air.
In general, the needs is for starting engines and also operating some pneumatic air valves.
It is difficult as im still at intermediate design studies and i dont have the consumers spec requirement.


I also refer to ISO 8573-1
There are several class defined but if i select the most stringent which is Class 1 (-70degreeC), but i afraid that i will over-design which it could impact on the cost as well as the size of compressor unit.

 

[MortenA]

check with a vendor e.g. Atlas-Copco. They also have info on their web page e.g. this:

https://www.atlascopco.com/content/...air/documents/2937016013 whitepaper EN LR.pdf

although that one is rather basic.

 

[MortenA]

ISO 8573 is for food manufacture - so is may or may not be applicable

 

[zeusfaber]

Is there any specific psychometric chart or calculators that can identify the dew point at pressure 50 bar?

Loads. I use the online one at

http://www.dew-point.com/dew-point_calculator.asp

when I haven't got one of the handy circular sliderule devices handy.

A.

 

[georgeverghese]

It is unusual that the all compressed air must be at 50barg just for the sake of enabling air start on gas engines. Ask the mechanical engineers to select between electrohydraulic start and air start first. If they can manage with E-H start, then you'll only need 8-10barg for instrument air, buffer air in case you've got gas seals on large compressorss and maybe some small power air users.
To be sure you get a water dewpoint of say 3degC at 8barg out of the PSA dryers, you'll still need oil free air compressors.