12 replies to this topic

[raj shekhar]

Hello All,

Can you guys please provide me some steps to start designing ring main (i.e. Loop designing) compressed air distribution system.
 

I am more familiar with X-mas tree designing concept. Couldn't understand the how we can start with compressed air loop designing system.

Will Hardy - Cross method help in the distribution calculation?

Regards,

Raj Shekhar Ghosh

[katmar]

The advantage of using a ring main for air distribution is not that you can take advantage of the air flowing through both sides of the ring (which could potentially make the pipe size smaller).  The advantage of a ring main is that a portion of the ring can be shut off for maintenance and still keep most of the distribution system live.  In fact this makes the pipe size potentially larger because you need to allow for the situation where the air has to flow the "long way around" when the shorter route is shut off.

 

I would not recommend using Hardy-Cross or any other network based process.  You should use the same process as you would for your Xmas tree design, taking into account the actual flow length when various sections are shut off.

 

The most difficult part is trying to work out what the design flow rates should be.  If you assume that all take-offs are being used at full capacity all the time it could make the pipe very large.  But you usually cannot ignore the possibility that several take-offs will be used at the same time.  This same design choice will have been made when specifying the air compressor capacity, so you may be able to get some help from that process.

[breizh]

Hi ,

On top what Harvey wrote you may consider to read the document attached.

Good luck

Breizh

[Bodhisatya]

Katmar Sir

 

Can you please share the concerned literature where I can learn more about the different types of Air Distribution piping commonly used and why are they named so - such as Hardy-Cross?

 

Bodhisatya

[katmar]

In addition to the reference posted above by breizh a useful document is available at

http://oaktrust.libr...e=4&isAllowed=y

I suspect that this article was also originally pointed out by breizh, but I can't find that post now.

 

The reasons for the names of the various methods are either to describe the shape of the layout (eg Xmas tree, loop, network, ladder etc) or they are named after the original developer of the method (eg Hardy Cross was a Professor of structural engineering).  Google will find the person behind the name.

[breizh]

Hi ,

To be considered the link attached .

 https://www.almig.co...stribution.html

 

Breizh

[raj shekhar]

Thanks Breizh sir and Katmar sir, these links are very useful.

[breizh]

Hi ,

Another one .

 

Good luck

 

Breizh

[Chemitofreak]

To All,

 

I have an additional query w.r.t the air distribution system.

 

Suppose I have a dried, dew pointed instrument air system and there is a leak in the distribution piping (we often face this in a plant).

 

Will the water vapour from the ambient air ingress in the instrument air system (considering there is difference in humidity). If yes, then what are the precautions one needs to take while designing the system.

 

Thanks in advance.

[breizh]

chemitofreak ,

I don't understand your query because there is a gradient of pressure from inside to outside ( leak), let say 3 bars inside and outside atm .

Breizh

Edited by breizh, 25 January 2016 - 06:17 AM.

[Chemitofreak]

Breizh,

 

Refer the highlighted portion in the attachment. Hope it clarifies my question.

 

Revert in case of any query.

 

Thanks in advance.

 

 

 

Attached Files

•  Air Network .pdf   429.6KB   30 downloads

[katmar]

The only experience I have of back-diffusion against the flow direction was when working with ultrapure gases in a chromatography installation.  It certainly is a real phenomenon and I found it totally non-intuitive.  Here is a reference to this type of behaviour.

 

In ultrapure gases a few molecules can make a difference.  My instinct tells me that it would be less of a problem with water in a compressed air installation, but I could be wrong.

 

Certainly it is my experience that good compressed air installations always have liquid separators mounted with the regulators at each consumption point, and this would help to remove any water that does get in by diffusion.  I think the overall lesson is that leaks should be avoided (even if only from a cost and noise pollution perspective) and liquid separators should be installed to protect sensitive equipment.

[Chemitofreak]

Thanks Katmar for your prompt reply.