7 replies to this topic

[sina]

Hi all!

I work on one refinery unit project.
To my instrument air subheader is attached 5 tubings 1/2" and each supply 5 control or on/of valves.
All together, that is 20 valves on one subheader.
Now I must make one document with air consumption calculation.
For now I don't have manufacturer or model of the valves.
It would be a great help if anyone has that document (or template) just to see how it looks like, what it contains and what are the formulas for calculating consumption.

PLEASE HELP!!!

[joesteam]

First, you will need to know the size of the valve, more specifically, the size of the actuator. For the on/off valve it is a simple calculation of how often the valve cycles and the volume of the actuator. For the modulating valves, it is tougher, because usually they move only a portion of the travel.

One way to get around this is to do a 'thought' experiment. You take the output of the control device (either solenoid, positioner, 3-15 controller, etc.) and use this as a max air flow. Then you try to figure out how many valves will be actuating at any specific time, this will give you a calculated instantaneous maximum air flow in the line.

[Majid-Process]

Hi Sina,
Normally there are three ways to calculate or estimate instrument air consumption. For brownfield jobs, you need just to retrieve pressure trend of instrument air receiver and volume. For greenfield you should use vendor data for continous and intermittent users such as control valves shut down and blowdown valves.

In absense of vendor data, you should use rule of thumbs for each type of users. I have recently done a similar calculation for Shell. In case you can not find any resource, flag up. I will try to give you a sample.

In total instrument air capacity take care about simultanous users. In refinery applications you can not just list out users and do sum.

Cheers,
Majid

[ankur2061]

Sina,

Have you tried using the search feature of the forum? There are many posts on instrument air consumption discussed in great detail on the forum. Newcomers, please use the search feature of the forum as time and again I have been telling that the majority of the queries you have, have been dealt earlier on the forum and it has been observed that at least 70 to 80% percent of the queries are repetitive in nature.

Just for this time, I am giving a link for an older post which has discussed instrument air consumption in great detail. Have a look at this:

http://www.cheresour...__1

Regards,
Ankur.

Edited by ankur2061, 27 April 2010 - 11:10 AM.

[adivaraghan]

mr.Majid

can you give sample calculation thank you

adi

[imran.idris]

Normally, 2 NMC/hr of instrument air is a safe estimate to start with.

Regards,
Imran Idris
http://forums.thepetrostreet.com

Edited by imran.idris, 25 April 2010 - 10:30 AM.

[markos]

Mr, Majid,

Please send me sample computation to makkee8@hotmail.com
Thanks in advance.

makk

[sheiko]

Hi

Attached file will help you.

Attached Files

•  Inst_Air_Consumption_Rev1.xls   15.5KB   1682 downloads

Edited by sheiko, 27 February 2011 - 12:31 PM.