6 replies to this topic

[Naeema]

Hi

I need to calculate how much instrument air will be required by a new plant. I know the type and size of devices that will be actuated. Can anyone suggest a method of how i can go about doing this?

Is there any information available with regards to estimated figures used by certain types of devices. When I do estimate the amount required do I just take into account the amount required during a full stroke position change or is there anything else I should consider?

How would I go about sizing the distrubution header and surge drum for this system.

Thanks
Naeema

[Qalander (Chem)]

Hi

I need to calculate how much instrument air will be required by a new plant. I know the type and size of devices that will be actuated. Can anyone suggest a method of how i can go about doing this?

Is there any information available with regards to estimated figures used by certain types of devices. When I do estimate the amount required do I just take into account the amount required during a full stroke position change or is there anything else I should consider?

How would I go about sizing the distrubution header and surge drum for this system.

Thanks
Naeema

Dear Naeema Kindly use'Search Feature this topic has been discussed in recent past
Thanks

[ARAZA]

Dear Naeema,

Depends on the following:

What kind of plant you are talking about? how big it is? How many devices are there using instrument air such as solenoid actuated valves, control valves, emergency depressurization valves and others utilizing instrument air. This kind of calculation is never perfect and most of the time you have to use rule of thumb.

You have to collect the data for the consumption of IA from your control valves vendor's and from your emergency valves actuators vendors. Use your judgement that how many control valves would be stroking at a given time. This will give you the normal and peak IA consumption. For instance, control valve positioner model:"3730" uses 8.5 nm3/hr of air at 90 psig for full 0-100 % stroke

Add another 20 % margin over of this number to size your IA header.

ARAZA

Hi

I need to calculate how much instrument air will be required by a new plant. I know the type and size of devices that will be actuated. Can anyone suggest a method of how i can go about doing this?

Is there any information available with regards to estimated figures used by certain types of devices. When I do estimate the amount required do I just take into account the amount required during a full stroke position change or is there anything else I should consider?

How would I go about sizing the distrubution header and surge drum for this system.

Thanks
Naeema

[ankur2061]

Naeema,

Check out this old post regarding instrument air consumption:

http://www.cheresour...;hl=consumption


It will provide you the answer for all types of devices. New members please make it a habit of using the search feature of the forum, since most queries are more or less repetitive in nature.


Regards,
Ankur.

[Jiten_process]

Hi

I need to calculate how much instrument air will be required by a new plant. I know the type and size of devices that will be actuated. Can anyone suggest a method of how i can go about doing this?

Is there any information available with regards to estimated figures used by certain types of devices. When I do estimate the amount required do I just take into account the amount required during a full stroke position change or is there anything else I should consider?

How would I go about sizing the distrubution header and surge drum for this system.

Thanks
Naeema

If you would have gone through the linked post shown by ankur which was started by me at that time, you would get most of the idea how would you approach this activity.

derive continuous and non continuous requirement and size your compressor accordingly. Within non continuous you have to analyse the frequency of operation (e.g. automatic on/off valve, control valve etc.). As far as control valves are concern you have to consult vendors, but i would suggest that it's better that you cross check with different vendor too.

Also, take care of units when you define the capacity for air compressor. Lot of terminology are prevailing for e.g. Nm3/hr, m3/hr at FAD, SCFM, ACFM etc. Each one has a specific condition w.r.t. temp, pressure and relative humidity. You may have to consider your site condition to correct the capacity of air compressor.

For air receiver sizing i am attaching one short and useful file which is given by a vendor.

Good luck...

Attached Files

•  Sizing_the_air_receiver.pdf   88.97KB   1310 downloads
•  Sizing_the_air_receiver.pdf   88.97KB   659 downloads

[dickson]

Thanks very much for the sharing.. i appreciate alot...

[deltaChe]

Dear Sir
Cause you don't provide information about amount of gas required, I only find
some approximated amount IA estimated guide for you:

The air consumption rate of each item can be obtained from the manufacturer. The
tabulation of the air consumed is a simple process if it is done after the mechanical
flow sheets are completed. If not, the design basis must be partially assumed.
However, when the flow sheets are complete, a final check must be made. Refer to
the previous discussions for general sizing guidelines. In estimating instrument air
demand, the following consumption rates can be used as a guide:
• 1.35 SCFM for each panel mounted small case controller
• 0.65 SCFM for each field transmitter, controller, and manual loading station
• 1.00 SCFM for each valve positioner or transducer using under 40 psig air
• 2.00 SCFM for each valve positioner or transducer using over 40 psig air

Control valves are not counted separately because the air used to actuate them does
not continuously bleed. Also, the applicable dryer purge air must be added to the
total system consumption.