Air compressor tank sizing scenario

[nli2]

A air tank (vertical) located in the discharge line of the existing 2 rotary screw air compressors: (1) to remove the possible contaminant. (2) provide buffer time and smooth the compressor operation.
we shall install a new compressor with same capacity as existing cmprs. Idea is try to share the existing air tank for the new compressor.

I know that there are two ways for the air tank sizing.
(1) estimating the required receiver size is based on compressed volume.
V= (Q *Pa)/ (Pi+Pa)
where: V= receiver size (ft3)
Q=compressor output (cfm)
Pa= standard atmospheric pressure (psi)
Pi= Compressed pressure (psi)
(2) based on a variable demand situation.
V= t (Qout-Qin)x Pa/ (P1-P2)
Where Qout:flow rate out; cfm.
Qin: flow rate in; cfm.
V: receiver size (ft3)
t: time to charge or discharge,min
Pa: atmosphere pressure, psi
P1: Initial working pressure,psi.
P2: Final working pressure, psi.

Question is for way (2):
Any normal practice or experience for formula 2 sizing scenarios in plant?
I can imagine that some,
plant has increased air demand for several minutes at some scenarios, the initial header pressure 7 barg, and the header pressure can not drop to ?? ...
or utility failure, compressor trips, have to provide some instrument air buffer time for emergency shut down etc. ...

thanks,
nli2

 

[dcasto]

Air compressor volume tanks are never big enough. By the time you study 1000 scerios like, electric power fail and time needed, you'll have some guy on an air grinder trying to run it or 5 instruments have a gasket leak taking more air. Or even worse, the line fails right next to the most critcle instrument that you are trying to make sure has enough air during a loss (put its own air reciever with check valves).

I look for some residence time in a reciever to help cool and drop out water before the driers as a criteria. Once we decided to have enough air to restart our turbine, we converted a 30,000 gallon propane tank to an air reciever, took a day or so for the compressors to get that one full.

 

[code1]

Nli2,

The example calculation procedure found in

http://www.drucklufttechnik.de/english/

and go to Chapter 8.5.
It maybe what you are looking for. Hope it helps.