System Design for Fire Hooter

[asghar]

I need assitance in designing a system that should be capable of providing air to a fire Hooter. The big hooter, having a range of 6 Killometers, has been procured, it requires 9.6 cu. ft per second air at 125 psig to blow. Since, No air is available therefore, I recommended three standard Nitrogen cylinders to blow the hooter. Standard Nitrogen cylinders are at 2000 psig that can provide Nitrogen for up to around 15 minutes based on Calculations (PV/nRT) . In each fire drill the hooter is blown for a max of two (2) minutes.

It is assumed that each regulator on a cylinder can provide a limited amount of nitrogen due to orifice size, around 2 cu. ft/sec (not sure, someone has to confirm). Questions:

Do I need a headder to which all cyliners are to be connected? If yes, then why and what pressure should be maintained?
Do I need a small surge tank (3ft dia x 5 ft) in between cylinders/ header and hooter? If yes, then why and what pressure should be maintained?
Would there be any temperature impact?
What safety precautions are to be taken?

Your input shall be appreciated. Any rough sketch will allso be helpful.

 

[TD2K]

I'm going to assume that the 9.6 ft3/sec is at standard conditions supplied at 125 psig (rather than as could be read, 9.6 actual ft3/sec at 125 psig).

For 2 minutes of operation, that needs 1152 scf. The OP has said that they have calculated 3 cylinders will blow the horn for 15 minutes. 15 minutes needs 8640 scf and works out to 2880 ft3/cylinder. An N2 cyclinder doesn't hold anywhere this amount of gas. Scuba tanks are typically pressurized (depending on the type and material) to about 3000 psig and hold 80 cf of air at atmospheric pressure. Now, an N2 cyclinder is taller but if its initial pressure is 2000 psig, you have a big disconnect somewhere on your calculations.

As for the capacity of a regulator, talk to a vendor, get the Cv of a regulator and calculate the flow you will get through it.

For the size of the line, you need to do a line loss calculation. Determine for a given line size (you know the flow rate) how much pressure drop you have between the regulator outlet and the horn? Is it okay or too much? Adjust line size as needed.

For temperature, it's going to get cold. Check out your thermodynamic tables to estimate the possible temperature drop. As for safety implications, think through what could go wrong. Just a few: if the regulator fails wide open, can you overpressure the line to the horn or the horn itself? If you have a slow leak, how are you going to detect a loss of pressure before you go to use the horn and it doesn't work.