Leo:
If you are going to be working with CO2 fire extinguishers protecting your gas turbines, I highly recommend you get thoroughly familiar in all the details surrounding the workings of a CO2 fire extinguishing system.
We don’t know what country or region you are living and working in since you fail to tell us those details in your personal profile. Therefore, we don’t know what the legal and safety regulations are where you are at. All I can refer to is over 25 years of working with CO2 and I can tell you that your CO2 cylinders probably have dip tubes connected to the inlet of the cylinder valve. This is an important detail that many engineers and so-called “experts” fail to know or even recognize. Allow me to share some basic CO2 facts and properties:
- CO2 is stored and transported in basically one of two saturated liquid states: at ambient temperature (80 oF) and 970 psia or at 265 psia and -8 oF.
- Your fire extinguisher cylinders are probably at the former condition.
- When you open the valve of a CO2 fire extinguisher, you are expanding LIQUID CO2 to atmospheric pressure and producing a mixture of approximately 50% solid CO2 “snow” and saturated gas at a temperature of approximately -107 oF. This produces a white cloud of instantly condensed atmospheric water vapor.
- The normal protective device for compressed CO2 cylinders is a rupture disc - never a conventional pressure relief valve.
What you describe is a manifold set up of various CO2 cylinders hooked up together to furnish enough extinguishing inventory for your turbines when needed.
If indeed I am correct that you are expanding liquid CO2, I would not employ a PSV on this system. I would use rupture disc(s). These have been (and continue to be used) on normal CO2 cylinders for close to 100 years.
Saml is guiding you in the right direction by identifying the CGA as an expert society in describing compressed gas equipment and its use. I recommend you obtain a copy of the “Handbook of Compressed Gases” as published by the Compressed Gas Association, Inc (CGA). Refer to the Chapter on Carbon Dioxide and the section on Containers (page 295). There you will find all the information you need to know about the system. Note that in the USA you should be hydrotesting your storage cylinders every 5 years.
I would never use a PSV on liquid CO2 because the solid produced on expansion tends to plug the valve seat and re-seating is hindered or not possible. Therefore, the usefulness of a PSV is out the window. For the pressures involved, a rupture disc is reliable, simple and the total venting of the inventory is not expensive and can be replaced. It is not realistic to expect a CO2 cylinder to be subjected to pressure relief. The critical temperature for CO2 is 87 oF and above that, it is a supercritical fluid. Analyzing and studying a Temperature-Entropy Diagram for CO2 shows you what I am referring to.
There is a lot of ignorant, junk science put out in the Internet about how CO2 fire extinguishers work and why. Even stuff like the U.S. Patent # 3901322A by Jack Winston is out in left field stating that it is expanding CO2 gas that produces “snow”. The CO2 fire extinguisher is very simple science when you know and dominate your basic thermodynamics and phase equilibria.