3 replies to this topic

[J_Leo]

Dear Friends,

 

I came across some PSVs on the headers of Fire Suppression CO2 system for gas turbines. The datasheet for these PSVs is within the gas turbine package.

 

The information from the datasheet:

Set P: 2030psig

Size: 3/4"X1"

Overpressure:10%

 

The cylinders and headers are inside an enclosure as shown in the image I found on the internet. there is one PSV on each header. Initially, the PSVs are inside the enclosure, but they are extended outside because there is not enough space for testing.

There are no scenarios mentioned. I have never worked on these systems before. What could be the sizing scenario? Hydraulic expansion? What is the state of the relieving fluid? Is calculation needed?

 

Thank you,

Leo

Attached Files

•  Fire Suppression CO2 system for gas turbines.jpg   43.38KB   1 downloads

[Saml]

First, if there is a local regulation, that will prevail.

Then you need to check the cylinders design code and what it requires in term of relief

If they are designed to DOT, the applicable RAGAGEP are the following.

 

NFPA Standards

NFPA-55

 

CGA Standards

S-1.1    Ed: 14 11/01/11 Pressure Relief Device Standards-Part 1-Cylinders for Compressed Gases

S-1.2    Ed: 9 03/18/09 Pressure Relief Device Standards-Part 2-Portable Containers for Compressed Gases

S-1.3    Ed: 8 12/03/08 Pressure Relief Device Standards-Part 3-Stationary Storage Containers for Compressed Gases

S-7       Ed: 6 01/18/18 Standard Method for Selecting Pressure Relief Devices for Compressed Gas Mixtures in Cylinders

[Art Montemayor]

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.

 

[J_Leo]

Saml and Art,

 

Thank you so much for the information, especially Art for spending so much time to explain the system to me. I will read the CGA once I get it. I work around Houston area.

From the vendor's handbook, each cylinder is equipped with a special quick release valve and siphon, and complete with a safety disk against over-pressure. The bursting pressure of the safety disk is 3626psi.

 

There is a quick discharge bank of cylinders and a slow discharge bank of cylinders. For each bank, there is one PSV, on the pipe after the combination of the flow from all the cylinders. The PSVs are set @2030 psig. The PSVs are installed already. I am trying to figure out what these PSVs are protecting and what is the sizing scenario. Maybe expansion from ambient temperature rise when the valve downstream is blocked? Do we need to follow API inlet and outlet pressure drop rules? It might be difficult to calculate the pressure drop, especially the outlet with mixed solid and gas as described by Art.

 

Regards,

Leo