Pressure Gauge for CO2 Cylinder

[azmirosman]

Dear All,

Good Day.

I would like to request for your advice regarding CO2 cylinder.

Recently we purchased CO2 Snuffing skid that consist of several CO2 cylinder inside the skid.

Our client request to have inventory monitoring of the cylinder skid using pressure gauge at the cylinder itself and was advised by the vendor that is not possible. They only mention the reason because of the safety but not mention specifically what is the safety reason.

They propose the inventory will be checked using manual weighing.

I need to convince my end user that monitoring the inventory of the cylinder using pressure gauge is not possible, but I don't have much point to convince them. Anybody have experience appreciate can share.

Thanks

 

[3DDave]

High Pressure CO2
High pressure liquid CO2 is produced by compressing the gaseous CO2 in multistage compressors to pressures in the neighborhood of 69 bar (1000,76 psi) pressure, then cooling it to around 18 °C (64,4 °F). It is customarily filled into specially constructed steel cylinders. Like water, liquid CO2 can be weighed, and this is the normal form of measuring it.

https://www.ascoco2.com/us/co2-production-and-co2-recovery-plants/general-information-about-co2

The pressure of the CO will depend on the temperature. There will be equilibrium between the gas and the liquid - weighing is the only means to tell the amount and pressure only works to see the condition of the gas after the last of the liquid evaporates if you also compare to the temperature.

Doubling absolute temperature increases pressure by a factor of ten times. This tells us that at about 40 degrees Fahrenheit, CO2 has a vapor pressure of 600 psi. At 72 degrees F, it's up to about 860. At about 80 degrees F, the CO2 vapor pressure rises to about 970 psi.

http://www.saltcorner.com/Articles/Showarticle.php?articleID=93

I worry any time someone is dealing with high pressure gases and don't know the basic properties.

 

[desertfox]

Hi azmirosman

Why not go back to the supplier of the skid and ask him can they elaborate on what the safety issue is, to me that seems the quickest route.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[azmirosman]

Hi desertfox,

Vendor not able to answer since they bought the cylinder from subvendor.

 

[3DDave]

"I need to convince my end user"

No. You don't. Buy pressure gauges and install them and make the client very happy. They won't work, but there is no safety hazard to using pressure gauges. At worst, they leak massively, but the installed location for any such array should be well ventilated, right? To avoid suffocation hazard, which you already know about and have already informed the client about?

 

[LittleInch]

My guess is simply that a bourdon type pressure guage is susceptible to leaks and breakage or the small bore tubing for any instrumented pressure guage is also vulnerable.

But 3D dave is totally correct and a pressure guage on a dense phase / liquid CO2 cylinder is next to useless as a guage telling you how much is left.

This is exactly the same as say an LPG cylinder. The pressure would stay more or less constant if the contents are kept at a similar temperature.

CO2 isn't like other gases like air, nitrogen or even Argon which at normal temperatures and bottle storage pressures are compressed gases. CO2 at high enough pressures and normal ambient temps exists as a liquid and a gas and as the gas is taken off, then some of the liquid turns into the gas at the same pressure once the temperature stabilises.

Find a CO2 phase diagram, understand it yourself, then explain this to your client.

E.g.

https://www.chemistrylearner.com/co2-phase-diagram.html

Basically as the pressure falls as the gas is taken off, once the liquid gas interface hits the phase line the liquid then tracks along it as the pressure and temperature both fall. The liquid does need some external heat to convert from liquid to gas so the pressure can drop a bit and the tank can get "cold" or even frost up) until the ambient temperature adds heat into the liquid and it then climbs back in pressure over time after a significant gas release.

Hence why a pressure guage does not actually provide you with an inventory figure.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[azmirosman]

Dear 3DDave and Littleinch,

Thank you very much for your help.

Really appreciate it

 

[LittleInch]

Hope you manage to educate your client....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.