CO2 cylinders

A lot of people use the smaller CO2 bottles used for soda pop machines abd beer kegs.

Make sure you find a steel tank. I was in AirGas yesterday and a guy was exchanging an aluminum tank, which he said he used for welding, and the guy there told him that was a no-no. I'm not sure myself, but the Airgas guy seems to have good answers most of the time.

Just one thing to worry about when buying from somewhere other than the refiller.

Rod

Ernie Leimkuhler wrote:

"rod richeson" wrote: Make sure you find a steel tank (clip) ^^^^^^^^^^^^ The CO2 cylinder provided by my welding supply is aluminum. They also seem to know what they are talking about.

In message , Leo Lichtman writes

CO2 is stored as a lquid and not a pressurized gas.I think the storage pressure is quite low.

Co2 (Carbon Dioxide) is stored in vessels as liquid and sold by the liquid weight. Liquid Co2 is under pressure, that pressure will change with gas use or added heat (don't heat the vessel). Suitable vessels can be made from stainless, carbon steel, aluminum, carbon fiber and other materials. Co2 is the only industrial gas that can be in solid, liquid, and gas form inside the same vessel. If you remove the presure to quickly liquid Co2 turns into dry ice (a solid) the right size usage vessel is important. Co2 vessels range in pressure from 300psig on up.

That's good to know. Learn something everyday here.

Rod

Lance wrote:

"Lance" wrote: Co2 (Carbon Dioxide) is stored in vessels as liquid and sold by the liquid weight.(clip) Liquid Co2 is under pressure, that pressure will change with gas use (clip) ^^^^^^^^^^^^ An otherwise accurate discussion contains this error: A liquid in equillibrium with its vapor reaches a pressure determined by the temperature. As the contents of a CO2 tank are consumed, the pressure does not drop. Liquid evaporates to keep the pressure the same. The same thing is true of propane and butane. That is why you can't use a pressure gauge to determine how much has been consumed. RV owners know that you have to use various tricks to determine how much is left in the tanks: weight, frost level, fractional vent lines.

Most of the CO2 cylinders I have seen were rated at 1800 PSI max working pressure. Link to chart showing CO2 pressure relative to temperature and percent full.

In a gases (vapor) Co2 usage application like welding, the pressure "will drop" and cause the liquid to boil off (vaporize) into vapor. If Co2 vapor usage exceeds the cylinders capacity to convert (vaporize, boil off) from liquid to gas the pressure will continue to drop until the liquid changes into a solid (dry ice). Liquified Co2 will start to form dry ice at pressures below 150psig, that's why you should not blow down your co2 cylinder. If a vessel or cylinder has formed dry ice it should be inspected, dry ice is -109 degrees F. Liquified Co2 will start to form dry ice at pressures below 150psig. A cylinder's capacity to vaporize liquid is reduced as the cylinder and ambient temperature declines.

The best way to determine the Co2 left in your cylinder is to know its empty and full weight. It's crude but you can use an old bathroom scale to weigh the smaller cylinders. Cylinder gases other than Co2 and fuel gases are sold by volume only the bulk vessels and some special use cylinders have liquid.

This information is given from my 15+ years in the industrial gas business. I worked for Praxair, Air Liquide, and Liquid Carbonic the 3 biggest industrial gas suppliers in the world. We supplied a lot of your local gas companies with equipment, bulk and cylinder gases. I spent 9 of the years in service, repair, manufacturing, and installation of industrial gas equipment and vessels. The other 6 years in production and distribution of bulk industrial gases. The information I gave you is correct.

If I may speak for Leo, I understand and believe your scientific explanation and is factual. Street understanding of a pressure drop is where a new argon tank has 2200lbs psi full and zero empty. With CO2, you can't judge the content volume by pressure because it's always at or near the same equilibrium pressure determined by ambient temperature. A full tank won't show much pressure difference than an almost empty one until there's none left... much the same as CC or CV machines try to maintain a constant flow of current/pressure and we could argue that this is impossible. In both examples there is a range that the subject will stay within and for conversation purposes is considered "right on the money".

That's a real good chart. I can see why it's a good idea to have tanks rated for at least 1800lbs. A full tank on a zero degree day would have only

300lbs pressure but at 120F degrees would rise to 1900lbs! At standard temperature it remains around 950lbs from 40% to 100% fill.

Dry Ice is very cold and will keep things frozen, or freeze them quickly. It's temperature is -109.3°F or -78.5°C. Dry Ice forms when liquid CO2 (800 psi*) is exposed to normal atmospheric pressure. About half of the liquid changes directly from a liquid to a solid the rest turns to gas. When Dry Ice melts it goes directly from solid to gas, skipping the liquid stage of normal ice. (WATER ICE) Hence the name "Dry Ice".

*Liquid CO2 comes in tanks which vary in size from 1oz to 75 lbs and hold the CO2 at from 422psi/20 degrees F to 969 psi/90 degrees F or Large Bulk Cryogenic Insulated tanks which maintain a pressure of 300 psi and low temperatures.

You will need a syphon cylinder of Liquid CO2. Check your local listing under "Gas". Usually about $25-$30 / 50 Lbs(+Tank Lease)

Attach the Frost-Stick to the Syphon CO2 Cylinder using an Adjustable wrench. Open the cylinder valve and direct the nozzle into a box until it is full. To make block of dry ice pack the snow down (you can use a cardboard box and a 2x4) and continue filling until it is tightly compressed.

It takes a little over 2 lbs of liquid CO2 to make a Pound of DRY ICE depending on atmospheric conditions

Christopher Frostic