Is there a limit to how much liquid can be vaporized by the internal gas use coil in a standard 160liter to 200liter 4L DOT cryogenic liquid cylinder?Yes. And that limit ranges between 300-400 standard cubic feet per hour (SCFH) depending on the make/model of the liquid cylinder, the gas in question, the external humidity and outside temperature. Direct exposure to the sun will also increase gas flow. This rating is for an 8 hour period and it diminishes rapidly with excessive flow or time.
Why does this matter?
The failure to use this information is one of the biggest contributors to dissatisfaction with liquid cylinder operations. Users who start with high pressure cylinders and “move up” to liquid cylinders are not accustomed to limits on how much gas they can draw. This is particularly true for operators of large tip cutting torches and oxygen lances. Drawn by the relative convenience and weight of liquid cylinders they do not realize that their operation requiring 700 to 1500 scfh gas flow simply cannot be supported by one or two liquid cylinders linked together with only internal vaporizing coils.
What happens if flow is too high?
Very simply- if the liquid is not vaporized then it comes out as liquid. This can be disastrous for many operations unable to withstand extremely cold cryogenic liquid temperatures. For instance, a carbon steel tank that is being purged with nitrogen gas can easily split when sprayed directly with liquid nitrogen.
Is there a way to get more gas flow from a cryogenic liquid cylinder?
Yes, absolutely. All you have to do is add downstream ambient vaporization. Remember, though, not all vaporization is the same. Some vaporization packages for liquid cylinders (ex- Dragons) take into account connecting vent line connections to balance pressure and withdrawal rates. A vaporizer added straight on to the gas use line will be more limited than one tied to the liquid line. The liquid line connection is larger internally and has less flow restriction allowing for more gross flow of molecules. Withdrawing product from the liquid connection also prevents chilling of the outer vessel skin enhancing the ability of the pressure building coil to produce gas that replenishes the head space.
Pressure building coil?
More next time…….
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