Weight of Beer Gas

[wickedbeernut]

How much does the 75/25 beer gas in a full 60 cu ft nitrogen cylinder weigh?

For the life of me, I can't find the tare weight stamp on either of my steel nitrogen cylinders.

I'm forced to exchange (rather than refill) my cylinders so I never have the opportunity to weigh them empty.

I've seen an estimate of 14-15 lb. That seems reasonable. A 60 cu ft nitrogen cylinder is about the same size as a 15 lb CO2 cylinder. However, CO2 is more dense than nitrogen.

Does anyone know the related math / science?

 

[Agent]

Well, those tanks probably don't have a tare weight stamp because they are filled by pressure (volume) rather than weight like CO2.

A quick Google says that 1lb of CO2 yields 8.7 cuft of gas. So assuming the whole 60 cuft tank was CO2, that'd only be like 7lbs.

Any reason you don't want to use tank pressure to determine your remaining gas?

 

[wickedbeernut]

A quick Google says that 1lb of CO2 yields 8.7 cuft of gas. So assuming the whole 60 cuft tank was CO2, that'd only be like 7lbs.

I'm assuming a full 10 lb CO2 cylinder contains 10 lb of CO2 (assuming it's filled properly). A 60 cu ft nitrogen cylinder is considerably larger than a 10 lb CO2 cylinder.

Any reason you don't want to use tank pressure to determine your remaining gas?

I have a PLAATO Keg (wi-fi digital scale) for each of my CO2 tanks and beer gas tanks.

 

[Agent]

I have a PLAATO Keg (wi-fi digital scale) for each of my CO2 tanks and beer gas tanks.

Gotcha.

So keep in mind that CO2 turns to liquid at normal storage pressures. And liquids always occupy far less volume than their gaseous counterparts.

Nitrogen does not turn to liquid until its stupendeously high pressured, or equally ridiculously chilled. So it had a direct correlation between tank pressure and remaining available gas.

Your best chance might be to just stop by your gas shop and ask if you can weigh a full and empty nitro tank. Either that or @doug293cz has all these numbers available and just hasn't chimed in yet! =D

 

[doug293cz]

What is the pressure in the tank? This can be used to get an estimate of the weight of gas in the tank. Won't be 100% accurate, because CO2 doesn't quite follow the ideal gas law (PV = nRT.)

Brew on

 

[doug293cz]

Gotcha.

So keep in mind that CO2 turns to liquid at normal storage pressures. And liquids always occupy far less volume than their gaseous counterparts.

Nitrogen does not turn to liquid until its stupendeously high pressured, or equally ridiculously chilled. So it had a direct correlation between tank pressure and remaining available gas.

Your best chance might be to just stop by your gas shop and ask if you can weigh a full and empty nitro tank. Either that or @doug293cz has all these numbers available and just hasn't chimed in yet! =D

The CO2 partial pressure in the beer gas tank needs to be less than the pressure at which CO2 liquefies for whatever the tank temperature is. It the CO2 partial pressure is higher than this limit, then some of the CO2 will liquefy, and the gas ratio will be off (more than 75% nitrogen.) The chart below shows the liquefaction pressure for CO2 at various temperatures, so for a given temperature the total pressure in the tank needs to be less than 4X the CO2 liquefaction pressure (for 75/25 beer gas.)

Brew on

 

[wickedbeernut]

What is the pressure in the tank? This can be used to get an estimate of the weight of gas in the tank. Won't be 100% accurate, because CO2 doesn't quite follow the ideal gas law (PV = nRT.)

Brew on

One tank is 2300 PSI. The other tank is closer to 2200 PSI.

 

[doug293cz]

According to this site, a 60 cu ft steel cylinder weighs 26 lb (11.8 kg) and has an internal volume of 660 cu in (11 L.)

Edit: 660 cu in actually equals 10.8 L, so at least one (and probably both) of the volume numbers is not exact.

Brew on

 

[Agent]

What is the pressure in the tank? This can be used to get an estimate of the weight of gas in the tank. Won't be 100% accurate, because CO2 doesn't quite follow the ideal gas law (PV = nRT.)

Brew on

The fact that the Ideal Gas Law has a lot of gray area explains why high school me couldn't use propane (without ignition) as a potato gun propellant.

In addition to how PVC pipe at 10F has a far lower pressure capacity than at 70F+

 

[wickedbeernut]

One of my 60 cu ft beer gas cylinders weighs 36 pounds. The other weighs 32 pounds. Both cylinders are supposedly full. The heavier tank is taller with a smaller diameter.

My OCD is flaring up. Maybe I'll just use the cylinder pressure to approximate the remaining gas as @Agent suggested. I had the PLAATO Kegs laying around and I thought it would be fun.