Several kegs from one co2 tank?

[chrisdelay]

So I've got a couple of probably pretty easy questions:

1.) Is there an upper limit to the number of kegs that can be attached to one co2? I'm not planning on something ridiculous...I've only got two corney kegs at the moment but the ULTIMATE goal is to have a chest freezer with a swapped out thermostat with probably 6-8ish (whatever will fit) kegs.

2.) Generally speaking, is there a rough estimate as to how much co2 it'll take to carbonate and serve an entire keg? Say, something like "a 10 lb co2 tank will carbonate and serve 3 kegs"?

3.) Will I need some sort of expansion chamber before the co2 hits the kegs, or will the regulator do that? I'm an old paintball player and I'm quite well aware of what happens when gaseous c02 is used too quickly and liquid co2 is introduced to a system...I'd hate to think what liquid co2 would do to beer.

Thanks to everyone here...I've already gathered so many ideas and helpful information here that I'm starting to obsess about homebrew...much to the chagrin of my gf, who got this stuff for me a few months ago.

Muwhahahaha!

 

[Bobby_M]

There are no dip tubes in beverage use tanks so no liquid co2 going anywhere near your kegs unless you invert the tank.

There's really no upper limit for one tank. You just won't want to hook up 10 kegs that are completely unpressurized and open the tank valve. It's not someone you'd do anyway. Once you have a bunch of kegs carbed up and under pressure, adding another one is no big deal.

According to as many calculations as I could muster, it should take about one pound of liquid co2 to carb and dispense something like a pale ale at 2.5 volumes and that includes minimal venting/purging. A 10lb tank with a non leaky system should go through 10 kegs.

 

[Funkenjaeger]

it should take about one pound of liquid co2 to carb and dispense something like a pale ale at 2.5 volumes and that includes minimal venting/purging. A 10lb tank with a non leaky system should go through 10 kegs.

Which weighs more, a pound of liquid CO2 or a pound of gaseous CO2?

I don't think your calculations are quite right. Offhand, based on past usage, I would bet I could even get 10 kegs out of my 5lb cylinder, if not more. Micromatic's site claims:

As a general rule of thumb, it takes about a ½ Lb of CO2 to dispense a ¼ barrel of draft beer

Obviously, force carbing in addition to dispensing will add more usage, but micromatic's figures put it at around 1/6 lb per 5gal keg for dispensing alone, so I would guess that the force carb + dispensing figure would still be WELL under a pound a keg.

 

[Bobby_M]

Right, so if it takes a 1/2 pound to dispense 1/4 barrel, (1 volume, fully displaced) and you want to carb to 2 volumes, it should take 1.5 pounds to carb and dispense. I know that's not true at all so Micromatic's estimate seems way off.

Here's something I posted on my website and I'd love for anyone to tell me where I went wrong, if I did.

One of the questions I see a lot is "How many kegs can you carbonate and dispense with a single fill on a xx pound CO2 tank"? There are a lot of variables of course based on how many volumes you carb each keg to (volumes) and how much you waste into the atmosphere. The typical average in my opinion is 2 volumes meaning there will be 2 times as much gaseous CO2 dissolved as there is beer. Example, 5 gallons of beer take on 10 gallons of CO2. It will take another 5 gallons of CO2 to push all that beer out of the keg. The real issue is figuring out how much liquid CO2 it takes to create a certain number of gallons of gaseous CO2.

According to http://www.ca.airliquide.com/en/business/products/carbon_diox/index.asp , 1 pound of CO2 (it's sold by the pound) is equal to 8.741 cubic feat of gaseous CO2 at sea level / 70F. If my logic serves me, this volume would actually be halved at typical carbonation pressure of say 14 psi (2ATM) for 4.37 cuft. I'm going to ignore the temperature.

5 gallons is .668 cubic feet. 4.37cuft (1lb co2) divided by .668 = 6.54. That means 1 pound of liquid CO2 is 6.54 volumes in a 5 gallon keg. For example, that would be enough to carb two kegs to 2.25 volumes and dispense both to empty. So if 2.25 volumes was an average carb level, and there was no wasted Co2 on purging/venting:

CO2 Tank Size Total Volumes 5 gal @ 14psi Total Kegs, Carb 2.5 vol + Dispense
2.5 lb 16.35 5.3
5 lb 32.7 10.6
10 lb 65.4 21.2
20 lb 130.8 42.4

I admit, I don't understand the ideal gas law in the slightest so I can't really know how the temperature of the beer is playing on the volume requirements. However, Micromatic, an authority on keg dispensing claims that it takes about 1lb of CO2 to "DISPENSE" a 1/2 barrel. This would mean that it takes 1/3rd or .33 pounds per volume on 5 gallons. Remembering that carbing to 2 volumes and dispensing actually takes 3 volumes, that's 1 pound per 5 gallon keg. On the same page, the chart shows a 20lb tank capable of dispensing at least 62 five gallon kegs but you have to remember that dispensing only takes ONE volume so carbing will require 200% more gas. So, the number I'm comfortable with right now is "about 1 pound per 5 gallon keg".

 

[Funkenjaeger]

I'm not so sure about your assessment of 'volumes'. I was under the impression that one 'volume' of CO2 in a 5g keg of beer was equivalent to 5g of CO2 at room temp/pressure, not 5g of CO2 at 14PSI and 40 degrees. By your logic, a keg would hold 2-3 times MORE gas if it had beer in it than if it was empty, because by your definition an otherwise empty keg, filled with CO2 at 14PSI, would hold exactly one 'volume'.

Edit: Well I guess I was half right about the definition of 'volumes' - found this PDF, referring to carbonation in soda, which defines carbonation 'volumes' as:

Carbonation Volume-The volume of carbon dioxide,
CO2, (at 0°C, one atmosphere pressure) that is
dissolved in the carbonated water divided by the volume
of the water at 3.98°C (39.16°F)

http://www.plasticsindustry.org/business/pdfs/pbi-26.pdf

So it's not that beer can hold more CO2 than the same volume of free space, it's that the keg itself would hold 2-3 volumes of CO2 whether it were empty or full of beer.

So my prediction is that when you pressurize a full keg of beer, you will use up 2-3 volumes of CO2 as it force carbs (basically close to the same amount of CO2 that the keg would have held if empty), and then another equal volume of CO2 to displace the beer as you dispense. If that is correct, you would use pretty close to twice the CO2 to carb+dispense as you would to dispense alone.

Doing the math, one pound of CO2 at 1ATM is 8.741/.668 = 13.09 volumes, for a 5 gallon keg. So if you just dispensed, you'd get 13.09/2.5=5.23 kegs per pound of CO2.
Checking that against micromatic's numbers, dividing it by 3 to translate to 1/4bbl kegs, you'd get 1.74 kegs per pound, which is in the ballpark of 1/2 pound per keg, the figure they gave.

So then, if you were to carb a 5g keg to 2.5vol and then dispense, you should use about twice that much CO2, ie - 13.09/(2.5*2)=2.61 kegs per pound, or about 0.38 pounds per keg. From a 5lb tank that should give you about 13 kegs.

Though I don't really keep track that closely, I do know that I've gotten much more than 5 kegs out of one 5lb tank, probably more in the neighborhood of 10, and that's including purging, slow leaks, etc.

 

[Bobby_M]

Yup, my math comes close too but my head still hurts from figuring...

2.5 lb 5.3
5 lb 10.6
10 lb 21.2
20 lb 42.4

See, 1 pound of CO2 is equal to 8.741 cubic feat of gaseous CO2 at sea level / 70F. The thing that's getting me is that volumes are calculated at 40F. I looked up Charle's law that says at a fixed pressure, volume is directly proportional to the temp. If that's true, the 8.741cuft at 70F (what a pound is good for) would only provide 5 cuft at 40F. That 5cuft is good for (5/.668) 7.45 volumes at 40F. So, a 2.5vol carb + dispense would be 7.45/3.5 = 2.12 kegs per pound.

Our answer is pretty darn close but one of us is missing something. I'm contending that the difference in temperature in the definition of "volumes"(40F) and the volume of co2 you get per pound (70F) needs conversion.

 

[srm775]

So I've got a couple of probably pretty easy questions:

1.) Is there an upper limit to the number of kegs that can be attached to one co2? I'm not planning on something ridiculous...I've only got two corney kegs at the moment but the ULTIMATE goal is to have a chest freezer with a swapped out thermostat with probably 6-8ish (whatever will fit) kegs.

No, there is no "upper limit" you can have connected to one tank, you'll just need to split the line enough to permit it. I just finished my Keezer and have 4 kegs hooked up to one 5lbs CO2 tank, and that will eventually change to 5 kegs. Obviously, you'll run out of gas with a smaller tank the more kegs you have hooked up to it.

2.) Generally speaking, is there a rough estimate as to how much co2 it'll take to carbonate and serve an entire keg? Say, something like "a 10 lb co2 tank will carbonate and serve 3 kegs"?

Without gettting into the math that the two previous posters got into, a general rule of thumb is 10 kegs per 5lbs tank. I consistently get about 10 kegs per 5lbs and everyone else I know does as well.

3.) Will I need some sort of expansion chamber before the co2 hits the kegs, or will the regulator do that? I'm an old paintball player and I'm quite well aware of what happens when gaseous c02 is used too quickly and liquid co2 is introduced to a system...I'd hate to think what liquid co2 would do to beer.

Not a paintball guy, but no you won't need anything more than a tank, regulator, gas disconnects and vinyl tubing. with two kegs on one regulator, you'll either need an additional regulator, a secondary regulator, a "t" or "y" splitter or a manifold. Hope that helps.

 

[Funkenjaeger]

The thing that's getting me is that volumes are calculated at 40F. I looked up Charle's law that says at a fixed pressure, volume is directly proportional to the temp.

One small but extremely important detail is that it involves temperature in degrees Kelvin. Numerically, a temperature shift from 70F to 40F is HUGE compared to the equivalent shift from 294K to 278K. That's only about a 5% change in the temperature in degrees K, thus the volume is only going to change by that much. So, ignoring the temperature difference is not going to dramatically screw up the calculations.

 

[david_42]

The reason you won't need an expansion chamber is the flow rates you'll see for kegging are much lower than you would for paintball. I've got my tank and regulator at about 34F and haven't had trouble. And that's with keeping a keg of soda water online in addition to 5 kegs in the conditioning cabinet.

 

[Bobby_M]

Excellent. So 1lb of CO2 at 40F is actually 8.2167, not 5cuft but then my math says a pound is good for 3.5 kegs. I give up ;-)

To the OP, sorry for using your thread as a scratch pad. The answer is "plenty".

 

[Funkenjaeger]

Excellent. So 1lb of CO2 at 40F is actually 8.2167, not 5cuft but then my math says a pound is good for 3.5 kegs. I give up ;-)

One last thing (what can I say, I'm pedantic)... You are saying dispensing uses one volume. Because it's under pressure, 5 gallons of CO2 is again going to be more than one 'volume' - if you only had one volume of CO2 in the keg when it emptied of beer, it would be at 1ATM. I would expect the volume of CO2 used to dispense to be pretty much the same as the carbonation level you targeted, in volumes, though you could double check with the ideal gas law or whatever. In that case, carbing a beer to 2.5 volumes and then dispensing would require 5 volumes of CO2, not 3.5.

 

[Bobby_M]

Seriously...F' you.

I see it now. Assuming you mainting the 2.5 volumes over the kegs entire dispensing, the displacment takes 2.5 volumes as well, otherwise you'll lose carb. Got it. Let's call is 2-3 kegs per pound and have some beers.

 

[chrisdelay]

Thanks for the info guys...good stuff!

 

[Funkenjaeger]

Let's call is 2-3 kegs per pound and have some beers.

I concur