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CO2 capture - rate of escape from a tank??

CO2 capture - rate of escape from a tank??

CO2 capture - rate of escape from a tank??

(OP)
I have an application in the brewing industry where CO2 is used to purge beer out of tanks. Once the liquid is all gone, the tanks are left full of CO2. When they open the hatches for cleaning, CO2 dumps out into the room and is a safety concern.

They have 2" valves at the bottoms of the tanks and vent valves that can allow air into the top of the tanks. I suggested that we might install some local exhaust on the 2" valves and open the vent valves to allow air into the top of the tanks.

The tanks are only under atmospheric pressure, but it is all CO2 which is heavier than air. Any idea how to calculate how much CO2 (in terms of CFM) will come out the valve? I don't have exact dimensions on the tanks, but let's say they are 10' in diameter and 40' tall.

Any ideas?

RE: CO2 capture - rate of escape from a tank??

BronYrAur,
Ithink you need to approach your question from the other end, " How much vacuum can you put on a 2" valve to get the CO2 out in a reasonable time?"
The other approach may be to drop a bigger hose from the top of the tank through the access hole and pull the CO2 out that way.
The only objection I can see to that would be maintaining cleanliness, but you said they are cleaning the tanks anyway.

http://www.plymovent.com/us/products/extraction_ar...

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

RE: CO2 capture - rate of escape from a tank??

The chemistry of beer fermentation is pretty well established. You should be able to calculate the rate of carbon dioxide released during this process. From micro breweries that I have seen the fermentation tanks have a continuous release of this gas via a hose discharging in a container of water, therefore the tank pressures are near atmospheric pressure and temperature. From that you should be able to figure the CFM of the gas itself since fermentation has a time element involved during which the sugar is transformed into alcohol.
Search the internet for further info.

RE: CO2 capture - rate of escape from a tank??

chicopee ,
He is trying to purge the tank, after it has been emptied using CO2 as a blow gas.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

RE: CO2 capture - rate of escape from a tank??

Assume the tank to have residual CO2 at atmospheric pressure and temperature. Volume of gas would be tank volume. Purging time would be based on volume flow thru inlet for fresh air and the above parameters.

RE: CO2 capture - rate of escape from a tank??

(OP)
Chicopee, That's the question I am asking. How do I determine the flow rate?

RE: CO2 capture - rate of escape from a tank??

BronYrAur,
The specific gravity of CO2 is 1.53 at 70 degrees F so you are dealing with a gas with a head pressure .53 greater than air.
Q scfm = (d^2/.0336 x [Delta P x ((P1 psig - Delta P) + 14.7)]^.5 / 1.024) x Cd
I do not know if this formula will work at differentials below one atmosphere.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

RE: CO2 capture - rate of escape from a tank??

You determine your own flow rate by allowing a certain amount of time to purge the tank.

RE: CO2 capture - rate of escape from a tank??

BronYrAur (Mechanical),
Since you are a heating and air guy, is there any way you can put an anemometer in the 2" outlet.
And measure the actual flow?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

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