Unitank Carbonation Problems

[Mthoreson]

Hello brewers,

We are a relatively new brewery (7th month of operation) and we are now locally distributing kegs to bars and restaurants. We have quickly realized the demand of our product is causing us to make some necessary adjustments to our brewing operation. We run a 10 BBL system with 6 cold storage 10BBL brite tanks, and 3, 10BBL conical fermentation vessels. Our fermentation vessels are classified as unitanks, double jacketed and glycol cooled, equipped with a PRV rated to 15 psi (tanks are tested to 30psi) Our goal is to ferment and force carbonate our beer in the same vessel. Once conditioning has completed and we are at 0-0.5c for temp in the tank, we increase the head pressure to roughly 5psi on the tanks pressure gauge. We then start flowing c02, slowly, through the carbstone and let the tank pressure slowly climb, overnight, until the vessel has hit equilibrium. In our brite tanks, we haven't ran into any issues when doing it this way, and are pleased with the end result. What we are finding when we do this in the unitanks is, overnight, the tank pressure rises to about 8.5psi and anything exceeding that 8.5psi on the tanks pressure gauge causes the PRV on top of the tank to hiss and slowly bleed off co2. We made sure all of the fittings and clamps are as tight as humanly possible, and even pressure tested our gauges to make sure they were accurate.

When we take a sample off the tanks the next morning, the beer is carbonated to our liking (or within an acceptable range), but our 700lb co2 tank has a thick frost ring around the middle of it and we are under the impression that we are wasting co2. We are completely at a loss as to why the Pressure Release Valve (tested to 15psi) is not holding pressure above 8.5psi. We even replaced the PRV with a brand new one, before we tried a second time, and the same thing happened.

Does anyone have any idea why this would be happening, or better yet, how to prevent or fix the issue? Any advice or solutions would be much appreciated!


Mike Thoreson
Chief Brewer
Prairie Brothers Brewing Company, Fargo ND

[UnFermentable]

Your pressure gauges are not calibrated correctly or your PRV's are not set to 15psi. That is the only reason you would have the PRV crack at a reading of 8.5 psi. Try a different (calibrated) gauge, if you experience the same issues, get a PRV from a different manufacturer.

Gauges do get out of calibration, so it would not be too surprising if this is your issue. PRV's usually crack right at 1 bar ~ 14.5psi. They will reset a little below that. If you still have issues, use a burst disk on top of a butterfly and know that your vessel is sealed completely. You will still need a properly calibrated gauge.

If you trust your brite tank PRV's are accurately holding the pressure, then swap one for a fermenter and see if it still holds true. If it leaks at 8.5 then you have a bad gauge. If it hold fine, then you have a bad PRV (now on your brite). You can also try swapping the gauges from the brite and PRV to narrow down the gauge. If the brite starts leaking at 8.5 with the ferm gauge, then you've isolated the issue (gauge).

Bottom line, if you are leaking out of the PRV at all, you are wasting some gas. Ice around your co2 tank is fine, but can be an indication of a high rate of co2 usage. If you aren't leaking out the gas, then don't worry too much about the ice. If you are leaking, that is the primary concern.

Gas moving from a high pressure to a low pressure will remove heat (get cold), so it is reasonable. If you move the gas too quickly, you will get the frost. Too much frost and too quick of a draw will eventually freeze the liquid inside the tank. At this point you will create dry ice and your pressure/fill gauge will register empty. If you watch dry ice, it converts to gas much slower than liquid. This will slow your draw flow considerably (almost stop). Warm up the tank (and/or stop the draw) for a while and the pressure will rise back up once the solid liquefies again.

[gitchegumee]

You should be setting your head pressure to 1 bar BEFORE you carbonate. And you need to calibrate your PRVs. If they leak at 8.5psi, then you have bad valves. If they leak at 1 bar, but your pressure gauge reads 8.5psi, then you have a bad gauge. Just like Unfermentable says. Some cheap equipment comes with brass tube pressure gauges that are garbage. Get stainless tube gauges. Do NOT put a rupture disk on top of a butterfly valve. It is illegal to have an isolation device (such as a butterfly valve) before your primary safety relief device. Reliefs must be in direct contact with pressure vessel and cannot be isolated.

[Mthoreson]

Thank you for the feedback, we have fixed the problem. Our gauges were the issue. I purchased new gauges for the tanks and tested them to find out our PRVs work great, our tank pressure was much higher than the original gauges were telling us.

Back to the grind! Thanks again.


Mike Thoreson
Chief Brewer
Prairie Brothers Brewing Company, Fargo ND

[olie]

How does one test pressure gauges/PRVs? (I have similar symptoms; am trying to isolate.)

[AGB]

Hello Lads, I know this is a few years old now, but I have three unitanks and two BBTs. The brites are full and I have a NEIPA in a uni. I figure that should be perfect to carb in a unitank. But, I forgot to insert a stone before filling the tank. I've read this thread and I watched a guy on Youtube carbonate with a stone via the racking arm. I have a pretty big stone and I had to add a site glass and a spool at each end of the site glass. I've tried multiple methods and once the CO2 starts to flow through the stone, it pressurizes the racking arm and blows most of the beer out which results in a lot of gurgling and splashing inside the tank. So, I guess I'm going to just let it hit head pressure of 13psi and then let it go a while longer. I'm also using a spunding valve so that I don't pop the PRV.

If anyone reading this has a suggestion please send it!

[gitchegumee]

Carbonate with a loop coming from the side of your tank and into the bottom of your tank. Insert your carbonation stone in a tee run as close to the start of the loop as you can. Certainly before your pump. You can carbonate in a few hours with ease this way.