Lager tank cooling
I am a private contractor working at a local micro brewery to implement a new Brew kettle and 7 new Lager / Ferment tanks. I built the controls and wired the complete system as well as the PLC program for controlling it.
We are using a Glycol solution for cooling and recently ran into an issue where we are getting a huge temperature difference between the top of the tank and the bottom. These tanks have separate dimple wall baffles for the top and bottom. We feed the coolant into the bottom sides of the baffles and exit at the top side where the control valve is located. One valve per tank controlling 2 separate baffles. We have a similar system in place for 15 years and it does not do the same thing as this new system.
The beer is kept at 36 degrees and the measurement is being collected by a single thermocouple that is located even with the access door. When the tank is emptied, the temperature will drop to 24 degrees. There is no ice in the tank and the freezing appears to be isolated to the top baffle. The tank is never full, maybe 180 barrels or ¾ full.
I realize there are many technical factors involved with the system but I don't believe it is a control issue (electical valve and temperature control) as much as it may be mechanical.
A point in a coupel directions would be helpful.
First thought is: are the separate glycol jackets plumbed in series or parallel? If parallel you could have different flow rates to the separate jackets and that could explain it. I have smaller tanks and the multiple jackets are plumbed in series, or they have individual valves for throttling if plumbed parallel. I had some larger tanks that had multiple ports for thermoprobes, and during ferment there was often a wide temperature variation. Another point regarding lagers is they love gentle cooling, at 2-3 deg/day, and even in primary fermentation we would throttle the flow rate back to about 1/2 so as not to shock the lagers. I hope this helps.
Beer becomes less dense as it approaches freezing. The crossover point is 39F (4C) degrees. You don't want your top jackets on after that point, or you will freeze the top of the tank.
Last edited by dberg; 09-16-2011 at 05:25 AM.
Beer reaches its maximum density at 36.5F. When beer is below that point the equilibrium in density makes the correct convection currents more difficult to achieve in a tank. If you are only cooling at the bottom jacket, you should be able to get a convection current up through the middle of the tank and down the sides to the conical. If you are cooling at the top, the beer will not circulate and you risk freezing it. Try to route the glycol lines so you can isolate the glycol to the conical when at low temps.
Thank you all for the information. I now have something to check out.
We do have valves to throttle the separate jackets.
Great web site....