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vickenlucy
27-09-2016, 07:36 AM
Hi
I have a mojonnier type carbocooler with flood type evaporator that has its surge drum just above the carbocooler. I use a Hansen 250psi relief valve on top of the surge drum for protection. In the past 5 months 3 of these valves have failed in the same fashion. They start leaking suddenly and keep open contionuously. Two things statrtle me. First, the pressure of the vessel never exceeds 200 psi, even with a hot sanitation carried out on the evaporator (at 65degC). Second, when we replace the bad relief valve, we find a lot of rust particled stuck between the valve and its seat.
What is the solution? The surge drum seems t be highly corroded. How to clean it? I have heard some suggestions about using water+oil, or white vinegar (I suppose this is acetic acid). Any suggestions? Will the location and orientation of the relief valve have any effect?

Magoo
27-09-2016, 08:56 AM
Check your pressure temperature of ammonia. 65'C sanitizing versus pressure relief valves, the relieve valve will slam open so quickly and damage springs and seals /seats.
Check design name plate attached to HX and surge vessels, should state max design pressure in degress C. generally + 50 C then select a relief valve under that figure, or the lowest of the two.
So 50' c design equals 285 psig, so the relief blows at 250psig., so drop the temperature of the sanitizing solution.

Josip
27-09-2016, 08:26 PM
Hi, vickenlucy :)

welcome to RE forums ... maybe you can introduce yourself here ... http://www.refrigeration-engineer.com/forums/forumdisplay.php?72-New-to-RE
to tell us more about yourself and your plant ... if you like ;)


Hi
I have a mojonnier type carbocooler with flood type evaporator that has its surge drum just above the carbocooler. I use a Hansen 250psi relief valve on top of the surge drum for protection. In the past 5 months 3 of these valves have failed in the same fashion. They start leaking suddenly and keep open contionuously. Two things statrtle me. First, the pressure of the vessel never exceeds 200 psi, even with a hot sanitation carried out on the evaporator (at 65degC). Second, when we replace the bad relief valve, we find a lot of rust particled stuck between the valve and its seat.
What is the solution? The surge drum seems t be highly corroded. How to clean it? I have heard some suggestions about using water+oil, or white vinegar (I suppose this is acetic acid). Any suggestions? Will the location and orientation of the relief valve have any effect?

Regarding your problem ...I am not sure if I catch it ... probably you have installed CIP (cleaning in place) system and for sure your evaporator should be empty when you start with CIP otherwise with so high temperature all liquid ammonia within evaporator will evaporate suddenly and you will have very high pressure what will open any relief valve ...

I'm not sure for your system (if installed), but for beer we usually have possibility to empty HE with hot gas and after that proceed with CIP (almost 80*C) ... less stress to HE ... and very clean process line ... and no activation of PSV or PRV ...

Not sure if you can reduce your cleaning temperature to reduce pressure on ammonia side ... question is how to keep hygiene required level at lower temperature (not an expert for that)

... but almost sure your surge drum is corroded internally (at what degree, you can check (if?) only with radiography. This usually happens when ammonia as refrigerant is not anhydrous i.e. refrigeration grade and can be dangerous if this situation persist longer time.

Water, within ammonia refrigeration system, we have to assume as a very dangerous liquid despite we cannot survive without;).

You can try somehow to wash your HE, but to be honest, I'm not sure what to suggest you ...

Another suggestion is to check your ammonia quality ... maybe you need to replace complete charge with new anhydrous ammonia ... but ... but ... if you empty your system you need to drain it completely then make a good vacuum to remove all water from your system and then recharge with refrigerant grade ammonia ... in any way this is not a simple task ...



Best regards, Josip :)

vickenlucy
10-10-2016, 06:29 AM
Thanks Josip and Magoo,
You may be right about the purity and dryness of the ammonia we are buying locally. We have decided to use a filter on the ammonia charge side (although it's too late) and we will probably do a thorough cleaning of all the vessets and pipes this winter.
As for the CIP temperature, we have created a 1/2" pipe link between the bottom of the evaporater(liquid side) and the outlet of the liquid SV. While doing hot sanitation on the carbocooler (hence the evaporator), the rise in pressure opens the spring loaded LSV and returns liquid back to the reciever, hence maintaining a pressure of less than 200psi within the evaporator. This is true even when the sanitation temperature is as high as 75degC. By the way all carbocooler parts including the evaporator and surge drum are pressure rated for over 250psi, and that is why we use safety relief valves of 250psi. I still don't see why the relief valve is blowing off, although I understand why it cannot shut off.