Can R507 work with overfeeed systems?

[VagAn]

As simple as the topis :)
Is there anyway to make possible a liquid overfeeed system to work properly with R507? the system was designed to use R22 but due to law restrictions no R22 can be used anymore.

[Sandro Baptista]

Yes you can. It is azeotropic so no problem.
We also have successfully with R404A (near azeotropic) many years ago on a big fish vessel.

[VagAn]

thank you very much for the quick reply. some people here said that it is impobible. is there any chance of oil foaming due to R507? We suspect that we have this problem due to liquid suction only and basicly because the previous technisian has added 230 litres of oil instead of 60 :P . Any suggestions for this problem? Have to note that emptying the whole circuit is not an option i'm afraid.

[Sandro Baptista]

For piston compressors to much oil can in fact to lead to foaming.
Are piston compressor that the plant work with? Why don't you get out some oil? What's the problem of that?

[VagAn]

yes they pistyon sompressors. we tryto get it out. from what i have read we try to take it out by taking it from the liquid surface of the vessel as i think we should in this kind of plant but another engineer suggested to drain it from the bottom of the vessel wich i think is not good since the vessel has no oil pot. The problem is that it probably circulates in the whole plant and we have to take out too much oil and we have to firstly stop the oil from recirculating again. we think that we have to pay more attention to the suction line so that we don't have any liquid in the suction to stop the recirculation and protect the compressors. And the biggest problem is that the previous engineer obviously has set all of the valves in the system by just lucky guesses....

[Sandro Baptista]

The oil POE have very miscibility with R507.

The good way is to keep the oil with low concentrations on liquid separator by an oil rectifier. For the R22 plant didn't exist one?!?

[VagAn]

What do you mean oil rectifier? we have installed oil separators in every compressor and linked it tho the oil level regulators via an oil receiver. but we try to take out the excess oil which i think is quite dificult just by waitng the oil to pass through suction.

[Quality]

Oil Rectifier
Oil pot
Oil pig
Sludge pot
Knock out pot
Separator

I think that I am on the correct wave length it can be called many names but the function is the same. it collects oil that needs to be drained periodically

[cricri]

Hi,
last year we have retrofited a medium plant (1 x WRV204 + 1 x RC9311 + 1xSMC104S) from R22 to R507 at -42/+35°C. no problem with oil return using POE oil. As you are probably using compound (or booster) pistons compressors, you must get about 20°K suction superheat. if not, also with R404, you can get liquid condensates during compression. then pistons rings can be damaged causing oil consumption.
before trying to recover the oil it's better to prevent oil loss. give us some descriptions of your system, easier to help you. type of: compressors,
interstage cooling ?
oil rectifier

[VagAn]

We have stopped oil circulation :) now compressors work as they should without lossing any oil. i'll try to find the exact type of commpresors tommorow. they are 2 linden wiith 35hp and one bitzer 30 hp working now. Unfortunately the linden tags were removed from the compressors but i'll try to find them.

[Sandro Baptista]

We have stopped oil circulation :) now compressors work as they should without lossing any oil.

Without loosing any oil? I would say that is impossible...

[VagAn]

Without loosing any oil? I would say that is impossible...

Just meaning oil not going to evaporators. Oil is being held in oil separators and then returned to the compressors. compressors not stopping to low oil levels anymore. And now we are mostly concerned on how to take out the excess oil.

P.S. Sorrry for my english especially in some technical terms

[Sandro Baptista]

About you english no problem the important is that we understand each other :)

About oil coming back to the compressors on a overfeed system you can only do it with an oil rectifier which is an heat exchanger where a mix of oil and liquid refrigerant passes through and this side of the heat exchanger is directly connected to the compressor suction. The liquid refrigerant will boil and carry on the oil that is mixed with the refrigerant.

Maybe the compressors haven't stop by low level because you have excess of oil or the plant haven't run time enough to the oil escape to the surge drum...it's a question of time.

After you have installed an oil rectifier (you already don't have one installed on the ancient R22 plant and working properly) you can taking the excess of oil periodically just purging the oil from the compressor as the returning oils cause the oil level up.

By the way the plant doesn't have an oil receiver to accumulate the excess of oil and doesn't your compressor have oil level regulators? with this equipment the excess of oil would go to the oil receiver.