R-507 ice rink oil problems

[davidlleida]

Hi,
Here I give you a thread to think about oil recovery.
We made a retrofitting of an old R22 ice rink working with high pressure pump from discharge.
The compressors (2 units 88.8 from York (317,6 m3/h dating 1985) remain the same.
The old oil separators were substituted by a new Henry S-5414 (High efficiency helicoidal system).
we made a pumping recirculation system with a Witt pump and receiver.
This receiver has an automatic oil recovery system that works (2 minutes every hour).
The rest of the installation is almost the same.
The problem is the oil recovery.
1,.) Henry says that the oil separator is well sized and that we don't have to oversize.
2.-) Looking the old separators I think the new one is much better.
3.-) But the compressors stop because the need oil, and whe we stop the system, there is not big amount of oil in the oil recovery line coming from separator...
4.-) The system has 4000 kg of R-507 and 10.000 mts of pipes
The question is: According to that amount of refrigerant and pipes, wich would the correct charge of oil in the system???
Actually the system has about 200 Litres of Suniso SL 32about 5%
Is about 5% of oil in the whole system enough???
The filters have been substituted, and the old oil also.
I would apreciate any suggestions
Do I have to check for oil traps??
Or the problem is the oil separator??
Do I have to install a coallescent separator???
Or maybe is the amount of oil in the system???

[Sandro Baptista]

David,

How do you have done the automatic recovery system from the liquid separator to the compressors? A schematic drawing would be appreciated.

Is the oil return line from the compressors to the oils separators is warm or cold?

[HVACRsaurus]

Hi,

"This receiver has an automatic oil recovery system that works (2 minutes every hour)."

Most of the flooded ***** systems that I've worked on run the oil recovery all the time that the compressor is running, usually from multiple points on the accumulator.

[Sandro Baptista]

Normally for R507 as the liquid is "totally" miscible with the liquid phase I get a % of pumped liquid and get passed it through the heat exchanger/oil rectifier and is always running during the compressor is ON.

[davidlleida]

Thank you so much for your help, Sandro Baptista, HVAC Saurus, we will try this as soon as possible!

[davidlleida]

Hi Sandro Baptista, here you have the drawing

[Sandro Baptista]

hmm...according with the connections of the Intercambiador 65 kW it seems this one is not purposed to oil rectifier. The plant are using a system used for R22 with mineral oil where the oil/liquid is get it to the upper part of the liquid level where oil tends to concentrate.

Can you also send me the part where the compressor also appears?

[davidlleida]

Hi Sandro I don't knoe if i inderstand..."the Intercambiador 65 kW it seems this one is not purposed to oil rectifier."
The suction line from the heat exchanger =(intercambiador) arrives to the Witt separator where we already have an oil recovery system...
So, don't need to make any additional recovery there.

[Sandro Baptista]

hmm...according with the connections of the Intercambiador 65 kW it seems this one is not purposed to oil rectifier. The plant are using a system used for R22 with mineral oil where the oil/liquid is get it to the upper part of the liquid level where oil tends to concentrate.

Can you also send me the part where the compressor also appears?

Hi Sandro I don't knoe if i inderstand..."the Intercambiador 65 kW it seems this one is not purposed to oil rectifier."
The suction line from the heat exchanger =(intercambiador) arrives to the Witt separator where we already have an oil recovery system...
So, don't need to make any additional recovery there.

Yes I understand that. The recovery system is the one I have marked.

However as I said previously for HFCs my opinion is this is not the best method for oil recovery but rather with a an heat exchanger, picking the oil from the main liquid.

[Sandro Baptista]

I was thinking better and I really don't see the reason for not working if you ensure liquid level at the blow oil/liquid picking point. However I would ensure that the recovery system/solenoid valve would be always ON just to be sure.

[davidlleida]

At this moment we recovery the oil 45 minuts for every hour of work of the compressors. We recently increased this time, at it seems to work better.
We will wait some time to check that the system is really recovering the oil.
We also have a heat exchanger on the right of the drawing.

Thank you so much for your help.

At the start up of the system, the relation (time of recovery/compressor working time) was lower, because we wanted to recovery only the oil, we did'nt wan't any risk of taking some liquid to the compressors.

[Sandro Baptista]

At the start up of the system, the relation (time of recovery/compressor working time) was lower, because we
wanted to recovery only the oil, we did'nt wan't any risk of taking some liquid to the compressors.

With POE oil and HFCs the oil is mixed with the liquid refrigerant...almost no oil layer is created so even you wait to long no upper oil layer will be created.
ADVICE: Keep the system always running readjust if necessary the needle valves so the heat exchanger can boils all the liquid that comes with the oil. You will see improvements.

Curiosity: That heat exchanger exchanges heat with the discharge gas?

[Sandro Baptista]

The important is that all oil that run away to the plant can be recovery at the same rate so no lack of oil at the compressors.

[davidlleida]

Hi sandro,
The heat exchanger takes the heat from the discharge line, and always runs with the compressors working.

[Sandro Baptista]

Do you all the oil back to the compressors. Attention: If you have charge with many times the compressors it can happen that the compressors crankcase flood with oil.

[Camille]

David,

R-507 is an HFC (hydrofluorocarbon), you normally need to use a polyol ester refrigerant oil. Mineral oils are not miscible with HFC refrigerants, Polyol ester oils are soluble in the R-507 or another word very miscible.

If am reading right ,the rink refrigeration was R22 system and retrofited to R507 , the floor was R22 direct expansion with steel pipes in the floor converted to pumped liquid recirculated R507, I am sure the homework was done to clean up the mineral oil residue from the system also the compressor for elastomer compatability , gaskets o'rings etc...
You have 200 litres of oil in the system a lot almost a drum and half, the downfall of pumping liquid recirculated R507 into the floor even you are gaining with high efficiency system no major temperature penalty for a direct system , you will loose the efficiency in time as the oil also circulate through the floor and in time will adhere to the inner steel wall of the pipe and hinder the efficiency of the system, and oil will be added for sure...., an indirect system is preferred.
Anyway this is not the topic , the topic is recovering the oil from the re-circulated vessel.
your approach by installing skimmers on different levels of the re-circulator is a fine one, even an additional one at the pump drop leg or float column will help.
Compressors will tolerate little bid of oil and refrigerant slugs in very small quantities .
I have attached an idea for future project that you can utilize using the new technology of refrigerant oil injector, that will be turned on when the machines are running of course through a programmable PLC for certain minutes during the day, needle valve will regulate the amount the flow, the hot high pressure gas will inject the oil while evaporating the refrigerant.
A subcooler can be added , superheat the oil line or heat trace to ensure no liquid carry over, suction branch from the manifolds to each compressor must be piped as per standard practices.

Regards

Camille Zabbal

[davidlleida]

Hi Camille,
Thank you for your comments.
I agree with you concerning that an indirect sytem has some great advantages.
I didn't hear anything about oil injectors, could you give me any reference or brand name?

I really apreciate your drawings also
Best regards,
David

[Sandro Baptista]

Davidlleida,

How is behaving the plant. Have you already recovery the extra oil you have added?

If it is working fine after several days I think it will keep fine.

BR

[davidlleida]

Hi Sandro, at this moment the plant has been working fine, the oil level compressors is correct, but:
The oil separator doesn't make any recovery of oil.
We have an accumulator after the separator wich is empty of oil
The oil recovery line after the separator is allways cold, so there is not recovery of oil in the pipe.
When we open the separator and we clean it, the separator is allways empty of oil, so the separator is not working correctly.
I have asked Henry technicians and they told me that:
1.-) separator is sized correctly.
2.-) The ony possible problem could be that the float valve system is blocked.
But, anyway the separator is not making any separation of oil because it is allways empty.

At this moment the plant is working, but there is too much risk if the separator is not workingm because even if i recover some oil from the suction side, I can have a stop of the compressor.

We will change the float valve, but sincerely, I'm not sure this is the solution...

I hop giving you goog news ASAP.

David

[mad fridgie]

Regardless of the sizing, some oil removal in the seporator should occur, you have indicated that the oil sep is always dry. You also indicated that the oil return line is always cold.
Could it be that infact the float valve is not blocked but the opposite is not closing. You are then feeding straight refrigerant into the sump, it could be that the vapour maybe actually condensing and you are feeding liquid into the sump washing away the oil.

[Sandro Baptista]

Hi Sandro, at this moment the plant has been working fine, the oil level compressors is correct, but:
The oil separator doesn't make any recovery of oil.
We have an accumulator after the separator wich is empty of oil
The oil recovery line after the separator is allways cold, so there is not recovery of oil in the pipe.
When we open the separator and we clean it, the separator is allways empty of oil, so the separator is not working correctly.
I have asked Henry technicians and they told me that:
1.-) separator is sized correctly.
2.-) The ony possible problem could be that the float valve system is blocked.
But, anyway the separator is not making any separation of oil because it is allways empty.

At this moment the plant is working, but there is too much risk if the separator is not workingm because even if i recover some oil from the suction side, I can have a stop of the compressor.

We will change the float valve, but sincerely, I'm not sure this is the solution...

I hop giving you goog news ASAP.

David

David,

1) Regardless if the oil separator is working fine or not we are sure that the rate of oil throw away from the comps is the same that is recovery since the oil level is correct.

2) If liquid slug is happening it possible some "strange" things happen. When you use R507 the liquid separator losses efficiency for the same evaporating temperature, since the vapor have more density so the liquid drops can't fall easily. Also as the discharge temperatures are smaller the oil/liquid evaporated one heat exchanger can still have liquid drops that go to the compressor, despite the mass flow discharge R507 is bigger than with R22.

3) For now, before changing anything I would close for a few hours the oil return valve from the oil separators, control the oil level if all is the same and then open the valves to see if the oil accumulator fills a bit.

[ccarlos196]

The plant are using a system used for R22 with mineral oil where the oil/liquid is get it to the upper part of the liquid level where oil tends to concentrate.
_________________

[davidlleida]

Hi Sandro, actually, the compressors begin have to oil recovery problems at about two weeks of work.
We have substituted the float valve kit of the separator, but it's not the solution.
We are thinking to add a new colalescent improved oil separator behind the first one.

[Sandro Baptista]

Hi Sandro, actually, the compressors begin have to oil recovery problems at about two weeks of work.
We have substituted the float valve kit of the separator, but it's not the solution.
We are thinking to add a new colalescent improved oil separator behind the first one.

hmmm...is my previous point 2) is correct or it is another cause? "If liquid slug is happening it possible some "strange" things happen. When you use R507 the liquid separator losses efficiency for the same evaporating temperature, since the vapor have more density so the liquid drops can't fall easily. Also as the discharge temperatures are smaller the oil/liquid evaporated one heat exchanger can still have liquid drops that go to the compressor, despite the mass flow discharge R507 is bigger than with R22."

Does the oil recovery system "stop" working?? Any malfunction on the oil rectifier/valves?

[davidlleida]

Actually the oil recovery system stops 5 minutes of every hour of work of the compressor.
What do you mean with: "If liquid slug is happening it possible some "strange" things happen??

[Sandro Baptista]

If much liquid go to the compressors the hot oil on the crankcase will intensive boiling the liquid and the oil will easily be carry out of the compressors. Also the wear will increase the clearance of the components (cylinder liners, piston rings) will help the run out of the oil.

[davidlleida]

Hi Sandro ,
By the recovery oil line I'm sure that there's no refrigerant liquid coming into the compressors.

[Magoo]

Hi.
with original system on R22 the oil is not miscable so would float on top of refrigerant, thats why they had three scavange pick up lines around liquid control level. R507 is similar to R404A. Either lift control level or/and use the lowest scavange pick up line to regenerate mixture through the recovery system.

[Sandro Baptista]

Hi Sandro ,
By the recovery oil line I'm sure that there's no refrigerant liquid coming into the compressors.

It could be the liquid separator small for R507. See an previously email:

"When you use R507 the liquid separator losses efficiency for the same evaporating temperature, since the vapor have more density so the liquid drops can't fall easily."

[Sandro Baptista]

See what happen when you put one of the compressor at 50% so reducing the vapor flow at the liquid separator. Then watch the oil recovery behave at the compressor which is at 100% during about 1 or 2 hours.