PDA

View Full Version : Oil Migration - R22 medium temp refrigeration system



lurioda
24-02-2004, 07:28 AM
We had a water chiller unit, originally consisting 2 circuits of 3 and 2 compressors, installed in direct parallel both suction and discharge line. The type of compressors were all 06EA299 from Carlyle. After years, and for some reasons, the system has been modified in preventing repetitive failure of compressors due to refrigerant floodback.

Now, each circuit in the system has their own evaporator, and the compressors were not installed parallel, but individual, and so the control. However we face new problem that not found in the book, where in circuit 1 (having 3 compressor, said no. 1, 2 and 3), if compr. 2 online and 1 and/or 3 off, the oil level in compr. 2 tends to rise above half of the sightglass, while no.1 dropped although this unit not running. But if compr. 1 running and no. 2 off, everything is OK and no indication of level increase in running unit.
After I checked compressor (all) internally, we found that the equalizing check valve lockbolt still there. Can we dismantle that check valve to prevent that problem? We have reviewed all the piping system, and the most probable source of loosing oil in compressor 1 was due to that "little" bolt, since there ia no other way that oil will migrate to others.
For your info, the suction line of those three compressors (in circuit 1) take from same manifold. We had suction accumulator out of evap and individual oil separators on the discharge side.
Therefore thru this forum I am asking your advice of my problems
Regards,
Lukito - Indonesia

chemi-cool
25-02-2004, 04:22 PM
Now, each circuit in the system has their own evaporator, and the compressors were not installed parallel, but individual

so how come, the oil return is still in paralell??


chemi :)

lurioda
26-02-2004, 07:38 AM
Chemi,
Just to clarify, the shared condensor inlet were came from the outlet of the individual oil separator of the compressor and we've checked in that line was almost "free" from oil mist. No oil line was shared directly.
What I am going to do is trying to provide a sharing line (3/8" copper tubing c/w valves) of the oil side, probably at the botom of the motor casing as Carlyle recommended as stated on page 23 of Carlyle Application Guide. What is the opinion?

For information we also had an a/c chiller unit, utilized 3 compressors with 1 evaporator and 1 condensor but the installation were treated as individual. They have individual oil separator, no oil reservoir, and the compressor type were also Carlyle 06EA (or 06EF before) and up to date there was alomost no problem at all. I wonder why? Is it because a different application or any other reason that I donot know of?

Please, please help me on this, ok.

Thanks
Lukito

chemi-cool
26-02-2004, 03:00 PM
hi lukito,

please try and post a diagram showing the pipe work on the unit after the change was made.

it will be easier for other members and myself to think and come with a solution for the problem.


chemi

shogun7
06-03-2004, 12:58 AM
.Lukito:

“We had suction accumulator out of evap and individual oil separators on the discharge side.”
After some consideration with this problem I was wondering if it was possible to get condensation of the refrigerant in the separator if the separator is installed in a cooler location then the condenser, in which case the liquid could boil off in the condenser and condense in the separator. In order to eliminate the possibility of liquid refrigerant draining from the oil separator into the compressor crankcase during the off cycle the oil drain line from the separator should be connected to the suction inlet of the compressor, rather then to the crankcase and the line should be equipped with a selenoidvalve, a sight glass, a hand expansion valve and a manual ball valve. AS you can see if refrigerant has accumulated in compressor #1 when #2 is running you may be boiling off in #1 and carrying oil with it!
Roger

lurioda
08-03-2004, 09:36 AM
Dear All,

Sorry for the long delay; anyway thanks for the info folks. And as per chemi-cool advice I've attached the diagram of the R22 and oil line of the system (in Excel). We do hope that we can have a best solution for our problem here.
By the way we intended to use an individual oil separator due to long before we made the last modification, the system had only one evaporator (with two R22 inlet tubes but in one shell) and never had problem. Then due to "other reason" I do not know" at that time, the people replaced this one evap to become two separate evaps, plus adding main oil separator for each circuit. Then the problem started after few months in operations, and once I've joined with the company, I try to study and give recommendation. However, due to management had turned down my proposal to replace the evap back to original, then to compensate and minimize the problem, I then come up with that solution. The refrigerant flooding had gone, but oil migration still exist, although not all as previously mentioned. Hoping that some of you can help us on this matter, once again thanks for your input. - lukito

Peter_1
08-03-2004, 04:40 PM
I don't see an oil reservoir in your drawing (took you some time to draw it).

You are using high pressure oil level controllers (electrically controlled) i presume. (Henry, Sporlan,???)

Are the oil separators coalescent types?

Do you have flow switches on each evaporator?
How do you manage it that both evaporators have enough water supply? I think when one becomes dirt --> DP rises and flow decreases --> one possible cause of liquid slugging.

Why not install a waterpump on each evaporator?


My opinion is that you should modify the oil circuit.
All the oil departures of each separator to an oil tank, fit an ERD, connect to LP and install an oil header in front of the compressor. Perhaps but not necessarily another type of oil float.

I think problems will be gone then.

What was the reason for the original floodback?
It was in my opinion better to solve the cause for that specific problem and you shouldn't have to modify the whole system.

Was there original no pressure egalisation line above the oil level?


We had a similar/comparable problem with a Profroid rack in a poultry slaughtery.

Installed then 4 different oil level controllers.

Very long story, in 2 years, 5 broken compressors, Profroid themselves intervented many times with 3 different technicians including the head of the R&D department, experts from Marseille and Paris came, but no one could point the correct cause.

Thereafter a judicial expertise (which is just finished after more then a year) and now ... a judicial fight between installer and client and lawyers for some years I think (Initial costs +/- 100.000 euro and +/- 200.000 damage costs all sorts, total +/- 300.00 euro!!)

Conclusion of the expert: "Installation can't be used for what client has calculated/bought it for: blast freezing" So,.. remove the bloody thing to the trash.

Happily not with me.

Gary
08-03-2004, 05:59 PM
It seems to me that if the oil level drops in #1 when it is not running, then there must be liquid refrigerant in the oil, which would mean that it was flooding back while running.

But if that were the case, then #1 oil level would drop when only #3 is running.

I suspect there is floodback to the compressor(s). What are the superheats at the compressor inlets when running?

What kind of oil are you using?

Are the compressors staged according to pressures?

What is the staging sequence?

Peter_1
08-03-2004, 07:26 PM
Or you have a leaking oil float on 1.

Perhaps you should try to install a SV in the oil feed which should be energized together with the compressor.

Or an NRV in the oil feed. Then you're sure this float is no leaking.

Try perhaps interchanging the floats and look if the problem remains or has switched with the oilfloats.

Gary
09-03-2004, 01:27 AM
I don't see any floats in the diagram. Am I missing something?

chemi-cool
09-03-2004, 04:38 PM
hi lukito.

thanks for the diagram.

if you look cerfully, the answer is there.

if three compressors are mounted in paralell, i.e. discharge lines and suction lines are connected, so is the oil lines should be.

one large oil separator should be installd, oil reservoir equipped with a reservoir pressure valve, this special valve maintain the pressure 5psi above crankcase pressure and willensure good flow.
on the discharge of each compressor, you will need to add a NRV.

oil level regulators should be connected to the compressors and an oil strainer before the OLR, before that an SV controlled by the compressors contactors and a 20s timer. this will ensure that you will not have excessive oil in the crankcase.

I suggest you read all about it at http://www.henrytech.com/techtips_pdfs/HT-TT6.pdf.

the SV before the strainer is not there but is important.

the reservoir will be above compressor level to keep the pipes full at all times.

any more questions?
you know how to find me.

chemi