Oil Carryover

[jbmorris]

I am NOT a refrigeration expert and I only have a basic understanding of refrigeration operation, but I need some help in fixing a problem.

I work at a chemical plant in China which has a newly commissioned Frick 2-stage system which has 2 reliability issues: Moisture in the system and oil carryover from the Booster Compressor.

The system data:
- ***** R507 with Frick 13 oil
- Booster suction pressure (Vac) -.15barG (-4.43"mg)
- Booster Discharge Pressure 2.1 barG (30.87 psig) Booster oil supply temperature 50Deg C (122 Deg F)
- Booster Discharge Temperature 60 Deg C
- High Stage Suction Pressure 1.85 barG (26.83 psig)

The oil separator has a 3 stage demister/coalescer but I have not seen the drawings of these yet...only relying on what I was told by our Chinese process engineer.

I have a couple of concerns I'd like opinions on:
1. How easily does the ***** disengage from the oil?
- At 45 Deg C, Frick 13 has density of 938.9 kg/m3 and specific gravity of 0.939
- at 70 Deg C R507 has specific gravity of 1.07

2. would running a higher oil temperature help?

3. We are contemplating raising our Booster suction pressure to slightly positive. What effects will this have on oil carryover and system operation.
- Right now our chillers on Booster suction operate at about -55 Deg C
- Our chillers on High stage suction operate at -16 Deg C

4. Is dP across our coalescers too high? Is it possible our biggest issue is gas velocity?

I'd appreciate your expert help on this problem.

[RANGER1]

tjbmorris


I am NOT a refrigeration expert and I only have a basic understanding of refrigeration operation, but I need some help in fixing a problem.

I work at a chemical plant in China which has a newly commissioned Frick 2-stage system which has 2 reliability issues: Moisture in the system and oil carryover from the Booster Compressor.

The system data:
- ***** R507 with Frick 13 oil

The Frick oil I don't know ,but someone will


- Booster suction pressure (Vac) -.15barG (-4.43"mg)
- Booster Discharge Pressure 2.1 barG (30.87 psig) Booster oil supply temperature 50Deg C (122 Deg F)
- Booster Discharge Temperature 60 Deg C
- High Stage Suction Pressure 1.85 barG (26.83 psig)

The oil separator has a 3 stage demister/coalescer but I have not seen the drawings of these yet...only relying on what I was told by our Chinese process engineer.

I have a couple of concerns I'd like opinions on:
1. How easily does the ***** disengage from the oil?
- At 45 Deg C, Frick 13 has density of 938.9 kg/m3 and specific gravity of 0.939
- at 70 Deg C R507 has specific gravity of 1.07

Usually pretty good if oil temp is 15deg C above saturated discharge temp

2. would running a higher oil temperature help

You could run it a bit higher but doubt it will reduce oil
carryover


3. We are contemplating raising our Booster suction pressure to slightly positive. What effects will this have on oil carryover and system operation.
- Right now our chillers on Booster suction operate at about -55 Deg C
- Our chillers on High stage suction operate at -16 Deg C

This could increase oil carryover , due to mass flow rate increasing through oil seperator & coalescers.




4. Is dP across our coalescers too high? Is it possible our biggest issue is gas velocity?
What is your dp acrross coalescers?


I'd appreciate your expert help on this problem.



Has anyone checked the basics like coalescer securuty in oil seperator?
Sometimes they can be dislodged or work loose in transport & handling.
Also oil return from coalescer compartment should really be very small , but can tell a story.
Basically confirm its working no matter what.

What problems is moisture causing?

Is there any oil foaming in booster compressor oil seperator?

What type of oil cooling do you have ?
-water cooled
-thermosyphon
-liquid injection

[TXiceman]

If it is a newly commissioned plant, I would presume you are still under warranty. have your contractor back to look over the problem before you go making adjustments.

Ken

[jbmorris]

Thanks guys. Our vendor support here in China has been very weak. We have struggled through several start-up issues with little assistance from them. But we continue to ask questions and try to get believable responses.

We shut down in April, and one of the things we will be doing is opening up the oil separator to take a look at its integrity. We hope there's an obvious problem.

We cool our oil with process water. One of the things that interested me about reading your posts from other threads was in raising oil temperature. In our compressor there is slight evidence that foaming could be an issue...If our oil level gets a little low, our oil pump will cavitate because the ***** hasn't had adequate time to disengage from the oil. We've asked York China about running this oil temperature up a little. Currently on our Booster compressor its about 50 Deg C. We haven't received a response yet.

The other thing that concerns me is the dP across our separator, 4 psig with only 25% slide valve opening. Does this seem a little high to you guys? Once our plant gets to full rate, this loading will increase and dP will increase.

These compressors were oversized by our design engineers, so one of the things I'd like to eventually do is raise suction pressure of the Booster compressor to slightly positive so that moisture won't be drawn into the system if the seal begins leaking. This, as I've read, will increase mass flow and increase the potential for more oil carryover, so I'll wait on this one.

Moisture has cause level control problems in our evaporators due to freezing.

[mbc]

dear sir

could you mail me your drawing with compressor type you have, might I help you .
I am family with there design for chemical factory (( chlorine --cl2)) factories .
might one of your return valve is close (oil separator to compressor)
or your floater valve is clasped or fitter of oil return on floater valve is blocked
gholbehan@yahoo.com

[RANGER1]

jbmorris,
Sounds like a poorly prepared plant if it has water in it but it does happen .

Maybe if evaporator is pumped out of refrigerant & warmed up the moisture.water could be blown out of low points on a shutdown period, then purged with dry nitrogen.
If you have moisture/icing in evaporator then would imagine problems with oil return system which should return dry clean oil .

Are you experiencing compressor oil filter issues , such as high dp etc?

I don't know much about Frick oil but from other posts on this site it is fully synthetic ,so would imagine oil temp can be increased to a least 55deg C.
Being a booster would have thought it has a fair temp difference against saturated discharge temp.

Is it possible that you may be experiencing periodic flood backs( liquid return ) to booster compressor washing oil out?

Coalescer filter pressure drop does sound to high so it may indicate that they havn't shifted inside seperators.
This is probably bad news in a way .

[jbmorris]

Thanks Ranger. Yes it is suspected the moisture came from poor start-up practice. We are planning on doing evacuation and drying in April shutdown.

Rookie question...what is flood back and how does this cause oil carryover?

We have had to change oil filters a few times.

With my limited knowledge, I also think dP is high which makes me wonder if velocity across the coalescer is making the inefficient. This is especially surprising since everything else is oversized on this unit and its only at 25% loading.

[jbmorris]

Thanks mbc. I will see what I can do about drawing. I don't think there are any IP protection issues with this package.

[Magoo]

who in their right mind would install a two stage R507 system, open compressor drives added.
The installers would be laughing all the way to the bank, and probably change there phone number as well.
Is there a possibility that it can be converted to ammonia?.

[jbmorris]

Magoo. Why is this installation such a poor decision?

[RANGER1]

jbmorris,
A floodback is where liquid refrigerant enters compressor suction line. This is not meant to happen , but thought its a possibility if you have level control issuesin evaporator.
This liquid may cause oil to foam or washout & then carryover into its discharge line.
On applications with ***** it acts as a cleaner & it scours everything clean.
This can cause a lot of oil filter blockages & possibly coalescers if your unlucky.
Steel pipe applications are renound for it if rusty or grinding dust enters pipework.

I think mbc is refering to oil return from coalescer compartment.
Any oil that passes through coalescers can be returned to compressor suction.
They can be either a float valve or orifice. Sometimes they have a sight glass so you can see whats going on.
A good set of coalescers with correct design would only allow a small amount of oil carryover into coalescer compartment.

[jbmorris]

Thanks Ranger, you along with the others are a big help. We have high level shutdown protection in all our evaporators and have suction knockout drums with high level protection as well. This should prevent washout I would guess.

It will be interesting to see if there is damage to the coalescers in April when we open the equipment, but with the dP we have across the coalescers (4 psig @low loading), I would have to agree with you guys, it certainly indicates there is no leakage. It would be nice to start with raising oil temperature, but to do that would mean changing out the temperature controller...there's no way to adjust it. This is also a shutdown job and a shutdown is out of the question due to plant operation.

[TXiceman]

If you are flooding back on the compressor, you will have oil foaming. How is the oil temperature? excessive refrigerant in the compressor can lead to excessive volume low in the oil separator and blown coalescing elements.

As for the plant design, R507 is an expensive refrrigerrant. I hope it is a tight piping system and no leaks. Did the client have a problem using ammonia as a refrigerant? Plenty ammonia systems operating in a vacuum and use Hansen purgers to handle non-condensibles.

Ken

[TXiceman]

Don't you just love it whan some ask for help and they never botther to come back with more information or how the problem as solved?

Ken

[Josip]

Don't you just love it whan some ask for help and they never botther to come back with more information or how the problem as solved?

Ken

Yes, that is not nice at all ... we are struggling to help and finally no response from original poster....

what to say ... neither the first nor the last one ...

.... keep on rowing guys ;)

Best regards, Josip :)

[Brian_UK]

Don't you just love it whan some ask for help and they never botther to come back with more information or how the problem as solved?

Ken
Bear in mind that he can't do too much until his April shutdown.