Disappearing Oil?

[Droptine75]

I have an FES, twin screw, 200hp, 140 ton ammonia compressor. At some point while it is running all the oil disappears and it shuts down. There is no oil in either side of the barrel (oil or coalessing). After a half hour to an hour all the oil is back again and I can start it up and run it. FES told us to check the oil heater, which was bad and we replaced. But the problem with the disappearing oil is still going on. So, my questions are, does anybody know what is going on? Where is the oil going? What can be done to solve it? And what does the oil heater have to do with the oil disappearing? I work night shift and am not able to talk to FES directly, I leave that up to the day shift tech who doesn't ask questions, he just does what he is told to do. I'm more the type that wants to understand the problem rather than just get parts and put them in. Any help would be great.

Thanks

[RANGER1]

Droppine,
He oil heater is normally only on when compressor is off.
It is used to keep the oil free of refrigerant so it does not become diluted.
Also so at a suitable suitable temperature to flow through components like oil filters
& to control oil pressure when using oil pump.
You say it looses it when running!

Is it a vertical oil separator on end of package, or is it a horizontal that compressor & motor sit on?

Does it have any other components like economiser or liquid injection cooling?

What are operating pressures & temps of this package?
suction, discharge pressure, oil & discharge temps.

Assume ammonia operation.

If if running normally & you turned it off, does the package stay above suction pressure (this checks if suction check valve is sealing).

We we will start with above questions & go from there.

[Droptine75]

Yes' it looses its oil while it is running. It will shut down on a low oil alarm. We first thought it was the oil level sensor being when we would find it the oil level was fine. It wasnt until I had walked in very shortly after it had shut down that I noticed all (in the sight glass) the oil was gone. I came back to it to check things out a while later and all the oil was back again. It has a horizontal separator. It has thermosyphen oil cooling, shell and tube. 28 psi and 145 psi for opperating pressures. 114 degrees F for oil temp and 170ish degrees F for discharge temp while running.The package will normally read higher than the suction pressure when shut off. I hope this helps.

[RANGER1]

All sounds normal.
What type of sight glass do you have?
If it's like a Phillips bullseye, how many do you have & what oil level do you keep in it.
Mare they clean to easily see oil level.
The lower the level the less oil reserve you have.

[Droptine75]

I guess I don't know what kind it is. It is a round glass with a little ball float in it. We keep it at around 3/4 full while running. I can see the oil (when it is there) on all the glasses. There are 2 glasses on it. One on the oil side and one on the coalessing side.

[RANGER1]

Could you verify when oil level drops & compressor running, what % load on slide valve.

Is it is unloaded for a period try loading it up a bit to see if oil level increases.

If it was running & you turned it off, how quickly package pressure drops (maybe there is a line around suction check valve to equalise package pressure for easy start up).

The oil return from coalesces, where does it go, upstream of suction non return valve or compressor side?
Is the oil return line warm when or hot when running, as usually needle valve restricted in this line returning oil to compressor suction, compressor side of check valve.

I think also coalesces should be checked regardless.
Normally remove inspection cover& visually check & also make sure they are secure & in place.
Normally check or replace if suspect to eliminate problem if it keeps occurring.
Oil can only disappear in coalescer compartment or for
some reason get hung up in compressor, suction strainer housing or suction line

[Droptine75]

I do not know when the oil level drops or what % the slide valve is at. It does drop while the compressor is running. It it happens at all different times of the day. We have sanitation cleaning during most of 2nd shift. During that time there is not much load on our system. After that we have a heavy load on our system getting things cooled back down for production. On night shift things are calming down and running pretty smooth up until after sanitation the next day. This has been happening on all shifts. During heavy load and after everything calms down. It can happen once a week or a few times a shift.

With that being said no one has been standing there when it happens.

There is a 1/4" line going from the the compressor to the upstream side of the suction check.

The oil return from the coalesces goes to the bottom side of the compressor. I am not sure if the line is warm or hot. I will have to check on that.

The coalesces were just replaced a few months ago. I will change them out again also.

I'm not trying to argue but wouldn't I see the oil in the coalesces sight glass if it were all going to that side?

We are going to be repacing a large amount of valves next week so we are going to have to pump out almost all of our system. 23000 lbs of ammonia. Do you think our problem could be the suction check? If so that would be the perfect time to replace it.

[RANGER1]

I would suggest check coalescers, as did not know they were changed recently.
Li would also remove/check/replace if suspectsuction check if you have the chance, so it can then be ticked off the list.
The 1/4" line should only normally be cracked open, close it, see what happens

[Droptine75]

Sounds good! thanks for all the help!

[PaulZ]

Hi Droptine
You said the package pressure normally reads higher then suction when it is off, can get a gauge on the suction before the check valve and let us know how much difference there is between this and the package pressure when the compressor stops. It sound a lot like the suction check is not shutting when the compressor stops and the oil is getting blown up the suction line. Once the compressor has been off for a while the oil drains back to the compressor and back into the separator.
Does the oil level rise a bit soon after starting or is it the same?
Also you didn't say if the compressor is economized, if it is it may pay to inspect the check valve on this line as well.
Regards
Paul

[RANGER1]

Makes me wonder if oil is foaming for some reason like liquid flood back occasionally.
Once foam settles oil level back to normal.
If it's on a common line maybe it's first to get it.
Do you have a trend or log on pressures & temps on compressor to see if discharge temp suddenly drops.
Does compressor have full line oil pump or pressure differential feed oil.

[Droptine75]

Well, I checked the valve on the line going from the compressor to the upstream side of the suction check and it was wide open. I closed the valve then cracked it open. We started the compressor and it has been running since yesterday morning with no problems. But like I had said before this is not always a costant problem. Sometimes it it will go a week with no issues other times its will shut down in a couple hours on low oil. I will keep you all informed on what happens.

There is no economizer.

There is no place for a gauge unless I would pump it down to add one.

I can't really tell if the oil level rises beacuse the sight glass it completely full when it has been off and drained down

I have never seen any foaming in the oil.

I would also like to thank you guys very much again with all your help! It is nice to know that I can get some answers working night shift rather than feeling like all I am doing is sitting on my hands with the issues we have. Again, you guys are awesome and thanks for the help!

[Droptine75]

I also would like to pick your brains about our master sequencing control system. I'm not sure if I should start a new thread or not?

My question is about head and suction pressure fluctuation. What is an exceptable amount? We run 28 psi suction and 145 psi head. We have a FES master controler but it never seems like it holds a constant pressure. I do have to say that I don't know alot about it and the Sr. Tech seems like he just flys by the seat of his pants. He is always changing sequencing on the compressors but it never levels out. It seems to me we could just as well run each compressor individually rather than having this panel. I would like to get an FES Tech here to show us how to run the system but all the higher ups think the Sr Tech knows what he is doing. My thought is you should be able to change it once or twice a year (if at all) and the system should run within a couple pounds of the set point on its own.

At times the suction pressure will range from 22 to 32 psi and the head pressure will go from 130 to 155psi. We have 8 compressors on the high side (2 recips and 6 screws) and 2 screws one the low side (one in opperation and one for backup). and 3 evap condensers on the roof.

[RANGER1]

I also would like to pick your brains about our master sequencing control system. I'm not sure if I should start a new thread or not?

My question is about head and suction pressure fluctuation. What is an exceptable amount? We run 28 psi suction and 145 psi head. We have a FES master controler but it never seems like it holds a constant pressure. I do have to say that I don't know alot about it and the Sr. Tech seems like he just flys by the seat of his pants. He is always changing sequencing on the compressors but it never levels out. It seems to me we could just as well run each compressor individually rather than having this panel. I would like to get an FES Tech here to show us how to run the system but all the higher ups think the Sr Tech knows what he is doing. My thought is you should be able to change it once or twice a year (if at all) and the system should run within a couple pounds of the set point on its own.

At times the suction pressure will range from 22 to 32 psi and the head pressure will go from 130 to 155psi. We have 8 compressors on the high side (2 recips and 6 screws) and 2 screws one the low side (one in opperation and one for backup). and 3 evap condensers on the roof.

New thread would be better, mods will be able to change it

I agree with you get FES in then more than 1 person knows something.
Word of advice though, refrain from talking about work coleagues as they can
look here to.
Ma few years ago a guy got caught out & he had to delete posts everywhere.

Do do you have any literature on the FES stuff, if not try to get it as a starting point.

[Grizzly]

Hi Droptine.

At times the suction pressure will range from 22 to 32 psi and the head pressure will go from 130 to 155psi. We have 8 compressors on the high side (2 recips and 6 screws) and 2 screws one the low side (one in opperation and one for backup). and 3 evap condensers on the roof.

With that number of comps and condensers being controlled.
I think you need to rethink your argument!
A plant that size controlling within the range you describe, Sound well set-up to me!
That's a huge potential variable load and you are complaining about 10psi and 25psi float.
That's close control to me?
Sounds like someone knows what they are doing. (Not you my friend!)
With that amount of plant to ask for a control to within a couple of psi is ludicrous.

You don't say what refrigerant we are talking about?

Grizzly
PS Ranger FES = Grasso / GEA.

[slingblade]

LOL. £55 per hour plus travel to the states plus hire car plus expenses to house my family for at least a month, i will consider your issue. Refrigerationengineer.com is for refrigeration engineers. Let me know when you qualify, or need help you can afford.

[Segei]

We need more info.
You have 6 high stage screw compressors. Does oil issue happen to only one compressor?
Usually, screw compressors have "freeze display". It shows the operating variables when compressor stop due to alarm. It will be better to how this compressor operates. Does it run continuously at 100% capacity or it load unload or start, stop?

[Droptine75]

The oil issue only happens on one compressor. The oil problem compressor loads, unloads, starts and stops by the master controler.

[RANGER1]

The oil issue only happens on one compressor. The oil problem compressor loads, unloads, starts and stops by the master controler.

Another possibility could be compressor cycles off oil foams due to equalising valve open to far.
Then it might bring up low oil alarm?
Only suggestions as friend at work thought of this scenario.

Oil il can foam like when draining oil if pressure reduced to quickly.
Sometimes you do not see this in that type of sight glass (maybe).

[Droptine75]

Thanks Ranger1. So far after cracking the valve (rather than wide open) it has been working without a hitch. I will keep an eye on it and let you know.

[Segei]

Two scenarios.
1. Compressor stops by controller, but suction check valve doesn't hold. Oil can fly into the suction line. When call to start compressor, no oil in oil separator. Alarm. Later oil can drain back. What alarm do you have? Low oil level or low oil pressure? What is the pressure in compressor when it stop? Try to run this compressor nonstop. Change compressor sequence in master controller.
2. Oil leave compressor and collect in vertical discharge line. This can happen when compressor run fully unloaded for long period of time. When compressor stop due to alarm, oil can drain back if discharge check valve is not tight.

[mbc]

Do you have drawing of your system ?
upload it it help you give you to get right answer very quick .
all suggestion might be right also pipe line from oil separator to compressor should be fully open .
check all valves and filters .

[Magoo]

I do not know your system but a valve and line around the suction check valve is a service item valve and should normally be closed. When compressor is stopped and you want to dump set pressure back into system open it.