Howden XRV204 compressor unit loosing alot of oil

We have two identical RSW units installed on a ship (horizontal oil separator), and one of the units is loosing a lot of oil out into the chiller, we thought maybe the coalescent filters were damaged, 2 months ago I inspected and changed them (they were not damaged but changed to see if it would make a difference.)

from the last feedback from the machinist, the problem unit has gotten worse and is now throwing out close to 20 liters in 24 hours.

the problem unit has also chewed through 2 or 3 shaft seals in short time.

I ran both systems and regulated the main oil injection valve so both systems now run with a discharge temperature between 76 and 81 C ,and 45 - 50 C oil temperature, depending on the speed and capacity position on the compressors.

I measured the temperature on the oil-separator and the temperature on the oil reservoir part of the separator was around 60C +/- 2 C measured at various places. The temperature on the coalescer part was 10 C lower on both units. the temperature of the discharge pipe close to the compressor compared to the inlet to the oil separator had a temperature drop of 4-5 C on both units.

This was measured when the compressors were at 100% and full speed (3600 rpm).

During start up and for maybe 5 minutes I noticed there was a lot of liquid ammonia passing through the oil return line from the coalescer part on both units, also in the oil level glass I could see a layer of liquid ammonia approx 5 mm on top of the oil level, this layer slowly evaporated after the liquid in the oil return had stopped, and it took around 15 minutes before it had dissolved completely after which it was replaced with a 10 mm layer of foam on the problem unit and a 5 mm layer on the good system, this layer stayed throughout the 3 hours I ran the systems.


One thing I noticed was that on the good unit there was a reasonable (normal) amount of oil passing through the oil return after the liquid coming during the start up had stopped, while on the problem unit there was not a single visible drop of oil passing through the sight glass, not even enough to make a distortion on the glass even if I opened the valve fully.

I tried running with the coalescer oil return valve closed for 15 minutes on both units, and when I opened the valves again there was a large amount coming through the glass on the good unit and nothing on the problem unit.


I have been thinking it might be wet suction or the NRV on the suction line malfunctioning, but I didnt notice anything unusual on the LT-LP and if the NRV was leaking the compressor would spool back when stopping and that did not happen.


Any thoughts on things I might have missed?

Tyco ,

Are you getting the oil back somehow that adds up to what is carried over .

What pressures when running ?

When you changed coalescers was there any oil in coalescer area at all ?

Are you sure 100% that oil return line is not blocked ?

What type of oil cooling does it have ?

I'm surprised even on the good one that you have a continual oil return .

Sounds like a blockage in the oil return line. Does return line heat up when the compressor is running? If the oil isn't getting returned to the compressor it will blow out into the system.

I have also the same experience with Howden screw compressors (both WRV and XRV's),they loose a lot of oil. We've taken into consideration the dicharge temp.,correct oil temp. and oil level,load/unload cycle,etc.,but still it consumes oil (approx. 1drum/month).:rolleyes:

Hi all, need to know operating conditions. Is oil cooling leaking thermosiphon cooler?

Hi Tycho.
if you are getting liquid levels on top of oil levels and frosting coming back from coalesar section, I would be looking really hard at check valve after the oil separator, and double check the oil heater in separator is working to spec..
magoo

Hi, Tycho :)

Quote:

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Originally Posted by Tycho

One thing I noticed was that on the good unit there was a reasonable (normal) amount of oil passing through the oil return after the liquid coming during the start up had stopped, while on the problem unit there was not a single visible drop of oil passing through the sight glass, not even enough to make a distortion on the glass even if I opened the valve fully.

I tried running with the coalescer oil return valve closed for 15 minutes on both units, and when I opened the valves again there was a large amount coming through the glass on the good unit and nothing on the problem unit.





Any thoughts on things I might have missed?

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Quote:

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Originally Posted by curtiswes

Sounds like a blockage in the oil return line. Does return line heat up when the compressor is running? If the oil isn't getting returned to the compressor it will blow out into the system.

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As Curtiswes said the similar happened to me ... I forgot to open manual stop valve on oil return pipe at oil separator ... there was also a solenoid which was working (from 8 evening to 8 in the morning I lost a huge amount of oil, unit almost stop to run :eek: all oil was in coalescing section of oil separator ;) and return after very short time when I opened manual valve ) .... try to check that line ... it must be warm when you adjust injection valves ... maybe ... somehow you do not have free pass through that pipe or clogged filter ... or solenoid is not working ... check setup in your PLC for automatic oil return, if ...

Best regards, Josip :)

Hi all

First it's running at +30C HP and -6.5C LP

The oil return line from the coalescer is not blocked, I checked that, as I said, in the first minutes after start up you can see liquid ammonia running through and I also checked it when I had the Coalescer section open.

the unit has a water cooled oil cooler

There was maybe 1-2 liters of oil in the coalescer when I opened it.


The standstill heating keeps the oil at 40-45C during standstill on the problem unit and 35-40 C on the working unit.

the oil return valve is just a manual shut off valve, no solenoid and as I said, I have tried running with it fully open with no result.

I also closed it for 15 minutes to see if oil would accumulate and give me some sort of oil return


I was guessing that the liquid that gathered on top of the oil was just gas condensing on the inside of the oil separator shell because of the temperature differences during the first few minutes of operation (shell is colder in the top part).

I guess next time we'll have to dismantle the nrv valve since that is the only thing we really didn't check

Did you check the check vav /stop check after the oil separator. Under a controlled condition try manually closing the stop vav after separator for a period of time and open when re-starting and compare the oil carry over oil recovery and what ever, for a comparison.

May be you loose oil in oil coolers.

Hi Tycho
I would agree with Magoo about the discharge check valve. You could shut the problem machine down and see if the pressure increases with the good compressor running. If you are not pulling liquid down the suction it's has to be condensing in the coalescer area due to a leaking check valve.
Let us know what you find.
Paul

Quote:

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Originally Posted by Segei

May be you loose oil in oil coolers.

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Oil coolers are fine, the oil is going out into the RSW chiller where it has to be drained off

Quote:

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Originally Posted by PaulZ

Hi Tycho
I would agree with Magoo about the discharge check valve. You could shut the problem machine down and see if the pressure increases with the good compressor running. If you are not pulling liquid down the suction it's has to be condensing in the coalescer area due to a leaking check valve.
Let us know what you find.
Paul

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It's two completely separated systems, the only thing interconnected is the water from the fish-holds

Do you have any difference in operating these 2 units? Start, stop, load, unload. Try to run oil loosing unit at capacity lower than 100%(90%, 80%..) and compare the rate oil carry-over.

Quote:

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Originally Posted by Segei

Do you have any difference in operating these 2 units? Start, stop, load, unload. Try to run oil loosing unit at capacity lower than 100%(90%, 80%..) and compare the rate oil carry-over.

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They are as identical as they can get

So we went on board the ship again about 3 weeks ago to see if we could find out what was doing it.

When we opened the coalescer section it was the same story, a small amount of oil, filters seemed fine.

We replaced the coalescer filters again, this time with a type we had had success with on another unit that had a large oil carry over.

When we ran the unit we actually got a small amount of oil in the sightglass for the fine oil return (from the coalescer and back to the suction) and we thought we might have solved it, but now earlier in the week, the engineer on ths hip tells us that the oil loss is slightly smaller, but not by much.


I'm about to go crazy here

Hi Tycho.
I can understand where you are coming from, if it was a horse you would take out back and shoot it.
Reality, are they vertical or horizontal oil separators, is the problem unit on the side of the ship or in the middle, are the oil pump amp draw similar, do you think it is over injecting.
I have had ships working fine when along side a wharf but go pear shaped when at sea, the roll and up and down factor particually if locate next to the side of ship, agrivated if horizontal separator. The slop factor.

It can be 2 reasons of excessive oil carry over.
1. Hardware. Something happen with compressor or oil separator. Try to switch parts(coalesent..) between good and bad compressors. Sometimes this approach can be helpful.
2. Operating conditions. Start, stop, load, unload, head pressure drop, suction pressure increase. Compare logbook readings of this compressor before and after this issue arised.

Quote:

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Originally Posted by Segei

It can be 2 reasons of excessive oil carry over.
1. Hardware. Something happen with compressor or oil separator. Try to switch parts(coalesent..) between good and bad compressors. Sometimes this approach can be helpful.
2. Operating conditions. Start, stop, load, unload, head pressure drop, suction pressure increase. Compare logbook readings of this compressor before and after this issue arised.

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As I have stated before

This is two units, completely separated from each other, they are completely identical in all running conditions, and upon inspection, both units appear identical inside the coalescer section and oil separator.

the only difference is, one unit is loosing oil out into the system.


Anyone know where I can get some TNT for cheap? :D

Tyco ,
Has the unit that uses oil ever been any good that you know of ?

Have heard of instances where divider plate that coalescers mounts onto is not fully welded or poorly welded causing bypass of coalescers .

What sealing method is used on end of coalescers ?
Maybe not sealing 100% on ends due to misalignment . The aussie Grasso packages have had some poor sealing in this area .

Problem may or may not be solved, YAY!


On my last visit on the ship, I was accompanied by a representative from the company that built the unit.

We did the same inspections and measurements we had before, and could find nothing wrong with the oil separator.
He scoped the inside as we had before and found nothing wrong.

We agreed that if the unit was loosing a lot of oil through the fine oil separator, we should also see a lot coming back through the oil return to the suction side.


Before opening the unit, we ran the compressor for a few hours with no visible oil return in the sight glass.


we opened the end cover on the oil separator and found the same small amount of oil in the fine oil separator.


We noticed that the bolts on the suction filter seemed untouched, and wondered if the start up filter was still there, so we opened it up, and could see that the Non return valve was open.

it was a parker NRV and it is a hinged flap valve, and the coiled spring was broken.

It baffled me, as I have said before here that the compressor didnt spool the wrong way when we shut it down.


Then I remembered that it is controlled by a danfoss frequency drive, and it doesnt coast to a stop, the frequency drive "runs" it all the way down to a stop.


and at under a certain speed, the screws will loose compression and will allow gas to pass the wrong way through the compressor. It will not be enough to shut the NRV if the spring is broken, but it will be enough to cause the oil injected to the compressor to foam up and pass through the suction, and as evidence of that, we found lots of oil in the suction pipe, even tho we had not seen any oil return.


Hopefully this will be the end of this story :)

and once again it conforms that you should not believe something is not the cause until you see it is ok :)


Thanks for all your input, and I'll report back when I hear from the ship if it was a success or not

How did oil get into the chiller?

Segei, any oil that leaves the separator winds up in the evaporator section.

Separators are generally 99% plus in stopping the droplet oil. Some of the oil is in a smoke state (depends on the vapor pressure of the oil) ans is carried to the condenser where it is condensed along with the refrigerant. From the condenser, the oil carried with the liquid refrigerant. In the evaporator, the refrigerant is boiled off or vaporized and the oil is left behind.

Ken

Quote:

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Originally Posted by Segei

How did oil get into the chiller?

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through the suction line.

when the compressor stopped the non return valve didnt close and caused the oil left in the compressor to foam up and fill the compressor and go the wrong way through the suction.

at least thats what I hope caused it, because we could not find anything else wrong with the unit

Quote:

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Originally Posted by Tycho

through the suction line.

when the compressor stopped the non return valve didnt close and caused the oil left in the compressor to foam up and fill the compressor and go the wrong way through the suction.

at least thats what I hope caused it, because we could not find anything else wrong with the unit

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Probably, this can happen if suction line is short.
However, I think that in situation like yours operation of the refrigeration plant should be monitored closely. If suction check valve doesn't hold, when you stop compressor you can see how oil boil wildly in the oil separator and compressor rotors will rotate backward(you can hear that). Major symptom of this issue is the pressure inside compressor. When you stop compressor it should be between suction and discharge pressures. If it is equal to suction, suction check valve doesn't hold, if it is equal to the discharge pressure, discharge valve doesn't hold.

Tycho
Nice bit of troubleshooting.
If anyone doubts this can remove the oil from a compressor, trust me I have seen it happen. I went to lunch and a compressor shut down. When we got back we solved the shutdown problem and noticed the oil was mostly gone. The suction check had not closed and it went up the suction line.

Quote:

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Originally Posted by Segei

Probably, this can happen if suction line is short.
However, I think that in situation like yours operation of the refrigeration plant should be monitored closely. If suction check valve doesn't hold, when you stop compressor you can see how oil boil wildly in the oil separator and compressor rotors will rotate backward(you can hear that). Major symptom of this issue is the pressure inside compressor. When you stop compressor it should be between suction and discharge pressures. If it is equal to suction, suction check valve doesn't hold, if it is equal to the discharge pressure, discharge valve doesn't hold.

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The compressor is driven by a frequency drive, and is powered all the way to a stop, that is why we didnt see it spool backwards when it stopped, and also the oil in the separator didnt boil.

but when the screw compressor reaches a certain speed, the screws will loose the ability to compress the gas, and the gas from the oil separator will go the wrong way, even tho the screws are rotating, and will pull the oil that is in the compressor with it, also the oil injection piped on the LP side of the compressor will drain into the compressor and fill it up with even more oil, so I'm guessing this is why we didnt see the boiling in the oil separator either.