Propane refrigerant Plant

We are running two Howden 504's in our refrigerant plant. We have been having issues with our lube oil backing up into the suction scrubber on the skid. So far, we have not been able to pinpoint how the oil is getting in there, but there are only a couple of possible ways. Right now, the thoughts are that it is backing up the suction line of the compressor and dumping in that way, just not sure how or why. The suction line is a 16" line and it comes down off the top of the suction scrubber aprox 5' high, so it would have to back all the way up that and into the scrubber. Just this past week we have emptied aprox 90 gallons from one unit, and 40 from the other. All units share a common suction header before it goes into the scrubber, including a smaller unit 204 which at this time we are not having this issue, so I don’t think its coming in that way. Is anyone running this similar setup, or have any input.

Basic rundown of process. Propane vapor enter into the suction side of the compressor through a common suction header then into suction scrubber so as not to introduce liquid propane into the compressor. Propane is mixed with lube oil within the unit, compressed then discharged into an oil separator where the oil is dropped out through coalescent filters. The compressed propane is the discharge into a common header then run through condenser fans. Suction pressures on are maintained at roughly 2psi using the slide valve. Discharge pressures run in the mid 140psi range. We also have a side stream into the compressor through what we call an economizer loup.

I would look at the efficiency of the oil separators.
Is there any other "low" points in the system where oil will pool if it travel around the system?

:cool:

We have an oil reclaimer system on the plant which is not building up any oil in it, also just replaced all coelecent filters in the sepperators, so I dont believe it is a carry over issue. Low point in the system would be our chiller, which is where the oil reclaimer is also located.

Quote:

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Originally Posted by cgrivois

We have an oil reclaimer system on the plant which is not building up any oil in it

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Hmmm, if it worked correctly wouldn't you expect it to trap some oil?

:cool:

Its not building up the volumes like were getting out of the scrubber, the opperators may get a gallon or so every couple of weeks out of the oil relcaimer, which tells me there is no carry over, the oil sepperator apears to be doing its job.

Cgrivois,
Do any of the compressors cycle off?
If you are collecting oil, I'm sure one of the compressors must need a top up, although oil separator must be quite big.
I'd assume compressors have a suction check valve this is one likely cause if compressor cycles off.
IF compressor cycles off monitor pressure in package & see if it drops to suction pressure, as if it does it should take a while. Monitor pressure & oil level.
IN some cases rotor may spin in reverse if suction check is damaged.
IS there any other lines returning into suction line upstream of suction check like oil return from oil separator etc

Hi, cgrivois :)

interesting issue ...

Quote:

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Originally Posted by cgrivois

We are running two Howden 504's in our refrigerant plant. We have been having issues with our lube oil backing up into the suction scrubber on the skid. So far, we have not been able to pinpoint how the oil is getting in there, but there are only a couple of possible ways. Right now, the thoughts are that it is backing up the suction line of the compressor and dumping in that way, just not sure how or why. The suction line is a 16" line and it comes down off the top of the suction scrubber aprox 5' high, so it would have to back all the way up that and into the scrubber. Just this past week we have emptied aprox 90 gallons from one unit, and 40 from the other. All units share a common suction header before it goes into the scrubber, including a smaller unit 204 which at this time we are not having this issue, so I don’t think its coming in that way. Is anyone running this similar setup, or have any input.

Basic rundown of process. Propane vapor enter into the suction side of the compressor through a common suction header then into suction scrubber so as not to introduce liquid propane into the compressor. Propane is mixed with lube oil within the unit, compressed then discharged into an oil separator where the oil is dropped out through coalescent filters. The compressed propane is the discharge into a common header then run through condenser fans. Suction pressures on are maintained at roughly 2psi using the slide valve. Discharge pressures run in the mid 140psi range. We also have a side stream into the compressor through what we call an economizer loup.

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Scrubber must be a separator vessel on the suction side if I am right ... here we call it separator ... to separate liquid (if any) from suction gas ...

Drain of 90/40 gallons = 350/150 liters is too much ... did you noticed lowering of oil level within oil separator, must be noticeable (maybe not if you have 500-600 gallons of oil within oil separator)

I assume that was not a case from the plant start up ... or maybe I'm wrong ....

Not sure, but seems you are pumping oil from one compressor during run of another one (assume one compressor is running another compressor is stand-by like in similar plants) ...

If I have a schematic or 3d drawing of your units/skids it will be more easier to suggest what to inspect, but let's try in this way (my English is not that good and unfortunately I do not follow above text in bold) ...

it is possible that some of NRV (Non return valve -Check valve) or solenoid/pneumatic valves on oil lines are leaking ... then from high pressure oil separator of running compressor is easy to push oil back to and through stand-by compressor back to suction header and further to the scrubber ...

it can be a problem with small pipe for oil recovery coming from oil separator coalescer section back to suction pipe before suction strainer ... if there is a problem with pipe slopes .... that oil is not flowing back to compressor but to suction scrubber ...

Piping of small 204 must be executed in some different way .. that is why you have no problem with that compressor ...

Also you can have a problem with NRV on oil pump delivery line pumping oil through stand-by pump back to stand-by compressor ... and back to suction header ...

Economizer NRV is Ok otherwise you'll find oil in ECO cooler what, according to you, is not a case ...

I can be wrong, because, we are discussing something what is virtual for me ... I have experience with similar plants, but each is designed and installed sometimes in some personal way and with "personal" bugs ;)

Hope this will give you some idea what to check ...

Best regards, Josip :)

.

I'd like to know how old the plant is?

How long has it ran?

How much oil you have put in?

How often the oil was put in?

How much oil was taken out (before this)?


If the suction scrubber works correctly it should have
a mechanism for returning oil back to the compressor.
In systems this size oil sometimes does end up in the
low pressure side, this oil needs to be taken out, but
it is done over time and should equal the amount you
put in.

If you have taken more than 100 gallons out, how long
have you been putting it in?

Rob

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hi

I think there will be a line connecting secondary oil separator to compressor suction through NRV , suction strainer and isolation valve therefore if primary oil separator is not working properly then there are chances that excess oil is separated at secondary oil separator which can be cause oil flooding in scrubber.

Please let me know what type of oil reclaimer are you using??

Is it a ejector system ??