Lube oil contamination - wet gas compressor

[kiwi2]

We have an oil injected screw compressor recovering heavy saturated gas off the top of a gas condensate stabilisation column. A PAG synthetic lube oil has been specified and with a discharge temperature of 100 deg C we have had no issues with dilution. However we do have a problem with wax in the oil which results in serious blocking of the oil filters on startup.
In theory any wax should be knocked out in the scrubber but we suspect that a small amount is being carried through and accumulating over time in the lube oil.
Has anyone experienced a similar phenomena?
Apart from changing the oil and flushing the system are there any other ways to strip out wax contamination?

Thanks

 

[zdas04]

You really need to be talking directly to your oil manufacturer. There are possible chemicals to disolve the wax (most look and smell like kerosene), but their impact on the lubricity, viscosity, and coalescing properties could be devastating.

I've been successful with a high velocity lube oil separator (the one I used was from DeLaval) running on the sump, but as I recall (it has been more than a few years) it took a while to make a difference and I had to use a pump to get it back into the process.

David

 

[pmover]

i believe that this question, if posted in the "chemical plant design & operations" forum, will be read by the chemE's that handle matters such as this.

my opinion . . .
i would have have substance analyzed and then consult with a chemE to have substance removed from gas stream before compression. it seems that by continuously adding wax to lube oil will impact the rotating parts (i.e. possibly shorten life span). any additives added to lube oil will only last for a specified period of time (i.e. need to add more additive to treat wax substance).

good luck!
-pmover

 

[dcasto]

As ChemE I've been waiting to see if there is any help here too. We've been able to track some of the parafins back to parafin cutting chemicals used by producers as a source. These chemicals seam to allow the parafins to stay in suspension in oils and even the gas phase.

 

[monaco8774]

I have had a similar issue before on oil wetted screw compressors on hydrocarbon gas service, if the gas is fairly heavy as it cools from the upstream vessel gas outlet to the compressor either in normal operation or especially after a shutdown, if left pressurised, liquid hydrocarbons will condense out of the gas and they will be absorbed into the lube oil. There are two or three tricks in the past I have tried that have helped with varying success:

1) adjust the cooler on the lube oil to keep it as warm as practical and keep it running after all but essential shutdowns, this helps reduce the contamination
2) Make sure the vessel upstream is as cool as you can manage to knock out heavy ends in the gas
3) Insulate the gas suction line (you might even consider heat tracing if you get extended pressurised shutdowns)

Just one thing to watch out for is sometimes the wax isnt wax, it should be parrafinnic to be wax and therefore should readily dissolve in kerosene or xylene if it doesnt you may be dealing with another contaminant that causes waxy looking deposits some favourites are glycols from upstream contactors (if you get enough heat from somewhere in the system) or production chemicals that are injected upstream