Dry Screw Compressors - how sensitive to lube oil in casing

[compo]

I appreciate by design dry screw machines in theory should avoid lube oil contamination into the process gas side/casing or importantly contamination of the lube oil from the process gas. However this depends on the seal system and barriers in place, barriers can be breached and propensity for this depends on the specific designs or manufacturers design in terms of opportunity.

I would like to know from the experienced compressor fraternity (manufacturers operators, machinery types) tuning in what are the issues if lube oil was to leak into the casing of a dry screw (not running), it then be drained from the casing leaving a film of lube oil and then the machine started. Specifically with dry screw applications used for air compression, or doing a shop test run using air, or a “hot” run. Is there any real issue with this as it is only a thin film of lubrication oil (may actually improve the sealing) surely the risk to spontaneous combustion of lube oil film, or ignition through friction due to the heat generated is extremely low, I doubt you could generate enough vapor to ignite even if there was enough heat to flash off the lube oil. Appreciate any feedback on this.

Are the lube oils typically selected by manufacturers with this in mind to ensure lube oil flash points are always higher than temperatures experienced?

If any issue what remedial measures would need to be done prior to a restart, e.g. clean out or nitrogen sweep, solvent flush (may create more problems).

Thank you for any feedback.

 

[DLite30]

On the process side there won't be too big of an issue, as long as you can live with a little oil in your process stream.

The biggest issue is oil contamination of the buffer and dry gas seals and cavities, and their continued ability to seal properly.

 

[DLite30]

Of course, I'm making the idiotic assumption that the oil "leaks" its way into the case via seals and shaft. How else would it "leak" into the case?

 

[zdas04]

I'm not sure how it would leak into the case, but when I had a dry screw (back in the days when I was a mechanic) every time we opened the case there was oil in there. Never very much, but always some. Didn't hurt anything.

David

 

[compo]

Thanks for the feedback so far..the question I am interested in is the concern with running air through a machine contaminated with lube oil and heating the oil in the casing which could coke out, char or combust --if the oil flash point is higher than the maximum heat of compression.. Would anyone see this as a concern worth worrying over or enough to have to clean out using nitrogen instead of air to clean out the film of lube oil ..

thanks again in advance