Separate lube oil and control oil systems
Separate lube oil and control oil systems
(OP)
In an API steam turbine driven centrifugal gas compressor application, what could be some of the potential reasons for a buyer to insist on separate lube oil and control oil systems ? As in, the control oil for turbine is not from a common reservoir (as is standard practice with some OEMS). Is the added complexity and cost worth it for a 20-30 year life period? Thank you for the insights.





RE: Separate lube oil and control oil systems
Potential reason is probably different oil specification requirement for each of lube oil / control oil system (special application?).
Possibly the user wants that the two systems are kept separate or isolated in order to address various scenario/consequences (view points of safety, oil contamination/degradation, etc). Maybe there are some functional and operational tests that are imposed on the control oil system that would require the system to undergo a dedicated test (unlikely...).
Maybe operational reasons necessitate otherwise a "delayed trip" in case of loss of oil pumps, whereby the turbine continues to be operated for a limited duration due to process reasons (such as plant safety) while it is accepted that the machinery bearings would be fed via the oil from the rundown tank (not an ordinary case nor something I've seen).
By the way, I think that the control oil system size should generally be small when compared to the lube oil duty (driven/ driver equipment) so its a bit difficult to justify a dedicated system, unless there is a real bottom line behind it.
RE: Separate lube oil and control oil systems
Once the systems are separated they can both be optimized. Each would end up using a different oil, different pressure, different filtration, different run-down/accumulator design, etc. This would tend to show that combining the systems will involve compromise in each of these areas.
Johnny Pellin
RE: Separate lube oil and control oil systems
another reason might be due to the fact that the control fluid does not circulate that much and thus might be subjected to a higher thermal load in terms of more units of heat per unit of volume. that may lead to deposit formation negatively influencing the control mechanisms involved due to sticking valves etc. a fluid with higher oxidation stability might then be a solution. however, with suitable filtration of the circulating bulk turbine oil deposit stimulating components of the fluid may well be kept to a safe minimum. especially bypass filters where the oil is cooled down considerably necessitating deposit formation components to fall out of the solution and being trapped in the filter are quite good at that.
RE: Separate lube oil and control oil systems
Same case with a control air system, some engineer though it was a bright idea to tap into the control air system to supply air to blast clean the turbine combustion air filters. We actually ordered a $250 000 control air package for a 10 MW Gas Turbine, before someone realized that we normally order a $ 10 000 system! The review meeting was interesting!
RE: Separate lube oil and control oil systems