In some of the steam turbine design's hydraulic oil will be taken from lube oil tank itself. But in some other designs, both lube oil & hydraulic oil will be from different tanks. What is the reason behind that?

 

> In some of the steam turbine design's hydraulic oil will be taken from lube
> oil tank itself. But in some other designs, both lube oil & hydraulic oil
> will be from different tanks. What is the reason behind that?

I have not seen a design where there are two lube oil tanks, but in my opinion if they go for two lube oil tanks then the reason could be mainly due to Different lube oil specifications in the tanks. may be they designed the hydraulic oil with a different oil spec. can you provide more info on what type of STG you have seen this ??

 

Dear Vinu, our system (ALSTOM) is like one you speak of where the hydraulic system is completely separate from the lube oil system. I do not have it in print but I believe the reason is as P/value mentions that this allows the use of different oils for specific reasons.

I know in our situation we use a fire resistant oil for the hydraulic system and a standard mineral based oil for the STG lube oil, both oils have extremely different lubricating qualities. I understand also that the lube oil is prone to picking up water from the STG which is undesirable for the lube oil, but even worse for the hydraulic control system. So in short I think separating the systems is a good idea in certain situations, which are up to the turbine manufacturer to decide on. Each idea (common oil VS separate) has merits and drawbacks, as with life in general!

 

Process Value,

MANY steam turbine manufacturers employ separate bearing lubricating oil and hydraulic oil systems, each in its own tank. This is done in many cases because a special hydraulic oil is used to help reduce fires if the hydraulic oil were to accidentally be sprayed on the turbine valves or turbine casing. In fact, one manufacturer of this type of hydraulic oil calls its product "Fyrquel".

 

>Process Value,
> MANY steam turbine manufacturers employ
> separate bearing lubricating oil and
> hydraulic oil systems, each in its own tank.
---=- snip ----
> In fact, one manufacturer of this type of
> hydraulic oil calls its product "Fyrquel".

Thank you CSA for your answer.

 

i am mentioning about ALSTOM steam turbines. in our site 2 plants are there. in plant#1 both oil source are same which was commissioned 5 yrs ago. in plant#2 both oil source are different which is in commissioning stage.

plant#1 oil - servo prime 32g

plant#2 lub oil - servo prime 32g
hyd. oil - fyrquel (fire resistant oil)

 

can you add some points on merits of having same oil source for both purpose?

 

In addition to all the valid answers - hydraulic oils are hygroscopic (absorb water), have higher resistance to shear stress degradation, system has higher requirements for cleanliness (5 micron filters), tend to operate at lower temperatures, hydraulic systems have different sealing materials(o-rings and seals).

Lubricating oils operating in combustion paths have better detergent capabilities, alkalinity to neutralize sulphur in fuel (TBN number), operate at higher temperatures, system has lower requirements of cleanliness, higher resistance to oxidation etc.

Regards,
Tomy Zacharia