seal oil explosivity problem

[pno1899]

Hi dears,
i have a project related to seal oil gas carry over with sweet oil in reservoir,
on a synthesis compressor consisting of three vertical split casing(suction pressure=25kg/cm2 and Discharge pressure=150kg/cm2) wet oil seal are used, complete seal oil system is working properly, differential pressure for seal rings across each casing is stable.
but the problem is that there is gas explosivity in sweet oil reservoir with previous 2 time explosion background.

observations include very small quantity of sour oil

 

[georgeverghese]

Two suggestions

a)Temporarily, we can exclude air or O2 from seal oil tank and replace with N2 blanket

b)Permanant solution would be to replace compressor shaft seals with dynamic gas seals which have an upstream lean fuel gas injection, followed by N2 or buffer dry air injection downstream and finally with seal oil injection - that will prevent seal oil from coming into contact with process gas. Vendors are John Crane, Borg Warner, Durametallic. Rotating machinery engineers are experts on this, and may add more useful suggestions.

 

[pno1899]

A) we have provided N2 to at least start plant and resume production.

B)OKay dear i agree that permanent solution is dry gas seal installation but here is a huge cost for revamp as its a dual train plant with 2 synthesis compressor(each with three casing, 6 end seals) and 2 refrigerant compressor (each with 2 casing, 4 end seals) so i have to provide some solution that should be cost reliable too.

 

[georgeverghese]

At a slight increase in risk, it should be possible to do without the intermediate dry N2 / dry air injection.

Temporary solution for N2 blanketing should be continous, not just at startup.

Is the seal oil drum currently being operated at slight vacuum conditions? - how is air getting into this drum to trigger this explosion ?

 

[pno1899]

before explosion N2 blanketing was not practice but after that it is continuous
Seal oil tank is operated under atmospheric conditions
but this is temporary solution,

again i elaborate, we have two seal oil tanks( on for sweet oil(explosivity>30%) and other as reservoir(Explosivity=NIL), after degasifier sour oil goes to reservoir )
hence the probable source of explosivity is sweet oil, how it is going with sweet oil if sour oil is there..??

 

[georgeverghese]

Yes, I suspected that previously you must have been operating the sweet oil tank under slight vacuum in order to completely degas the seal oil.

Now that you have this tank under slight positive pressure, the risk of air entry in to this tank is reduced. My guess is that the additional H2S that may not be degassed from this recirculating seal oil (by having increasing this tank pressure from slight negative to slight positive) is only a very small amount.

Long term solution for dry gas seals is the industry practice in these applications.

Maybe you could talk to the compressor vendors to see if they have any concerns with this sweet oil tank operating at slight positive N2 pressure for long term operation.