I have been working as third engineer on board a RORO ship for five years and the problem of contamination of L.O is really a big nightmare for me!
Every diesel engin has its L.O purifier. the problem is that the heater of L.O mounted just before the purifier becomes very dirty within only two weeks (the temperature of L.O coming from the heater to purifier falls from 95°C to 80°C only in two weeks even with a new heater).
With such a low temperature the purifier would not be efficient and there is no purification! Sending some oil samples for analysis and there is nothing to note.The oil used is cladium 400 SAE 40.
The engine is, MAN 6L32 3000kW, equiped with VIT, running on heavy fuel oil (120 - 130°C) with only 1% sulphur.
Recently we have made a complete overhaul to those engines (piston, bearing, cylinder head, injection pumps…) and notice abnormal carbon diposit on piston top.
The purifiers’ type is Westfalia GEA OSE 20 and they are being overhauled every 4000 hours as it is recommanded by the constructor but even when reducing the maintenance period the problem persists.
There is aloso centrifugal oil filter and when overhauling didin’t show any thing abnormal.
Meanwhile the main engines (MAN 12V Cr 14000KW, equiped with VVT) are running with the same L.O and using ‘GEA OSE 40’ purifiers with of course bigger heaters but there is not any problem!
If there is nothing to note and nothing abnormal it sounds like a personal problem. Carbon on the piston crown is probably a fuel or load related issue, not lube oil.
Are you sure this buildup is carbon? It might be excessive LO additive as you are using a 40 TBN oil with only 1% sulfur fuel. Check your manual but that seems like too high of a TBN for your application to me.
As far as your fouled LO purifier heater, can you provide more details? Diagram of the piping system that feeds the unit, system flowrate, and how often the unit is started up and shut down would be a good start. Also is this a problem on this one generator/purifier or are all the generator purifiers experiencing this?
As a guess (wild guess at this point with the limited information given), I’d look to see if the steam and condensate valves to that heater might be leaking by. With the unit secured, feel the lines going to/from the heater. If they are hot, then the idle oil still in the heater is getting cooked onto the coil when it’s shutdown.
Lots of good info here also.
Thank you for answer.
I have read the pdf file and have noticed that , “the engines have been readjusted to fulfil these requirements by means of retarding the fuel injection.” and I membered that these engines are equipped with the VIT (variable injection timing) but there is always a problem when starting the engine, an error message always displayed : " VIT ERROR ". also, there an oil leakage coming from this unit (VIT).
I’m not sure the buildup is carbon. Concerning the TBN, as know, the engine manufacturer and the L.O supplier have together decided to use this oil.
The heater is supplied with oil from a pump wich pressure is 2 bars and the flow-rate installed just before the purifier is about 1500 – 2000 L/hr, there is 2500 – 3000L of L.O in the engine (sump tank and circulating oil).
Concerning the leakage, I am sure there is no steam leakage because when dismantling the heater bundle, I didn’t notice any steam and the temperature was very normal.
this problem is the same for the generator “always” running (stopped only for maintenance) and for generator running only when manoeuvring.
Are there any strainers inline that can be checked? A Y strainer that has been overlooked?
95 degrees seems higher than what I’m used to, have you tried a setpoint of 90 on a clean heater?
Well 95°C is the temperature recommanded by the manufacturer to have efficient separation ( matter of viscosity). there is Y strainer only in steam pipes.
If your (assumedly) quarterly LO samples are good, particulary on soot, TBN, and viscosity, I don’t think contamination is your problem. I still say the problem is likely to be excessive heat/lack of flow thru the heater. How long is flow maintained through the heater after steam is secured? Is the steam secured manually or via the purifier automation? Is the same person operating the DG purifiers (which are having problems) and the ME purifier (which is not having this problem)?
There should be a strainer in the suction line before the purifier feed pump as well as a very coarse strainer on the suction pipe in the engine sump, but I don’t expect you to find either of them fouled.
You sure that isn’t a steam trap?
You may think you have adequate flow if you’re only looking at the gauge on the purifier. If the backpressure gets adjusted slowly as the heater fouls, then you might be fooling yourself into thinking you have a proper flowrate.
I’ve never seen a LOPX that didn’t have a strainer in the system. If you did an overhaul and then put the purifier on the sump the strainer should have picked up all the little bits of lint/string from the rags.
OK I should check if there is a trap between the purifier and the engine but if there is a trap and if it is fooled so the outlet pressure of the purifier would normally rise.
I have also tried to close the heater by-pass valve and open the back-pressure valve at the outlet of the purifier 100% and put orifice (there is a diagram in the manufacture book showing which orifice to choose to get wanted flow) but didin’t get a result.
today I should have the purifier diagram and I will share it.
when on board I am the only person in charge of the purifiers and when stopping a purifier I let the oil circulation during10 min (manual and pneumatic steam valves are closed) before stopping the purifier L.O supply pump.
Is there lube oil contamination? Whatever happened to that idea?
Or is the problem just heater fouling because the oil is too hot?
If the oil is too hot there are only two possible reasons, too little oil or too much steam. Sounds like a job for a good man with a couple of thermometers and pair of pressure gauges.
There should be a feed pump for the purifier mounted somewhere nearby the unit. The pipework immediately preceding the feed pump should have a strainer. You should check and clean the strainer.
Does the heater have a vent? Have you tried venting the heater to make sure it is filled with oil?
I would like it was as simple as you wrote!
I have received the L.o purification diagram if you want to take a look.
Both the heater and the purifier are only rated for 900L/hr. Try lowering your flowrate and see if you can maintain your temperature.
I did reduced the flow to the minimum rate but always the same problem.
What valve are you using to control flowrate? Specifically, if you open the heater bypass valve (LP-412/413) fully and you want to lower purifier flowrate even more, what valve do you manipulate?
415 and 414 will only have oil flow during re circulation (during shoots, or getting the bowl up to speed during startup.) They shouldn’t affect flowrate and should be left fully open.
Where and how are you measuring flowrate?