What IS bunker oil?

Greenheart

Greenheart

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I imagine bunker oil is a really horrible glutenous dark mass, deep and almost unmoving at the bottom of the tanks of old ships...so that when 'fresh' fuel is added, the muddy unfiltered filth remains at the bottom.

Presumably a heavy-duty pump sucks enough from the top of this grubby fuel, to push through an initial filter - into a day-tank, containing sufficient for the day's running?

Is the idea based on expectation of dirty oil being supplied, so that regardless of how grotty the tank's contents may be, a flammable portion can be extracted?

Aren't bunker-oil tanks ever actually cleaned? If a 1930s oil-fired steamer is still going today, is there likely to be eighty-year-old crud in her bunker oil?
 
dancrane said:
I imagine bunker oil is a really horrible glutenous dark mass, deep and almost unmoving at the bottom of the tanks of old ships...so that when 'fresh' fuel is added, the muddy unfiltered filth remains at the bottom.

Presumably a heavy-duty pump sucks enough from the top of this grubby fuel, to push through an initial filter - into a day-tank, containing sufficient for the day's running?

Is the idea based on expectation of dirty oil being supplied, so that regardless of how grotty the tank's contents may be, a flammable portion can be extracted?

Aren't bunker-oil tanks ever actually cleaned? If a 1930s oil-fired steamer is still going today, is there likely to be eighty-year-old crud in her bunker oil?
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The oil in the bunkers is heated to make it viscous
 
Google is your friend.

"Bunker fuel is technically any kind of fuel oil used in ships." It gets its name from the containers that hold it. Traditionally steam ships stored their fuel (coal) in bunkers (my parents had one in their back garden for coal - remember smashing it up when they installed gas central heating) and the same term is used for oil storage on both ships and in ports.

Lots more fascinating stuff on the subject on Wikipedia if you are still bored today.
 
OK, but just how viscous is bunker oil at room temperature? Is it like diesel fuel, single cream, treacle - or thicker?

It was being described on BBC R4 (prog on the Costa Concordia) yesterday as a something resembling soft tar which I find hard to believe, even FFO wasn't that thick was it? - and no one uses that any more. Surely marine diesel fuel is much more fluid than that?
 
MASH said:
Surely marine diesel fuel is much more fluid than that?
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Yes, but ships don't burn diesel.

Big ships, anyway. Stavros at 600 tons is small enough that her engines are diesels, but when we were due to fuel up in the middle of the night in Cherbourg once, the engineer was at pains to make sure the watch leader who'd be on duty at the time knew we needed diesel and not heavy fuel oil, and that he was to make sure the dockyard mateys understood. They would have been more used to supplying the heavy stuff.

Pete
 
Thanks for these helpful replies. It hadn't occurred to me that heating is helpful (or necessary) to 'defrost' heavy oil in its normal state.

I wonder if the boat/car diesel we're familiar with, is just the thinnest, floatiest percentage of ships' heavy oil, or whether there are essential differences in the ingredients?
 
dancrane said:
Thanks for these helpful replies. It hadn't occurred to me that heating is helpful (or necessary) to 'defrost' heavy oil in its normal state.

I wonder if the boat/car diesel we're familiar with, is just the thinnest, floatiest percentage of ships' heavy oil, or whether there are essential differences in the ingredients?
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Think you will find the Wikipedia entry will answer all your questions.
 
dancrane said:
I wonder if the boat/car diesel we're familiar with, is just the thinnest, floatiest percentage of ships' heavy oil
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I think that's essentially the case. Crude oil is a mixture of hydrocarbon molecules - the longer they are, the heavier a fluid made up of them will be. Refining is just sorting the molecules into their different size categories - so all the small ones come out at the top as LPG, a bit lower down you get petrol, then diesel; paraffin, naptha, and similar stuff fits in around there too, can't remember exactly where. Keep going down and you get heavier and heavier oils until eventually you're scraping road tar out of the bottom.

That's how they explain it to GCSE level, anyway. Someone here probably used to design refineries or something and can tell us the details :)

Pete
 
prv said:
I think that's essentially the case. Crude oil is a mixture of hydrocarbon molecules - the longer they are, the heavier a fluid made up of them will be.
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And because we need more of the light stuff than is naturally in crude, cracking is the process of breaking up the heavy stuff to the light stuff.
 
MASH said:
OK, but just how viscous is bunker oil at room temperature? Is it like diesel fuel, single cream, treacle - or thicker?

It was being described on BBC R4 (prog on the Costa Concordia) yesterday as a something resembling soft tar which I find hard to believe, even FFO wasn't that thick was it? - and no one uses that any more. Surely marine diesel fuel is much more fluid than that?
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Furnace Fuel Oil (FFO) as was once used by the RN was very much lighter than "Bunker C" as used in the commercial shipping world. With heating we ran large diesels (Sulzer RD90) etc. on it. Modern motor ships, for example C.C. ferrys now use Marine gas oil. Even this is being phased out to be replaced with low sulpher content diesel, hence the weeping, wailing and gnashing of teeth from the ferry companies who have to use it from early next year. Whitelink ferries have stated that their new ferrys from Portsmouth will be bigger but slower to reduce costs incurred by using diesel.
 
Whilst bunkering in LA the barges hose burst.Panic stations as their trip failed. The result was about 1 ton in the drink, No oil on the surface. but about 1 ft below. Soon found out why when we started to use the stuff, very high % of sand and solids the Delavals had to be cleaned every 3 hours all the way home, Cold one could walk on it and the aroma when hot was very strong.
 
prv said:
I think that's essentially the case. Crude oil is a mixture of hydrocarbon molecules - the longer they are, the heavier a fluid made up of them will be. Refining is just sorting the molecules into their different size categories - so all the small ones come out at the top as LPG, a bit lower down you get petrol, then diesel; paraffin, naptha, and similar stuff fits in around there too, can't remember exactly where. Keep going down and you get heavier and heavier oils until eventually you're scraping road tar out of the bottom.

That's how they explain it to GCSE level, anyway. Someone here probably used to design refineries or something and can tell us the details :)

Pete
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used to work for an oil major (at sea and afloat) and now in my current role have to supply the different bunker grades for the ships at sea. In a nut shell that is exactly how Crude Oil is refined. Fuel Oil is pretty much all the stuff left over when you have taken all the good stuff out to make the Petrol / diesels / plastics / lube oils etc. The only bit worse then Fuel oil is the stuff they spread on the roads!

Refining Crude really is very productive as out of every 100cbm of Crude oil, the only by product from a good refinary is about 1cbm of water! everything else is refined into differnt products. Dependant on the source of crude anyway!

Back to bunkers, it gets more complicated as most ship fuel oils are 'cut' with MArine Diesel OIl (MDO, not like the stuff you put in car enginges which is called Gas Oil - GO) to make the fuel easier to run, and so you would have to heat the fuel less before you inject into your engine. Of course the more MDO you 'cut' into the FO the more expansive the FO is to buy to run the ship. Bunker costs is the most expansive part of running a ship at present with average bunker prices in Europe being $680 per mt.

To add to the confusion in various parts of the world you have to use Low Sulphur fuels (1.5% Sulphur in Northern Europe and North American Waters, which is available as a Fuel Oil) and also in EU ports you have to use 0.5% Sulphur which is only available as a MGO / MDO at about $1000 per mt so you hjave to have engines which can burn both 'heavy' fuel oils and also diesel fuel, same as would go into your car.

I am just a simple Deck Officer so need to go and have a lie down now....

:D
 
The heavy oil is heated in the main tanks up to around 120C and the pipes are trace heated to the centrifugal purifiers and then pumped on to the service tank where the heating is maintained. The trace heating on the pipework is continued all the way to the main engine injectors. Prior to arriving in port(at least 30 mins) the fuel supply is changed over to diesel so that the injectors have diesel in them when the engine is shutdown and this prevents heavy oil solidifying in them. The trace heating and tank heating is generally in the form of steam supplied either from the economiser or auxiliary boiler. The diesel generators, as their name suggests, run on diesel and not HO.
 
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Thank you, gentlemen. I didn't need to know, but I'm very glad I asked! I'll never look at a ship the same way again.

All the lengthy warm-up times at the dockside and smoke drifting for hours from anchored vessels, starts to make sense.

I'm guessing fuel-dumps have to operate similar heating systems, just in order to make the oil movable to ships' tanks?
 
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