Oil fired boiler explosion

[DetroiTug]

One of my buddy's just called from Lees Mills steamboat meet and said he "just blew his boiler up". Then he clarified it was the oil fired burner had a late ignition and blew all the casings off the boiler. I immediately asked him if he was ok, which he replied, he is, but shaken up. They said it could be heard for a long way off and sounded like a cannon went off. He was out on the lake under way and standing right next to it when it happened, luckily no one was injured. be careful..

He's looking for a wood fired VFT, and said "I am through with oil". I guess this is the second time this happened, the first time was a light woof. That was the warning.





-Ron

[barts]

A casing that was fastened together would have redirected the overpressure (which was likely quite mild) out the stack, where it helps loosen stubborn soot .
I've done this several times with both the current and previous boilers in Otter w/o adverse (other than soot and heartrate spikes) issues.

- Bart

[dhic001]

What was the fuel? What type of oil?
Daniel

[DetroiTug]

Daniel,

Not sure, I'm assuming kerosene/heating oil or maybe deezel. He just said "oil" which is the common term for kerosene or heating oil here in the states. It was a gun burner.

-Ron

[barts]

I've had this happen w/ both diesel and kerosene.
I had a stack fire once w/ kerosene and a sooty vaporizer... Otter's titanium has some purple area as a reminder.


- Bart

[dhic001]

Won't happen with vegetable oil, will just slowly burn. Will often happen with diesel.
Daniel

[barts]

Won't happen with vegetable oil, will just slowly burn. Will often happen with smelly long-chain hydrocarbon.
Daniel

In either the steam or pressure atomizing burners, the fuel is broken into very small droplets which are easily burned. Normally, these burn as part of a jet of fire from the burner. If the flame separates from the burner, it may go out, and fill the combustion chamber with 'atomized' fuel. Should this cloud encounter a source of ignition (a piece of glowing carbon, an ignitor on the burner, a burning propane torch, etc), the entire cloud will burn quite quickly, causing a 'whoomp' and sudden pressure spike. As we saw in the picture, this pressure spike can disrupt less than rugged boiler enclosures, and rain soot/flame out of the stack and firebox doors.

Any fuel that will burn in either a steam atomizing or pressure burner will do this, because the flammability of the fuel cloud is the same mechanism that allows the burner to function in the first place.

Insuring that the burner flame has a hot target that will relight a suddenly blown out flame helps a lot; so does waiting a few seconds between relighting attempts. On steam atomizing burners, a pressure regulator on the atomizing steam helps prevent the 'runaway' behavior that can occur as the boiler steam pressure rises, increasing the burner output and chance of 'blow out'.

In Otter's boiler, the flame path is circular due to the tangential burner placement; this helps relight the flame should it get blown out. Most people using steam atomizing burners on the west coast use a wood fire as a target; this largely prevents this from occurring.

- Bart

[DetroiTug]

Good points Bart. One thing that should be considered is the size of the combustion chamber. The Roberts and similar style boilers have a much larger inner combustion area. Looking at those flat sides and top and considering the area, even if they were attached it may rip the screws out and maybe why they weren't fastened to begin with. The Stanley liquid fuel burners have a bad habit of backfiring, it's common practice to never latch the hood over the boiler, because an explosion can rip the hinges off.

-Ron

[dhic001]

Well we've tried hard to make vegetable oil explode, but it just doesn't happen. The same steam atomising burner will do it with diesel on the same setting very easily. The resulting whoomph made all the floorboards jump out of the bilge. The vegetable oil just ends up coating everything and when it does light, just burns like any other fire. Of course it does take time to burn off, so you try and avoid putting the flame out for long periods, but with five different boilers in four different boats, we haven't had a vegetable oil explosion yet.
I know what fuel I'll use when i'm oil firing.

Daniel

[DetroiTug]

Even if the attempts to make it happen have been unsuccessful, I would treat it as if it can happen. Even dust in grain mills and coal mines can explode. It's rare, but it has happened.

-Ron