Accessible metal product for a combustion chamber

[parkland]

TL;DR Summary

Looking for ideas for an easier to find metal product that can take intense heat over a long duration

So I'm still playing with my waste oil heating system, and as I figured the oil spraying out of the burner doesn't burn 100% clean without a combustion chamber.
I set it up outside with the burner pointing into a 12" section of 6" steel stove pipe with an elbow on the end, and it works perfect, but turns red hot almost instantly.
So, I need to find either a similar pipe made from a better material, or another material that I can form into some type of firebox combustion chamber.

I *could* look into making a combustion chamber from refractory cement, but it has its limits and I would like to have an intensely hot combustion to burn incredibly clean.

 

[parkland]

I was thinking about using stainless steel stove pipe, but not sure if even stainless would handle thousands of hours being red hot

 

[JBA]

You are probably better off using a refractory material because that will maximize the temperature in the chamber by minimizing the heat that is lost through the conduction through a metal containment. It does not necessarily need to be a cylinder, it could just as well be a rectangular tube built from refractory bricks as long as adequate air flow is provided to insure complete combustion.

 

[parkland]

This was the Beckett burner damage to the oil furnace. It took hundreds of hours to degrade this bad but the rear of the combustion chamber is disintegrated finally. It still worked but I decided it's not worth keeping anymore. The waste oil spray pattern is more narrow than heating oil thus the flame constantly hits the combustion chamber at the back.
My boiler firebox is 40" long so it's more accommodating to this burner on waste oil

 

[dlgoff]

I was thinking of lining your chamber with ceramic sheets.

 

[parkland]

I was thinking of lining your chamber with ceramic sheets.

I was literally just thinking almost the same thing

 

[parkland]

I've never worked with ceramic fiber blanket, I assume I could make a metal frame to hold it because the heat would be primarily contained on the one side

 

[JBA]

Just a note: Keep in mind that the ceramic blankets are an insulator that will reduce but not eliminate the heat transfer to the surrounding metal and what is OK for a wood fireplace may not cut it for your full combustion oil spray condition; and, may also become oil saturated from the oil spray resulting in burning within the fiber blanket.

Edit: At the same time there is also a ceramic fiber board that may work instead, see below:

https://www.amazon.com/dp/B07QBPVMJZ/?tag=pfamazon01-20

 

[parkland]

A warning that I ran across looking at the ceramic wool products is that the fibers can come loose and become an inhalation hazard. This might be more of a hazard for using with a foundry more than a firebox use, but there are products to apply to the fiber mat to secure the fibers from what I've read so anyone playing with ceramic wool should probably look into that before deciding if they require it. I think I like the ceramic wool more than the ceramic plate or solid board, because it seems like it could be easily cut and bent etc and shaped to fit many uses.

In my application, the fire box is 8x8 x 40 inches long ( deep) x 1/4 thuck and it's submerged in fluid, along with the 6 1.5 inch tubes that are 1/8 inch thick. Also submerged.
So I don't *think* there is really a possibility of the metal heating anywhere enough to damage it, since the fluid on the other side would carry heat away better the hotter it gets.
What I'm interested in though is keeping an immense amount of the combustion heat concentrated close to the burner, so that the combustion is complete and clean.

It was a worthwhile comment about the ceramic wool being saturated by oil. I'm sure it could happen, but I assume during regular operation any tiny amounts of oil hitting it would instantly vaporize.
In an event where it did become soaked and burning, it's still inside the firebox so I don't see a major issue other than a bit of a mess.

 

[JBA]

At this point I am a bit confused because you say that the box is submerged in liquid but also initially state that it immediately turns red hot (which is an indicator of a temperature of 900° for steel). What type of fluid is it submerged in that will stand that temperature without boiling off.

 

[Tom.G]

Fire Bricks are an old go-to for such use, some are good up to 3000°F. Here is a link for a decent overview:
https://www.brickwoodovens.com/fire-brick

Cheers,
Tom

 

[parkland]

Ok new question...
I experimented with drawing the exhaust gasses through a heat exchanger with coolant running through it, and the exhaust temp after was 30*c with the water being 20*c.
Obviously this would be a great way to capture waste heat, and seems to be a safe temperature for any heat exchanger to work with, but the issue would be the heat exchanger building up with residual unburned fuel from startups.

So, could ceramic wool be used to make a combustion chamber with no opening? Maybe just a big cylinder with the burner poking into the one end, and rely on the gasses passing through the wool?
It would work like a dpf filter on a diesel truck I suppose. Does anyone have any idea if the wool would work in that arrangement?

 

[parkland]

At this point I am a bit confused because you say that the box is submerged in liquid but also initially state that it immediately turns red hot (which is an indicator of a temperature of 900° for steel). What type of fluid is it submerged in that will stand that temperature without boiling off.

Sorry I had the burner in a standard oil furnace and moving it to a boiler. The furnace is out of the picture now.

 

[JBA]

The way to reduce residue and have maximum heating efficiency is to provide the most complete combustion possible and for this you need to supply the correct amount air (oxygen) to insure that. This is the reason that commercial oil burners have either blowers on the air inlet or exhaust fans on the discharge; so, I doubt that you could get sufficient air flow to achieve that by trying to exhaust through the wood blanket. Also, incomplete combustion increases the risk of dangerous Carbon Monoxide discharge.
Keep in mind that you are burning waste oil with potentially unburned contaminants in the discharge gas that would be quick to clog the blanket.

 

[parkland]

This is what I built, inline fuel settling contraption. To help clean waste oil before the main filter on the burner.

 

[parkland]

The way to reduce residue and have maximum heating efficiency is to provide the most complete combustion possible and for this you need to supply the correct amount air (oxygen) to insure that. This is the reason that commercial oil burners have either blowers on the air inlet or exhaust fans on the discharge; so, I doubt that you could get sufficient air flow to achieve that by trying to exhaust through the wood blanket. Also, incomplete combustion increases the risk of dangerous Carbon Monoxide discharge.
Keep in mind that you are burning waste oil with potentially unburned contaminants in the discharge gas that would be quick to clog the blanket.

The burner has a forced air fan and air intake adjustment, fuel pressure adjustment. When it was installed in the furnace, it burned very clean. The exhaust only had heat waves and no odour.

Yes pushing exhaust through ceramic wool blanket would reduce flow, it does seem like a bad idea. But then again a dpf on a truck cleans exhaust and burns contamination off and is made from a similar material

 

[Tom.G]

So, could ceramic wool be used to make a combustion chamber with no opening? Maybe just a big cylinder with the burner poking into the one end, and rely on the gasses passing through the wool?
It would work like a dpf filter on a diesel truck I suppose. Does anyone have any idea if the wool would work in that arrangement?

I think that is a false analogy, not applicable as you have described. A DPF on a Diesel truck is in the exhaust system, well away from the combustion activity. As such it does not impact the flame developement.

Perhaps you could do further research on the DPFs themselves to find out what their operating mode is (just a filter? catalyst bed? or...??), what temperature they operate at and if they can withstand a direct flame.