Fire to crown sheet distance

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cp4449
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Fire to crown sheet distance

Post by cp4449 » Mon Jan 22, 2018 10:56 pm

Working on a burner problem. What should be the average distance of propane burner flame to the crown sheet? I know this sounds crazy, but my loco used to be coal. The grate is x distance to the Ca, and figure 1” of coal burning, x-1”. If you convert to propane, would the burner be at the coal level in the firebox, or even at the grate level? Would you want the propane flames let cling the crown sheet? (Assuming you had rosebud burners or any other style?

I think my burner is to low, and I know how need a arch. I plan to turn her over and measure the insides of the firebox, plus the distanc between the current burner and the crown.

Thank you in advance
C.P. Mahony
Former 1" Foreman
Los Angeles Live Steamers

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NP317
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Re: Fire to crown sheet distance

Post by NP317 » Tue Jan 23, 2018 11:20 am

cp4449:
I placed my propane burner manifold low (uses LocoParts rosebud burners) so that the flames contact the side sheet just above the mud ring.
With an arch preventing flames from going directly into the flues, my Ten Wheeler's boiler steams quite well and quickly.

The issue is less about the distance to the crown sheet as it is the length of the combustion path, and full contact with the firebox sheets. The arch should force the flame path aft, up past the fire door, and then forward to the flues under the crown sheet. This should decrease the chance of unburned gasses making their way into the flues.
Same for an oil burner.

My 90-ton 2-8-2 uses "hole" burner tubes that more closely replicate a coal fire bed, and it is also placed so the flames are just above the mud ring.
~RN
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cbrew
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Re: Fire to crown sheet distance

Post by cbrew » Tue Jan 23, 2018 12:01 pm

i concur with Russ, you need to have enough space for a complete burn, so setting the burners as low as possible is best.
I currently have the boiler off the locomotive, servicing the burner assembly, adding an arch (recycled the stainless plates from the oil firing pan).
after reshaping them,
as you can see how i shaped the arch to allow as much room as possible for the front burners but still prevent the flame from being sucked into the lower flues
arch1.jpg
profile
test fit
arch.jpg
Test Fit
the only challenge i see with this setup is inspecting the lower flues during the yearly hydro. so i am looking at buying a bore scope.
If it is not live steam. its not worth it.

cp4449
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Location: Granada Hills

Re: Fire to crown sheet distance

Post by cp4449 » Tue Jan 23, 2018 1:29 pm

Thank you gentlemen, that all helps a lot. I suspect all of my heat is going down the lower flues (I have 9 1/2" flues). Time to seriously redesign the burner.
C.P. Mahony
Former 1" Foreman
Los Angeles Live Steamers

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makinsmoke
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Re: Fire to crown sheet distance

Post by makinsmoke » Tue Jan 23, 2018 1:59 pm

Ahhhh, Man.
I tried to beat you out of your oil pan and stuff a few years ago but you wanted to hang onto it.

Now you've cut it up!!

😫


Hey, beats going to the store and buying stainless, right?

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Bill Shields
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Re: Fire to crown sheet distance

Post by Bill Shields » Tue Jan 23, 2018 7:24 pm

CP:

The only realistic answer is related to the flame that comes out of the burner and you have to think it through.

If you have SOLAR type burners and an arch, what you see is one answer. you want to remember that these burners don't heat everywhere, only around the tip at a 2" diameter or so, and up from there.

If you have a multi hole / slot burner, what you see is another answer.

If you have blowtorch type burners under the throat, pointed at the fire door (like an oil burner), the answer is completely different....and very successful for a smaller firebox...just don't open the fire door when the gas pressure is up. This technique works very well and is not often seen in smaller models (no idea why...).

One of the most important concepts you need to deal with is that you don't want any more air in the combustion area than the burners need to support proper combustion.

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ChipsAhoy
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Re: Fire to crown sheet distance

Post by ChipsAhoy » Tue Jan 23, 2018 9:46 pm

...And to add to that, I wouldn't think that you would want ANY flame impingement on the metal walls.

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Bill Shields
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Re: Fire to crown sheet distance

Post by Bill Shields » Wed Jan 24, 2018 7:37 am

actually you do want flame impingement on the metal walls.

why not????

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ChipsAhoy
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Re: Fire to crown sheet distance

Post by ChipsAhoy » Wed Jan 24, 2018 9:29 am

Why would you want it?
I've worked in Jet engine operation and repair, and in very large gas fired heat exchanger and boilers in petrochemical process. In training for both they specified that flame impingement on the metal excellerated the decomposition of the metal. This is during continual heat exchanging, I don't know the effect of short term heating as in metal working.
https://www.johnzink.com/parts-service- ... uary-2010/
John Zink made the liners in our stationary boilers. Liquid on one side helps to disburse the heat, but still causes hot spots and shelling/delaminating on carbon steel.
http://www.nationalboard.org/index.aspx ... 164&ID=238

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Bill Shields
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Re: Fire to crown sheet distance

Post by Bill Shields » Wed Jan 24, 2018 9:52 am

No disagreement with what you say (been there done that with GE / WESTINGHOUSE, and yes even Zink), but flame on our boilers doesn't realistically hurt...cannot say that I have ever seen a steel (or copper) model boiler that failed as a result of this type of impingement...and cannot say the delam would even be a consideration here.

I spent a couple of years repairing bad spots in a HYDROFORMER, so I know exactly from where you are coming.

Actively TRYING to keep the flame away from a firebox this size of boiler is a bit like tilting at windmills since the variations in operation will gobble up any dream of clearance control unless you are running the multi-slot / hole furnace type of burner.

My Solar type of burners impinge directly on the sides of the firebox and the crown sheet. I HAD them backed off at one point and the heat just was not there. Yes, my 'arch' setup is a little bit different, but it works very well.

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ChipsAhoy
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Re: Fire to crown sheet distance

Post by ChipsAhoy » Wed Jan 24, 2018 10:39 am

I am playing with Marty Burners. They don't seem to behave too badly, having so many that are each individually adjustable, makes it somewhat easier to "fine tune" . Somewhat!! Am even able to dovetail the "lifting blue flame" between each burner to squeeze them closer together. But, I was more over addressing CP Mahoneys original post question. Sounded like he was tempted to crowd the crown sheet with flame and i could see only potential trouble by raising the Delta T in any one spot.

cp4449
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Re: Fire to crown sheet distance

Post by cp4449 » Wed Jan 24, 2018 12:56 pm

Chips-thanks for your reply. No I was not going to flame the crown sheet. Just want to know if there was a optimum distance. I am building a multiple style burner, with a professional air mixer that I have found on the east coast.
C.P. Mahony
Former 1" Foreman
Los Angeles Live Steamers

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