Combustion Chamber Questions...

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Old 08-22-12, 08:32 AM
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Combustion Chamber Questions...

Itís time for me to start thinking about how Iím going to address a combustion chamber that has been breaking down over time and is now on its last leg.

The boiler is an early 1960's vintage National-US Radiator (#7-25B) w/Carlin 102CRD oil-fired burner. Over the years the unit has been considerably "down-fired" and currently operates with a 2.5 GPH nozzle @100psi.

The combustion chamber is made of several sections of fireproof "tiles" which are cracked in a several places. The tiles are also separating from themselves at the joints. There was originally a thin steel band wrapped around the entire chamber that helped keep it together, but the band is now broken and the tiles are free to move about.

The inside of the combustion chamber measures approx. 27"L x 17"W x 16"H.

What I will call the "firing area" inside the boiler measures approx. 36"L x 23"W x 24"H.

More detailed specs and related diagrams/illustrations can be found here: National-US Radiator 25B Series I/O Manual.

If you scan through I/O Manual you will notice that the instructions indicate that a combustion chamber is "not furnished nor necessary" for the boiler if it is going to oil-fired (bottom p.7). Which to me means that, in such cases, a chamber is optional (Figure 2 in the I/O Manual even shows an oil burner firing into the boiler without a chamber). Which brings me to my first question:

Based on the information set forth in the I/O Manual (and any other related facts or experience one might have), do you think it would be OK for me to just remove the broken-down chamber entirely? This would obviously be much simpler and cheaper than trying to repair or replace it.

Also, in the event I do remove the chamber, would it be wise to at least provide some sort of "target wall" by utilizing Kaowool Board or something similar against the back wall of the firing area?

All questions and comments are welcome. TIA
 
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Old 08-22-12, 12:42 PM
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The purpose of the combustion chamber is to provide a hot environment for proper combustion of the oil. Since you have "downfired" this boiler that becomes even more important. I would NOT try to go without the combustion chamber unless you want to increase the firing rate back to the maximum listed for your boiler/burner combination.

A Kaowool chamber would have the advantage of heating up fast but would probably deteriorate quicker than one of hard refractory. Grady may have some recommendation for a soft, but high temperature material that will heat up quickly (seconds to a few minutes at most) that is currently being used. My experience in combustion chambers is mostly on larger (commercial and industrial sizes) and is at least ten years out of date.
 
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Old 08-22-12, 04:24 PM
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Hi Furd, thanks for responding.

Your point about the boiler being downfired is a good one. I did consider that as probably being one of the factors against removing the chamber.

On the other hand, I have read up on the Carlin 102 CRD and, like other retention-head burners, the flame is supposedly hotter and more stable than with old-style conventional burners. The 102CRD install manual even notes that the burner generally works fine with or without a combustion chamber. So I was wondering if that might be a factor in favor of removing the chamber.

Also, the "firing area" of the boiler isn't all that much wider than the chamber. But it is quite a bit longer, which is why I was thinking of some kind of target wall placed at an appropriate distance away from the burner, along with some kind of refractory wall to protect the burner. In short, two refractory walls with something on the bottom...
 
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Old 08-22-12, 04:46 PM
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Refractory does NOT "protect the burner". It MAY under certain circumstances protect the boiler heating surface from intense flame or if this boiler's combustion chamber (furnace) has a "dry" bottom there might be an insulating refractory used to protect that area. Insulating refractory offers more resistance to heat transfer while also providing a non-combustible 'face" exposed to the flame, albeit a lower temperature rated material than a high temperature refractory.

In all cases a lightweight refractory is for proper combustion of the fuel. It may be that your specific burner will be okay without any refractory. So-called "target" walls are for the protection of the boiler and have little bearing on the combustion process. If your flame length is significantly less than the length of the furnace then you do not need a target wall.
 
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Old 08-22-12, 06:09 PM
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Look up Lynnmfg.com/hvac/chamber-perfect-fit I might even try a quickie 300 and go down to a 3.25 nozzle with a little rework and dry blanket.
 
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Old 08-23-12, 09:33 AM
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Hello guyold,

I've looked over the Lynn website and see that it offers a bunch of great refractory products and chamber kits. The only problem is that, the chamber kits are marketed according to boiler type, and not according to size. Not surprisingly, my 50 year-old National/US Radiator 25B-Series is not one of the boilers listed in the Lynn Reference Manual. So I'm probably looking at a "custom build" situation. Although I think I might try contacting Lynn directly to see what they think.

I'm carefully considering what Furd has said regarding the purpose of light-weight refractory vs. combustion chambers in general. Good stuff to keep in mind.

Something I forgot to point out: at the bottom of page 8 of the Boiler I/O Manual is a chart showing the GPH and other specs of the original oil burners that could have come equipped with the boiler (as an option). Note that the "92A" burner is rated at 2.6GPH and uses a 2.5GPH nozzle. The chart does not discern between the different 25B-Series sizes (i.e., number of sections). As I noted in an earlier post, I'm currently going with a 2.5GPH nozzle on my Carlin 102CRD.
 
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Old 08-23-12, 03:04 PM
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The chart does not discern between the different 25B-Series sizes (i.e., number of sections).
A correction is in order. The sentence should read:

"The chart does discern between the different 25B-Series sizes (i.e., number of sections)."


 
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Old 08-23-12, 03:21 PM
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Hi Rockledge, meant to say 2.25 gal. Be sweet if the quickie 300 would fit thru your door.could not bring up your referances.What I would do often was cut the front off a quickie,set it back so the flame would not quite lick the back wall,lay blanket to chamber and more folded to secure around it or use "legs".Faster then boards or custom. Good luck.
 
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Old 08-28-12, 06:07 PM
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Guyold speaks with many years experience & having been down the chamber road more than a time or two. The quickie chambers do work quite well even with some sometimes needed field modifications.
 
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