Secondary burn chamber questions.

[warno]

I'm wanting to add a secondary burn chamber to my boiler I'm just wondering if it would even work fully surrounded by the water jacket. I believe the water jacket will cool the chamber too much to allow the gases to burn off properly. Does anyone have any input on this?

 

[Eric Johnson]

You're correct about the water in the jacket making the secondary burn chamber too cool. You need a good, solid chunk of refractory on all six sides to keep it hot enough. And to achieve a secondary burn in the first place, you'll need another big refractory mass with a nozzle that mixes superheated air with the wood gas as it passes through nozzle into the secondary burn chamber. Not sure, but I suspect it would be an engineering challenge to get everything sized and mixed correctly. But I could be wrong on that.

 

[warno]

What kind of temperatures happen when wood gases ignite and burn? I read alot of different ranges online, I was just wondering if I could get a definite answer.

 

[BrotherBart]

Secondary combustion starts in a firebox between 1,100 and 1,200 degrees. A little earlier aided by the flames coming off of the wood into the gases.

 

[warno]

Thank you. I have been reading temperatures upto 2000 degrees.

 

[warno]

Is there any truth to dropping the chimney down in the fire box leaving the space between the top of the box and chimney opening to act as a secondary burn?

Like this

http://www.outdoor-wood-furnace-boiler.com/images/firebox_lg.jpg

 

[maple1]

I think that question was already asked & answered in the other thread a few days ago?

But - no.

 

[tom in maine]

Worth a look. One way to get there:

http://hotandcold.tv/woodfiredfurnace.pdf

 

[warno]

I think that question was already asked & answered in the other thread a few days ago?

But - no.

In the other thread it was stated that nobody had seen a system like that in a boiler.

So that's basically a marketing scheme? To get people to think that's what's happening?

 

[Eric Johnson]

Thank you. I have been reading temperatures upto 2000 degrees.

That's the temps you get in the secondary burn chamber of a downdraft gasifier. What BB is saying is that in a wood stove, you need those minimum temps for secondary burn to occur. Apples and oranges. For one thing, there's no water jacket around a wood stove. For another, gasifiers (most of them, anyway) have forced air induction to initiate the secondary burn. Most wood stoves rely on natural draft of some sort.

 

[maple1]

In the other thread it was stated that nobody had seen a system like that in a boiler.

So that's basically a marketing scheme? To get people to think that's what's happening?

Perhaps a re-reading of the other thread is in order.

 

[warno]

I guess I jumped the gun a little before asking about a secondary chamber. I was Confusing the difference between burn tubes and a gasifier type unit.

I'm wondering about secondary burn tubes. If i add fresh hot air to top of the firebox, will the gases burn off before the smoke enters the smoke channel at the front of the box and goes out the chimney?

Or will the top of the firebox be to cool for this to happen?