Post Gasification Stage... creosote worries?

[ClydesdaleBurner]

Hi,

I was wondering when you set up for an overnight burn, you load your firebox full, get it going strong, adjust the air down and let it cruise... with the air turned down low, when the wood reaches and passes the gasification stage and moves on to the coaling stage can any cresote form during the coaling stage???

Thanks!

 

[gyrfalcon]

Hi,

I was wondering when you set up for an overnight burn, you load your firebox full, get it going strong, adjust the air down and let it cruise... with the air turned down low, when the wood reaches and passes the gasification stage and moves on to the coaling stage can any cresote form during the coaling stage???

Thanks!

Can't answer your question as to when the creosote forms. Somebody who can will surely be along shortly. But if you have a good chimney and good dry wood, it shouldn't be a big problem. If you can, do check your chimney periodically this winter just for your peace of mind. Pay for a sweep to come look at it in a month, if you can't do it yourself-- as I can't. But I made a lot of lousy, low-temp fires from inexperience and poorly seasoned wood all last winter during the day, not just overnight, and my chimney sweep this fall found only a very small amount of creosote. So do check, but don't make yourself crazy until you do.

 

[gyrfalcon]

Meant to add that a dangerous creosote build-up isn't going to happen in days or even a few weeks, so you have plenty of time to do your overnight burns before checking or having the chimney checked.

 

[begreen]

Once the stove is in the coaling stage, the gases that can condense and create creosote deposits have been burned off.

 

[Backwoods Savage]

Like BeGreen say, no worries there. So sleep comfortably.

 

[jebatty]

Not meaning to pour water on your coals, but it might be helpful to use the term "gasification" with a little more clarity. While technically all burning is of gases, the term "gasification" is a term of art used in application to a specific high temperature combustion process employed in gasification wood boilers, not space heating wood stoves. The secondary burn in wood stoves is at a temperature far lower (approximately 900-1200F, others free to be more specific here) than the gasification temperature in wood boilers (about 1800-2000F). That difference translates to a burn efficiency in gasification boilers of 98-99%, and about 65-85% in wood stoves, and about 30% or a little better in traditional OWB's.

My understanding is that wood stoves normally do not burn off CO or H, which occurs at 1200 to 1400F and up. Gasification boilers are designed with special refractories and high temperature combustion and forced air designs that achieve the temperatures to combust CO and H. Typically a gasification boiler emission also will not contain the fragrance smells of wood burning stoves, which many enjoy. Gasification boilers also combust these fragrances gases.

 

[thechimneysweep]

I think this discussion is simply about two different usages of the term gasification.

Gasification, by basic definition, is conversion to gas. In a woodstove, the bound moisture in the fuel wood (wood resin) gasifies at about 500f, which happens during stage 2 of the fire. The resulting gases are ignited and burned in a non-catalytic secondary burn system at ~1100f (500-600f or even lower in catalytic stoves).

The wood fiber itself doesn't gasify so readily: in a woodstove, it is consumed by pyrolysis during stage 3 (charcoaling).

Gasification of the wood fiber (or any carbonaceous material, such as coal, petroleum, biomass or even plastic waste) requires higher temperatures (1300f - 1800f), ultra-precise control of oxygen and, often, the introduction of steam. This process produces a product known as sythesis gas, or syngas. Syngas can be burned directly in internal combustion engines, used to produce methanol and hydrogen, or converted into synthetic fuel.

So... in a woodstove, gasification of the wood resins does occur, and gasification of the wood fiber doesn't. By the time the fire has reached the charcoaling stage, there will be very little unburned exhaust gases to fuel the secondary burn or foul the chimney.