Gasifier design - refractory placement

[ISeeDeadBTUs]

Seems ALL gasifiers have at least some refractory. But I see a trend and am curious what each of you with different brands sees.

Forced down draft styles seem to have full refractory in the secondary CC. In the primary though, it seems they have refractory only in the bottom and 1/3 or less up the sides.

RMND units (Seaton, GreenWood,Greenfire,Adobe, etc) have the primary CC completely refractory. I would describe the secondaty CC as part refractory (back wall of primary CC) and part insulation over steel.

Assuming I am correct above, my observation is that

1)Creosote does NOT stick to refractory. It does seem to stick to the primary CC where the steel is exposed. Not knowing much about those styles, is there water behind the steel there?

2)Forced down draft styles like the CB eClassic started out with refractory, but users have found the need to remove the refractory. Why, and how has it helped?

 

[tom in maine]

Refractory is only there to allow heat to build up for a complete burn.
It becomes hotter than the surrounding surfaces and, at least in theory, any unburnt hydrocarbons that come off
the wood as gas or particles hit this hot surface and completely burn.

There have to be some surfaces that can get above 1400F to allow this complete combustion. How you get there does not
necessarily rely on refractory, but it works the best for striking a balance between standing up to the heat, storing some for later
use (clean combustion) and not costing a lot.

Refractory does steal energy from the process and can water down the efficiency of a unit if the heat that is stored cannot be used in the
building being heated.

Realize that rising in temperature from room temp to 2000F in a unit that weighs 1500 pounds is a lot of energy. Likewise, if this unit is outdoors or
in an out-building, that energy that is left in the unit is doing no useful heating for your home, except for keeping you warm while operating the it.

 

[Singed Eyebrows]

If you have access to the German Kunzel you don't need to worry about refractory, there isn't any. They are about $13,000 US in Germany for the fancy one, Randy

 

[kabbott]

The Varmebaronen has only one piece, between the primary and secondary chambers. The piece under the nozzle opening is
steel. How it survives is beyond me, Must be some tuff stuff.

 

[slowzuki]

There is less refractory in the primary chamber so the wood doesn't gasify too quickly. The refractory where logs touch is a hard type suitable for impact, not rated for as high of temps and doesn't insulate the best. The nozzles and exhaust paths are high temp, highly insulating type to get quicker light off and good burn temps for complete burn of the solid particles blasting through.

Once you get about 3 ft of high temps at the velocities needed to burn correctly you have consumed the solids and you can start sucking the heat out.