It will be interesting to see if this shape is better able to handle the fines in raw unscreened machine processed woody material with it's resultant fine char. The inverted V and Tube style hearths good as they are for block form fuel choke out on the fines. SteveU.

Steve!

I think you are barking under the wrong tree! As a hearth is dimensioned for ONE SIZE fuel at a time, it needs to be trimmed, when changing fuel size!

As long as the gas load is kept the same, but fuel bit mean size is decreased, the reaction surface is greatly increased. The same entering airstream looses its oxygen in a shorter entering distance from the nozzle tips.

Additionally, charring advances also progressively.
These CONCRETE changes result in the oxidation region not reaching to the entrance of the restriction. This opens the “free” route for tar-gases to get “unharmed” around the oxidation process and down into the reduction zone. Additionally ash can start piling up from the reduction zone if the velocity is too low to blow out the ash.

ONE HAS to decrease the physical dimensions accordingly.
As it has the form of a cut cone, both the diameter and height have to be decreased proportionally.

So the restriction is not to be blamed! The volume and passage area in the reduction area, as well as grate arrangement may need adjustment too, to match the smaller grains.

Good luck!

Max

Steve!

One more! Forgot to mention that the blast velocity may have to be radically increaced too! In some bigger hearths up to 36 m/s

Max

Max thank you for the information. When your voice speaks I hear experience not just speculation. Many will try to operate the GEK with machine processed wood chips. You Finns? have the most experience in the world in doing this.
The stationary engines I need to fuel for electrical generation will only draw/flow 40-80 cubic feet per minute. I have my own fir trees and my own sawmill so I can make chunk wood whatever size is needed for the gasifier to do this job. I will try the default inverted V hearth first but I expect to evolve to a height adjustable, pull out replaceable (for diameter and length) reduction/fire tube with an adjustable internal grate to have complete control over these variables. Stainless steel of course. My chickens get the sawn dust. Not luck, just like you - try/change, try/change, again and again. Steve Unruh

Hmmm. Yes I see now Max. For complete control the air nozzles need to be length adjustable toward the center too..
Again, thank you. Steve Unruh

Hello, Steve!
The standard for smaller gasgenerator nozzles has been a common area of 5% of the restriction area--NOT DIAMETER! (with ~cubic fuel) AREA % of AREA! If you cannot get the oxidation temperature up enough, take a nozzle common AREA = 4 % of the restriction AREA. I bet it gets hot!

Listening,
Max

Hello All
I've been staring at my 3' x 4" cast reducer cone an unhealthy amount for the last two days. What I keep seeing is on three of the times we let Marcus Bryners GEK consume down to out of fuel it was possible to look in and see the glowing cone of char in the reduction cone oxidizing and shrinking away.This was creating an escape gap for gasses to flow around the char zone unaffected. Char will shrink, this is normal as it is converted (hopefully to CO and not just CO2). When I stand the the reduction cone the large side up I can easily see the shrinking char following it down in with no gas escaping. Yes, the top half of an Inbert. The bottom half would be created as the char spills out onto the grate. Has this been tried by anyone yet? Steve Unruh

Jim Mason has answered my question in a comment on Brian G.s user page. I have to start thinking in terms of the increased gas volumes created that must be accomodated.
Steve Unruh