gasifier build info please

[jj2003]

Hi Im wanting to build a gasifier I love the Garn style , and was thinking of doing a similar design for my oyn use of course..
However ,, without proper seasond wood it worries me . would i be better off to go with a down draft design instead of the cross style garn uses?
Also I have aquired a 36 dia. by 36 long first burn chamber this is a serios piece of pipe being a half inch thick .. does anyone see any problems using something that thick?

 

[Gooserider]

Hi Im wanting to build a gasifier I love the Garn style , and was thinking of doing a similar design for my oyn use of course..
However ,, without proper seasond wood it worries me . would i be better off to go with a down draft design instead of the cross style garn uses?
Also I have aquired a 36 dia. by 36 long first burn chamber this is a serios piece of pipe being a half inch thick .. does anyone see any problems using something that thick?

NO gasifier will work properly without properly seasoned wood - nor will any other form of wood burner, though some will sort of let you get away with it if you are willing to make a lot of pollution and not get as much heat out of your wood as you should... Sorry, but they don't make boilers that allow revocation of the laws of physics, and if you try to burn green wood, those laws say that you are going to spend most of your BTU's drying out the wood before it will burn...

In terms of home build boilers, there is a lot more subtlety in the design of a gasifier than it appears. It is an instance of a very simple looking construction with a lot of engineering behind it that won't work properly if you don't get everything just right... However I suspect the Garn type design is probably a little more forgiving than the down-draft units. If for whatever reason you couldn't do a Garn style design, I'd probably want to look at a Seton style unit, which is a design that seems particularly more suitable for home building.

Biggest problem I see with trying to build a Garn-clone is that you are looking at some really big hunks of metal to weld up, and all of the welds need to be watertight... This is going to take some serious equipment and skill, not just for the welding part, but also just the basic metal handling tools. However there have been at least a couple of our members that have done Garn-clones, and if you do a search you should be able to find their threads on how they did it...

Gooserider

 

[Singed Eyebrows]

You might want to PM Garnification & see if he will help. Dectra(Garn) gets a little nervous when too many details are posted I've read. Garn is a great boiler & Garnification made it even better with his heat exchanger. As Goose says this is not something you just slap together, there are some critical dimensions you are going to need. Being non pressurized anybody with average welding skills can safely weld this up, to get the leaks out might take some second passes. Good luck, these are really nice boilers, Randy

 

[jj2003]

I appriciate the feed back from both of you.. Id have to disspute the forgiveness of the garn and wet wood being its a hoizontal burn , but I could be tottally wrong being I dont own one..
My understanding is that with a down draft you have a chance to heat the gas threw the coals witch makes it a more forgiving unit.?
Any info on this matter would be great....
Im not claiming to know everything there is about gasification , but over all design I dont beleave is much of a challange .
PLEASE tell me if Im wrong , but the overall principle is much like a rocket stove ,and a blast furnace combo.

I believe the most diffcult issue one faces with a boiler is if they decide on a pressurized unit..
My build would be definetly unpresurized iliminating a bunch of probs for myself.

The other question I had was does anyone think the 1/2 inch 1st burn chamber is to thick , not allowing enough heat transfer?
If anyone has any design that they would work great Id love to see and hear about them , I just dont want enother chimney fire....


Thanks for all the info......

 

[leaddog]

first off the 1/2 in isn't a problem for heat transfer as you get very little transfer from the burn chamber. The burn chamber is just to get the fire burning at about 500* and put off the gases. Then the gases go into a chamber , mixes with more air at the right amount and burns at 2000*. Then the burnt gases,air water vapor, etc passes through a hx where the heat is transfers into the water and lowers the temp to around 400*. If you lower it to much you condense and rot out you chimney and pipe and if you don't remove enough heat you waste btu's out the chimney. Thats where the engineering comes in. You need just the right amount of primary air and just the right amount of secondary air mixing in just the right amount at different stages of the burn. That's why in the newest boilers they are starting to put o2 sensors in the smoke stake so they can adj the primary and secondary air as needed.
Th reason you need dry wood is you need to get the gases at about 1100* to start burning completely and if you have to much moisture in the wood it steams off and lowers the gases under that magic number and they don't burn. Then you get LOTS of smoke and creosote and loose most of the btu's.
Also in that secondary burn chamber where the gases are burning at 2000* you have to have ceramic as steel won't hold up.
If you look at all the gasers including the garn you will find ceramic in the bottom of the primary chamber and ceramic in the secondary where the flame hits.
It is possible to make a gaser as several have done it but it isn't easy to do and you will redo and redo before you get it right if you do. If you are doing it because you like to experiment and do things like that I really think it is a great project but if you are doing it to save money probably you would be better off buying one already proven. The OWB manufacturers have been working on this for many years and any of them that I've seen are still works in progress.
leaddog