wood chip burning outdoor hot air rocket furnace

[treeclimber1]

Howdy every one

   I am starting to plan a wood chip burning outdoor hot air furnace. I am hoping to make it gravity feed even if it is a little finicky.   
If it will feed by gravity, it will be easy to add an auger later.
    Has any one tried to build a gravity feed for wood chip or pellets? I would like to see what you have done.
If you have any ideas post them here.

    Does a square bell work well. I was thinking of building a square bell with thin wall tubing inside running vertically along one side for a heat exchanger. Using a square bell will enable the insulated furnace jacket to maintain a small consistent gap for max heat exchange.  

    This furnace will sit outside the shop. It will have an insulated heat duct going into the shop and a cold air return duct coming out. The draft for combustion will be to the outside air. This will reduce the risk of fire when painting in the shop etc. Also will not take up any space inside the shop. 

Here is a picture of the wood chips after screening them.

Attachments:

[treeclimber1]

What do you think of this idea? www.instructables.com/id/Gravity-fed-pellet-burner/ (Disregard the use of steel in the burn tunnel ) Of course every thing will have to be bigger to feed wood chips.


     Here is a picture of the wood chips before screening.    Less than ten percent will be too large to go through the screen.

[satamax]

www.youtube.com/watch?v=lx_9cvd5sQ0

Not mine.

[colinsaengdara]

Hi treeclimber! Just found this post. I replied on another post before. I am working on designing a stove that will burn wood chips so I will follow this thread with interest.

What are you using to screen the wood chips? and do you have a method for drying them?

[treeclimber1]

Hi colinsaengdra I am using expanded steel. The openings are about one and One half by three quarter inch.
However my chipper generates very little material over two and a half inches long, even with small twiggy material.
I live in the western United states where we do not get very many inches of rain. If the wood chips are made during the winter when there is not leaves on them they do not take very long to dry even in piles
How are you thinking of make the feed?

[Rinchen]

This could be of interest to you as well.
www.youtube.com/watch?v=K96u_eEbfqg

[colinsaengdara]

I'm thinking of a standard batch box with a dense firebrick oven above it that I could put a sealable 5 gallon can inside and cook the sawdust (or wood chips) to do slow, lower temperature pyrolysis. The wood gas would be piped to the batch box combustion chamber to hopefully keep the setup going. From what I understand about wood gas, a more controlled lower temperature is desirable because the products of pyrolysis are easier (require less energy) to combust. I'm rusty on the chemistry, but I believe it had to do with single vs. double bonds in the carbon chains.

The higher density of the chamber would provide a more consistent and hopefully controllable temperature of pyrolysis.

The purpose of the stove would be primarily experimental. But if I was able to work out a desirable design, I would use it to heat an aquaponics system and or greenhouse in my cold climate.

[treeclimber1]

I will be working on some experimenting with wood chips tomorrow to see what angle they flow at. I thinking of using a square tube at the bottom of the feed. Probably will be 5x4inches. I think a polished square tube will feed better than a round one. What do you all think? The funnel will be built with the back horizontal. The sides and front will be made very steep.
I was just reading this thread: donkey32.proboards.com/thread/327/reverse-engineering-riley-pellet-burner I think it holds the key to getting this to work if I can get it to gassify in the mouth of the feed tube like rectifier's.

[treeclimber1]

Here is what I worked on today    This seems to feed well when we hang it up about an inch and half then scrape the chip out from underneath. It starts a hole along vertical back side then starts caving in from the front. I did have it bridging when I filled it with chips then just picked it up. So I guess, there is nothing to do but construct a working model and see how it works or not. Probably will have problems.

[satamax]

I think, a funnel shape won't work. It will bridge sooner or later. A long straight metal tube, rectangular in section should do the trick. With 6 feet of it, it could feed for a fair while.

[treeclimber1]

Satamax
Yes I think you are probably right I will start testing with a straight metal tube.

[joseph]

If the only problem you are having is bridging in the feed funnel, I would suggest you consider using a "bin vibrator" (search for "bin vibrators"). It is much easier than an auger.

[treeclimber1]

joseph That is exactly what I was thinking. Probably just put it on a timer. I will be experimenting with a straight tube just to remove the extra variable during initial trial and error.

[treeclimber1]

Hi everyone
 Here is what I have been working on. This is my test burner. I will be insulating it with a sheet metal jacket filled with ash.                   
feed tube detail notice air gapI will add slots to the feed tube.

[treeclimber1]

And we have singed Eyelashes!
 Looking down p channel
Slots on the side of feed tube