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Rocket Mass Wood Dryer - An Ecoquest Project for Willie Smits  RSS feed

 
Olof Jönnerstig
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Thanks Matt!

This is what we did today... we  Burned out the core to get it drying .. still not quite dry when we left today but I'm hoping by tomorrow morning it will be done. Seem to be working well no heat can be felt on the outside of the core and it had been burning for most of the day so its definitely insulated.
We also got the Heat riser molded today, We just taped some aluminum sheet together and filled it up with the rice husk clay mixture and plan to take the metal off it when its dry .. hopefully that will work



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Olof Jönnerstig
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Thing don't feel 100% optimistic today...  the core is quite crumbly on the inside of the wood feed...
but we have trying out some new mixes with sawdust which i hope will have a similar effect as sand in cob but still have an insulative effect, so maybe if that works out we could line the inside of the core with some of that mix.. obviously still keeping the 8 inches
apart from the crumbliness it's holding up pretty well in terms of insulating enough... 

We had to change the plans today,.. the heat riser looked like it would take 100 years to dry out so we decided to start again, we figured that a metal mesh would give better air circulation and dry better than the aluminium sheets,
so went for a quick ride down the hardware store and got 2 types of mesh one with larger holes for support and one with smaller to hold in the mixture...

We also did 2 insulated duct pipe elbows, first we made some molds out of carboard tape, wire mesh and i even used some banana leaves to keep the cardboard from getting wet... and then we covered it with our mixture of clay-sawdust rice husks and Arenga palm fiber,  this was totaly experimental.

As we were leaving some dark clouds were gathering in the distance so We tucked our clay creations in with some plastic sheets and hope it won't rain tonight.

things would definitely be easier if we had some perlite, fire bricks and some ready made duct pipes   



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Olof Jönnerstig
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here is my elbow mold... i have no idea if this will actually work just hope the palm fibers can give it some strength and hold the shape
I forgot to take a picture of when it was "cobed" over.. will post one tomorrow
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Olof Jönnerstig
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Turns out the mesh wasn't that great of an idea after all... well i think we should have packed it in tighter and also our mixture was perhaps too wet...

Anyway putting it in the mesh definitely helped it to dry out quicker but the clay mix wanted to sink down and it had started to dry and solidify at the top so basically the top part detached and formed a donut of dryish clay mix that was still stuck to the aluminium and the mesh.
So I had to cut the mesh open stick some more clay mix in between the donut and push it down to glue it back on to the heat riser... it seemed to do the trick.
I also think it would that sawdust works better than rice husks it seems to be more stable and equally as insulative...

We Put the heat riser on the core today, with the help of a tiny trolly and muscle power.  It was still a bit wet and quite heavy.  As soon as we got it on we started a fire and it really took off.
A nice roaring rocket sound blared out of it and steam started coming off the heat riser so this gave me a boost of confidence that at least its doing what it should be doing
the aluminium pipe evaporated pretty quickly and we even got flames peeking out from the top of the heat riser, so on that front, it feels good!

We also cut out the exhaust holes on one of our barrels and we ordered some stainless steel sheets to make some duct pipe out of to go from the heatriser to the barrel wich we are thinking to insulate with rock wool instead of our clay mix this time.


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Olof Jönnerstig
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got a hole all the way through the wall now too
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Erica Wisner
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Location: Okanogan Highlands, Washington
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Hi Olaf,
What happens next!

If you can get perlite shipped in, it's light weight and not that expensive, it is a lot easier to get your mix to work with perlite than sawdust.
If not, consider using a longer fiber (like short straw fines, or donkey poop) in the clay mix.  It will burn out on the inner layers, but can help hold together the outer layers, especially if there is good insulating properties to reduce the charring of the outer layers.
Vermiculite is not as useful because it loses a lot of its insulating properties in the mix - it's little flat plates, and the clay tends to fill between them as it holds them together.

We did a local mix in Morocco that was about 2 parts perlite, 1 part chopped straw, 1 part very sticky local clay, and it is not as strong as fire brick but works pretty well. 
Another option would be to build with much thicker earth blocks.  You are not constrained by volume, your heat riser doesn't have to fit in a barrel, so why not make the whole thing really big - like a foot or two, or half-a-meter thick? 
As long as the inside shape is the same, you should get rocket type performance, and the added thickness will help it be self-supporting and fixable if there are cracks.  Might cast the heat riser in sections - rings or halves - so that it can crack in a non-destructive way.

I would also consider how to vent the shed, vents you can control from the outside to increase air flow if it gets too hot (without needing to go inside, where it might be dangerously hot).  Vents up high, and down low, and maybe a peek-hole around 1/3 of the way up the shed or in the door (neutral pressure zone).

-Erica
 
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