Rocket Mass Wood Dryer - An Ecoquest Project for Willie Smits

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

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  

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

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.

got a hole all the way through the wall now too

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

Erica Wisner wrote:Hi Olaf,
What happens next!


-Erica

Hi Erica! Thanks for your reply Yeah perlite seems like good option to go for as its light weight and would be easy to ship in..
So what happened next...  we completed the contraption  and I have been meaning to post the rest of the sorry for ages ! never really got around to it So i will take the time now

Continuing the story...


So the Rice husk sawdust clay mix is definetly insulating enought but having said that... its kind of crumbly and not great around the wood feed and the little bridge that creates the U-shape.
infact the bridge part started to cruble quite a bit and i realized it wouldnt hold so at that point i just cut it out created a shelf of lava rock slabs that i found in a garden store in manado
Then lined the wood feed walls with lava rock slabs too to prevent any wear and tear from the wood. and it worked pretty well.

then also filled it all back up with new  mixture again

here is the elbow all cobbed up

Once the elbow had dried we attached it with some more cob.
sugarpalm fibers where used in the cob mix this time and wraped around both components.

Franky put together put it all together.. and we moved it over to the shed and installed it

Firing it up

Here is a a video showing how the temprature goin up to 174 ... it eventualy whent up to 200+  and ambent temprature of 70 in the shed


Here is when we show willie the project

(From Willies Twitter)
Willie Smits:

With Olof and Anna in front of their latest Permies project to help local people with an efficient drying method!

You don't mention the exhaust pipe temperature, this could be interesting. And I spotted a possible flaw: the inlet and exhaust of the barrel bell are on the same level. With such a tight bell I would regard it best to elevate the hot inlet just above the level of the exhaust opening. Having both pipes at the same level bares the risk of short cutting by the hot gases.

Peter van den Berg wrote:You don't mention the exhaust pipe temperature, this could be interesting. And I spotted a possible flaw: the inlet and exhaust of the barrel bell are on the same level. With such a tight bell I would regard it best to elevate the hot inlet just above the level of the exhaust opening. Having both pipes at the same level bares the risk of short cutting by the hot gases.

Hi Peter

it was still kicking out a fair bit of heat about 100 ºC so there is definitely room for improvement maybe would be good to channel the pipe through a Mass bench around the floor.
The exposed parts of the inlet pipe that connects the heat raiser to the barrels was about 400 ºC the rest was insulated with rock wool
Regarding the inlet pipe. It enters at the bottom of the barrel next to the exhaust but has a elbow on the inside that takes the pipe up to about the top of the first barrel.
I was hoping that that would be enough to have the hot air rise and not go straight out of the exhaust. Perhaps that should be higher.

I know I was warned to not let the exhaust leak out in to the shed for health and safety reasons... thats how it ended up
there are slits in the roof so the exhaust would leak out from the shed from that but it would still fill the shed up with some of the exaust.
not ideal but at the time we didnt get a chance to cut a hole for the exaust.   this will be contributing some to the ambient heat of the room I think ..

Olof Jönnerstig wrote:it was still kicking out a fair bit of heat about 100 ºC so there is definitely room for improvement maybe would be good to channel the pipe through a Mass bench around the floor.

Olof, I'd think that 100º C is necessary to keep the draft going strong. With a temperature of say, 40º C outside the temperature difference is only 60º C. Adding a bench would kill the draft and thus the clean burning.

Olof Jönnerstig wrote:The exposed parts of the inlet pipe that connects the heat raiser to the barrels was about 400 ºC the rest was insulated with rock wool
Regarding the inlet pipe. It enters at the bottom of the barrel next to the exhaust but has a elbow on the inside that takes the pipe up to about the top of the first barrel.
I was hoping that that would be enough to have the hot air rise and not go straight out of the exhaust. Perhaps that should be higher.

The inlet ending inside the tower at the top of the first barrel is excellent, probably more than is strictly necessary. The only downside is that the pipe inside the bell takes up space so the lower third of the bell won't be heated up that much due to higher air velocity downwards around that pipe.

Olof Jönnerstig wrote:I know I was warned to not let the exhaust leak out in to the shed for health and safety reasons... thats how it ended up
there are slits in the roof so the exhaust would leak out from the shed from that but it would still fill the shed up with some of the exhaust.
not ideal but at the time we didnt get a chance to cut a hole for the exaust.   this will be contributing some to the ambient heat of the room I think ..

So the shed doesn't act itself as a bell, but instead all the heat is exhausted into the shed, taking out the moist with it. All the heat produced is already fed into the shed, again no need for a bench of whatever construction. The temperature difference between the exhaust pipe and the surrounding air in the shed is thus 30º C, I personally wouldn't dare to lower that level. It is demonstrating though, how efficient a well-built bell system really is.

The stench of wood smoke is caused by aromatic hydrocarbons, the human sense of smell is able to detect that at very low levels. Almost up to the last molecule, so to speak. You filmed inside the shed with the door opened, did you smell any wood smoke, and how bad was that? When the only thing you could detect was a laundry dryer sort of smell, wet socks or something similar, the contraption was running very close to complete combustion. Not uncommon in rocket mass heater department but it is worth a congratulation!

Peter van den Berg wrote: it is worth a congratulation!

Thanks

I was wondering if you could improve the drying time by adding a feature in some of the solar dehydrators.
What if you put an air inlet into the shed up high that gets it air from a ceramic pipe laid into the ground so the air would be cooler going in, so less moisture, and then had the air going out come from the bottom of the room and then pipe it to the chimney and have this pipe surround the chimney and exit up and out of the building with the warm exhaust. The top of the chimney would look like a donut and the lower inlet pipe could act as an air lock. My theory is that like the solar ones the warm moist air will flow easily down because of the weight and then the double chimney will create the suction to pull it out of the building like the black pipe does on the downdraft solar dehydrator. Just a thought.

What an awesome build!