Rocket Mass Wood Dryer - An Ecoquest Project for Willie Smits

Hi fellow Permies and Rocketeers!

Its Anna & Olof here from The Ecoquest!
We are Building a rocket mass heater that will be used for drying wood in the tropics. It will also be used to demonstrate a sustainable and clean way to dry fruit, coconut and other foods for the local farmers.
The potential benefits could be huge for the local community as up to 60% of the fruit produced in the tropics don't make it to the market because of mold and damp conditions. Another reason is the current practices of drying coconut by the locals is inefficient and harmful, they use a lot of wood which produces toxic smoke and stains the coconut yellow, which in turn yields a 50% lower price in the marketplace. So if we can convince the locals to start using rocket mass heaters for drying, we could be saving them a lot of hassle, money and perhaps even their lives.


THE VILLAGE HUB
This project will take place at Willie Smits Masarang foundation, village hub site, in north Sulawesi.



We would like to invite the Permies community to contribute with ideas, and also any insight form past experiences they may have had from using RMH to aid drying.
We are currently in the research and design phase of our project and aim to document every step along the way, as we will be producing a step by step guide in Indonesian for the locals, with the help of the staff at the Masarang foundation.

We will be using a wood shed that is already on site made out of standard masonry bricks and mortar with a cement plaster. The walls are about 12.5 cm thick, the shed itself is 3m x 3m  and 3.5m high.
The shed also has a wooden door which equates to 2m x 2.10m. The roof is currently made up of some wooden planks. no air vents or holes are installed as of yet and there is no insulation.
We will be basing our design on Ianto Evan's & leslie Jackson's 8" Rocket mass heater,  that they present in the book ( Rocket Mass Heaters: Super efficient Wood Stoves You Can Build)

We will shortly be posting our initial designs and ideas and we hope to get your feedback especially if you have RMH expertise and or experience in fire wood or food drying sheds.
We are super excited about this project and hope guys will like it too!

I'm assuming the shed need to get an hot air (or exhaust gases from the rocket) inlet and an exhaust to vent the moist outside. There's a problem in this respect, wood combustion produces water as a byproduct, close to 1/2 liter for every kilogram of fuel. Adding this to the process means the wood or food is expected to dry by adding moist hot air.

What I would do is building a thin metal canister inside the (middle of) the shed, for example three 200 liter barrels on top of each other. Some lids cut out in order to create a single cylinder which is open inside and closed at the top and bottom only. When the rocket feeds low or maybe halfway up into that cylinder and exhausted close to the bottom and out of the shed into a chimney stack it would act as a bell system. It will get awfully hot inside the shed without adding water vapor. While the fire wood or food is stacked around the barrel but not touching it, I imagine it would dry quite quickly. Especially when the shed is equipped with low exhaust opening to get rid of the moist. In fact, the shed itself could be acting as a bell system as well when the exhaust opening is equipped with a chimney stack higher than the shed itself.

An example of of such a barrel tower can be found here and how a bell works can be found here.

I might be mistaken about the intricaties of wood drying in the tropics but I think the above is worth consideration.

I just got off the phone with Olof.  

Here is my feeble attempt at a design.

I want to keep the barrel inside a big stratification chamber.  The wood sits on top of the stratification chamber.  The wood is the mass.  

So the building would have two parts.  One part is where you put the wood.   It has small vents at the top and bottom.   The lower part is the stratification chamber.  

The heat is spread out evenly in the stratification chamber - all of the wood is heated evenly.

Peter van den Berg wrote:I'm assuming the shed need to get an hot air (or exhaust gases from the rocket) inlet and an exhaust to vent the moist outside. There's a problem in this respect, wood combustion produces water as a byproduct, close to 1/2 liter for every kilogram of fuel. Adding this to the process means the wood or food is expected to dry by adding moist hot air.

What I would do is building a thin metal canister inside the (middle of) the shed, for example three 200 liter barrels on top of each other. Some lids cut out in order to create a single cylinder which is open inside and closed at the top and bottom only. When the rocket feeds low or maybe halfway up into that cylinder and exhausted close to the bottom and out of the shed into a chimney stack it would act as a bell system. It will get awfully hot inside the shed without adding water vapor. While the fire wood or food is stacked around the barrel but not touching it, I imagine it would dry quite quickly. Especially when the shed is equipped with low exhaust opening to get rid of the moist. In fact, the shed itself could be acting as a bell system as well when the exhaust opening is equipped with a chimney stack higher than the shed itself.

An example of of such a barrel tower can be found here and how a bell works can be found here.

I might be mistaken about the intricaties of wood drying in the tropics but I think the above is worth consideration.

Thanks for your input Peter! i Will definetly be taking this in to consideration.
Loved your batch box stuff on the innovates event, I had a sneaky peak on the dvds.

Olof, maybe you can make a sketchup (or something similar) of what i drew?

paul wheaton wrote:I just got off the phone with Olof.  

Here is my feeble attempt at a design.

I want to keep the barrel inside a big stratification chamber.  The wood sits on top of the stratification chamber.  The wood is the mass.  

So the building would have two parts.  One part is where you put the wood.   It has small vents at the top and bottom.   The lower part is the stratification chamber.  

The heat is spread out evenly in the stratification chamber - all of the wood is heated evenly.

Great drawing skills .. thanks for the feedback i think the stratification chamber idea is very cool,  
and i also liked the idea of the pepple style mass heater with airflow going through the mass. but i guess something similar would happen with the stratification chamber.

Here i our first draft.. but now after this stratification chamber has come about and the barrel tower we have some more food for thought....

paul wheaton wrote:Olof, maybe you can make a sketchup (or something similar) of what i drew?

I will give it a shot..  the only problem though is the height of the barrel.. and how high the chamber ends up being ...
and also we need to take in to consideration how it could also apply to dry food, but i guess the food would just have to be further away form the metal box perhaps...
and also in the food drying version of this there wouldn't be any mass as there is no wood...

Been thinking how this could perhaps be incorporated to add more airflow and push air through the wood
http://www.ecofan.co.uk/index.html



not sure if this would be easy to get shipped out here by the locals.. but i like the concept of it

Hmm little pre bed time sketch...
thinking  Eco fans, cobed in barrel maybe even perlite clay plastered , then a mini stratification chamber coming off the top of the barrel to support the top wood shelf. then a pebble style mass to go on the bottom...
hmm... well im going to sleep on it Tomorrow we are souring some supplies

Paul

For the stratification chamber to work would you have to have the barrel inside it or could you have the barrel on the outside of the chamber as a conventional rocket mass heater,
But insulate the barrel with a thick perlite cob plaster and channel the gases in to two stratification chambers?

Im developing three concepts a Pebble style version, a Stratification chamber Version, and a barrel tower bell shed version... here is the pebble style one so far...

PEBBLE STYLE VERSION 1.0

I know this may be a dumb question but have you thought about solar kilns. http://www.solarkilns.com/timber_drying/index.htm

Building a new structure (could be black painted corrugated iron) may be better than burning wood to dry wood.  Tobacco curing sheds that are tall are a design with a good air flow might work even with high humidity. http://www.mountaincreekarch.com/images/Tobacco%20shed%20refurbish%20%20186%20Pic%20Charlie%20BrownAnd2more_tonemapped.jpg

Even if you need supplementary heating from a rocket stove these tall designs with airflow in at the bottom and out at the top would provide airflow to promote drying

STRATIFICATION CHAMBER STYLE 1.0

Alan Loy wrote:I know this may be a dumb question but have you thought about solar kilns. http://www.solarkilns.com/timber_drying/index.htm

Building a new structure (could be black painted corrugated iron) may be better than burning wood to dry wood.  Tobacco curing sheds that are tall are a design with a good air flow might work even with high humidity. http://www.mountaincreekarch.com/images/Tobacco%20shed%20refurbish%20%20186%20Pic%20Charlie%20BrownAnd2more_tonemapped.jpg

Even if you need supplementary heating from a rocket stove these tall designs with airflow in at the bottom and out at the top would provide airflow to promote drying

Hi Alan! i don't think its a dumb question at all ..I much rather use the sun instead of burning wood too ... I asked that same question my self when we got here and basically the reason is
there are quite a lot of rainy days out here and cloudy weather.. its one of these places where even the laundry never gets quite dry and gets a slightly funky smell...
And i suspect that Willie is wanting to use the rocket dryer in even more humid environments like in the rain forests communities etc where there also is have the canopy of the trees giving shade..

Although when the sun is out it gets warm of course and things get dry. and i have seen people drying peanuts and rice just on the side of the road in the sun etc..
When it comes this project though its also about the speed in witch we can dry the wood so the factory can operate continuously without depending on the weather.
and its also about trying to do something low tech and not too pricey that the locals can emulate.

The solar kiln looks really cool!  Adding it to my bookmarks!!  

attaching a pic for some facebook sharing

A bell is a stratification chamber in itself so I think the whole drying shed could be utilised as such a chamber.
Extracting moist from wood is done best at the end grain, so I envisioned the fuel stacked around the heat source as the rays of the sun. The heat is highest on top, the fuel (or fruit) would be drying top down, which is also the direction of the air stream since the exhaust vent of the shed is also close to the floor. At first, at floor level vapour would condensate so this fluid could be drained before it would evaporate again, making the whole process much more efficient.
The barrel tower could be fed with a rocket which is largely situated outside without a barrel but with a lengthened riser and elbow, feeding the tower halfway up. Only the riser end situated inside the shed, this way the combustion core could also be a batch box rocket instead of a J-tube. Mass is no need for here, all the heat produced would be better used for the drying process directly.

Just some random thoughts.

Peter van den Berg wrote:A bell is a stratification chamber in itself so I think the whole drying shed could be utilised as such a chamber.
Extracting moist from wood is done best at the end grain, so I envisioned the fuel stacked around the heat source as the rays of the sun. The heat is highest on top, the fuel (or fruit) would be drying top down, which is also the direction of the air stream since the exhaust vent of the shed is also close to the floor. At first, at floor level vapour would condensate so this fluid could be drained before it would evaporate again, making the whole process much more efficient.

Just some thoughts.

have just been mocking up your tower.. roughly   ... and also had a go at mimicking your batch heater too in the same floor plan i have been using for the other designs i have posted...
The only thing with having the heater in the middle is it might not give so much space for move around..

PEBBLE STYLE 2.0

I edited my last post, please see the added remarks.

Thanks peter.  okay that's a bit more clearer in my mind now .. was thinking it might be a bit too dangerous with the burner on the inside of the shed..
I think making the whole shed in to a stratification/bell sounds like the way to go..  

Perhaps this will give some ideas...

http://aprovecho.org/publications-3/#agricultural-dryer    " The Winiarski Wood Fired Agricultural Food Dryer " used to be on the net, but now a PDF for download

Fred Morgan built a rocket wood-drying kiln in Costa Rica for drying tropical hardwood lumber.  The conditions for success in lumber-drying are more delicate (hold a steady temperature so the wood doesn't crack as much while it dries) but the basic idea is similar.

We helped with the initial design; I will try to find drawings.

I agree with the ideas so far of
a) keeping any wood exhaust separate from the air for drying, if possible
b) build the building with excellent ventilation in mind.  Air movement is the key to good drying conditions.
In humid climates, you want air movement plus some "conditioning" of the air (either pre-chilling it and collecting the condensed moisture somewhere else, or pre-heating it to drive down the relative humidity)
c) keeping in mind the accessibility for loading & unloading; in fact, you may want to think in terms of "cycles" where one part is freshly loaded wood, while the other part is finished and being unloaded.

I would also add a caution: piling wood on top of hot things sometimes catches the wood on fire.
There will be a balance between enough heat, and too much heat.  A bigger space with more wood drying more slowly may be safer, and more practical.  Piling wood, or food-drying racks, directly above the barrel is a recipe for accidental fires.

I second the notion to make the shed double-action: solar drying PLUS wood-fuel assist.  I assume you've already tried building a simple wood shed, with natural ventilation, and it is not working well enough for the project's needs.  



Side notes about drying wood in general:
Wood holds moisture very well.  Getting the wood down smaller will allow its moisture content to change more rapidly to match the dry (or wet) conditions of the storage.  
In the wild fire setting, we are taught to think of dead twigs and grass as "one-hour" fuels, meaning they can dry out and be ready to burn within one hour after conditions change from wet to dry.  (To burn clean and efficient, it might take several hours; we are just talking going from sopping wet to 25% moisture content.)
Finger-sized twigs (up to 1 inch / 1-2 cm) are called ten-hour fuels.  Wrist-sized to leg-sized sticks are 100-hour fuels.  And big mamma logs are 1000 hour fuels - meaning they can remain damp at the core for months into the dry season, or can remain dry enough to burn for months after the hot summer winds are finished.  Again, these are very rough estimates; designed to let you guesstimate the fire risk in rough terrain, not burn a perfect cooking fire.

If you are able to achieve a big enough, dry enough storage to keep a lot of wood ready-to-use, then there is some advantage to keeping larger logs (they will "hold" their dryness longer) and splitting them down immediately before burning.  If you are drying fuel as quickly as possible for immediate use, then consider using smaller sticks, split or de-barked, wrist- to finger-sized, and give them a few days to a week to fully dry.  

There is advantage to cutting or breaking the sticks relatively short (whatever their intended size), because this exposes more end-grain and surface area, and the wood will dry faster.


I looked up Borneo's relative humidity and temperature.  
The Interwebs says it is typically 27-33 C, with relative humidity around 80%.

In North America we typically understand that wood should be down below 25% moisture content to burn, and below 15% to burn efficiently and clean.  (In our semi-arid Western summers, the hottest part of the day may be 4% to 12% humidity.)

I found this online calculator which takes a known temperature and humidity, and calculates the new relative humidity if you heat that air up in an enclosed space.
http://www.lenntech.com/calculators/humidity/relative-humidity.htm

According to that calculator, at about 50 C you would get below 25% humidity (the calculation gave 50 C = 23% humidity)
and to get down below 15%, 60 C is hot enough.  (the calculation gave 60 C = 12.5%  humidity).
If you consider that the wood is adding moisture to the air as it dries, but air movement is taking this moisture away, then 60 C seems like a reasonable target for average temperature in the shed, with good air circulation to encourage the moisture to move out and away.

Dangerous temperature zones:
For people working: In saunas, where people go for only a few minutes, max. temperature ranges from 70-90 C.  (In the US and Canada, the hottest legal temperature for a sauna to reach is 194 F (90 C), but pregnant women are advised not to go in saunas hotter than 70 C).  If the wood is being handled by someone working, fully clothed, in a space, who may need to be in the space for more than a few minutes, these temperatures could be too hot.  
Sauna "competitors" have died from only a few minutes' exposure to temperatures of 110 C.  (The human body core temperature is usually 38 C, all of these temperatures are hot enough to cause heat illness over time, especially if for any reason the person working can't cool themselves by sweating.)

In homes, if you put wood (furnishings or trim) in proximity to heat, and that wood gets over 65 C (150 F), it is considered unsafe because the wood can slowly char, and over time you could have a fire.  At around 95 C (200 F), you are approaching the boiling point of water, and things can dry out (and accidentally catch fire) more quickly.  This temperature could be useful in a drying kiln IF careful controls are maintained so that it never gets too hot or catches fire.   I would consider it a maximum temperature for the hottest corners of the room - consider a way to shut down the fire or divert the heat if it gets this hot at the hottest points inside the room.

So I would suggest to be careful about where the wood racks go around the barrel - in the hottest corner, the wood closest to the heat could easily get up into the danger zone.
I would suggest perhaps creating a buffer space, and bringing the fresh air intake into the room around that barrel area.  Incoming air could be quickly warmed by the barrel, while the buffer space would reduce the chance of overheating the wood.

I would also suggest making the room easy to clean, since there could be a fire hazard in case of long-term buildup of wood debris at these temperatures.  (Also there might be insect problems, spider nests, etc.)

So I would add: Screened air inlets behind the barrel, with some brick or tile directing the cooler incoming air up around the barrel on the sides closest to the wood.  Attention to rack design and stacking so that there is natural air flow from this area, past both ends of the wood, to the air outlet (which might be centered or sort of above the access door area).

If the access door is left open, there would be a tendency for the air to shortcut from the access door to the outlet, and the circulation pattern around the lower air intake could weaken.  Any gaps around or under the door should be considered as air inlets, and the outlet might need to be larger than the intended "inlet" to maintain a good draft.

For safety, I would suggest that the door open outward, so that if there is a very bad accident with the stacks of wood falling or catching on fire, it is not possible for the wood to block the door closed.

Those are my thoughts at the moment.  I hope this is helpful.

-Erica

I wonder if this could be done as a solar dryer and/or rocket dryer.

I want to second what peter said:   wood dries about four times faster when put on end.  It's just that it does not stack well that way.

Erica Wisner wrote:I found this online calculator which takes a known temperature and humidity, and calculates the new relative humidity if you heat that air up in an enclosed space.
http://www.lenntech.com/calculators/humidity/relative-humidity.htm

According to that calculator, at about 50 C you would get below 25% humidity (the calculation gave 50 C = 23% humidity) and to get down below 15%, 60 C is hot enough.  (the calculation gave 60 C = 12.5%  humidity). If you consider that the wood is adding moisture to the air as it dries, but air movement is taking this moisture away, then 60 C seems like a reasonable target for average temperature in the shed, with good air circulation to encourage the moisture to move out and away.

An average air temperature in the shed of 60 ºC would be too much to ask from a rocket mass heater I'm inclined to think. Only the barrel is capable of heating the air inside the shed to that level, probably by going over 200 ºC at the barrel surface which is a situation to avoid close to the drying wood or food. Surrounding the barrel by mass will lower the temperature so in that case it will take a huge amount of time to get to the desired temperature. That's why I think mass isn't very handy here unless you have lots of time and an enormous pile of stuff to dry so you need a full-continiously process. In that case it would be very difficult to get the dry stuff out and the fresh stuff in when the process of heating is still going on.

I know how a barrel tower with no mass to speak of works, I've done exactly the same in my former workshop. Piling fuel around the thing in order to maximise the radiation benefit. Also, when the batch of stuff is ready you simply stop feeding the fire and the thing will cool down within an hour or two so it will be safe to get the dry stuff out and the wet stuff in and start the process again. The barrel tower won't be as hot as the single barrel with mass behind it, because all of the power is distributed over the whole outer metal surface. The top will still be hotter although but the spot where the heat is fed in isn't close to the top, so insulation of the barrel lid would be sufficient to protect the roof of the shed.

Hope this is clear enough, formulating isn't my forte.

Hey guys ! I want to reply to all the great posts on this thread but I'm falling asleep as im typing so will have to do it in the morning !!
Thanks so much for the replys !!

but ill quickly just let you know the latest scoop...
Today we did some scouting for supplies, oil drums was a breeze, duct piping not so available... only 4 inch or ridiculously expensive galvanized 6 inch pipe.
So looks like we will be making our own in the workshop from aluminum sheets... When it comes to the bricks it seems we have run in to a brick wall... well an invisible brick wall of nonexistant firebricks...

Basically, firebricks are very hard to come by here. There are some leftover firebricks bricks that we thought we could get a hold on. These had been specially imported and donated to a pottery co-op group in a village nearby by a Canadian charity. It would seem that for the last 8 years these firebricks had just been gathering dust...
and if we had asked for them a while back we probably could have bought them but now their ceramics kiln has broken and they will use the left over bricks to fix it. So we could not snap them up and  there is no supplier on the entire island... the closest one is on java and to order new ones would take up to 3 months perhaps even longer...  so its time for some improvisation ...   on our visit to the potters village i did spot that they had made some cylindrical molds that looked to me like they could be vermiculite clay mix..

Anyways i'm going to sleep on this conundrum....

Some more pics from today

So if i have understood you correctly peter,  this is kind of what you mean right?

Think it's going to be maybe a bit tricky to stack the wood this way but i like it .. .. I'm thinking why not make some more doors all the way around this shed and then its easy to access the wood and stack it...
this way the exhaust from the boiler could also be channeled to the barrel tower when the stove is not in operation perhaps ? .. going to do a mockup

If piping is hard to get perhaps you could use half barrels for the exhaust see http://donkey32.proboards.com/thread/609/heated-seating-nyc-restaurant

Yes Olof, that's kind of what I meant, although the distance between the fuel and the tower feels a little bit cramped. You'll probably need some sort of horizontal stabilizers in the shape of long sticks every two or three layers.

I now understand there's a running boiler at the premises. When the exhaust gases are warm enough this could be channeled to the tower, yes. In order to avoid friction in the system I would prefer to make the elbow above the riser much wider. And it need to be made from something other than aluminum, to avoid melting. You could build the riser out of bricks, directly against the barrels and at half height feeding into it.

The two chimney stacks could be inside the shed in a corner and venting through the roof, now I come to think about it. The shed exhaust ventilation could be just one simple straight pipe up, starting some distance above the floor. This way you would be able to tune the thing also, shifting the pipe up and down in order to find the best working position.

How about something more like this?
So we can get more wood in there...   the shed is right on the edge like this so maybe the wood feeder could be situated on the lower level perhaps ?
and there would be doors on 3 sides of the shed... and in the doors, there could be air vents at the bottom of the doors too.
Idealy there would be 3 x 1m wide 3 meeter heigh doors on each side of the building and you could then acces 3 kubic meters of wood per door

Some more pics of the shed

I spotted two errors: first being the fuel should be away from the walls in order to allow the hot air to sink down at the wall side, so both grain ends could be drying simultaniously. Second the inlet and exhaust of the barrel tower should be just the other way around. Inlet higher than the exhaust, otherwise the gas stream could shortcut instead of going up the tower. The exhaust pipe would be best placed half a diameter of the pipe from the bottom and the inlet slightly above that somewhere around the perimeter.

By the way, this little baby is definitely yours, I am just the godfather.

Whats the least amount of distance form the wall we can get away with do you think ? we haven't got that much room to play with...
Other than those two things...  do you think this baby can work ... what I was most concerned with was to have the burn chamber/wood feed on the lower level..  

I think what we will do first is just o build a prototype and see how we get on i guess..

Got a few questions that have been spinning around in my head...

1 what do you guys think would be the best alternative to firebricks?  should we make our own perhaps ? or do we do some kind mold with perlite/vermiculite and clay and cure it in the potter oven ?

2 Would it be worth plastering the inner walls with a wallpaper of aluminum foil to bounce any radiant heat back to the wood ?

3 Would it be worth insulating the floor with a perlite concrete slab perhaps?  

Olof Jönnerstig wrote:Whats the least amount of distance form the wall we can get away with do you think ? we haven't got that much room to play with...

15 cm should be enough I'd think.

Olof Jönnerstig wrote:Other than those two things...  do you think this baby can work ... what I was most concerned with was to have the burn chamber/wood feed on the lower level...

The elbow above the riser could be a problem, metal could become red hot. Apart from eaten away, it would also loose quite a lot of heat at that point. Having the core at such a low level isn't a problem in itself, getting the heat into the heat extractor can't be done with an extended heat riser because this can't be built into the shed in its entirety.
Apart from that, it should work flawlessly I'd say. Using three barrels, you need a 200 mm J-tube or a 150 mm batch box as the combustion core.

So we have decided to go for this type of core mold to start with

https://www.youtube.com/watch?v=7ANMXGrxgnE

I would love to make a batch box, but i think ill have to wait a bit and see if the material we have for the core works well etc..
We are going to use a clay-sawdust and rice husk mixture ... the village here use this to make their own version rocket stoves


( side note ironically, they are drying cloves on the ground in the sun in this pic.... )

So big day tomorrow we are actually going to do some stuff
finally quite excited we got some sheet metal to make the pies, we got the barrels which need the paint removed. and we will be building the core and heat riser...  

Today's events...

Some more pics

Looks great Olaf!