[Stoves] Thanks to all, from EWB Princeton in Peru

[Charlie Sellers]

Back from Peru (I flew out of Lima 3 hours before the earthquake, then slept for 2 days solid) and everyone's advice was a huge help - the completely local stove design that evolved has the most complete combustion I have ever seen; the local people cannot believe that it puts out zero visible smoke as long as there is even a tiny flame in the combustion chamber!  And it continues to boil water long after all the fuel is removed - another surprise.  Shannon, Rebecca, and Doba are still in Huamanzana for a few more weeks, improving the design and reducing the build time, and customizing each stove for the individual kitchens and cooks.

The hollow bricks turned out to be a huge boon - my lean manufacturing experience in China taught me that reducing both the number of components and the number of steps is important, and these few huge bricks are the closest you can get to a pre-cast mono body stove like the ONIL.  Each kitchen has a low concrete/rock/brick/wood platform that holds their traditional "trench fire" (two parallel stacks of bricks, with the pots either inside them in the fire, straddling them, or on the tops when not as much heat is needed); once that "stove" is demolished the new hollow brick walls are cemented to it.  The family guinea pigs live underneath the platform, and they can carry on their business of putting on weight for the soup pot even during construction.

The 30 cm tall hollow walls are filled with ash, then with a few rocks at the very top so that a concrete surface can be made - the plancha (6 mm thick and about 1200 cm2) is temporarily set into this while it is wet to make a sealing and positioning lip.  Under the refractory cylinder combustion chamber there is a hollow ash box constructed of cheap glazed floor tiles, so that the heat is not absorbed as much into the platform - the cylinder is made locally for use with giant honeycomb coal briquettes, in a smelly stove used just by outdoor food vendors.  The stove body is then filled with a variety of more hollow bricks, scrap soft bricks and brick rubble, and ash - depending on the proximity to the highest temperature.  The chimney is a stack of 8 of the big bricks with eight holes in them (with broken interior walls to connect them at the bottom), but 2 of them are used to create full height concrete "tubes" that are reinforced with rock and steel rebar, for earthquake
 resistance.  It goes up quickly by sliding each new brick down the rebars from the roof, and filling the tubes as you stack.  The stove body is filled with wood ash from their bread ovens to within 6-7 cm of the plancha, to give a 200 cm2 cross section - which is the same as the area of the rocket elbow, the combustion chamber cylinder, and the chimney.  Everyone's comments of the flexibility of the "constant area" rule helped us keep from worrying too much about just how close we had to make them all.

Still to go are cost reductions (most of the costs are in the metal plancha and grate) and characterization of the thermal situation using a thermocouple - is the ash a decent insulator, what minimum thickness of it is needed, what stove performance tests will best illustrate the cooking advantages and disadvantages, etc.  And more cultural brainstorming is needed, so that the stoves will continue to be used as they are supposed to be - I have revised my estimate of what percentage of a stove project might be "technical" and it is now 10%.

More soon, plus photos.

Charlie





jpmanley at midcoast.com wrote: When I worked for a mason 35 years ago, we never used cutting blades to
shorten a flue tile.
One additional hint for cutting them shorter is to start your cutting
(hammer & chisel) on the corners, before cutting the lines in between the
corners.
This is in addition to the filling with damp sand.




> I imagine that you already know this trick, but just in case.
>
> If you want to cut/punch a hole in a hollow clay brick first pack it
> thoroughly full of slightly damp sand.   Pack it in as hard as is
> practical and then you can take a hammer and chisel, and cut openings in
> the tube, without shattering the rest of the tile,  The same trick if
> done carefuly will allow you to cut the tube to length,  just remember
> that you need the sand there to back up the tile, so wrapping a rope
> around the end you are cutting off can help to keep it all together, and
> thus the sand in place.  It works best if the sand is a little damp as
> that lubricates the packing, and allows you to reach a higher packed
> density.
>
>
> Drew
>
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http://improvedstoves.blogspot.com/ - just R&D related to fuel efficient biomass stove issues
  http://travelswithcharlie.blogspot.com/ - most recent travel posts
http://new.photos.yahoo.com/csellers42/ - travel photos, of everywhere - click on the country albumns on the left
http://huiplesofguatemala.blogspot.com/ - my textile project in Guatemala - what colors!
http://travelswithcharlie2.blogspot.com/ - older travel posts, including Nepal travelogue 
http://ewbappropriatetechnology.blogspot.com/ - just posts for the ATDT of the EWB-SFP; AT for developing countries

       
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