Hi, all. As I mentioned in another thread, I'm interested in partially fueling a rocket stove with the pyrolysis gases from converting sweet sorghum crop residue into biochar (and use the heat to cook the sorghum juice into sorghum syrup). My current plan is to have two shelves in the combustion chamber: a lower shelf for a wood fire, and an upper shelf for 1 or 2 lidded stainless hotel pans (steam table trays, 4-5 gal) to hold the shredded biochar feedstock. When I see that they have stopped emitting pyrolysis gases, I can swap in new trays of fresh feedstock.
While it's easy to build the sides of the combustion chamber out of refractory brick, the top becomes more challenging because the hotel pans are about 12" x 20", and I don't know what to use to span that width. Cinder blocks are 16" long, but I don't know if they can withstand the heat. I suspect metal would be even worse, although I was thinking maybe I could design a metal top to serve as an air channel to feed oxygen into the heat riser/chimney (would that air flow keep the metal cool enough?). Any suggestions?
As Alden mentioned ceramic blanket will insulate any roof you want to use.
Ceramic boards are another option. I used 1" thick ceramic boards to build the burn tunnel on my RMH, they can take the heat.
Alden Banniettis wrote:Have you considered a ceramic refractory blanket?
Thanks for that, I had not considered them. Actually, I know nothing about them. How would you use one? Put a rigid (metal?) backing on it and lay it over the top of the combustion chamber? Would I need a barrier between the flames and the blanket? I assume the porosity could be problematic, with the pyrolysis gases blowing around.
A really simple way of spanning a 12+ to 16" space is to corbel in the walls until a standard firebrick can span them. 9" long firebricks can be turned to project 3 or 4 inches into the space, and if the ends are 8" apart, 9" firebricks will close the top safely. This gives a clear interior width of 14" or 16". Add another course of firebrick continuing the original walls, to weight the corbelled bricks and strengthen the construction.
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