Since clay is a readily available resource in Ladakh, and perlite is not, I’ve been exploring ways to make cost effective burn tubes using local clay mixed with various other local ingredients to make stable, long lasting insulative burn tubes. Testing at the workshop has been interesting as we look for various products to mix with the clay to both give it stability, and insulating properties. So far the clay has been mixed with sawdust, ashes, chopped and dried alfalfa grass, puffed rice, barley, machine threshed barley grass (very short), hand threshed barley grass (longer) and local grass seeds growing nearby. These various clay experiments are in various stages of drying out and will be soon be ready for rocket testing… which means the tubes will be placed into a rocket burn situation to see how they hold up. We are looking for both durability and insulation, which is easy to measure. If the inside of the tube is over 800C and the outside is still cool to touch, then its insulating well.
Clay Burn Tubes in Rocket Stoves
This is great. I look forward to seeing an update as you learn more from these tests.
My greatest fear with your design is the area right before the ‘burn tube’ or ‘heat riser’ where the wood is on fire (sometimes called the ‘fire box’ or ‘wood chamber’ and the horizontal ‘burn chamber’). I have not seen any design last for years that uses any type of metal; cast iron or stainless. If they are not insulated, they are far less efficient at extracting the wood gas (but they, being metal, may last longer this way). And if only made with clay or some type of refractory material, would be easily broken during transport or while in use as they’d have minimal support.
It seems the only happy marriage between the two that I see is to join them; have the metal house the insulative refractory material. The strength of the metal would support the fragile insulative material, and the insulative material would protect the metal from the heat. My guess would be to use standard clay flue liner (square) that could be cut a the proper angles (or mass produced to your custom specs) and design the metal to hold them.
On my way to Nepal for the first time and hoping to teach many how to make rocket stoves using the clay they have and whatever organic material they might be able to mix in for the heat riser and the wood and fire chambers.
God bless!