A prototype gasification biochar stove with an added cooktop to utilize waste heat.
I named this stove “The Rocket” because of its shape. While not a true rocket stove it does incorporate several rocket stove features like an insulated firebox and a tall vent stack. But the Rocket is actually a gasification biochar stove. It is lit from the top and the draft goes upward making it fit the description of a TLUD. The chief difference between this and earlier designs is the incorporation of a cook top in the venting system to use the waste heat from the bochar process to heat water or cook a small meal.
The concept is simple: make a small biochar stove and use the waste heat to cook with. As the diagram shows, this is achieved by simply putting a cook top on top of the stove. As this type of gasification stove doesn’t function well without a tall vent stack, the cooktop is raised two feet above the stove making it approximately three feet off the ground. Perfect height for cooking.
The Fire Box:
At the heart of the stove is a small firebox. This has small outside air holes that feed two rows of holes inside the fire box. One small row of holes at the bottom introduces primary air and a row of larger air holes at the top to provide secondary air.
Outside air and secondary air holes.
The outer housing provides insulation for the firebox allowing better combustion. A gap between the bottom housing and the riser allows a final blast of tertiary air to complete combustion making the exhaust gasses relatively clean.
At the top of the double walled riser an opening blasts the bottom of the pot or pan being used heating it before the gasses finally escape out through the upper vent stack.
I have now done two runs with this stove, one with a small pot in which I cooked some oatmeal and one with a small cast iron pan in which I cooked a bratwurst. Both runs generated a small amount of charcoal which could be used to make biochar or be used as cooking fuel in a charcoal burner.
Both trials were a success. Though several short comings were apparent.
- The pan and pot did not get as hot as I’d hoped. That is, the fire was hot enough but the heat transfer to the cooking vessel was not as efficient as it could have been. I suspect if I redesign the stove to put the riser closer to the bottom of the pan it would heat up faster.
- The heat generated, though sufficient for the experiment, did not last long enough to cook more than one thing. I surmise if I made the fire box slightly larger to acomodate more fuel or redesign it to allow for adding more fuel, it would burn longer and be more useable to a broader range of cooking, (i.e. simmering rice or beans.)