Rich Points wrote:How big would you like the retort to be?
Perhaps something like the rocket stove pizza oven that has been discussed here on the forums. These ovens have me asking the same question, how do you maintain a constant temperature.
I recently built a J Tube system with a high temperature sensor at the top of the heat riser. I tend to see sharp spikes as new fuel is introduced. My heater is only 5 weeks old so I've only had it for a short while but I've been able to play. I tried to maintain a constant temp in the core but found it difficult. I suspect a batch box would produce more of a consistent output.
Here's another thread of mine discussing the sensor and it's output.
Data logging RMH temps
Daniel Bowman wrote:I'm interested to see a diagram of the Exeter internals.
The major disadvantage I see to the Hookway design or the Carbonzero retort I linked to above is that the retort is more or less located inside the firebox. The retort is effectively a heatsink, particularly in the first phase of cooking.
Having a heatsink in your firebox is always a bad idea. Without an effectively insulated firebox and riser, the fire cannot reburn its own flue gases, causing smoke and efficiency losses. In all these similar designs, therefore, the burn temperature is drastically impeded during the initial cooking phase, when the retort is steaming all the moisture out of the feedstock.
It makes a lot more sense to have a super efficient rocket stove with a fully independently insulated riser and then a retort chamber that is only heated by the subsequent flue gases (which will actually be equivalent to or even hotter than the temps in these designs with a compromised firebox). Then, once the moisture has been cooked out of the retort, it can begin sending its own syngas back to the firebox for a self-sustaining burn for the rest of the cooking process.
When set up properly, one should be able to calculate the percent moisture content of the feedstock when loading the retort, then use that percentage as a guideline for determining the amount of fuel needed to get to the point of syngas production, which would then complete the burn on its own.