Daniel Bowman

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since Jan 24, 2013
Sandy Mush, NC
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Recent posts by Daniel Bowman

Does anyone know if Zaytuna or other permaculture farms in the area have been affected? It is shocking how much has burned so far, in the millions of hectares.
1 year ago
Thanks, William! This is exactly the direction we need. At some point I watched both those videos, but at the time they were just head-scratchers to me. I tried to look up more about the Hornito design but was coming up empty handed. I just did some more serious sleuthing and found the design is apparently the property of PODERCO S.A and developed by Robert Lerner. Since more searching found me this pdf of a stove design by the same person, although it looks different from the image you posted and I can't say I fully understand it or that it would help me build anything:


Maybe more experienced RMH folks can help with an actually buildable design. I don't have very much hands-on rocket stove experience at this point. I may be able to employ some folks to design and build one of these, though, so if anyone is excited by the prospect of doing that, contact me.

I like the idea of saving the oil, it seems potentially less complicated than having to count on it to finish the current batch, easier to just stoke with already prepared fuel.
2 years ago
Here's my first attempt at modeling a Rocket Char Retort.

Obviously this needs a lot of flushing out, but it shows the basic idea of a rocket connected to a bell style flue with a retort built into it. Also indicated is the porting of syngas back into the firebox, which is too simplistic since it would need to allow venting of steam for the initial phase and ideally a condenser port for catching tar/oil/vinegar in the early stages of pyrolyzing. The outside of the bell and door into the retort would be super insulated.

Also usually the chimney exit from the bell is at the bottom, I'm not sure if the location matters as much in this instance since the whole bell will be surrounded by as much insulation as possible. I kinda lazily put the chimney pipe on the top but maybe it should still be at the bottom back corner?

I would love for one of the RMH and SketchUp experts here to carry this forward. I probably won't have time to get too hands on with this for a while, but I wanted to put the idea out there!
2 years ago
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.
2 years ago
I know the New England Biochar facility at Living Web Farm in WNC is very quick and their retorts are very large. A lot probably depends on the gas flow through the feedstock. Also with a retort there's no need to quench it like in a pit or TLUD kilns, so you can just leave it, but yeah it might take several days depending on the heat exchanger.

I am picturing this setup either mostly inside or at least next to a large greenhouse with hydronic recirculating heat and a 5,000gal or so storage tank. Biochar would only be made in the retort in winter. In summer, in this climate at least, the best method is the open pipe setup such as this:

2 years ago
Hmm.. I think the bigger the better! Mainly because a larger retort will function as a better heatsink (probably difficult with a smaller pizza oven) and, being heavily insulated to the outside, could then sustain a good temp. I'm thinking 4'x8'x4' or so.

Maybe one strategy could be catching the syngases out of the retort and having a thermostatically controlled mixing valve for reintroducing them only when the temp is going to fall below a certain threshold?
Or maybe a better approach would be to just quickly dump excess heat into a large water storage tank with a fast flowing hydronic heat exchanger whenever things get too extreme.

I wonder what insulation material and how much would be needed. Could anyone do the R-value calculations for it?
2 years ago
Here is a good explanation of the pyrolyzation process, in case my description was lacking:


(Also the photo with the caption "Batch Roo Pyrolyzer" looks really cool but can't find any info about it)

This is an interesting attempt to make a retort kiln that uses firebricks and insulation, which could maybe help form the basis for a better design:


I'm not sure I agree with their claim about lower temps, though. Most sources I've found say that biochar quality is better with sustained temps of 500-600C, although there are some benefits from lower temp batches, so being able to do custom temp control would be a nice feature too.
2 years ago
Thanks for the encouragement!

Biochar is basically just a preparation of wood similar to charcoal but more suitable for use as a soil additive, in addition to many other uses. It is closer to food grade activated charcoal in that it has a much higher porosity then regular bbq charcoal and is a much more pure carbon. Biochar is usually soaked in compost tea, urine, etc to charge it with biotic life beneficial to plants. There is a lot of research showing it was essential to creating fertility in the Amazon and also the N American prairie.

Ok so the basic parameters are: maintain a temp above 100C for 30-60min drying stage, then hold a temp of around 500-600C for at least another hr.

I guess the first question I have is, while I know that rocket stoves reach some incredibly high temps at the riser, is it feasible to hold temps of 500-600C in a bell sized flue (although most of the bell volume would be occupied by the retort, which is NOT open to the flue).

Another design factor to keep in mind is that the retort, while blocked off from the flue, will need separate ducting to exhaust steam (100C-250C temperature range) and then condense and collect tar/oil/vinegar (around 250-400C) then finally above this temperature the remaining VOC gases can also be ported back into the firebox to supplement the burn.
2 years ago
I've been researching biochar production with the goal of designing something accessible and relatively affordable but also clean and capable of processing large amounts of material from varied feedstock. Looking at the best medium-scale commercial design (New England Biochar), which is essentially a large steel gasifier stove connected to a convoluted flue that runs under a super insulated and airtight steel dumpster, I immediately start to imagine a batchbox RMH with a double-wall bell that contains a retort chamber, accessible from a sealed loading hatch. Doesn't seem that much of a variation from the popular RMH design. The main question is how to set up this heater to maintain the proper pyrolysis temps for the right durations in the retort. The mass would need to be sized precisely to achieve for this function and any excess heat should be captured in a hydronic system with a simple waterpipe heat exchanger. Anyone else excited about this style of build?
2 years ago