That was a lot of posts to read. The Simple-Fire thread was pretty active until the winter. Things kind of tapered off. I spent quite a bit of time in the shop running the Simple-Fire to power a larger gen set. Keeping track of run times, weight of charcoal used, trouble shooting problems, trying different nozzles, and so forth. At Argos, I was somewhat surprised by the amount of interest in the charcoal. A few guys saw it last year and felt the same way you did, but expressed more interest in it this year.
Making charcoal loses about half the energy value in the wood. With that said, it is a more refined fuel which has advantages. Waste is a relative term in some ways but will save that discussion for later. On to your “few” questions.
1) Why do you prefer the double barrel method of making charcoal over putting a small barrel in a larger barrel with the openings along the bottom of both barrels and getting the pyrolysis off the wood to feed the fire.
Answer. What you are describing is the indirect method of making charcoal. The wood you place around the inner barrel is set on fire to bring the wood in the retort up to heat. Once up to heat, the gasses given off from the wood in the retort will produce the heat to finish the charring. The wood you use to start the process is totally burned up and does not add to your final product. The direct method works well for me so I have never tried the other method. Let me put that on my list of things to do this summer. I should at least give it a try.
2). You mention adding "pellets" into the charcoal during a run on charcoal gasifier. Is that correct/ok and why?
Answer: That is correct, I add pellets, plastic, sawdust, deer poop, to my Kahle style charcoal gasifier. It has an air inlet that is centrally located on the top of the gas generator. Do not confuse this style with the Simple-Fire which has a nozzle entering at the bottom of the generator.
3). It appears that even with the exhaust gas recirculated as the charcoal supply burns down the unit gets hotter. That is correct. The depth of the charcoal above the hot oxidation zone is slowly being lowered as the charcoal is consumed. There comes a time when the layer of charcoal becomes insufficient to insulate and the heat comes through.
4). In building a Simple gasifier, would it be better to build the unit taller rather than short and wider. My thinking right now is; the smaller diameter can, with equal amounts of charcoal, the gas would travel further vertically through the charcoal to get to the outlet, thus being cooler on exiting. That is what I am thinking too. In fact my latest Simple-Fire is built out of a 40 gallon hot water tank. This gives me a much higher bed of fuel and therefore longer run times.
5). What is the limiting factor when it comes to adding exhaust gases? Is it that the more exhaust we add, the less oxygen we add cutting down on the combustion and thus cutting down on the manufactured gases. Answer: You can add too much engine exhaust gas. Too much will restrict the amount of oxygen available to react with the charcoal thereby lowering the temperature in the oxidation zone. If this temp drops below 1800F (have to pin this temp down better) the CO2 produced will not decompose into carbon monoxide. I am looking for a bright red heat.
6). I realize the "oil drip" is a recent innovation, but how about a little more detail?
Answer, Let me save this for tomorrow. I was using it last night while splitting wood and ended up turning it off. Still need to do some more experimenting.
Got to go, but will continue.
Gary in PA