Hi Andy,and Colleagues, It's been a while since we have heard from you, but hope you won't mind my reply in the text of your message:
At Abu grab in Iraq, Bruce Jackson had good sucess gasifying charred shipping pallet-wood. That seems like a long time ago now, but I remember Bruce had it tough, and gasification gave him a tool to handle his stress. I've since become friends with Bruce and have visited his camp in Michigan. He operates gasified four-cylinder tractors for powering saws in the bush. He invited me down if I ever got into the area, but never did except on Google Earth. Seeing the beauty of his area, no wonder Iraq took a chunk out of his soul. Our Friend Greg Manning says most understandably that slipped-char is the "conveyor-belt for ash". This makes sense to me. A hearth can plug up quickly with fines, if not removed continuously. I haven't heard it described like that before, but yes, moving char beds prevent the ash from staying in one place where they can melt and cause problems. When driving moderate distances on wood blocks last year, I became flooded with quantities of excess char removed from my imbert ash-pit. I bagged up the char, and gave it to friends involved with cutting and removing a prolific tree-species that had begun to displace native beech/maple stands. They burned the char to ash in a special pizza oven during their autumn music-fest just for fun. They had been using raw wood in the oven, but it smoked objectionably during the party the year before. They loved the char product. Well charcoals are well known as a smokeless fuel, even used inside in table stoves in some cultures. After smoky wood, who wouldn't love it(:-) Visiting Jim Mason's shop this spring, and talking with biochar experimenters there, I learned the char from my imbert may not be most useful for gardening, because my char is made at temperatures way higher than temperatures at which the most beneficial biochar is made. With so many now involved with biochar production, because it is the in thing, you will hear many say this or that! Because the char from gasification can vary across a wide spectrum of quality and optimum end application, you can only discuss the char that you have left over from your own equipment. For what it is worth to know, a traditional Imbert with a lower grate under the Bell reduction zone, has two types of char in that mass we call the reduction zone. The core char down to the grate is just supporting the total char mass right up through the gasifier. It doesn't move naturally until shaken. The gas flow through the throat follows the suction, and takes the shortest route through the bed, down the walls of the bell. This char is the reduction char, and the support pyramid of char remains just charcoal, because it is not swept by incandescent CO2. If you have a grate vibration that very slowly drops the char, then there is a more consistent quality of the char closer to the properties of the reduction char. This can be described a slippage. Now having said all that, reduction char should be very light and porous, not heavy and dense, because it is activated carbon (of varying quality). As such, it is ideal for soil applications, because it's porosity provides a habitat for soil bacteria. A test we had done in Germany, found it was good enough to clean the condensate from the gas cooling, but there were no tars present. The harder heavier charcoals are more directly applicable to carbon sinks. The bottom line is that differing woods and the char they might make as a waste out of a gasifier, are not easy to discuss other than in a general way. I have friends who specialize in char making, and they are very focused on how they grade and make char to specifications. Excess quantities of char required for cooking pizzas at parties will be expected when heavier imbert gasification use of this invasive-species biomass is at the higher potential. The trees sprout anew from cut stumps faster than the boys in the woods can saw, and skid. If that is the only local use for these coppicing trees, then you either eat a lot of pizza after making charcoal, or you get the local gasified power generation going into the grid. What size char is good for the charcoal cross-draft you described? No dust I assume.. All these charcoal gasifiers like evenly graded charcoal, and the size will depend on the species. I would aim for a walnut size if hardwood, and half fist size for say pine or soft wood. The dust can go to compost. The engine displacement-fit here is about 5 Liter, give or take 1/2 L. They used single nozzle systems for big engines during WW2, so other than making sure the nozzle has plenty of water cooling to prevent it melting, you should have a lot of fun playing with the concept. It should be less of a challenge than cherry pits(:-) Regards, Doug Williams. Fluidyne.
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