WOOD-GAS UPDATE
(Page 2 of 4)
September/October 1981
By the Mother Earth News editors
So, rather than look for an especially dry fuel to suit the machine, we decided to try to adapt the gasifier to the large supply of moist wood we'd already gathered. We aimed to make the "burn" more efficient by redesigning the air inlet system to include a preheating section that tempers the atmosphere before it enters the combustion zone. The new manifold is made up of a series of sixteen 3/8" black iron pipes, which are evenly spaced around the hearth area and extend from the top of the gasifying chamber (where they're connected, through a distribution ring, to the inlet check valve) to a point about four inches above the restriction at the base of the hearth. This setup allows incoming fresh air to pick up waste heat from the chamber itself, and especially from the area surrounding the combustion zone through which the hot fuel gases pass on their way to the condenser and filter.
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Then, to solve the bridging problem, we oriented the outlet tips of the manifold pipes so that the "odd" eight point straight upward ...and the remaining "even" nozzles aim inward, toward the center of the hearth opening (see the illustration). The benefits of this arrangement are twofold: The horizontal jets provide combustion air for oxidation at the entrance level ...while the vertical outlets reduce the size of the chunks of wood about to enter the hearth by cutting away at them like miniature torches, thus eliminating the possibility of having a "logjam" block the flow of fresh fuel.
Finally, in an effort to decrease the amount of moisture collecting within the gasification tank, we provided a pair of condensate outlets—one of which is a 1" pipe near the unit's fill lid, and the other a condensation ring fastened to the inside of the tank at its midpoint—which together route excess liquid from the gasifier, through individual water traps, and into a small storage container that can be drained periodically. This vessel, in turn, is plumbed into a check valve—equipped steam relief tube, which vents excess pressure and vapor as they build up. (The water traps, of course, prevent unwanted air from being drawn into the gasifier, by vacuum, when the engine is running.)
A THREE-PART PROCESS
After modifying the gasifier, we decided—in order to reduce weight and space requirements—to go ahead and redesign the condenser/filter system as well. The new unit is nothing more than a 16"—diameter water heater tank encased in a larger (20") vessel. The space between the two containers is filled with a heat exchanger coil (through which cool water is routed when the gasifier is in operation), and the inside of the smaller tank houses a roll of woven hog-hair matting that's wound around a removable frame. Inlet and outlet pipes allow the fuel gases to pass through the system.
