This is the wood dryer I just built. Pretty simple. Helps if you have an old Weber Grill. Started out building a rocket stove out of 3 inch pipe and channel iron. My experience with Rocket Mass Heaters says that the cross sectional area needs to be pretty much the same throughout. I don’t think that applies to rocket stoves but I built it that way anyway. The fuel feed and heat riser are 3 inch ID pipe. The burn tunnel is a piece of 5 inch channel on the bottom capped with a 4 inch channel. All welded solid.
The top is a 55 gallon barrel with the top of a weber grill screwed to the bottom. The bottom of the barrel was cut out and the center section of a wheel was attached across the opening. The was probably not entirely necessary. I did it in case the flames came up from the heat riser they would be stopped by the wheel and diverted downward. So far that hasn’t happened.
A 3 inch piece of pipe was welded to the base of the grill lid to add some extra height to the heat riser and allow the barrel to rotate for emptying. Inside the barrel I made a four inch riser to keep the grate and wood a little higher from the direct heat. The grate from the grill fits exactly inside the barrel without modification.
Right now the lid has a piece of six in stove pipe for a flue to help draw the hot air up and out of the barrel. I will have to experiment with different sizes of flue to see what is most efficient.
Running the heater I took a lot of reading with a IR thermometer. The burn tunnel is the hottest area running just below 500 F with a maximum burn. The heat riser has stayed near or below 300F and the interior of the barrel and the base has not exceeded 250F so well below the combustion point of wood. The stove will run about an hour on a load of fuel. Of course some sort of platform will be necessary to load the barrel but the gasifier is also fairly high. I’ll build a platform between the two when I get them set up. This is area is surrounded by trees so it only gets about six hours of direct sun a day but in a better location I would build a solar collector and cut a slot and rectangular duct in the grill bottom section, attach that to the barrel and heat the thing that way. I’m also going to build a plenum over the burn tunnel and run a flexible duct into the bottom of the grill top to utilize the extra heat. Just didn’t have the extra materials handy.