Some of the most economical heat options for a wood drying kiln include using wood residue, including sawdust, shavings, chips, and bulk wood.
Conifer Sawdust Burner (direct fired):
Sasmo Corn and Pellet Burner: This unit burned waste seed corn into a vertical boiler. The low pressure steam was used in a double expansion steam engine to drive both a feed-pump (boiler water) and 2 kW generator.
Waterwide Solid Fuel Burner (Hastings, New Zealand): The Waterwide unit was popular in the 1980’s and used all over the world for grain drying, wood/timber drying, and sawdust dryers. The company had a sales and licensing agreement to bring the technology into the USA by a company in Erie, PA called Skinner Engine Company, in 1989 to sell and distribute solid fuel burners in the USA (they lasted less than a year then cancelled those plans). I installed and sold several of these in Australia and the USA. In Australia, the larger units were used to direct fire plywood dryers in plywood mills. The thin laminates were lathed off a spinning log of Radiata Pine. The thin sheets of sweet smelling wood were then put through a direct fired continuous dryer. The sheets were then laminated together and pressed to make plywood. The thin off-cuts were shredded and the waste wood was stored in large bulk storage silos. The most costly part of the solid fuel system was the fuel handing and storage. The solid fuel burner worked great, with cyclonic combustion of the gas. The hot gas was filtered through high temperature low micron filters (called a baghouse). The hot gas then was mixed with ambient air to cool a bit, then routed to the dryers. In the USA, the model DF80 (3 million btu/hr rating) was the most popular.