PELLET STOVES WOOD ENERGY FOR ALL

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In 1979 I appeared on a Maine Audubon TV program called "Woodburners" that examined the past, present and future of this most abundant of self-renewing energy resources. Most of us in the cast and crew had been heating with conventional log-wood for years, and what got us most excited was the future prospect for a new arrival in Maine: pelleted fuel.

Pellets are manufactured from wood products that normally go to waste: "trash" wood such as roadside saplings culled by road crews; limbs, tops and other residue of logging; sawdust and wood chip byproducts of lumber mills and wood manufacture; and cardboard and other wood fiber such as paper packaging that normally goes to clog our landfills. The raw material was ground, dried and compressed—through the same kind of equipment used to form livestock feed—into pencil eraser-sized biscuits of uniform size, dryness and (with minor variations depending on source) energy content.

For the first time, pellets promised to convert wood into a uniform, concentrated product that could be delivered to a heating fire every bit as easily as coal, oil or gas. Loose, dry and easily transferred by auger, conveyor or simple gravity, it could be transported at a competitive price, in bulk, to industry or in convenient bags to homeowners in the country as well in cities and towns. We foresaw a second revolution in wood energy.

Ecological Benefits

Maine and Eastern Canada as well as the Pacific Northwest on each side of the border stood to benefit from increased use of wood pellets. Both areas are heavily forested and logged for lumber and wood pulp. Pelletizing the slash would clean up the woods while adding jobs to their often-troubled economies.

Indirectly, pellets also promised to help clean up the air. We anticipated that a ready supply of cheap wood pellets could supplant coal and oil and bring an end to much industrial pollution. In industrial applications, pellet exhaust could be easily "scrubbed" 100 percent clean. There was even talk of pellets serving as feedstock for industrial-scale production of a clean-burning auto fuel as is done in Brazil.

Combustion

In a stove, logs are placed on a grate, grille or on the floor facing a door with one or more air inlets in front and a dampered flue in back. The flue's draft sucks in a large volume of air, pulling a constant flow of oxygen past the fire from front to back. Logs can take the oxygen they need as they need it, so they needn't be uniform in density, size or water content from one armful to another.

But not all the oxygen going by is exposed to burning wood, and vice versa, and different parts of different logs are burning at different speeds and efficiencies at any one time, so combustion efficiency varies widely throughout the fire. Also, the logs contain about 20 percent water, which must be boiled off before the wood will ignite, so a great deal of fuel energy is wasted, sending up the flue a combination of water vapor, gases and incompletely burned hydrocarbons, or smoke (which, in an EPA stove is reclaimed in part by being converted to heat in a combuster or engineered air flow system).