A Wood Drying Kiln for Cameroon
Thanks to the support of donors like you, our center was able to construct the first wood drying kiln in the Northwest Region of Cameroon in a town called Kumbo.
When the School of Carpentry & Construction (C&C) opened in 2009, local carpenters revealed that they were using unseasoned lumber to build furniture. Unseasoned lumber is wood that is still green and contains moisture. Furniture made from unseasoned wood falls apart as the wood dries and begins to warp and twist within a few months; finish peels away.
WiseGeek notes that without the proper humidity controls, the wood could still warp as it contracts.
Using seasoned wood was time-consuming and expensive—it can takes six months for properly stacked wood to air-dry in Cameroon, which is cost-prohibitive for carpenters. To remedy the situation, C&C, with local labor and a little innovation, constructed the first wood drying kiln in the region!
The custom-made kiln, constructed with readily available material, is an enclosed space with temperature and humidity controls, and provides the ideal wood drying conditions year-round. The large metal building is lined with wood panels that provide strength and insulation for stacked wood. The roof, made of corrugated sheet metal (painted black to help absorb solar heat) and transparent panels, installed at regular intervals, allows the sun to heat the sealed space. Electric fans, installed at strategic locations, circulate the air and facilitate the removal of excess moisture from the lumber. Hot air is funneled in to the top of the kiln from the heater, and cool air is circulated out of the kiln by way of a vent near the floor. For a solar design that you can build yourself, see what the folks at American Woodworker have to share.
Each type of wood has its own characteristics (based on species, moisture level, thickness of the cut, and density) so the heat is adjusted to quickly evaporate the moisture from the surface of the stacks of wood, drying the lumber as evenly and as quickly as possible without warping, cracking, or case-hardening. Engineers use a chart, like the one provided on the Structural Engineering Blog, for taking a range of tolerance into consideration when selecting standard connectors for construction.
A custom-built brick structure next to the kiln houses the sawdust burner. Sawdust, which is available in abundance from C&C, provides additional heat for the kiln. The sawdust burner, another local innovation, constructed from a 30-gallon oil drum encased in a 55-gallon oil drum—provides clean, renewable heat to take over for the sun in the rainy season.
The double-barrel design that prevents the outside metal surfaces from getting too hot also prevents carbon monoxide poisoning and prolongs the life of all the components. To use, the removable inner barrel is filled with compacted sawdust that is lit with kindling in the ash-cleaning draw.
Two exhaust pipes (also custom-made local innovations), attached to the side of the large barrel, exhaust the smoke and allow for easy control of the heat level.
On the day of the initial testing, the temperature of the stove quickly reached 750 degrees and stayed hot for hours, burning efficiently and cleanly. For kicks, our staff put a kettle on the burner to boil water.
People still come from all over the region to marvel at the wood drying kiln, which dries wood in four months or less, is very cost-effective to operate, and consistently dries wood throughout the year. That’s progress!
