Opeongo Forestry Service, a specialty lumber producer in Renfrew, Ontario, Canada, installed a biomass boiler in late 1997 for the purpose of providing heat to its lumber drying kilns. The biomass boiler heats a mill shed and two dry kilns located inside a lumber storage building. Approximately 50,000 m³ (2 million board feet) of lumber are dried annually in the two 1,000 m³ (40,000 board foot) kilns, resulting in each kiln being loaded 25 times per year. The kilns utilize a combination of dehumidification by heat pumps and air heating by biomass. The biomass system is fired by waste wood products from the plant. The use of biomass for kiln heating is very cost effective. This is due primarily to the availability of wood waste that would otherwise have to be disposed of at a cost of $17/ton.

System description

The plant installed a 146 kW Bioblast biomass burner system designed and built by Grove Wood Heat, located in Prince Edward Island, Canada. Wood chips are stored in a bin and fed to the combustion chamber with a screw auger. The biomass combustion system consists of two chambers. The primary chamber uses a fixed grate with under-fire air. It has a water chamber to preheat the water. The burning gases enter the secondary combustion chamber. It is equipped with a thermostatically-controlled induced draft system that regulates the combustion temperature. Slab wood can also be fed into the secondary chamber. The boiler is located above the secondary chamber. The system efficiency is estimated to be 65% when using fuel with 20 to 30% moisture content on a wet basis. The fuel moisture content is usually slightly higher during the winter months, reducing the system output.

During the summer months the plant is operated at full capacity during the initial stage of the heating cycle and then is set back to a pilot state. In the winter the biomass system operates continuously at 100% capacity.

Lessons learned

• Kiln space heat and mill floor heat can be provided by cheap onsite wood biomass with minimal daily labor requirements. This includes preheating (thawing or warming lumber) and base load heating.
• Reduced loads on the heat pump dehumidifiers can be achieved by adding dry heat to the kiln and allowing the rejection to outside of moist air instead of re-circulating all air through the dehumidification cycle.
• Wood waste can be diverted from a landfill site and turned into a profitable resource with the installation of a biomass energy system.

Drying of lumber in many forest product companies uses heat pumps for air dehumidification. The kiln is preheated to 32 °C (90 °F) with electric heaters and heat pumps being used to dehumidify the kiln (thereby drying lumber) by extracting moisture using the latent heat of condensation. Dry heated air is re-injected to the kiln. This method is used for specialty lumber because it is a slower less heat intensive method - about 10% of Canada's lumber is dried this way. Without lower cost supplemental heating annual electricity cost for kilns of the size used by Opeongo Forest Products would be about $50,000 at $0.08 / kWh.

© Minister of Natural Resources Canada 1997-2009
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