Biomass recovery and drying trials in New Zealand clear-cut pine plantations
New Zealand commercial pine plantation forests are grown on a regime to maximise the recovery of higher value veneer or sawlogs. In some locations a lack of fibre market or long transportation distance can result in negative returns for the lower value logs. With log specifications that focus on quality, not quantity, radiata pine plantations generate relatively large numbers of reject logs that can include oversize logs, logs with large knots, excessive sweep or other defects. A small, but increasing, market for higher quality biomass product is developing. This includes pellets for wood burners as well as low moisture content chips for medium sized commercial boilers. Radiata pine at time of harvest typically has a moisture content (MC) of 55- 60%, whereby the preferred MC for higher quality chips is less than 30%. City Forests commenced a production focussed trial for woody biomass by stacking 1500 tons of pine logs in rows. The study location is just south of Dunedin in a location with relatively low humidity in the summer. An additional study was set up to assess moisture content change over time of stacked logs, with treatments of covered and larger logs split. The wood was stacked on pallets and weighed at approximately 1-2 week intervals. This latter study was supported by the NZ Energy Efficiency and Conservation Authority (EECA). The study showed that the larger split logs dried to 21% in 17 weeks. Small diameter logs dried more quickly than large diameter logs (23 and 32% respectively). Covering the stacks did not show to be beneficial for summer drying.