Report on Trials of Farm Grain Driers for Woodchip Moisture Reduction

There is a large amount of timber in the North of Scotland that could be used as a fuel for heating of domestic and commercial premises. Chipping is needed so that it can be fed automatically into the boilers. The value of the chips is increased if the moisture is low, as less of the heat released during burning is used to evaporate moisture. The moisture of the timber is lowest outwith the growing season so felling before spring will produce timber of around 50-60% lower moisture content (around 50-60% compared to up to 80% for growing timber). The timber will slowly dry if the logs are stacked but it could take a year or more to fall by 20 – 30%. Chipping is best done when the timber is around 35% moisture otherwise the stress on the chipper increases. This level of moisture content is also the maximum that many wood fuel boilers can take. Speeding the reduction of moisture down to 35% will help with cash flow, and reducing the moisture as far below 35% as possible will make the combustion process most efficient.
Timber is mostly produced in rural areas and there are benefits to drying the woodchips locally, in reduced transportation costs. Farms in rural areas are equipped with drying equipment that are used for drying grain for 4 – 6 weeks each year. If the same equipment could be used to increase the value of the chipped wood as a fuel then it could make wood fuel more available, make farm woodlands and other sources of timber more valuable and provide an income for the operator of the drier. This project was designed to evaluate two types of farm driers for use with woodchip: a high capacity batch tray drier and a continuous flow drier The other two main types of grain drier: mixed flow driers and recirculating driers being ruled out due to either problems with flow of woodchips through the drier or potential for fires.