Wood has the characteristic of adapting its moisture state to its environment (hygroscopic behavior). Changes in the moisture of the wood are associated with changes in shape: dry wood absorbs moisture in a humid environment, it will swell.
Wet wood loses moisture in a dry environment and also changes its shape, it will shrink.
Each wood must therefore be brought to a dry state that is as close as possible to the climate to which the finished product will be exposed to.
Wood chips, as a renewable fuel, replace the limited availability of fossil fuels such as oil, coal or gas.
Wood chips from local forests make an important contribution to a sustainable and crisis-proof energy supply. The demand for dried wood chips will increase in the future. In contrast to pellets, dried wood chips are cheaper and also offer a high level of operational reliability for the heating systems. Little technical effort is sufficient to process the forest wood and produce wood chips.
The calorific value of wood chips primarily depends on the water content, while the type of wood has only a minor influence on the calorific value. Freshly harvested wood chips with a water content of 55% (W55) have a calorific value of approx. 2000 kWh per ton. By drying to a water content of 20% (W20), the heating value of the wood chips is doubled to approx. 4000 kWh per ton.
This means that around 400 liters of heating oil can be saved with a ton of dry wood chips.
Dried wood chips can be stored with almost no loss in calorific value.
Wood chips with a water content of 25% or less are considered "suitable for storage". No (further) microbial decomposition of the wood and associated mass and energy losses are to be expected. Lower transport weight and more storage (energy / ton), without loss of rotting and harmful spores and fungi are further advantages.
Energy storage by using heat surplus for drying.
If the wood chips are dried using available heat surplus from biogas plants and combined heat and power plants, we achieve an economical, storable and regenerative energy gain.
Source: "Doubling" the forest; Prof. Dr.-Ing. Horst Kreimes at CARMEN Congress “Alternative raw materials for bio energy“, Nov. 2008