Wood chip press!
Mechanical drying

For mechanical drying of wood chips and wood waste to remove the dissolved water. This enables a continuous supply of material for the downstream belt dryer.

Yes! With around one kilowatt hour of mechanical energy, more than 70 liters of water are pressed out of the wood chips. Conventional systems with classic hot air drying require 1.7 kWh electrically and 90 kWh thermally.

This significant improvement in the energy balance results in considerable savings compared to conventional thermal drying processes. A large proportion of the free water that is not bound in the cell wall is removed mechanically. This makes the entire drying process more efficient and economical compared to conventional thermal processes. This results in further potential savings in drying costs.

Yes!

The resulting press water (approx. 1-2 m³/h) contains minerals and organic components. These are then flushed out of the wood, which brings important advantages in the event of subsequent combustion: the proportion of mineral residues in the crushed wood chips is significantly reduced. This reduces the amount of ash and, in particular, the amount of fine dust in the exhaust gas. The systems operated with the pressed wood chips have a considerably reduced ash accumulation and fewer deposits in the combustion chamber.

The savings potential due to the reduced water content in direct combustion is around 10-12%, according to previous experience. If the improved system efficiency is taken into account, experience has shown that fuel savings of 15-20% can be achieved.

Around half the weight of freshly harvested softwood consists of water. This water impairs the storability (rotting, mold growth) and reduces the calorific value.

An almost completely dry wood raw material is required for further processing into chipboard or pellets. Technical drying is essential here, usually using large, continuously operated belt dryers. There, the wood chips pass through a hot air stream on an air-permeable conveyor belt. The belt runs more slowly for particularly wet woodchippings and faster for pre-dried woodchippings. In practice, the hot air is often generated using natural gas or, depending on availability, with the help of process heat available on site.

The wood chips should also have a certain degree of dryness for combustion in order to achieve optimum combustion. If the wood chips are very moist, an unnecessarily large proportion of the thermal energy is consumed for the evaporation of the water alone. For this reason, a drying process is almost always installed upstream of wood chip combustion systems. Drying is often carried out by storing the woodchippings for a longer period of time, whereby microbial activity heats up and dries the pile. However, this type of drying results in a significant loss of calorific value.

There is another good reason for crushing woodchippings directly at the sawmill: if half of the water disappears directly at the mill, a quarter of the weight of the woodchippings also disappears – and a superfluous quarter at that. This immediately saves transportation costs. In practice, this means that the usual large-capacity trucks can be fully loaded with pressed wood chips. With naturally moist woodchippings, a maximum of 80% of the filling quantity can generally be loaded – after that there is a risk of overloading. Experience to date has shown that between 20% and 25% of the transportation costs are eliminated during onward transport.

A dew system was developed to ensure stable year-round operation. It can be fed from the waste heat of the biomass power plant. The circulation of the (deep) frozen wood chips in a counter-current process and the screw conveyors used have proven themselves in everyday operation.