Torrefaction and transport conditioning of wood
Wood or lignocellulose is one of the most important renewable raw materials. In the EU SteamBio project, Fraunhofer IGB has developed a process for the pretreatment and torrefaction of raw materials and residues containing lignocellulose. This process is based on the principle of drying by means of superheated steam at atmospheric pressure. During torrefaction, the biomass is heated in an oxygen-free steam atmosphere for a certain process time. At approx. 220 – 250°C, the process temperature is below the value above which carbonization (pyrolysis) takes place. Water and hemicellulose are driven out together with other volatile substances and selectively condensed for use as platform chemicals. What remains is a hydrophobic material of high energy density that can easily be grinded into a highly reactive substrate.
Demonstration on industrial scale
To demonstrate the process on an industrial scale, a semi-mobile plant was built as part of the SteamBio project. The plant consists of a 20-foot container with a storage hopper and energy center as well as a 40-foot frame accommodating the reactors for drying and torrefaction, a device for solids discharge (with cooling) and condensers for the volatile fraction. The throughput of the plant can be adjusted flexibly depending on the substrate and is designed for 150 kg/h of raw material (freshly harvested wood chips). Agricultural waste such as vineyard pruning or press-cakes (olives, wine, fruit) can also be processed.
The system is designed for automated, continuous 24/7 operation and is controlled by software with integrated data acquisition developed at Fraunhofer IGB, which also allows remote control operation. A heating capacity of 155 kW using electrical elements is installed in order to permit compact construction, flexible operation and better measurement of the energy flows. A demonstration operation for the torrefaction of different substrates and the characterization of the products is currently performed in Spain.