Researchers from the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB and partners have developed a special steam-drying process for wood as part of the EU project SteamBio. The researchers say the process will significantly reduce transport costs and create valuable starting materials for the chemical industry. The process is already being used in a Spanish pilot plant.
"Instead of transporting the biomass chopped up, we torrefiy it," explains Siegfried Egner, coordinator of the SteamBio project. "We heat the biomass in a steam atmosphere without oxygen. Of the three main constituents of the biomass - cellulose, lignin and hemicellulose - we drive out one of them completely, namely the hemicellulose.
"The weight is reduced considerably, the specific calorific value is significantly increased and the material can be ground into highly reactive powder.”
The torrefected biomass is water repellent and has a much better burning behavior, since it consists only of hydrogen and carbon. The biomass can be transported as open bulk material, as rain rolls off the surface without penetrating the interior. In addition, the torrefied biomass is significantly lighter than the untreated material - which saves on transport costs.
Particularly valuable are the volatile substances that are produced during torrefaction. They can be used to produce chemicals that can be used as starting material for many other industrial products. These platform chemicals used to be derived from oil or natural gas, but can be sustainably produced through torrefaction.
"The platform chemicals are making so much money on many biomass materials that they finance the entire torrefaction process," says Dr. Antoine Dalibard, group leader at the Fraunhofer IGB.
"Torrefaction itself is not a new process," explains Bruno Scherer, project engineer at the IGB. “In the SteamBio project, we are relying on the steam-drying technology developed at the IGB, which we have adapted for this process. We work here at temperatures between 200 and 250 degrees Celsius.
"The special feature of the technology: the moisture contained in the biomass as well as the vaporous reaction products of the torrefaction are held in a controlled manner in the process chamber and themselves form the process medium.
"So we work with superheated steam," said Scherer.
The high temperature dries the biomass and causes low-boiling organic compounds to become volatile. While cellulose and lignin remain as a solid, the volatiles go into the gas phase. Using special capacitors, the researchers capture these gaseous substances, selectively cool them and recover them as liquids.