Biomass is the main resource of the bioeconomy. However, biomass has a low energy density and also needs to be used decentrally where it grows. There are a few challenges that have to be overcome in order to make biomass conversion economically viable. A project group involving researchers from the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart and other institutions in Europe is addressing these challenges and demonstrating how biomass from rural areas can be made suitable for industrial processes.
Renewable resources are the basis of every bioeconomy. Agricultural and forestry residues are regarded as promising resources due to their wide availability and low cost. However, they are not necessarily available in the appropriate forms for convenient industrial use. Biomass is generally characterised by a relatively high moisture content. Compared to fossil resources such as coal, this results in a lower energy density and susceptibility to biological degradation processes. In addition, agricultural and forestry raw materials can only be provided decentrally and are available as solids, which is why, for example, transporting them in pipelines, like oil and gas, is not possible. Taken together, these factors complicate the industrial use and processing of biotic resources and may affect the profitability of biobased value chains. Innovative concepts must therefore meet these challenges and ensure their profitability before a fossil fuel-based economy can be successfully transformed into a biobased one.
A European project consortium led by the Fraunhofer IGB in Stuttgart addressed this problem by setting itself the goal of turning biomass from rural areas into a flexible alternative to fossil resources and exploiting it for industrial processes. As part of the project, the project partners focused on making lignocellulosic materials from agriculture and forestry suitable for the production of energy and chemicals using a semi-mobile, decentralised process module. The aim was to use an innovative process to produce an optimised solid material as well as organic substances as valuable platform chemicals for use in the chemical industry. It was hoped to find a cost-efficient way to supply remote industrial and processing sites with biobased feedstock. Between February 2015 and July 2018, eleven partners from four European countries* pooled their skills and abilities in an interdisciplinary team. Team members came from research institutions as well as companies and covered the engineering, economic and ecological aspects of the project.
* Great Britain, Sweden, Spain and Germany
The project partners combine drying and torrefaction processes to dry the residual materials. During the drying process, the water contained in the biomass escapes; the hemicellulose is subsequently driven out during torrefaction. Hemicellulose is one of the three major biomass constituents. During torrefaction, the biomass is treated in an oxygen-free steam atmosphere at temperatures of up to 250 °C. The final product is a coal-like solid material, mainly consisting of cellulose and lignin with significantly improved transport and storage properties due to higher energy density (compared to the starting material) and hydrophobic properties. This torrefied biomass can then be used as a flexible, climate-friendly alternative to fossil fuels or undergo gasification to produce biofuels or chemicals.
The special feature of the process used in the project lies in the choice of the process medium. The process differs from traditional industrial drying processes in that it uses superheated steam. The process was developed at the Fraunhofer IGB in Stuttgart for industrial applications and, with the help of special capacitors, enables valuable organic components to be recovered during torrefaction. Depending on the biomass used, up to 25% of the input weight can be recovered as organic substances. In the case of beech wood, for example, this allows the extraction of acetic acid, furans or phenols, which can be further processed to substitute fossil-based platform chemicals. Due to the intrinsic value of some of these chemicals, relatively low mass flows are often sufficient to significantly increase the profitability of the entire biomass processing process.
Within the framework of the project, the applicability of the method was tested and demonstrated on a demonstration scale (150 kg biomass per operating hour) in an environment that was as close to practical application as possible. Most of the necessary process technology was fitted into a standardised 40-foot container to meet the requirements of a semi-mobile demonstration unit. The tests themselves were carried out at a test site in northern Spain, where locally available biomass such as olive tree or grapevine pruning and various wood chips served as input substrates to investigate the applicability of the technology to a wide variety of different agricultural and forestry residuals. It was shown that the commercially relevant recovery of the organic components by means of the process is possible and that regional agricultural and forestry residuals can be stabilised in an economically feasible form. It became clear that adding value to the organic substances plays a key role in the successful commercial use of the process. For this reason, the project partners and the Fraunhofer IGB will continue their work by specifically focusing on this area.
The concept of decentralised processing of agricultural and forestry raw materials also lays the foundation for improved value creation in rural areas. For example, the selection of a test site in a structurally weak but biomass-rich area in northern Spain was not at all down to chance and highlights the potential of such areas. The project also fits into the context of the Baden-Württemberg government’s bioeconomy vision. The Baden-Württemberg government favours a modular, decentralised bioeconomy1, which among other things is expected to contribute to the strengthening of rural areas. In Baden-Württemberg too, there are many unused resources such as grapevine pruning or forestry residuals available. The process described by the SteamBio project consortium may also be a promising approach for processing and potential exploiting the state’s agricultural and forestry biomass residuals.
(1) Baden-Württemberg Landtag, printed matter 16/2665; statement of the Ministry of Rural Areas and Consumer Protection, "Chancen der Bioökonomie – insbesondere für die ländlichen Räume in Baden-Württemberg"