Efficient use of biomass residues for combined production of transport fuels and heat

VTT Technical Research Centre of Finland Ltd has developed a new technique based on gasification, which offers a sustainable way to turn forest industry byproducts, such as bark, sawdust and forestry waste, into transport fuels and chemicals. The new approach uses gasification to transform biomass into intermediate products – liquid hydrocarbons, methanol or methane – in production units that are integrated with communal district heating plants or forest industry power plants. The intermediate products are processed further in oil refineries to produce high-quality renewable fuels or chemicals. VTT developed and piloted the new gasification process and evaluated its the competitiveness in the course of a recently concluded project called BTL2030. The distributed generation process developed by the project team makes efficient use of the energy content of biomass. Approximately 55% of the energy content is turned into transport fuels and another 20–25% can be used to provide district heating or to produce steam for industrial processes. The process is based on VTT's low-pressure, low-temperature steam gasification technology, simplified gas purification and small-scale industrial synthesis. Thanks to the small-scale approach, the heat generated by the process can be used throughout the year, and the process can be fuelled with local residues and wastes.

The process development was realized using the pilot-scale Dual Fluidized-Bed (DFB) gasification test rig located at the Bioruukki Piloting Centre of VTT. Different DFB gasification alternatives were tested, including operation with two CFB (Circulating Fluidized-Bed) reactors and with a combination of a CFB gasifier and a BFB (Bubbling Fluidized-Bed) oxidizer. Both steam-alone gasification and gasification with a mixture of steam and a small amount oxygen/air were tested. The oxidizer was fluidized with air. The raw gasifier gas was purified in a hot filter unit and the hydrocarbon gases and tars were reformed in a catalytic reformer. Final gas cleaning was tested in a smaller slip-stream test facility. The DFB gasification process was operated for a total of 400 hours under gasification conditions using forest residues, bark, crushed wood pellets, used wood and crushed straw pellets as feedstock.

This report is mainly focused on presenting the results and experiences of the experimental process development. In addition, the effect of the gasification process performance on the overall efficiencies of industrial production plants was estimated using an Excel-based flowsheet model. The results of the more detailed techno-economic evaluations carried out in the project is presented in separate publications.