New bench-scale high consistency bioreactor in biomass refining

Tuesday, 29 November 2011 08:38

VTT and Gebrüder Lödige Maschinenbau GmbH have designed a new type of small bioreactor for use in high consistency biomass treatments in Otaniemi Biotechnology pilot hall. It provides the possibility to process biomass in very high consistency allowing the development and optimization of several different types of processes in the field of biomass refining. The equipment offers efficient processing of different kinds of raw materials, e.g. cereals and berries in high consistency.

This ensures significantly lower drying costs for example after an enzymatic hydrolysis or fermentation of cereal bran, if the aim is produce a dry product.

In biorefinery processes it is important to produce the desired end-product in high concentration to facilitate its purification and post-treatment. Working in low water content also decreases heating and cooling costs and investment costs through reduced vessel sizes. Thus a high concentration of the biomass and low content of water is generally preferred in biomass refining.

In the production of bioethanol from lignocellulosics this means that the process can be started with biomass in 20-30% consistency consisting only of insoluble solids. During the course of enzymatic hydrolysis, cellulose and hemicellulose hydrolyse to soluble mono- and oligosaccharides leaving the final insoluble solids content in the process approximately 10-15%. Microbial conversion is often used simultaneously or separately to convert the released monosaccharides to end-products such as bioethanol. This task requires efficient mixing that can adapt to various viscosities and can handle biomass impurities such as sand and pieces of wood.

The new Druvatherm DVT 5 reactor design makes possible this kind of processing in bench-scale experimental setting. The ploughshare mixing element was originally designed for drying slurries to powder, but it functions very well in mixing materials in various insoluble solids contents. The reactor may be sterilized allowing the use of aseptic conditions and the instrumentation include pH and temperature probes and possibility for automated control. Feeding is easy via vapour dome and sampling is possible though a piston valve in the bottom of the reactor. In addition to enzymatic and microbial processes, the reactor is highly suitable to smalls scale biomass extraction in high solid-to-liquid ratio. Vacuum drying as well as particle size reduction by using the chopper element is possible in the 5 L reactor. The reactor design is very similar to the 100 L and 250 L Draiss reactors situated at VTT Rajamäki pilot plant, but the small size and extensive instrumentation allow experiments in the earlier phase of the R&D under industrial type of mixing conditions.

Druvatherm reactor is used in joint research projects funded by Tekes and European Commission but is also available for contract work for VTT’s customers.

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