Matthias Kraume

In general, there is always a trade-off between the information output and the process throughput. The automation of micro- to small-scale bioreactors is considered necessary as this can facilitate a straightforward bioprocess development to reach its commercial success. A small-scale, dead-end enzymatic membrane reactor system has been realised. Reactor system was tested for the continuous transgalactosylation of lactulose using commercial β- galactosidase.

Even though digestate is rich in plant nutrients, its value as a fertiliser is low due to its high water content of 90 to 95%. Therefore, the main objective of digestate treatment is to extract clean water in order to concentrate the plant nutrients. These are either in solution or attached to organic particles. Roughly, more than 70% of the digestate’s solid particles are smaller than 1 mm and are not easily separated, because of particle size, charge and density. This is one of the reasons why a simple screen separation provides no solution to the problem; however, it is an important step in the treatment chain. During the research project, many different digestate treatment techniques were considered – all of these are recorded in Figure 10. This article provides an overview of the possible techniques for digestate treatment, how they work, and their central research parameters.

For developing a control system for these agitators, the analysis focused on the rheological characteristics of digestates, the open jet in non-Newtonian fluids and the flow conditions in a biogas reactor. In addition to a clearly visible shear-thinning effect, the viscoelastic proportion of these substrates was also determined. Depending on the stirrer speed and the rheology, the angle of spread varies and a reverse flow can occur directly at the stirrer. Therefore, not only can the position of the stirrer be used to optimise the flow field. The conical spreading of the liquid jet also enhance the mixing process. By using thrust measurements, their suitability as controlled process variables could be demonstrated.

BADANIA DOŚWIADCZALNE NAD ROZWOJEM SYSTEMU STEROWANIA MIESZADEŁ W INSTALACJACH BIOGAZU

W pracy przedstawiono możliwość sterowania mieszadłami w oparciu o analizę charakterystyki reologicznej odpadów pofermentacyjnych, przepływu w płynach nienewtonowskich oraz warunków przepływu w reaktorach biogazu. W zależności od szybkości mieszania i reologii zmienia się kąt rozprzestrzeniania i możliwy jest przepływ wsteczny bezpośrednio przy mieszadle – oprócz położenia mieszadła również stożkowe rozprowadzanie strumienia cieczy może wzmacniać proces mieszania. Potwierdzono przydatność pomiarów tensometrycznych do kontroli zmiennych procesowych.

In this work, a tool for calculating viscoelastic flows with rotating geometries in OpenFOAM based on the finite-volume method is presented. The tool combines the split-stress tensor approach and viscoelastic differential constitutive equations with the sliding-mesh technique. With this tool, a CFD simulation was run for a geometry of a spherical stirrer in an aqueous solution of carboxyl cellulose. Additionally, a rheological characterisation of that solution was conducted. For validation, the simulations were compared with flow field data acquired through particle image velocimetry measurements.

This project is motivated by the challenge of cleaning flat sheet membrane surfaces with the help of aeration. On the basis of earlier experiments and CFD simulations, a decision was made to use the CFD-tool OpenFOAM in contrast to earlier simulations which were performed with Ansys Fluent. In the new simulations, the advancing computing power allowed the simulation of a bubble ascent in the full channel which is of special interest in cases where the bubble size is smaller than the channel depths. Besides saving the licensing cost, OpenFOAM allows access to the source code and, therefore, easier implementation of sub-models if necessary.