(390c) Discrete Element Simulation of Particle Motion in Rotating Drum Bioreactors for Solid State Fermentation

Solid state fermentation (SSF) has got more attention in recent years, due to its characteristic advantages compared with traditional submerged fermentation (SmF) or liquid state fermentation (LSF): lower overall capital costs, higher volumetric yield, simpler downstream processing owing to low water, and cheaper substrates such as agricultural solid wastes. Among these several types of SSF reactors, rotating drum bioreactors (RDB) which typically is a horizontal cylinder, provide relatively gentle and uniform mixing by improving baffle design, since there is no agitator within the substrate bed. Rotation can be intermittent or continuous, depending on the importance of mixing effects on the solid substrate. The mixing occurs by a tumbling motion of the solid substrate particles, aided by baffles on the inner wall of the rotating drum. Motion of solid particles gives help in mixing and mass-heat transfer inside RDB. In this paper, RDB was used to ferment sweet sorghum stalks into fuel ethanol by SSF technology, and discrete element method was used to simulate three-dimensional motion of solid particles in the RDB under various kinds of conditions: 1) without baffle, only considering the effect of rotating speed; 2) with baffle, considering the effect both of its different shape, size and location, and of rotating speed. For whether with baffle or not, particle motion during not only fermentation stage but also load/unload stage are simulated. The simulation results were compared with experimental data obtained from a glass RDB device with a length of 0.4m and diameter of 0.3m. Motion of solid particle inside the device was observed and recorded by a high-speed video camera, and could agree well with that simulation predicted. All these work mentioned above help us in designing the right baffle and other operating parameters such as rotating speed, energy consumed for rotation, etc.