Project Details
Projekt
Model-based control of the dynamics during fine grinding in wet-operated stirred media mills
Subject Area
Mechanical Process Engineering
Term
since 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 504930816
Stirred media mills play a central role in ultra-fine comminution processes across various industrial sectors. In such mills, the operating parameters, primarily stirrer tip speed, bead size, solids content, and flow rate, interact with the evolving suspension properties to govern both the kinetic energy of the grinding media and the overall transport dynamics. Particularly under continuous operation, these factors lead to complex, non-uniform axial distributions of grinding media within the mill, significantly affecting grinding efficiency, power input, and energy utilization. However, when targeting submicron particle sizes, it also introduces significant temporal dynamics into the particle size distribution, viscosity and colloidal stability of the suspension, creating a coupled system that evolves over multiple time scales. As particles become finer, the increasing viscosity alters the effective grinding conditions by damping bead movement, modifying stress transmission, and reshaping the local hydrodynamic environment. Moreover, it affects the axial distribution of the grinding media, a key variable for uniform energy input. These changes are not externally imposed but emerge intrinsically from the system’s progression, meaning that process control must dynamically respond to internal feedback signals. Conventional control strategies that assume constant rheology or homogeneous media distribution are thus inadequate. Complicating matters further, as particle sizes decrease, the stress intensity required for breakage decreases, and the optimal operating point of the mill shifts toward lower energy inputs. This requires an adaptive control strategy that balances energy efficiency, product quality, and throughput. Despite the availability of empirical models and simplified mechanistic approaches, there is currently no comprehensive framework capable of dynamically controlling stirred media mills, capturing the coupled effects of particle size, rheology, energy input and process dynamics in real time. The integration of a high-speed separator introduces additional complexity by coupling fast classification dynamics with the slower grinding process. The separator changes the particle size distribution on a much shorter time scale, resulting in abrupt changes in suspension properties. These effects form a highly non-linear, time-sensitive feedback loop where small changes in classifying conditions can significantly affect the grinding environment, where particle size distribution, rheology, energy input and separation dynamics must be co-optimised in real time. The separator thus transforms the process into a tightly coupled, multi-scale system.
DFG Programme
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