Control-oriented modeling of direct-heat co-current rotary dryers for energy demand flexibility

The contribution presents a new control-oriented model for direct-heat co-current rotary dryers with a focus on demand-side flexibility considering the variation of material throughput and heat source. The dryer model is based on partial differential-algebraic equations covering time- and location-dependent gas and particle velocities taking phase interactions into account. In addition, a steady-state model of a heat supply unit covering electricity-based and chemical heat sources is presented. The model is qualitatively compared with measured data and models from literature showing good overall agreement. Furthermore, simulations of the flexibility mechanisms are performed and their effect on temperature and humidity profiles as well as input and output streams of the dryer are analyzed. On this basis, requirements to process control are discussed. The simulations show that the variation of the throughput is associated with significant changes to the gas input stream, while only small changes are observed for the variation of the energy carrier.