Simulation model for the transient process behaviour of solar aluminium recycling in a rotary kiln

Abstract

The German Aerospace Center has developed a process concept for the solar thermal recycling of solid residues and waste materials in a commercial scale and applied this concept to the production of secondary aluminium. In this context a mathematical model for the simulation of the unsteady-state behaviour of a solar heated rotary kiln has been developed, which is used to figure out the specifics of the solar boundary conditions like intermittent insolation and at least one start-up period per day as well as for process design purposes. This model is also capable to simulate hybrid and conventionally fossil heated processes in rotary kilns. The model was adapted and validated by recycling experiments using a rotary kiln in mini-plant scale heated by a solar furnace. Subsequent experimental results were in good agreement with the data predicted by the transient calculations. Taking this as a basis the model was applied to predict a possible operation concept for a stand-alone plant operated solar-only at El Paso, Texas. An important step for further design studies was the calculation of the overall efficiency and the number of cycles feasible at representative days in such a plant. In a representative parameter studies the influence of geometrical kiln parameters on the efficiency and cycle duration of the batch process was investigated.