Experimental and numerical analysis of a solar rotary kiln for continuous treatment of particle material

Several energy intensive industrial processes, such as cement production, require particulate material to be treated at high temperatures. Renewable energy could be used to remove the reliance upon fossil fuels in such processes, and of the available technologies concentrated solar energy is perfectly adapted to provide a high temperature energy source. With this objective, the present study focuses on a solar reactor continuously transferring concentrated solar radiation to a bed of flowing particles. Rotary kilns are the chosen concept due to their technical maturity, easy control and simple design. The feasibility of a solar driven rotary kiln has already been proven at lab-scale, with the successful calcination of materials up to a scale of kg/h. The present work describes a large solar rotary kiln able to heat particles to over 1000 °C at flow rates of up to 20 kg/h. The thermal performance of the reactor was evaluated through an on-sun experimental campaign, performed in the high flux solar simulator at the DLR. During one test, 17 kg/h of particles were heated up to 990 °C, with a thermal efficiency of 45 %. An improvement of the efficiency can be obtained by optimizing the reactor. To do this, a numerical model was developed and its parameters fit to the measured data. Simulations were used to quantify the different heat loss mechanisms, and to explore ways of reducing them. The promising experimental results, together with the improvements suggested by the model, provide the basis for an upcoming chemical campaign, where the calcination of CaCO₃ and the effect of endothermic reactions on the temperature distribution will be investigated.