Solar treatment of cohesive particles in a directly irradiated rotary kiln

[Display omitted] •Solar calcination of cement raw meal in open and directly irradiated rotary kiln.•Mixing of bed identified as the key to achieve high calcination above 90%.•Analysis of heat losses performed and shows promising ways for improvement.•Review of literature on solar calcination reactors. Although the utilization of concentrated solar power (CSP) for electricity production is already at commercial stage, the application to energy intensive industrial processes is still at an early stage. Among these, the cement industry is one of the biggest CO2-emitters and requires temperature levels achievable with concentrated solar radiation. Since fine particles have to be treated in this process, several challenges arise from the implementation of solar energy in such applications. In this work we present the design and experimental assessment of a high temperature solar rotary kiln to perform the calcination of cement raw meal. With input powers of about 14 kW, material flows of 4–12 kg/h were treated and calcination degrees ranged from 24 to 99%. The chemical efficiency was between 8 and 20% while total efficiencies (thermal plus chemical) between 19 and 40% were achieved. The creation of dust, which is a major issue with particles in the µm-range, could be kept under control by applying a suitable suction system at the reactor aperture. The influence of the mass flow rate, residence time and kiln temperatures on the calcination were analysed to identify key points for further improvement.