A predictive CFD model for a falling particle receiver/reactor exposed to concentrated sunlight

Abstract

Computational fluid dynamics (CFD) is employed in the evaluation of a 1.5 MW th solar chemical receiver/reactor proposed for the thermal decomposition of limestone (CaCO 3), which is the main endothermic step in the cement production process. Among potential receiver/reactor configurations, the falling particle reactor (FPR) has been selected as the candidate conceptual design. The concept includes a field of tracking mirrors (heliostats) used to focus the incident solar energy onto the aperture of the receiver/reactor mounted at the top of a tower. The concentrated solar radiation is absorbed directly by a curtain of free-falling solid particles that are heated to temperatures in excess of 1200 K over approximately 5 m height of fall in the presence of a radiant flux of less than 1 MW m -2. The CFD simulations predict that the FPR can be operated without major problems under ambient conditions. However, when exposed to concentrated sunlight, particles with diameters below about 300 μm are likely to be entrained by convective air streams. These particles might either leave the reaction site if the reactor is open, or they might pollute the transparent window if the reactor is a closed cavity. Implementing suitable mechanical devices inside the FPR could eliminate these critical issues and, at the same time, increase the residence time to ensure complete calcination.