An important factor identified for the efficiency of falling particle concentrating solar applications is the falling particle curtain opacity. Low curtain opacity results in increased radiative losses. Candidate multi-stage configurations that can increase particle-curtain opacity were simulated for the existing 1 MWth falling particle on-sun receiver at Sandia’s NSTTF. In the candidate configurations, falling particles were collected periodically in sloped troughs spanning the width of the receiver. A small lip at the front of each trough causes particles to accumulate, allowing subsequent particles to spill over. Particle surface boundary conditions were represented with an empirically based model created to approximate particle behavior observed in testing. Curtain opacity increased using a multi-stage approach and decreases in radiative losses were outweighed by decreases in advective losses which were the dominant loss mechanism. The ability to alter the flow of air within the receiver using multi-stage release resulted in the greatest efficiency gains by reducing advective losses. Additionally, multi-stage release substantially decreased back wall temperatures within receiver.
The thermal performance of a candidate next-generation falling particle receiver (FPR) is analyzed subject to various expected operating conditions. This receiver design was created from the result of an extensive optimization study and developed to support the Generation 3 Particle Pilot Plant (G3P3) project. Previous analysis demonstrated high thermal efficiencies for the receiver at nominal quiescent conditions, but further analysis was required to demonstrate that the receiver could maintain that thermal performance in a wide range of anticipated environments. In this study, the thermal efficiency was numerically evaluated using a CFD model for different wind conditions and shown to maintain a thermal efficiency above 83% for considered wind conditions. Moreover, the effect of radiative spillage from the incoming concentrated solar beam on the receiver exterior was investigated using ray tracing and CFD models. The exterior wall material temperature limits were not exceeded for the anticipated design power from the heliostats. Additional features were numerically explored including the addition of a chimney to capture particle fines and waste heat and a multi-stage concept to maximize curtain opacity. Particle fines of 10 μm were shown to preferentially flow into this chimney rather than out of the aperture, and the multi-stage design decreased radiative losses and minimized wall temperatures behind the particle curtain.
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