Evaluation of Performance Factors for a Multistage Falling Particle Receiver

Abstract

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.

Design Evaluation of a Next-Generation High-Temperature Particle Receiver for Concentrating Solar Thermal Applications

“…The StAIR concept was also tested on-sun using up to two hybrid troughs retrofitted into the existing 1 MWth FPR at the NSTTF [75]. Cold flow testing within the receiver prior to on-sun testing showed improved curtain uniformity compared to free-fall.…”

“…A proportional-integral-derivative (PID) controller was used to actuate the receiver slide gate to continuously control the mass flow rate through the receiver and maintain the receiver outlet temperature at a given setpoint in recent on-sun tests [75,79]. Previous control strategies with only a proportional control created undesirable oscillations in the outlet temperature [27].…”

“…Although there are oscillations in the response, the measured particle outlet temperature adequately tracked the desired setpoint temperature as it evolved through the test. The PID controller was also evaluated following a ~20% perturbation in the incident radiative power (achieved by removing a portion of the heliostats during operation) [75]. Two standard deviations in the particle outlet temperature was targeted to remain within ±10 °C of the setpoint temperature in the minutes following the perturbation.…”

“…In tests of the RVR concept on-sun, the existing NSTTF FPR was retrofitted with a cavity truncation that approximated the shape of the optimized geometry. Using repeated experimental conditions from the previous test campaign [27] (with as similar wind conditions as could be achieved), additional tests [75] compared the receiver thermal efficiency with the cavity truncation against the cavity without the truncation as shown in a parity plot in Figure 11. All of the repeated experiments with the cavity truncation are at or above the parity line showing a consistently higher thermal efficiency providing confidence of the improved benefits with the optimized FPR cavity.…”

“…Figure 11. Parity plot comparing the receiver efficiency for previous experiments[27] and with the FPR retrofitted with a cavity truncation approximating the RVR concept[75].…”