This paper provides an overview of a next-generation particle-based concentrating solar power (CSP) system. The Gen 3 Particle Pilot Plant (G3P3) will heat particles to over 700 °C for use in high-temperature air or supercritical CO2 Brayton cycles with 6 hours of storage. The particles, which are inert, non-corrosive, durable, and inexpensive, are used as both the heat-transfer and storage media. Details of the operation, requirements, and design basis for the G3P3 system are presented, including a description of expected operational states and major components. Operational states include start-up, transients, steady-state operation, off-design conditions, and idling. The key components include the particle receiver, storage bins, heat exchanger, lift, and tower structure subsystems. Design bases and innovative features of each component are presented that will aid in achieving the desired cost and performance metrics.
A strategy to optimize the thermal efficiency of falling particle receivers (FPRs) in concentrating solar power applications is described in this paper. FPRs are a critical component of a falling particle system, and receiver designs with high thermal efficiencies (~90%) for particle outlet temperatures > 700°C have been targeted for next generation systems. Advective losses are one of the most significant loss mechanisms for FPRs. Hence, this optimization aims to find receiver geometries that passively minimize these losses. The optimization strategy consists of a series of simulations varying different geometric parameters on a conceptual receiver design for the Generation 3 Particle Pilot Plant (G3P3) project using simplified CFD models to model the flow. A linear polynomial surrogate model was fit to the resulting data set, and a global optimization routine was then executed on the surrogate to reveal an optimized receiver geometry that minimized advective losses. This optimized receiver geometry was then evaluated with more rigorous CFD models, revealing a thermal efficiency of 86.9% for an average particle temperature increase of 193.6°C and advective losses less than 3.5% of the total incident thermal power in quiescent conditions.
Two active airflow control methods are investigated to mitigate advective and particle losses from the open aperture of a falling particle receiver. Advective losses can be reduced via active airflow methods. However, in the case of once-through suction, energy lost as enthalpy of hot air due to active airflow needs to be minimized so that thermal efficiency can be maximized. In the case of forced air injection, a properly configured aerowindow can reduce advective losses substantially for calm conditions. Although some improvement is offered in windy conditions, an aerowindow in the presence of winds does not show an ability to mitigate advective losses to values achievable by an aerowindow in the absence of wind. The two active airflow methods considered in this paper both show potential for efficiency improvement, but the improvement many not be justified given the added complexity and cost of implementing an active airflow system. While active airflow methods are tractable for a 1 MWth cavity receiver with a 1 m square aperture, the scalability of these active airflow methods is questionable when considering commercial scale receivers with 10–20 m square apertures or larger.
Falling particle receivers (FPRs) are an important component of future falling particle concentrating solar power plants to enable next-generation energy generation. High thermal efficiencies in a FPR are required to high thermodynamic efficiencies of the system. External winds can significantly impact the thermal performance of cavity-type FPRs primarily through changing the air flow in and out of the aperture. A numerical parametric study is performed in this paper to quantify the effect of wind on the thermal performance of a FPR. Wind direction was found to be a significant parameter that can affect the receiver thermal efficiency. The particle mass flow rate did not significantly change the overall effect of wind on the receiver. The receiver efficiency was strong function of the particle diameter, but this was primarily a result of varying curtain opacity with different diameters and not from varying effects with wind. Finally, the model was used to demonstrate that receiver efficiencies of 90% were achievable under the assumption that the effect of wind/advective losses were mitigated.
Falling particle receivers are an emerging technology for use in concentrating solar power systems. In this work, quartz tubes cut in half to form tube shells (referred to as quartz half-shells) are investigated for use as a full or partial aperture cover to reduce radiative and advective losses from the receiver. A receiver subdomain and surrounding air volume are modeled using ANSYS® Fluent®. The model is used to simulate fluid dynamics and heat transfer for the following cases: (1) open aperture, (2) aperture fully covered by quartz half-shells, and (3) aperture partially covered by quartz half-shells. We compare the percentage of total incident solar power lost due to conduction through the receiver walls, advective losses through the aperture, and radiation exiting out of the aperture. Contrary to expected outcomes, simulation results using the simplified receiver subdomain show that quartz aperture covers can increase radiative losses and, in the partially covered case, also increase advective losses. These increased heat losses are driven by elevated quartz half-shell temperatures and have the potential to be mitigated by active cooling and/or material selection.