Particle Solar Receiver Research Articles

Radiation Absorption in a Particle Curtain Exposed to Direct High-Flux Solar Irradiation

Radiation absorption is investigated in a particle curtain formed in a solar free-falling particle receiver. An Eulerian–Eulerian granular two-phase model is used to solve the two-dimensional mass and momentum equations by employing computational fluid dynamics (CFD) to find particle distribution in the curtain. The radiative transfer equation (RTE) is subsequently solved by the Monte Carlo (MC) ray-tracing technique to obtain the radiation intensity distribution in the particle curtain. The predicted opacity is validated with the experimental results reported in the literature for 280 and 697 μm sintered bauxite particles. The particle curtain is found to absorb the solar radiation most efficiently at flowrates upper-bounded at approximately 20 kg s−1 m−1. In comparison, 280 μm particles have higher average absorptance than 697 μm particles (due to higher radiation extinction characteristics) at similar particle flowrates. However, as the absorption of solar radiation becomes more efficient, nonuniform radiation absorption across the particle curtain and hydrodynamic instability in the receiver are more probable.

Numerical study on the influence of vortex flow and recirculating flow into a solid particle solar receiver

Abstract This paper presents a numerical study of a well-established vortex flow receiver and a proposed recirculating flow Solid particle solar receiver (SPSR) capable of achieving high air temperature which is perfectly suitable for the hybrid solar thermal power plant. Solar particle receivers are modeled using discrete particle model (DPM), RNG k- e flow model and discrete ordinate (DO) radiation model. Numerical analysis is done by considering two cases (i) Recirculating flow solar receiver with non-reacting particle and without non-reacting particle as a medium of transferring heat (ii) Vortex flow solar receiver with non-reacting particle and without non-reacting particle as a medium of transferring heat. The examination is carried out to compare the parametric sensitivity of both solar particle receivers with particle and air and without particle as a medium of transferring heat by considering the solar flux that incident on the aperture of the receiver and varying the air flow rate and particle concentration, recirculation rate. The results depict that use of particle enhance the heat transfer for both cases. It is concluded from the thermal behavior of recirculating flow SPSR that about 30% higher cavity thermal efficiency and exhibit higher and uniform heat transfer than a vortex flow SPSR.

Evaluating thermodynamic performance limits of thermochemical energy storage subsystems using reactive perovskite oxide particles for concentrating solar power

Concentrating solar power with cost effective and efficient thermal energy storage (TES) has the potential to achieve high dispatchability and enable high penetration of other renewable energy sources. However, levelized cost of electricity of integrated CSP systems remains prohibitively high, and new storage subsystems with higher specific energy storage (kJ kg-1) and overall solar-to-electric efficiencies are needed to lower the costs of dispatchable electricity from CSP. This paper explores the potential for increased specific energy storage and solar-to-electric efficiencies of a TES subsystem that combines sensible and chemical energy storage (i.e., thermochemical energy storage – TCES) using a redox cycle of reducible perovskite oxide particles. The TCES subsystem stores energy through sensible heating and endothermic perovskite reduction in a concentrated solar particle receiver at high temperature (Thot from 700 to 1100 °C) and low O2 partial pressure (pO2 from 10-2 to 10-4 bar). Stored energy is recovered as needed in a particle reoxidation reactor/heat exchanger fed by air. Energy parasitics to lower pO2 for perovskite reduction in the receiver by vacuum pumping or inert sweep gas generation depend on system design and operating conditions. In this work, TCES with the perovskite strontium-doped calcium manganite (Ca0.9Sr0.1MnO3-δ) is evaluated for specific storage and overall solar-to-electric efficiency in a subsystem using vacuum pumping or N2 sweep gas for the reducing environment in the receiver. Vacuum pumping parasitics increase proportionally to changes in oxygen non-stoichiometry (Δδ) and are prohibitively high for Δδ>0.1. Sweep-gas parasitics to separate N2 from air asymptote to smaller constant values at large Δδ. Thus, a sweep gas subsystem has lower balance-of-plant parasitics at Δδ needed for high specific TCES. Improvements in vacuum pump efficiencies from current commercially available values to >10% could reduce pumping parasitics and achieve solar-to-electric efficiencies approaching 35%. Various combinations of reducing pO2 and increasing Thot can achieve the same energy storage for either inert sweep gas or reversible vacuum-pump systems with solar-to-electric efficiencies above 35%.

Effects of particle polydispersity on radiative heat transfer in particle-laden turbulent flows

This study considers the effects of polydispersity of particles on thermodynamic and hydrodynamic behaviour of solid particle solar receivers. To this end we consider a canonical setting of a semi-periodic domain and perform DNS of turbulent flows interacting with point particles subject to a heating source. The turbulent flow is seeded with polydisperse particles that have a specific cumulative distribution function of particle sizes that is tuned based on available measurements. A thermodynamically equivalent monodisperse particle size is calculated, in a sense that the mass loading ratio of particles to gas and the total frontal area of particles available for radiation absorption are matched between the polydisperse and monodisperse particles. Our results show that the effective heat transfer rate between the two phases is significantly impacted by both particle clustering and polydispersity. We compare our DNS results to the predictions of a semi-analytical 1D model that assumes uniform particle concentration and gas properties per streamwise cross-section. Gas and particle temperatures predicted by this 1D model show least agreement with DNS at a Stokes number close to unity, where particles are most preferentially concentrated. Capturing the quantitative effects of particle preferential concentration on the effective heat transfer leads to a closure problem in the context of the 1D model. Using the DNS data, we examine such closure models and assess whether closure corrections inferred from monodisperse DNS can be applied to polydisperse mixtures viewed as superposition of multiple monodisperse systems.

Characterization of desert sand to be used as a high-temperature thermal energy storage medium in particle solar receiver technology

Desert dune sand is considered as a potential sensible heat thermal energy storage (TES) material. Several samples are collected from different locations of the desert in the United Arab Emirates (UAE), and relevant thermophysical and mechanical properties are measured. In addition, the optical properties of desert sand are investigated to evaluate its performance as a direct solar absorber. Thermogravimetric analyses show that the samples appear to be thermally stable between approximately 650 °C to 1000 °C following an initial mass loss occurring during the first heating cycle. The transformation of calcium carbonate into calcium oxide at higher temperature during the first heating process has a negative impact on the solar absorption of the sand. In addition, the high calcium content leads to sand agglomeration which has significant implications on receiver design and operation. It is therefore critical to locate sand collection points with low carbonate content.

Characterization of Particle Flow in a Free-Falling Solar Particle Receiver

Falling particle receivers are being evaluated as an alternative to conventional fluid-based solar receivers to enable higher temperatures and higher efficiency power cycles with direct storage for concentrating solar power (CSP) applications. This paper presents studies of the particle mass flow rate, velocity, particle-curtain opacity and density, and other characteristics of free-falling ceramic particles as a function of different discharge slot apertures. The methods to characterize the particle flow are described, and results are compared to theoretical and numerical models for unheated conditions. Results showed that the particle velocities within the first 2 m of release closely match predictions of free-falling particles without drag due to the significant amount of air entrained within the particle curtain, which reduced drag. The measured particle-curtain thickness (∼2 cm) was greater than numerical simulations, likely due to additional convective air currents or particle–particle interactions neglected in the model. The measured and predicted particle volume fraction in the curtain decreased rapidly from a theoretical value of 60% at the release point to less than 10% within 0.5 m of drop distance. Measured particle-curtain opacities (0.5–1) using a new photographic method that can capture the entire particle curtain were shown to match well with discrete measurements from a conventional lux meter.

Parametric study on the performance of a solid particle solar receiver

Solid particle solar receivers (SPRs) can be used as a high efficient solar energy absorber to collect concentrated radiation energy. The high temperature heat energy from SPRs can be applied as a heat source in a thermo-chemical water-splitting (TCWS) hydrogen production process. A parametric study has been conducted on a conceptual design from Sandia National Laboratories (SNL). A Computational Fluid Dynamics (CFD) model which includes the heat transfer and aerodynamics behaviors between the air and the particles is used to evaluate the performance of the SPR, both the cavity efficiency and the exit particle temperature. The main purpose of this study is to find the optimal design and working conditions of the SPR.

Fluidized-bed Technology Enabling the Integration of High Temperature Solar Receiver CSP Systems with Steam and Advanced Power Cycles

Solar Particle Receivers (SPR) are under development to drive concentrating solar plants (CSP) towards higher operating temperatures to support higher efficiency power conversion cycles. The novel high temperature SPR-based CSP system uses solid particles as the heat transfer medium (HTM) in place of the more conventional fluids such as molten salt or steam used in current state-of-the-art CSP plants. The solar particle receiver (SPR) is designed to heat the HTM to temperatures of 800 °C or higher which is well above the operating temperatures of nitrate-based molten salt thermal energy storage (TES) systems. The solid particles also help overcome some of the other challenges associated with molten salt-based systems such as freezing, instability and degradation. The higher operating temperatures and use of low cost HTM and higher efficiency power cycles are geared towards reducing costs associated with CSP systems. This paper describes the SPR-based CSP system with a focus on the fluidized-bed (FB) heat exchanger and its integration with various power cycles. The SPR technology provides a potential pathway to achieving the levelized cost of electricity (LCOE) target of $0.06/kWh that has been set by the U.S. Department of Energy's SunShot initiative.

Energy and Exergy Analysis of a Novel Gravity-fed Solid Particle Solar Receiver

An energy and exergy analysis of a novel solid particle solar receiver is presented based on experimental data and well-known correlations found in the literature. A sand sample from the deserts of the United Arab Emirates has been chosen as the solar absorber and heat carrier material. The intent of the receiver is to be used as a part of a sensible thermal energy storage system for concentrated solar power plants based upon the concept of storing solar heat in sand particles for a later discharge through a specific sand-steam heat exchanger. The results of the analysis indicate low efficiency figures that can be caused by imperfections on the experimental setup and on the original design. Several paths of improvement are discussed in conclusion.

Improvement of Radiative Performances of High Temperature Solar Particle Receivers Using Coated Particles and Mixtures

The use of HfB2, ZrB2, HfC, ZrC, W, and SiC particles in a high temperature solar particle receiver (SPR) is analyzed. The SPR is modeled as a 1D slab of spherical particles dispersion, submitted to a concentrated and collimated solar flux (q0 = 1500 kW/m2). The temperature inside the SPR is taken constant (T = 1300 K), as for a well-stirred receiver. For the W and SiC, the refractive indexes reported in the literature are retained while the real and imaginary parts of the refractive indexes of the others materials are obtained from available reflectance data, using the Kramers–Kronig (KK) relationships. Three SPR configurations are considered: a homogeneous medium with only one kind of particles, a medium with a mixture of two materials and a medium with coated particles. The three configuration results are compared with those obtained using particles made with an ideal material. For the first configuration, the lowest radiative losses are found using small particles of sizes close to d = 2 μm. For the second configuration, non-noticeable improvements are found by the use of mixtures of the studied materials. For the third configuration, when the SiC is used as mantle, the radiative losses decrease to approach the ideal minimum. The best combination corresponds to a particle with a core of W coated by SiC. Improvements of 2.6% and 2.8% may be achieved using coating thickness of 50 nm with particles of d = 2 μm and d = 100 μm, respectively. The use of coated particles may thus lead to significant improvements in the radiative performances of a SPR working at high temperature.

Optical and thermal performance of a high-temperature spiral solar particle receiver

A spiral solar particle receiver (SSPR) with a conical cover was proposed, and the performance was experimentally and numerically investigated. The SSPR was heated by a concentrated radiant flux of ∼5kW over a 10cm-diameter aperture with a maximum irradiance of over 700kW/m2. The experimental results indicated the particle temperature increase reached over 625°C in a single pass with an optical and a thermal efficiency of ∼87% and ∼60%, respectively, when the mass flow rate was 0.21kg/min. The optical performances of the solar simulator and the receiver were combined and simulated by the Monte-Carlo ray-tracing method. Based on the optical model, a dynamic thermal conversion model was built, which indicated the particle temperature and the overall efficiency of SSPR would reach 628–673°C and 58.9–63.7%, respectively, when the SSPR was coupled with a 3m two-stage dish concentrator with a solar inclination angle ranging from 60° to 120°.

Assessment of the Overall Efficiency of Gas Turbine-driven CSP Plants Using Small Particle Solar Receivers

While current commercial Concentrated Solar Power (CSP) plants utilize Rankine steam cycles in the power block, there is a goal to develop higher-efficiency plants based on Brayton cycles or on combined cycles. In this paper, we present an assessment of a gas turbine-driven CSP plant using small particle solar receivers. In particular, a recuperated, single-shaft gas turbine engine and a Small Particle Heat Exchange Receiver –a high temperature receiver for solar tower power plants developed in the framework of the U.S. DOE's SunShot Program– are the technologies employed for the gas turbine and the receiver, respectively. The curves of the solar receiver and the gas turbine engine were first obtained using in-house codes, and then coupled together. A backup combustor fueled with natural is used to compensate the variable nature of the solar resource. For a more flexible and optimum operation, the guide vane angle of the compressor is allowed to vary, and so is the position of the valves of the receiver and combustor bypasses. Two different operational strategies were analyzed: maximizing the overall efficiency of the plant and maximizing the net output power. Hence, the overall efficiency of a gas turbine-driven CSP plant based on a Small Particle Heat Exchange Receiver is estimated, and the potential to generate electricity is assessed. This analysis reveals the strengths of small particle receivers with respect to molten salt tubular receivers due to the much higher temperatures that can be achieved while maintaining (or even increasing) the receiver efficiency.

Design Space Exploration of a 5 MWth Small Particle Solar Receiver

We present a design space exploration of a 5 MWth Small Particle Solar Receiver for solar tower power plants. This new solar receiver, developed under the support of the U.S. Department of Energy's SunShot Program, aims to volumetrically absorb concentrated solar irradiation using an air-particle mixture to drive a gas turbine or a combined cycle at much higher temperature than the state-of-the-art molten salt receivers. Among other advantages, the thermodynamic efficiency of the power block and the overall efficiency of the plant would considerably increase with this technology. The design space consists of the wall angle of the receiver, the geometry of the window (necessary to allow the solar irradiation to enter into the receiver) and the radiative properties of the walls. The constraints are based on material limits, ensuring the mechanical integrity of the quartz window, and other technical issues; though some of them are imposed via a penalty method. The design space is explored through parametric studies and a multidisciplinary approach is adopted. The aluminum oxide walls, the 45° spherical-cap window and the 45° wall- angle receiver are preferred due to their best compromise between thermal efficiency and wall temperature.

Optical Analysis and Thermal Modeling of a Window for a Small Particle Solar Receiver

Concentrated solar power (CSP) systems use heliostats to concentrate solar radiation in order to produce high temperature heat, which drives a turbine to generate electricity. A 5 MWth Small Particle Solar Receiver is being developed for power tower CSP plants based on volumetric absorption by a gas-particle suspension by the support from the U.S. Department of Energy under the SunShot Initiative. The radiation enters the pressurized receiver (0.5MPa) through a curved window, which must sustain the thermal loads from the concentrated solar flux and infrared reradiation from inside the receiver. The thermal load from the solar flux on the window is calculated by using the computer code MIRVAL from Sandia National Laboratory which uses the Monte Carlo Ray Trace (MCRT) method, along with two other codes developed by the authors. Thermal loading was calculated from energy absorbed at various points throughout the window from both the heliostat field and inside the receiver. Transmission and reflective losses were also calculated for different window materials in order to find out how much radiation will enter the receiver or will be lost. The three dimensional temperature distribution of the window is analyzed by an energy balance taking into account spectral volumetric absorption, spectral surface emission, conduction within the window, and convection from both surfaces. A maximum window temperature of 800°C must be enforced to prevent cracking and/or devitrification due to overheating. Several grades of quartz are considered for this study with detailed spectral calculations. For a chosen material, the window temperature was found to be held under 800°C. The results showed that most of the heat load on the window comes from the inside of receiver due to spectral variation.

Optimization of the optical particle properties for a high temperature solar particle receiver

A non-homogeneous slab of particle dispersion composed of two-layers at high temperature, submitted to a concentrated and collimated solar radiation flux with a reflective receiver back wall is considered as a model of a solar particle receiver. The Radiative Transfer Equation (RTE) is solved using a two-stream method and an appropriate hybrid modified Eddington-delta function approximation. The single particle optical properties are modeled using the Lorenz–Mie theory, the single particle phase function is approximated by the Henyey–Greenstein phase function. A Particle Swarm Optimization (PSO) algorithm is used to optimize the particle radius (0.1μm⩽r≤100μm), the volume fraction (1×10-7⩽fv⩽1×10-4) and the refractive index (2.0⩽n≤4.5 and 0.0001⩽k≤25) of an ideal theoretical material to use in a solar particle receiver. Single- and two-layer receivers with known temperature profiles were optimized to maximize the receiver efficiencies. Spectral selective behavior of the optimized refractive index is discussed with the influence of particle radii and volume fractions. The theoretical ideal optical properties found for the particles have given the maximum efficiency reachable by the studied receivers and have shown that an optimized single-layer receiver will perform as well as a two-layer receiver.

Simulation and experimental study on a spiral solid particle solar receiver

A solid-particle solar receiver was proposed to convert concentrated solar beams into heat for high-temperature thermal storage in a two-stage dish system. Spherical Xe-arc lamps were used to simulate a solar light source. The performances of this receiver under a Xe-arc lamp array system were experimentally and numerically investigated. For a single pass, the temperature increase exceeded 350°C, and the optical efficiency and thermal efficiency were ∼84% and 60%, respectively, when the average flux on the aperture was ∼19.3kW/m2. A Monte-Carlo ray-tracing method was used to simulate concentrating beams, which was integrated with a thermal conversion model. The coupled model was validated under low radiation flux conditions and then used to predict the solid-particle receiver performance under high radiation flux conditions. The simulation results indicate that the final temperature of the single-pass particles would increase to over 1100°C under an average flux of 150kW/m2. In addition, the efficiency of the receiver could be enhanced by reducing the radiative emission.

Wind effect on the performance of solid particle solar receivers with and without the protection of an aerowindow

The wind conditions affect the performance of a solid particle solar receiver (SPSR) by convection heat transfer through the existing open aperture. Aerowindows have the potential of increasing the efficiency of an SPSR. In the present paper, the wind effect on the performance of an SPSR is investigated numerically with and without the protection of an aerowindow. The independence of the calculating domain in a wind field has been studied in order to select a proper domain for the numerical simulation. The cavity thermal efficiencies and the exiting temperature of the solid particles have been calculated and analyzed for different wind conditions. The numerical investigation of the SPSRs’ performance can provide a guide in optimizing the prototype design, finding out the suitable working condition and proposing efficiency enhancing techniques for SPSRs.

A study of solid particle flow characterization in solar particle receiver

The solid particle receiver (SPR) is a direct absorption receiver in which solar energy heats a curtain of falling ceramic particle to a temperature in excess of 1000 °C. A small scale test platform was built to investigate particle flow properties. The curtain was comprised of approximately 697 μm ceramic particles that were dropped within the receiver cavity of the test platform. Tests were conducted to experimentally determine the distribution of particles velocity, curtain thickness, and curtain opacity along a drop length of approximately 3 m. Velocity data were measured using a high speed digital camera to obtain images of the particle flow at 1000 frames per second with an exposure time of 100 μs. Five mass flow rates ranging from 1 kg/s-m to 22 kg/s-m were examined, and it was found that all flows approached a terminal velocity of about 6–7 m/s in a vertical drop distance of 3 m. The experimental results were validated with computational results and were found in excellent agreement with the simulation results. In addition, a similar study was performed with various sizes of the particles to better understand how the particle flow characteristics were affected by the size of the particles.

04/02889 Experimental evaluation of a non-isothermal hightemperature solar particle receiver: Bertocchi, R. et al. Energy, 2004, 29, (5–6), 687–700

04/02889 Experimental evaluation of a non-isothermal hightemperature solar particle receiver: Bertocchi, R. et al. Energy, 2004, 29, (5–6), 687–700

Experimentally Determined Optical Properties of a Polydisperse Carbon Black Cloud for a Solar Particle Receiver

Measured physical and optical properties of a stable polydisperse carbon black particle cloud at 532 nm and 1064 nm are reported. The particle cloud consisted of 99.7% spheroid primary particles (45–570 nm diameter) and 0.3% large irregularly shaped agglomerates (1.2–7.25 μm equivalent diameter). Although the numerical fraction of the agglomerates was only 0.2%, they contributed 60% to the cloud’s scattering cross section. The extinction coefficient, scattering coefficient and the scattering phase function were measured for both parallel and perpendicular polarized radiation at linear extinction coefficients ranging from 0.6 to 4.1 m−1. The cloud exhibited strong forward scattering, with 62% of all scattered energy in a forward lobe of 15° at 532 nm and 48% at 1064 nm. The scattering albedo was measured to 35% at 532 nm and 47% at 1064 nm. The dimensionless extinction coefficient was measured to 8.25 at 532 nm. The experimental data was compared to standard Mie theory by integrating the weighed contribution based on particle size, including agglomerates, according to the detailed measured population distribution. Neglecting the contribution of the agglomerates to the cloud’s optical properties was shown to introduce discrepancies between Mie theory and measured results. The results indicate that the-Mie theory can be used for estimating the optical properties of a partially agglomerated carbon black particle cloud for simulation of a solar particle receiver.