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Researchers from all around the world have been paying close attention to particle-based power tower technologies. On the King Saud University campus in the Kingdom of Saudi Arabia, the first integrated gas turbine–solar particle heating hybrid system has been realized. In this study, two different types of experiments were carried out to examine how susceptible prospective liner materials for thermal energy storage tanks were to erosion. An accelerated direct-impact test with high particulate temperature was the first experiment. A low-velocity mass-flow test was the second experiment, and it closely mimicked the flow circumstances in a real thermal energy storage tank. The tests were conducted on bare insulating fire bricks (IFBs) and IFBs coated with Tuffcrete 47, Matrigun 25 ACX, and Tuffcrete 60 M. The latter three lining materials were high-temperature-resilient materials made by Allied Mineral Products Inc. (AMP) (Columbus, OH, USA). The results showed that although IFBs coated with AMP materials worked well in this test, the accelerated direct-impact test significantly reduced the bulk of the bare IFB. As a result, lining substances must be added to the surface of IFBs to increase their strength and protection because they cannot be used in situations where particles directly impact their surface. On the other hand, the findings of the 60 h cold-particle mass-flow test revealed that the IFBs were not significantly eroded. Additionally, it was discovered that the degree of erosion on the samples of bare IFB was unaffected by the height of the particle bed. [ABSTRACT FROM AUTHOR]

Tests were performed at the particle-based CSP test facility at King Saud University to demonstrate a viable solution to overcome the limitations of using molten salt as a working medium in power plants. The KSU facility is composed of a heliostat field, particle heating receiver (PHR) at the top of a tower, thermal energy storage (TES) bin, a particle-to-working fluid heat exchanger (PWFHX), power cycle (microturbine), and a particle lift. During pre-commissioning, a substantial portion of the collected solar energy was lost during particle flow through the TES bin. The entrained air is shown to be the primary cause of such heat loss. The results show that the particle temperature at the PHR outlet can reach 720 °C after mitigating the entrained air issue. Additionally, during on-sun testing, a higher temperature of the air exiting the PWFHX than that of the air entering is observed, which indicates the effective solar contribution. Half-hour plant operation through stored energy was demonstrated after heliostat defocusing. Lastly, a sealable TES bin configuration for 1.3 MWe pre-commercial demonstration unit to be built in Saudi Arabia by Saudi Electric Company (SEC) is presented. This design modification has addressed the heat loss, pressure build-up, and contamination issues during TES charging. [ABSTRACT FROM AUTHOR]

This paper presents a thermal performance evaluation of a novel particle-to-air heat exchanger. The heat exchanger has a patented design with a shell-and-tube configuration. Solid particles move as a dense packed-bed inside the vertical tubes of the heat exchanger whereas air flows on the shell-side. This design avoids a number of limitations associated with the state-of-the-art heat exchangers in the same category, such as the stagnant/void zones and the prolonged residence time. The heat exchanger has a 50-kW thermal duty; it has been integrated into the particle-based concentrating solar power facility located at the campus of King Saud University in Riyadh, Saudi Arabia. The detailed description of the heat exchanger and the integration process is introduced. The recuperated air of the facility's power cycle is used to heat the solid particles being circulated inside the facility. The solid particles used in this study are engineered particles called Carbobead CP with 0.3 mm mean diameter. The effect of particle flow rate on the thermal performance of the heat exchanger is investigated. The results show that as the particle flow rate increases, the overall heat transfer coefficient (U) increases; a maximum value was measured to be 150 W/m2-°C based on LMTD calculations. The measurement accuracy was verified by repeating several tests; a slight variation was observed in the measured U. The results also show that only a small air pressure drop (~5 kPa) was measured across the heat exchanger. Furthermore, it was found that a significant part of the heat exchange occurred at the bottom section of the heat exchanger. [ABSTRACT FROM AUTHOR]

Utilizing solid particles as a heat-transfer medium in concentrated solar power applications has gained growing attention lately. Unlike molten salts, solid particles offer many benefits, which include: high operating temperatures (greater than 1000 °C), a lack of freezing issues and corrosivity, abundant availability, high thermal energy storage capacity, a low cost, and applicability in direct irradiation. Comprehensive knowledge of thermophysical and optical properties of solid particles is essential to ensure an effective harnessing of solar energy. The most important considerations when selecting solid particles include: thermophysical and optical properties, thermal resistance, crack resistance, satisfactory health and safety risks, availability, and low cost. It is also imperative to consider optical and thermophysical characteristics that might change from what they were "as received" after cyclic heating for a long period. Therefore, the knowledge of thermal performance of particulate materials becomes significant before using them as a heat-transfer medium. In this study, some particulate materials were chosen to study their feasibilities as heat-transfer and storage media for a particle-based central receiver tower system. These particulate materials included white sand, red sand, ilmenite, and Carbobead CP. The candidate particulate materials were heated at high temperatures for 6 h and then cooled to room temperature. After that, cyclic heating was performed on the particulate materials for 500 h at 1200 °C. The optical properties were represented by weighted solar absorptance, and the thermophysical properties of the particulates were measured "as received" and after cyclic heating (aging). EDX and XRD were conducted to quantify the chemical composition and interpret the changes in appearance associated with the particulate materials after cyclic heating. The results showed a considerable agglomeration in all particulates except for white sand in the 6 h heating test, and high agglomeration in the ilmenite. A slight decrease in the optical properties in the white sand and Carbobead CP was found after the aging test. The specific heat was decreased for red and white sand. The EDX and XRD results for white sand and Carbobead CP showed chemical stability, indicating high durability and reliability. [ABSTRACT FROM AUTHOR]

In this paper, techno-economic analysis and the experimental campaign for a new solar concentrating system are presented. Two novel receivers (Jet impingement receiver with mesh structure & helical channel receiver) are tested on a novel collector technology. The collector technology integrates the two established models of solar concentrating technologies, which are linear Fresnel reflector technology and central receiver technology, into the new concept called the Point Focus Fresnel Collector (PFFC). It is found that the PFFC system with jet impingement receiver and mesh structure provides higher thermal efficiency and manufacturing ease compared to parabolic dish systems. Maximum thermal efficiency of jet impingement receiver is highest at 87% whereas that for helical channel receiver is 83%. Average thermal efficiency of jet impingement receiver is 61% whereas that for helical channel receiver is 58%. Economic analysis of the system reveals that the discounted payback time for the PFFC system is only 5.5 years and less than one year compared to diesel and electricity powered steam generators respectively at an inflation rate of 2.5%. Substantial saving is predicted with PFFC system compared to diesel and electricity powered steam generator. For all discount rates in the range of 2.5–25%, the levelized cost of energy (LCOE) for PFFC system is much lower than that of LCOE in Saudi Arabia for conventional system. Since the LCOE in most of the Middle East and North Africa (MENA) countries is higher than the LCOE in Saudi Arabia, therefore, the PFFC system is also suitable for other MENA countries where average direct normal irradiation values are comparable to Saudi Arabia. • Results for a novel CSP system are presented with two new concepts of receivers. • Efficiencies of 58% and 61% are found to be higher than the commercial CSP systems. • Jet impingement receiver is best at 87% while helical channel receiver is at 83%. • Payback time is only 5.5 years compared to diesel driven steam generators. • LCOE is 0.075 SAR/kWh, substantially lower than that of Saudi Electricity Company. [ABSTRACT FROM AUTHOR]

Abstract: Grid-quality parabolic trough collectors utilize expensive receivers that maintain vacuum in their annuli to reduce convection losses. On the other hand, receivers with air-filled annuli, currently used mainly for process heat applications, are significantly less expensive, but their thermal performance is inferior to evacuated receivers. A promising technique that can bridge the cost and performance gap between the two types of receivers is introduced in this work. A heat-resistant thermal insulation material is fitted into the portion of the receiver annulus that does not receive concentrated sunlight. The presence of this insulation material is expected to reduce not only convection heat losses, but also radiation losses. This study focuses on the calculation of conduction and convection heat losses from the proposed receiver using numerical modeling. The performance of the proposed concept is compared to that of a conventional receiver with an air-filled annulus. The results have shown that the combined conduction and convection heat loss from the proposed receiver can be smaller than that from a receiver with an air-filled annulus by as much as 25% when fiberglass insulation is used. However, the fact that the thermal conductivity of the insulating material increases with temperature reduces the benefit of the proposed concept at high temperatures. As a result, the proposed receiver is expected to be suitable as a replacement for receivers with air-filled annuli or as an economical alternative to evacuated receivers that are used at the lower temperature end of utility-scale solar power plants. [Copyright &y& Elsevier]

The use of central solar particle-heating receivers (SPR) in concentrated solar power (CSP) systems offers numerous advantages over other central receiver concepts. The two main advantages are: (1) ordinary particulate minerals can allow collection temperatures approaching 1000 °C compared with conventional molten salts which are limited to about 650 °C, and (2) the low-cost high temperature particulate material can also be used as the storage medium in a highly cost effective thermal energy storage system. An innovative SPR design invented by researchers at King Saud University and Georgia Institute of Technology allows the particulate material to flow downward through a stationary porous structure where the concentrated solar energy is absorbed. The porous structure reduces the speed of the falling particulate material, i.e. increases its residence time within the receiver, thereby allowing a large temperature rise to be achieved in a single pass. The design increases absorption of the incident solar radiation (i.e. receiver efficiency) and reduces convective heat loss and particle loss (Al-Ansary et al., 2013). A numerical two-fluid solid–gas Eulerian–Eulerian flow model has been used to evaluate the effect of the porous structure on particulate flow through the receiver. The stationary porous structure was modeled using the packed bed concept in the FLUENT commercial CFD code. Two benchmarking experiments were conducted to assess the validity of the two-fluid flow and packed bed model for flow through the porous structure. This paper describes the two benchmarking experiments, and provides a comparison between the model predictions and the measured data. In the first experiment, particle flow rates through variable-width slits at the bottom of a constant head plenum were measured. In the second experiment, a porous layer was placed above the opening at the bottom of the constant head plenum to limit the particle discharge flow. Experiments with two different porous layer heights were conducted using two particle materials with different diameters and densities. The simulation results were in reasonable agreement with the test data. [ABSTRACT FROM AUTHOR]