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During commissioning of the CSP test facility at King Saud University, a large temperature drop was noted when charging the thermal energy storage (TES) bin. Heat loss can be mitigated by using an airtight TES bin. In this paper, we present a small-scale TES bin, which can be isolated and sealed from its surroundings, i.e., the TES bin can be confined, isolated and sealed from its environment. There were two operational scenarios simulated, namely the start-up and steady-state scenarios. In the start-up scenario, the bin's centerline temperature was almost the same as the particle inlet temperature. Thus, the bin's wall was the sole cause of heat loss. Entrained air did not contribute to heat loss. Based on the results of the steady-state scenario, an air-tight bin can reduce the charging/discharging loss sufficiently. Additionally, no "significant" build-up of pressure was detected during bin charging. [ABSTRACT FROM AUTHOR]

The usage of solid particles as solar thermal energy absorption/storage medium requires particle heating receiver to be developed. King Saud University and Georgia Institute of Technology have been collaborating in designing and testing obstructed particle heating receiver. Size of the receiver is 1.2 m x 1.2 m; the base of it is made of duraboard on which chevron-shaped meshes, made of Inconel 601, are installed as the obstructions in a staggered arrangement. The receiver is employed in the particle-based solar power tower experimental facility at King Saud University. To evaluate performance of the receiver, on-sun tests were conducted on two types of particle material, i.e., red sand and CARBOBEAD. Results show that CARBOBEAD absorbed more solar thermal energy and achieved higher temperature rise across the receiver compared to red sand, which is, most likely, due to a higher radiation absorptivity. It was also found that red sand tended to agglomerate at the tip of the chevron mesh during the test, blocking the concentrated sunlight. Moreover, as these agglomerates crumbled, they created many smaller agglomerates that can block the filter downstream, which will, consequently, block the particle flow path. Mesh material also needs to be analyzed further to avoid particle agglomeration, because it is expected that it has a significant role in this matter. [ABSTRACT FROM AUTHOR]

Particle-based solar power tower is a promising technology that can surpass the temperature limit of today's commercial molten salt systems, which will improve the system's efficiency. King Saud University (KSU) in collaboration with Saudi Electricity Company (SEC) have built an experimental particle-based power tower system integrated with gas-microturbine at King Saud University. This test facility is, mainly, aimed to: (1) prove the concept of using solid particles as a solar thermal energy storage medium from which the gas-turbine receives its heat source; therefore, fossil fuel consumption decreases, and (2) prove the system's ability to raise the temperature of the solar-heated particles above 600 °C, surpassing the temperature limit of molten salt power tower systems, i.e., typically limited to around 600 °C. Previous on-sun tests using red sand have shown the system's ability to achieve both goals independently, in separate tests. The current paper presents further tests using red sand to reach both goals simultaneously and with better results, i.e., better solar contribution and higher temperature of solar-heated particles. Results show that the system is able to raise the particles temperature to a maximum temperature of 630 °C and to increase the compressed air temperature by around 17 °C before entering the combustor by utilizing the heat from solar-heated particles. It was also found that one of the issues that can decrease or prevent the solar contribution is the temperature drop on the hot particles as they flow from the particle heating receiver (PHR) outlet to the inlet of particle-to-working-fluid-heat exchanger (PWFHX). This can happen if the thermal energy storage (TES) bin, located upstream of the PWFHX, is nearly empty/partially filled, allowing outside air to be entrained with the particle flow into the bin; on the other hand, fully filled TES bin blocks the air to enter it, which will reduce the temperature drop significantly. [ABSTRACT FROM AUTHOR]

This paper explores one important issue related to the operation of particle-based concentrating solar power (PBCSP) systems which is the heat that might be lost through the main components comprising such systems. Tests conducted at the PBCSP test facility at King Saud University (KSU) in Riyadh, Saudi Arabia reveal significant heat loss in several components, including the thermal energy storage (TES) bin, the particle-to-working-fluid heat exchanger (PWFHX), the particle lift system, and the air piping. On-sun tests results show that only a small portion (16%) of the net thermal energy captured in the particle heating receiver (PHR) was transferred to the turbine's air, which was then converted into electrical power. The remaining amount of energy was either leaked or consumed to heat up the thermal mass of facility's components. The air entrained with particles flowing to the TES bin resulted in a heat loss across the bin amounted to 24% of the collected energy. The large thermal mass of the PWFHX consumed more than half of the collected energy to be heated up, although some heat might had leaked to the concrete platform on which the PWFHX is placed. The reasons for this enormous loss are explained, and recommendations for ensuring efficient construction and operation of such systems are suggested. [ABSTRACT FROM AUTHOR]

This paper presents a thermal performance evaluation of a pilot 50 kWth moving packed-bed particle-to-air heat exchanger. The exchanger has been integrated into the particle-based concentrating solar power (CSP) test facility located at the campus of King Saud University (KSU) in Riyadh, Saudi Arabia. The configuration is a shell-and-tube design in which solid particles move downward by gravity as a dense packed-bed inside the vertical tubes whereas air flows on the shell-side. The detailed description of the heat exchanger and integration process is presented. Tests were conducted to investigate the effect of particle flow rate on the heat exchanger performance. Although the heat exchanger was tested at off-design conditions using a recuperated air of a gas turbine as a heat source, the results show high values of the overall heat transfer coefficient (up to ∼120 W/m2-°C) in accordance with shell-and-tube indirect contact heat exchangers. The heat exchanger will be tested at the design conditions in the near future when the weather conditions in Riyadh city improve and the direct normal irradiance (DNI) increases. The particle heating receiver (PHR) will be used as a heat source in the upcoming test campaign. [ABSTRACT FROM AUTHOR]

Utilizing the solid particles as a heat transfer media in concentrated solar power systems offers many advantages over other current commercial heat transfer media like steam, oil, air, and molten salt. These advantages are: high operating temperature (>1000℃), abundance, low cost, high thermal energy storage capacity, no freezing limit, and its ability to be irradiated directly. The solid particles do not need to be pumped to the system facilities. Friction properties play the main role in the transfer of particles from one place to another. However, it is important to study the flow kinematics in which the particle flow behavior is affected by friction or interparticle properties such as the angle of rest and the internal angle of friction. Knowing such angles is important to design components like chutes, hoppers, particle-to-fluid heat exchanger, etc., and understanding the characteristics of particle flow. In this study, the verification of friction properties for different particles was studied based on its dynamic resting angle, internal angle of friction, and static resting angle. The revolving cylinder method was used to measure the dynamic angle of repose while a transparent glass cylinder with a small hole in the center of the bottom surface was used to measure the internal angle of friction. The static angle of repose was verified using two methods: The hollow cylinder method and the fixed funnel method. Three natural particulate materials with different particle sizes and sphericity were used namely: Riyadh white sand, Riyadh red sand, US olivine sand (Green Diamond) and one engineered particulate material called Carbobead. [ABSTRACT FROM AUTHOR]

Direct particulate heating receivers (DPHR) are the most important part of the particle-based concentering solar power (PBCSP) systems in which the particles are exposed to direct high-concentrated sunlight. One variation of DPHRs is the obstructed flow receiver, which King Saud University (KSU) and the Georgia Institute of Technology have been developing for years. In this type of PHR, the particles fall freely in the form of a curtain through some obstruction to decelerate flow and allow the falling particles to absorb a considerable amount of thermal energy. The discrete structure presented in this design uses chevron-shaped mesh made of metallic alloy (Inconel 601) that was fixed on a Duraboard HD (an alumina-silica ceramic fiberboard). The design has been successfully tested using red sand and CARBOBEAD as heat transfer media. However, the interaction between the particulate and chevron mesh screen needs to be considered carefully at high operating temperatures. Careful consideration is the softening of the tip of the metallic chevron facing the sun. The tip of the mesh becomes soft at high temperatures and deforms which causes the particles to agglomerate on the chevrons, clog the chevron opening, and prevent particles from moving down to the end. Also, the particles get exposed to high flux for a long time which leads to particle fusing. Finally, a high degradation in the thermal efficiency of the system occurs as a result of this agglomeration and stops the whole operation of the plant. So, it is very important to study the interaction between the particulates and obstacles at high temperatures before installing it in the PHR cavity. This paper addresses these issues by presenting a study of the interaction between several chevron candidate materials and high-temperature candidate particles. The test was conducted in two stages: On-sun test and the lab test. Lab test is done by immersing the mesh screens with particulate materials and then heating at a specific temperature for several hours. For the chevron material, three candidates were considered: (a) stainless steel 316, (b) Inconel 601, and (c) ceramic mesh (WHIPOX). Three candidate particulate materials were considered: (a) Riyadh red sand, (b) Riyadh white sand, and (c) CARBOBEAD CP. Three temperature levels were considered in the lab test: (a) 800℃, (b) 1000℃, and (c) 1200℃. [ABSTRACT FROM AUTHOR]