Preliminary Design Development, Laboratory Testing, and Optimization of a 6.6 MW-Thermal All-Refractory Particle Heating Receiver

Heat receiver design is an essential portion of Concentrating Solar Power (CSP) plants, particularly within CSP systems that are particle based. Particle based CSP promises higher operating temperatures and more cost-effective thermal energy storage than existing systems. Two general types of Particle Heat Receivers (PHR) are under development, variations of the free-falling curtain concept being developed by Sandia National Labs and an obstructed flow concept being developed by King Saud University (KSU) and Georgia Institute of Technology (GIT)[1, 2]. The obstructed flow design utilizes specifically engineered obstacles placed in the flow path of the particles to remove momentum and kinetic energy and promote lateral and depth-wise mixing. This design is named the discrete structure or DS-PHR. This paper focuses on development and design work that has been done with the existing DS-PHR developed by GIT and KSU. Previous iterations of the DS-PHR have utilized obstruction materials that include simple metal meshes, and ceramic formed into an inverted V-shapes or chevrons. However, these previous designs have some shortfalls. The metallic mesh design has structural integrity issues under intense radiation, inherent in a DS-PHR. The ceramic chevrons have a disadvantageously thick leading edge, which may intercept too much radiation and overheat. Current development has continued with improvements to remedy the issues of the previous design work. Experience, modeling, and testing have shown that a cavity receiver is preferred to reduce heat and particle loss in the system. Recent work has been devoted to developing a Discrete Structure Refractory Particle Heat Receiver (DS-RPHR) suitable for cavity installation working with a north-located field. The simplest suitable configuration is 5 flat ceramic plates, or absorber panels, arranged in an arc, forming a 15° angle of inclination, to improve particle retention in the system. To increase particle residence time, quartz rods are placed onto the back plane of the DS-PHR, in a hexagonal configuration. These serve as the momentum scrubbing obstructions as mentioned above. The performance of this design will be discussed in the following paper. This design has been extensively modeled using NREL’s Soltrace to evaluate thermal and optical performance. Modeling has shown high thermal efficiency in the design, as well as promising heat flux profiles across the receiver. Currently at KSU, a 300 kW-thermal testing facility has been constructed and used for high temperature testing. The final proposed 6.6 MW-thermal design, called the pre-commercial demonstration, will be built at a site owned and operated by Saudi Electric Company, in Waad Al-Shamal, 20 kilometers east of Tuarif, Saudi Arabi.

Mass spectrometry of refractory black carbon particles from six sources: carbon-cluster and oxygenated ions

We discuss the major mass spectral features of different types of refractory carbonaceous particles, ionized after laser vaporization with an Aerodyne high-resolution soot-particle aerosol mass spectrometer (SP-AMS). The SP-AMS was operated with a switchable 1064 nm laser and a 600 °C thermal vaporizer, yielding respective measurements of the refractory and non-refractory particle components. Six samples were investigated, all of which were composed primarily of refractory material: fuel-rich and fuel-lean propane/air diffusion-flame combustion particles; graphite-spark-generated particles; a commercial fullerene-enriched soot; Regal Black, a commercial carbon black; and nascent aircraft-turbine combustion particles. All samples exhibited a spectrum of carbon-cluster ions Cxn+ in their refractory mass spectrum. Smaller clusters (x < 6) were found to dominate the Cxn+ distribution. For fullerene soot, fuel-rich-flame particles and spark-generated particles, significant Cxn+ clusters at x &amp;gg; 6 were present, with significant contributions from multiply charged ions (n > 1). In all six cases, the ions C1+ and C3+ contributed over 60% to the total C1 5 were present. When such signals were present, C1+ / C3+ was close to 1. When absent, C1+ / C3+ was < 0.8. This ratio may therefore serve as a proxy to distinguish between the two types of spectra in atmospheric SP-AMS measurements. Significant refractory oxygenated ions such as CO+ and CO2+ were also observed for all samples. We discuss these signals in detail for Regal Black, and describe their formation via decomposition of oxygenated moieties incorporated into the refractory carbon structure. These species may be of importance in atmospheric processes such as water uptake and heterogeneous chemistry. If atmospherically stable, these oxidized species may be useful for distinguishing between different combustion sources. If unstable, they may provide a means to estimate the atmospheric age of an rBC sample. Future studies should attempt to establish which of these scenarios is more realistic.

Mass spectrometry of refractory black carbon particles from six sources: carbon-cluster and oxygenated ions

We discuss the major mass spectral features of different types of refractory carbonaceous particles, ionized after laser vapourization with an Aerodyne High-Resolution Soot-Particle Aerosol Mass Spectrometer (SP-AMS). The SP-AMS was operated with a switchable 1064 nm laser and a 600 °C thermal vapourizer, yielding respective measurements of the refractory and non-refractory particle components. Six samples were investigated, all of which were composed primarily of refractory material: fuel-rich and fuel-lean propane/air diffusion-flame combustion particles; graphite-spark-generated particles; a commercial Fullerene-enriched Soot; Regal Black, a commercial carbon black; and nascent aircraft-turbine combustion particles. All samples exhibited a spectrum of carbon-cluster ions Cxn+ in their refractory mass spectrum. Smaller clusters (x<6) were found to dominate the Cxn+ distribution. For Fullerene Soot, fuel-rich-flame particles and spark-generated particles, significant Cxn+ clusters at x&amp;gg;6 were present, with significant contributions from multiply-charged ions (n>1). In all six cases, the ions C1+ and C3+ contributed over 60% to the total C15 were present. When such signals were present, C1+/C3+ was close to 1. When absent, C1+/C3+ was <0.8. This ratio may therefore serve as a proxy to distinguish between the two types of spectra in atmospheric SP-AMS measurements. Significant refractory oxygenated ions such as CO+ and CO2+ were also observed for all samples. We discuss these signals in detail for Regal Black, and describe their formation via decomposition of oxygenated moieties incorporated into the refractory carbon structure. These species may be of importance in atmospheric processes such as water uptake, aging and heterogeneous chemistry.

Chemical mass balance of refractory particles (<i>T</i>=300 °C) at the tropospheric research site Melpitz, Germany

In the fine particle mode (aerodynamic diameter <1 μm) refractory material has been associated with black carbon (BC) and low-volatile organics and, to a lesser extent, with sea salt and mineral dust. This work analyses refractory particles at the tropospheric research station Melpitz (Germany), combining experimental methods such as a mobility particle size spectrometer (3–800 nm), a thermodenuder operating at 300 °C, a multi-angle absorption photometer (MAAP), and an aerosol mass spectrometer (AMS). The data were collected during two atmospheric field experiments in May/June 2008 as well as February/March 2009. As a basic result, we detected average refractory particle volume fractions of 11±3% (2008) and 17±8% (2009). In both periods, BC was in close linear correlation with the refractory fraction, but not sufficient to quantitatively explain the refractory particle mass concentration. Based on the assumption that BC is not altered by the heating process, the refractory particle mass fraction could be explained by the sum of black carbon BC (47% in summer, 59% in winter) and a refractory organic contribution estimated as part of the Low-Volatility Oxygenated Organic Aerosol (LV-OOA) (53% in summer, 41% in winter); the latter was identified from AMS data by factor analysis. Our results suggest that organics were more volatile in summer (May–June 2008) than in winter (February/March 2009). Although carbonaceous compounds dominated the sub-μm refractory particle mass fraction most of the time, a cross-sensitivity to partially volatile aerosol particles of maritime origin could be seen. These marine particles could be distinguished, however, from the carbonaceous particles by a characteristic particle volume size distribution. The paper discusses the uncertainty of the volatility measurements and outlines the possible merits of volatility analysis as part of continuous atmospheric aerosol measurements.