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Journal ArticleDOI

Performance characteristics of the Spiky Central Receiver Air Pre-heater (SCRAP)

01 May 2020-Solar Energy (Pergamon)-Vol. 201, pp 773-786
TL;DR: In this paper, a spiky central receiver air pre-heater (SCRAP) technology is proposed to overcome barriers experienced to date, which can transfer heat from concentrated solar irradiation to a pressurized air stream in a gas turbine.
About: This article is published in Solar Energy.The article was published on 2020-05-01 and is currently open access. It has received 14 citations till now. The article focuses on the topics: Thermal efficiency & Compressed air.

Summary (5 min read)

List of Figures

  • 1 Heat transfer coefficient htip for different nozzle diameter dnozzle . .
  • The deviation of the measured pressure drop slope error, ∆p′, over the comparison between fD,sim and fD,exp, computed from experimental data.
  • Photograph of the 114 mm section after EDM machining and the same section from the other side with inner tube inserted . . . . . .

Subscripts

  • CSP plants are currently considered to provide LCOEs at about 0.12 USD/kWh, whereas new built coal in South Africa is estimated at about 0.07 USD/kWh (DoE, 2016) and solar PV has recently reduced to 0.04 USD/kWh (Bischof-Niemz and Fourie, 2016).
  • As with the PTC, also with CR, the HTF limitations dictated the operating temperature of the receiver outlet temperature.
  • This trend is explained by the higher plant performance and thereby reduced LCOE is expected from these plants.

2 CHAPTER 1. INTRODUCTION

  • This current generation of CSP CR plants operates with molten salt as HTF, as well as sensible thermal storage medium (using a two tank system).
  • Furthermore, cost reduction can be achieved by an increased large scale roll out of CSP, as well as further innovation into increasing plant performance.
  • The SUNSPOT cycle is a manifestation of a possible next generation CSP CR plant utilizing pressurized air as HTF and an asynchronous combined cycle (CC) for efficient and dispatchable power generation.
  • The turbine outlet air, as in conventional CC plants is used to drive a steam generator for the bottoming Rankine cycle.
  • Not shown are dish projects due to marginal capacities as well as solar park projects.

1.2. REVIEW OF PRESSURIZED AIR RECEIVER TECHNOLOGY 3

  • A central receiver technology, heating a pressurized air stream inbetween the compressor and the turbine stage, should be able to heat the air to outlet temperatures of above 1000 ◦C, while at the same time, operating at a low pressure drop to minimize the performance drop in the Brayton cycle.
  • The proposed SCRAP receiver is an attempt to overcome weaknesses of the current technologies.
  • 2 Review of pressurized air receiver technology A common goal for developing a central receiver is maximized central receiver system solar-thermal efficiency.
  • This review describes initially the relevant optical and thermal losses influencing that efficiency.
  • Numerous criteria influence the design of a central receiver system.

1.2.1 Receiver efficiency

  • The total losses affecting receiver system efficiency are the optical losses, thermal losses and pumping losses (Stine and Geyer, 2001).
  • The optical loss of solar re-reflection from the receiver is typically represented as part of the thermal efficiency, while the remaining optical losses only appear in a total efficiency analysis.
  • One attempt is the application of a selective coating to the absorber surface, improving the absorptive capabilities of the absorber directly, while providing low emittance values at the temperature range of the material.
  • Typically, spillage losses are not accounted for in the receiver efficiency, ηthermal, but are represented in a total systems analysis.
  • Heliostats at different distances to the tower cast images of different sizes and shapes onto the absorber.

1.2. REVIEW OF PRESSURIZED AIR RECEIVER TECHNOLOGY 5

  • A homogeneous flux distribution over the absorber surface.
  • While spillage losses are usually small (Stine and Geyer, 2001) and apply to a certain degree to any receiver design, CPC losses can be significant (Ávila-Marín, 2011; Hischier et al., 2012).
  • These are losses of minor nature and are often neglected (Solgate Report, 2005).
  • Radiative heat losses occur from hot receiver surfaces towards the environment.
  • Heat transfer fluid pumping losses can be of relevance in terms of parasitic losses or, as in the case of a Brayton cycle, directly reducing the pressure ratio on the turbine side.

1.2.2 Overview of generic receiver concepts

  • The central receiver concepts of interest for a pressurized air system are reviewed.
  • The overarching concepts of external and cavity receivers are first discussed, before elaborating on proposed concepts.

External receiver

  • The conventional external receiver is the simplest and cheapest receiver design, where the absorber system, usually numerous vertical tubes, is externally mounted to the receiver tower.
  • For a surrounding heliostat field multiple similar panels can be mounted to cover larger areas, e.g. reproducing a rectangular or cylindrical shape system).
  • The external receiver concept shows high exposure of the absorber tubes to ambient.
  • This results in high heat losses by means of convection and radiation.
  • Presently, external receivers are widely used for molten salt and DSG systems (both operating below 600 ◦C).

1.2. REVIEW OF PRESSURIZED AIR RECEIVER TECHNOLOGY 7

  • The external receiver, as shown in Figure 1.3, can utilize a surrounding heliostat field.
  • An advantage that a surrounding heliostat field shows over a polar3 field is a stable solar field optical efficiency over the course of the day, while a polar heliostat field has a higher noon performance (Vant-Hull, 2012).
  • Hence, employing a surrounding receiver system can allow for an increased optical efficiency of the heliostat field.
  • For large scale plants, the surrounding field becomes inevitable, as the distance of the farthest heliostats grows too large for efficient operation.
  • A conventional external receiver is not suited for low heat transfer coefficient fluids, such as air, as the required large exposed absorber surfaces would lead to significant heat losses.

Cavity receiver

  • A cavity receiver is a receiver system where the absorber system is encased inside a space with an opening towards the heliostat field.
  • Having the absorber system encased, can improve the thermal efficiency by means of reducing the convective heat loss (which can further be enhanced by a window in the opening), as well as by trapping reflected light and radiated heat.
  • At a more sophisticated level, high temperature systems such as pressurized air receivers have been conceived as cavity receivers (see chapter 1.2.4).

1.2.3 Overview of generic absorber concepts

  • It is employed to effectively transfer the energy of the concentrated sunlight into the heat transfer fluid.
  • The two absorber types commonly employed are then introduced.
  • These are the tubular and the volumetric absorber principles.

Tubular absorber

  • Current central receiver technologies for molten salt and direct steam generating systems use a number of tubes to form the absorber surface.
  • The heat transfer fluid is pumped through the tubes and is heated up in the process.
  • In order to minimize absorber surface area and temperature, fluids with high thermal conductivity are preferred, as they maintain an efficient system.
  • As shown in chapter 1.2.4, innovations in pipe manufacturing, heat transfer enhancements and intelligent receiver design can make tubular receivers a viable technology for pressurized air systems.

Volumetric absorber

  • Increasing attention has recently been given to volumetric receiver/absorber systems.
  • A porous surface, allowing the radiation to penetrate into the depth of the absorber, reduces reflection losses.
  • The heat transfer fluid, which is forced through the porous absorber from the irradiated side, provides the highest cooling effect at the exposed surface.
  • The volumetric effect can be described by the peak surface temperature occurring deep in the structure.
  • It furthermore does not expose the highest temperature parts of the system, reducing the exposed surface temperature and with that heat losses.

1.2.4 Review of existing pressurized air receiver concepts

  • The research area of air receiver systems for elevated temperatures, capable of supplying a Brayton cycle, is relatively young.
  • To date, mainly the German Aerospace Center (DLR) and the Weizmann Institute of Science (WIS) have driven development, leading to demonstration scale systems with published findings.
  • Both research institutions have developed cavity receiver systems with volumetric absorber technology, capable of reaching mean outlet temperatures of above 1000 ◦C.
  • This review covers the progress to date and highlights important problems encountered.
  • The gap between the lower air temperature after a solar receiver and the turbine requirement is usually overcome by introducing a fuel combustor.

Attempts by DLR

  • The DLR began tests on volumetric pressurized air receiver systems in 1989 with the PLVCR5 receiver, which employed a dome-shaped quartz glass window (Pritzkow, 1991).
  • The receiver concept has since been continuously improved, and the current version is known as the REFOS receiver, shown in Figure 1.6.
  • The volumetric absorber material used in the receiver can be either a silicon-carbide (Si-C) ceramic mesh for high temperatures or a metal wire mesh for pre-heating purposes.
  • In the SOLGATE project, a hexagonal compound parabolic concentrator.

1.2. REVIEW OF PRESSURIZED AIR RECEIVER TECHNOLOGY 11

  • (CPC) and two pre-heating sections (with identical CPCs) were included into the setup.
  • The receiver cluster consisted of a multi-tube coil pre-heater , a medium temperature REFOS pre-heater and a high temperature REFOS receiver.
  • The aforementioned tubular pre-heating section was not satisfactory.
  • More importantly, the cross-sectional temperature gradient between the radiated and unradiated pipe surface was calculated at up to 220 K, resulting in high thermal stresses, thereby reducing the receiver lifetime (Heller, 2010).
  • The new SOLUGAS receiver was meant to replace the tubular cavity receiver pre-heater and the REFOS receiver pre-heating stage of the SOLGATE project.

12 CHAPTER 1. INTRODUCTION

  • The target of the SOLTREC project was to achieve a mean air temperature of 1000 ◦C.
  • The SOLUGAS receiver was successfully operated at air outlet temperatures of 800 ◦C (Korzynietz et al., 2016).
  • The solar-thermal efficiency of the SOLUGAS receiver reached just below 80 % during testing which uses the flux on aperture as reference.
  • During the same test series the receiver system pressure drop was measured at around 200 mbar (Korzynietz et al., 2016).
  • Buck et al. (2002) stated an efficiency goal for the REFOS receiver (without a pre-heater system) of 80 % at 800 ◦C, including the optical losses of the CPC but did not report test results.

1.2. REVIEW OF PRESSURIZED AIR RECEIVER TECHNOLOGY 13

  • The quartz glass of the dome-shaped window needs to withstand high temperatures and pressures in order to separate the hot pressurized air flow (up to 20 bar) from ambient.
  • With the mentioned 500 h of test time, representing about 60 days of normal operation, deterioration was already visible within a fraction of a plant’s lifetime (Hofmann et al., 2009).
  • Concerns are that besides deterioration of the optical quality, cracking of the window occurs under pressure and high solar flux density (Grange et al., 2011).
  • For unpressurized systems higher diameters are possible.

The DIAPR receiver

  • In parallel to the DLR, the WIS (Weizmann Institute of Science) developed a pressurized air volumetric cavity receiver, the Directly Irradiated Annular Pressurized Receiver .
  • The DIAPR is based on the porcupine model, where concentrated solar radiation impinges on high temperature resistant alumina-silica pins (Karni et al., 1998).
  • The pressurized air stream is guided past the pins and is heated up in the process.
  • In an attempt to increase the system efficiency, a multistage DIAPR was developed that employed, similarly to the DLR approach, a coiled tubular cavity pre-heater (Kribus et al., 1999).

14 CHAPTER 1. INTRODUCTION

  • Efficiency information on the cluster or the pre-heater is not available.
  • These values were provided for a flux density of 5 MW/m2 on the receiver aperture.
  • Even though the DIAPR also utilizes a pressurized fused quartz glass, no concerns with regards to its durability were mentioned, and even up-scaling of the receiver was discussed.
  • While further work has been proposed, no new information on development progress with regards to the DIAPR system has been published in recent years.
  • The DIAPR technology was recently implemented in the 100 kWe AORA Solar micro-turbine central receiver system (Ávila-Marín, 2011).the authors.the authors.

1.2. REVIEW OF PRESSURIZED AIR RECEIVER TECHNOLOGY 15

  • With increasing attention to the development of pressurized air receivers, new concepts were recently proposed.
  • Further results, limitations and capabilities of the system are not provided.
  • The Australian Commonwealth Scientific and Industrial Research Organisation is developing a solar Brayton cycle system in cooperation with the Japanese Mitsubishi Heavy Industries (MHI).
  • In the PEGASE project, the development of a pressurized air receiver, based on compact heat exchanger technology, is pursued by the French CNRS/PROMES.
  • The experiments reported on in Bellard et al. (2012) highlight problems with unexpected high pressure drop, but no information on thermal efficiency of the system has been provided.

16 CHAPTER 1. INTRODUCTION

  • Hischier et al. (2012) proposed a cavity receiver design with a similar absorber system approach to the PEGASE receiver.
  • The absorbed radiation in a cylindrical cavity receiver is conducted into an annular reticulate porous ceramic (RPC) foam material (SiC), through which the pressurized air is sucked and in the process heated up .
  • The ceramic foam is shielded from the cavity by the absorber surface.
  • Small scale laboratory testing has been conducted with a 3 kWt receiver prototype.

1.2.5 Conclusion on review of current systems

  • The field of pressurized air receivers is relatively young, with only two research institutions driving development to prototype and demonstration scale.
  • Generally, limited information is available on the proposed systems.
  • The tubular pre-heating sections are equally poorly discussed in literature.
  • It can furthermore be concluded that the volumetric receivers and tubular pre-heaters proposed by DLR and WIS (and in fact also the new approaches introduced in Section 1.2.4) are cavity receivers, mostly equipped with secondary concentrators.

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01 Jan 2016

1,633 citations

Journal ArticleDOI
01 Jan 1920-Nature
TL;DR: In this article, it is stated that it is hopeless to expect to be able to effect anything of this nature with the heat engine, for with this we should scarcely reach the 2 per cent, efficiency nearly attained by vegetation.
Abstract: MR. A. A. CAMPBELL SWINTON, in his letter on the above subject in NATURE of December 18, states that “it is hopeless to expect to be able to effect anything of this nature with the heat-engine, for with this we should scarcely reach the 2 per cent, efficiency nearly attained by vegetation.”

114 citations

Proceedings ArticleDOI
01 Jan 2010
TL;DR: In this paper, a high-temperature pressurized air-based receiver for power generation via solar-driven gas turbines is experimentally and theoretically examined, which consists of an annular reticulate porous ceramic (RPC) foam concentric with an inner cylindrical cavity-receiver exposed to concentrated solar radiation.
Abstract: A high-temperature pressurized air-based receiver for power generation via solar-driven gas turbines is experimentally and theoretically examined. It consists of an annular reticulate porous ceramic (RPC) foam concentric with an inner cylindrical cavity-receiver exposed to concentrated solar radiation. Absorbed heat is transferred by combined conduction, radiation, and convection to the pressurized air flowing across the RPC. The governing steady-state mass, momentum and energy conservation equations are formulated and solved numerically by coupled Finite Volume and Monte Carlo techniques. Validation is accomplished with experimental results using a 1 kW solar receiver prototype subjected to average solar radiative fluxes in the range 1870–4360 kW m−2 . Experimentation was carried out with air and helium as working fluids, heated from ambient temperature up to 1335 K at an absolute operating pressure of 5 bars.Copyright © 2010 by ASME

13 citations

Journal ArticleDOI
TL;DR: In this article, a simultaneous outlook on the heat transfer and total pressure loss (performance) characteristics of several jets impinging on a concave hemispherical surface are investigated experimentally and using an axisymmetric Reynolds averaged Navier Stokes (RANS) Computational Fluid Dynamics (CFD) model.
Abstract: Jet impingement heat transfer finds applications where a large heat flux is required between a fluid and a surface. Impinging jets can be implemented in Concentrating Solar Power (CSP) thermal receivers and bayonet tube heat exchangers. A simultaneous outlook on the heat transfer and total pressure loss (performance) characteristics of several jets impinging on a concave hemispherical surface are investigated experimentally and using an axisymmetric Reynolds averaged Navier Stokes (RANS) Computational Fluid Dynamics (CFD) model. The four equation Transition SST RANS turbulence CFD model demonstrates to be most suitable for this domain with a mean absolute deviation from the experimental results of < 7% for the heat transfer coefficient and < 8% for the total pressure loss. Empirical correlations for the Nusselt number as a function of the nozzle outlet Reynolds number and Prandtl number are fitted. Relatively good agreement is found between the Nusselt correlation and existing literature. An empirical correlation is also presented for the total pressure loss factor for the jet impingement domain in general because it is found that the dominating total pressure loss occurs because of rapid expansion, which occurs in any impinging free jet. The developed empirical correlations and CFD model can be used to estimate the heat transfer and pressure loss characteristics of a bayonet tube heat exchanger, a solar thermal receiver employing impinging jets as well as other jet impingement domains.

6 citations

Journal ArticleDOI
TL;DR: In this paper , the direct normal irradiance was predicted at ground level using a total sky camera, TSI-880 model, and these DNI values were used as the inputs for a heliostat model (Fiat-Lux) to trace the sunlight's path according to the mirror features.
Abstract: As part of the research for techniques to control the final energy reaching the receivers of central solar power plants, this work combines two contrasting methods in a novel way as a first step towards integrating such systems in solar plants. To determine the effective power reaching the receiver, the direct normal irradiance was predicted at ground level using a total sky camera, TSI-880 model. Subsequently, these DNI values were used as the inputs for a heliostat model (Fiat-Lux) to trace the sunlight’s path according to the mirror features. The predicted valuex of flux, obtained from these simulations, differ of less than 20% from the real values. This represents a significant advance in integrating different technologies to quantify the losses produced in the path from the heliostats to the central receiver, which are normally caused by the presence of atmospheric attenuation factors.

3 citations

References
More filters
Book
01 Jan 1980
TL;DR: In this article, the authors focus on heat and mass transfer, fluid flow, chemical reaction, and other related processes that occur in engineering equipment, the natural environment, and living organisms.
Abstract: This book focuses on heat and mass transfer, fluid flow, chemical reaction, and other related processes that occur in engineering equipment, the natural environment, and living organisms. Using simple algebra and elementary calculus, the author develops numerical methods for predicting these processes mainly based on physical considerations. Through this approach, readers will develop a deeper understanding of the underlying physical aspects of heat transfer and fluid flow as well as improve their ability to analyze and interpret computed results.

21,858 citations

Journal Article

2,683 citations


"Performance characteristics of the ..." refers background in this paper

  • ...Nusselt numbers for fully developed laminar flow inside rectangular ducts for a variety of boundary conditions are provided by (Shah and London, 1978)....

    [...]

01 Jan 2016

1,633 citations


Additional excerpts

  • ...Another way frequently employed is the trapping of radiation by the application of coatings that form microscopic voids, thus increasing the absorptivity (Duffie and Beckman, 2006)....

    [...]

BookDOI
24 Nov 1999
TL;DR: In this article, the authors present the principles of control volume early for use throughout the book and emphasize the constitutive equation that relates deformation to stress, which can be easily generalized to non-Newtonian fluids mechanics.
Abstract: * Presents the principles of control volume early for use throughout the book * Emphasizes the constitutive equation that relates deformation to stress. * Examines in detail the flow of Newtonian fluids-which can often be easily generalized to non-Newtonian fluids mechanics. * Includes many applications on topics like liquid droplets, gas bubbles, microelectronics processing, injection molding, painting and coatings.

1,217 citations


Additional excerpts

  • ...12) which is valid for 3000 ≤ Re ≤ 10(5) (White, 1991)....

    [...]

Book
01 Jan 1997
TL;DR: In this article, the authors present an approach for reducing the number of cycles of alternating and static stress in a two-dimensional problem with respect to a given r D or r H 76.
Abstract: Index to the Stress Concentration Factors. Preface for the Third Edition. Preface for the Second Edition. 1. Definitions and Design Relations. 1.1 Notation. 1.2 Stress Concentration. 1.3 Stress Concentration as a Two-Dimensional Problem. 1.4 Stress Concentration as a Three-Dimensional Problem. 1.5 Plane and Axisymmetric Problems. 1.6 Local and Nonlocal Stress Concentration. 1.7 Multiple Stress Concentration. 1.8 Theories of Strength and Failure. 1.9 Notch Sensitivity. 1.10 Design Relations For Static Stress. 1.11 Design Relations for Alternating Stress. 1.12 Design Relations for Combined Alternating and Static Stresses. 1.13 Limited Number of Cycles of Alternating Stress. 1.14 Stress Concentration Factors and Stress Intensity Factors. References 2. Notches and Grooves. 2.1 Notation. 2.2 Stress Concentration Factors. 2.3 Notches in Tension. 2.4 Depressions in Tension. 2.5 Grooves in Tension. 2.6 Bending of Thin Beams with Notches. 2.7 Bending of Plates with Notches. 2.8 Bending of Solids with Grooves. 2.9 Direct Shear and Torsion. 2.10 Test Specimen Design for Maximum Kt for a Given r D or r H 76. References. Charts. 3. Shoulder Fillets. 3.1 Notation. 3.2 Stress Concentration Factors. 3.3 Tension (Axial Loading). 3.4 Bending. 3.5 Torsion. 3.6 Methods of Reducing Stress Concentration at a Shoulder. References. Charts. 4. Holes. 4.1 Notation. 4.2 Stress Concentration Factors. 4.3 Circular Holes with In-Plane Stresses. 4.4 Elliptical Holes in Tension. 4.5 Various Configurations with In-Plane Stresses. 4.6 Holes in Thick Elements. 4.7 Orthotropic Thin Members. 4.8 Bending. 4.9 Shear and Torsion. 5. Miscellaneous Design Elements. 5.1 Notation. 5.2 Shaft with Keyseat. 5.3 Splined Shaft in Torsion. 5.4 Gear Teeth. 5.5 Press- or Shrink-Fitted Members. 5.6 Bolt and Nut. 5.7 Bolt Head,Turbine-Blade, orCompressor-Blade Fastening (T-Head). 5.8 Lug Joint. 5.8.1 Lugs with h d 0 . 5. 5.8.2 Lugs with h d 0 . 5. 5.9 Curved Bar. 5.10 Helical Spring. 5.10.1 Round or Square Wire Compression or Tension Spring. 5.10.2 Rectangular Wire Compression or Tension Spring. 5.10.3 Helical Torsion Spring. 5.11 Crankshaft. 5.12 Crane Hook. 5.13 U-Shaped Member. 5.14 Angle and Box Sections. 5.15 Cylindrical Pressure Vessel with Torispherical Ends. 5.16 Tubular Joints. References. Charts. 6. Stress Concentration Analysis and Design. 6.1 Computational Methods. 6.2 Finite Element Analysis. 6.3 Design Sensitivity Analysis. 6.4 Design Modification. Index.

1,020 citations

Frequently Asked Questions (1)
Q1. What have the authors contributed in "Performance characteristics of the spiky central receiver air pre-heater (scrap)" ?

The novel spiky central receiver air pre-heater ( SCRAP ) technology is proposed to provide such a receiver and overcome barriers experienced by developments to date. The SCRAP receiver is a novel metallic receiver technology aimed at preheating an air stream to about 800 ◦C, either prior to a combustion chamber or alternatively a cascaded secondary non-metallic receiver system, capable of achieving elevated temperatures.