Volumetric Receiver Research Articles

A new closed/open volumetric receiver concept for parabolic trough collectors (test results)

A new closed/open volumetric receiver concept for parabolic trough collectors (test results)

The duct selective volumetric receiver: potential for different selectivity strategies and stability issues

Recently much theoretical and experimental work has been conducted on volumetric receivers. However, not much attention has been paid to the possibilities of using different selectivity mechanisms to minimize radiation thermal losses, which are the main ones at high operating temperature. In this paper we present a duct volumetric receiver model and its results, which allow the evaluation of different selectivity strategies such as: conventional ε/ α, geometry, frontal absorption and diffuse/specular reflection. We propose a new concept of selective volumetric receivers based on a solar-specular/infrared-diffuse radiative behaviour and evaluate its potential for efficiency improvement. In recent work on volumetric receivers based on simplified models, it has been concluded that the duct volumetric receiver is inherently unstable when working with high solar flux. We didn’t find any unstable receiver behaviour even at very high solar fluxes, and conclude that a substantial potential for efficiency improvement exists if selectivity mechanisms are properly combined.

CO 2 reforming of methane in a solar driven volumetric receiver–reactor

CO 2 reforming of methane in a solar driven volumetric receiver–reactor has been investigated. This reactor was successfully tested on the Solar Tower Test Facility of the Weizmann Institute, Israel. The power absorbed by the reactor was between 200 and 300 kW. Typical operating temperatures ranged from 700°C to 860°C, with an absolute pressure of 3.5 bars, reaching methane conversions over 80%. Two solar-specific, catalytically-active absorber systems have been developed. These being based on ceramic foam structures, made from α-Al 2O 3 and SiC ceramics, respectively. γ-Al 2O 3 was used as support material and Rh was applied as active metal. The absorber systems were characterised by pre- and post-test analysis. Both inserts showed coke deposition after solar testing, this resulting from problems with the methanator part of the test loop. Some sections in the irradiated front side of the first absorber system, being located close to the gas inlet, were subjected to catalyst poisoning by Na deposits. The second absorber insert has not yet been fully characterised after solar testing. Despite local degradation effects, both absorber systems performed well during solar operation.

Modeling and Optimum Design of a Wire Mesh Solar Volumetric Air Receiver

This paper describes the development of a computer model to predict the performance of a discrete layer wire mesh solar volumetric air receiver. The model accounts for all important energy transfer processes within the absorber and allows for the use of two different types of wire mesh screens. Model predictions are compared to experimental results for validation purposes. An optimum design analysis is performed to determine optimum receiver characteristics and performance. Results show a predicted efficiency in the range of 89 percent to 87 percent when the outlet air temperature is between 700°C and 820°C, respectively.

EXPERIMENTAL CHARACTERIZATION OF A HIGH-TEMPERATURE, HIGH-FLUX, SOLAR VOLUMETRIC RECEIVER

This article focuses on experimental techniques for characterizing the performance of a wire mesh, solar, volumetric air receiver. The solar volumetric receiver is a type of solar energy collector that operates in a high-temperature and high-radiative-flux environment. Primary areas of experimental measurements were (1) solar radiation properties of the wire mesh, (2) convection heat transfer rates between the wire mesh and the surrounding air, (3) temperature and radiation flux levels during operation, and (4) overall efficiency of the receiver. Experimental work was performed with an average solar flux over the absorber aperture of approximately 660 kW / m2. Tests were conducted with the average outlet air temperature typically ranging from 310 to 790°C and resulting efficiencies from 77% to 67%, respectively.

Experimental and numerical evaluation of the performance and flow stability of different types of open volumetric absorbers under non-homogeneous irradiation

Numerical results found in the literature predict the capability of volumetric receivers to produce gas outlet temperatures of more than 1000°C. Other approaches found the tendency for an inherent flow instability for volumetric absorbers at high outlet temperatures. Both aspects, which are based on one-dimensional approaches, do not fit the experimental experience available even for semi-commercial volumetric receivers in the case of non-homogeneous flux distribution. Since this is the general case in solar power plants, a new analytical approach which takes into consideration a three-dimensional irradiance distribution and its influence on fluid flow and radial heat transfer is presented in this article. A comparison with experimental data for four totally different volumetric absorber types coincides well with the measured overall thermal efficiency as well as with the local temperature distribution. The model helps to explain how thermal efficiencies and temperature distributions are strongly influenced by non-homogeneous irradiation. Moreover, it demonstrates how flow instabilities are partly prevented by radial heat transfer. Finally, it is shown that a volumetric receiver consisting of sufficiently small absorber modules which are equipped with an additional orifice plate at the rear side will always run under stable flow conditions.

The Effect of Irradiation Directional Distribution on Absorption in Volumetric Solar Receivers

Volumetric solar absorbers are designed to enable the penetration of radiation deep into the absorber in order to improve the efficiency of the energy transfer from incoming radiation to the working fluid. The design of such absorbers is usually based on the irradiation energy flux distribution. We show that the directional features of the irradiation also affect the absorption characteristics of volumetric absorbers, present criteria for the characterization of directional attributes, and describe a method for their calculation. The significance of the directional data is demonstrated for two types of volumetric absorbers. Receiver design and modeling guidelines are presented.

96/06222 A new fabrication method for multicrystalline silicon layers on graphite substrates suited for low-cost thin film solar cells

A new absorber for a volumetric air receiver was designed, built, and tested on an existing volumetric receiver test bed (200 kWt) at the Plataforma Solar de Almeria test facility in Spain. Volumetric air receivers are currently being investigated for use in solar central receiver power plants because of their inherent simplicity. The volumetric air receiver is a unique type of solar central receiver that uses a porous absorber (heat exchanger), on which the solar energy is concentrated and absorbed within its volume. Air flows through the absorber, convectively transferring energy from the absorber to the medium. Volumetric receivers have applications in electricity production, industrial process heat, and chemical processing. We designed this new volumetric receiver absorber to use a porous ceramic material. This material was selected because of its structural strength, high-temperature capability, and the potential for using smaller pieces to build up an absorber. The ceramic absorber was tested at the Plataforma Solar de Almeria with a solar flux of up to 824 kW/m2, and it produced outlet air temperatures of 730°C. The porous ceramic material has exhibited reasonable thermal efficiencies and excellent structural integrity in the high-flux, high-temperature solar environment. In this paper we summarize the design of and test results of the porous ceramic absorber.

Calculation of the View Factors for Radiant Heat Exchange in a New Volumetric Receiver With Tapered Ducts

The need to increase efficiency of volumetric receivers for use in solar power plants by reducing reradiation losses and increasing the ``volumetric effect`` has promoted the idea of a receiver with tapered ducts. These seems to be very promising since higher efficiency and considerable saving of material can be achieved, as compared to conventional receivers perforated with ducts of constant cross-section. A finite element program is being developed to calculate stationary heat transfer in the tapered ducts by free and forced convection in the gas flow, conduction in walls and in the gas, and solar and thermal radiation. Gas and wall temperatures are considered to be varying only in the flow direction. In order to perform the highly nonlinear calculations of radiative exchange, the exact knowledge of the view factors is necessary. The aim of the present work is to evaluate analytically the view factors in tapered ducts.

Modelling and optimization of a two-slab selective volumetric solar receiver

The two-slab volumetric receiver is theoretically studied and the results are compared with experimental data. Two systems are described; for both of them, slab 2 is composed of SiC particles. Slab 1 is made of glass beads for the first system and silica honeycomb for the second system, the latter being the more efficient. Predicted and measured data show that the efficiency ranges between 70 and 75% for a gas outlet temperature of 1100 K. Predicted results are proved to be very sensitive to slab 1 depth, optical properties, and to the numerical solution of the radiative transfer equation. Band models and a discrete ordinate method are used in this paper. Finally the variation of the receiver efficiency is calculated as a function of slab 1 scattering albedo; a maximum efficiency of about 90% is reached at 1300 K for albedos in the solar spectrum and the infrared region equal to 0 and 1, respectively.

Investigation of a Direct Catalytic Absorption Reactor for Hazardous Waste Destruction

Direct Catalytic Absorption Reactors (DCARs) use a porous solid matrix to volumetrically absorb solar energy. This energy is used to promote heterogeneous chemistry on the catalytic surface of the absorber with fluid-phase reactant species. Experimental efforts at Sandia National Laboratories (SNL) are using a DCAR to destroy hazardous chemical waste. A numerical model, previously developed to analyze solar volumetric air-heating receivers and methane-reforming reactors, is extended in this work to include the destruction of a chlorinated hydrocarbon chemical waste, 1,1,1-trichloroethane (TCA). The model includes solar and infrared radiation, heterogeneous chemistry, conduction in the solid absorber, and convection between the fluid and solid absorber. The predicted thermal and chemical conditions for typical operating conditions at the SNL solar furnace suggest that TCA can be destroyed in a DCAR. The temperature predictions agree well with currently available thermocouple data for heating carbon dioxide gas in the DCAR. Feasibility and scoping calculations show trichloroethane destruction efficiencies up to 99.9997 percent at a trichloroethane flow rate of 1.7 kg/hr may be obtainable with typical SNL solar furnace fluxes. Greater destruction efficiencies and greater destruction rates should be possible with higher solar fluxes. Improvements in reactor performance can be achieved by tailoring the absorber to alter the radial mass flux distribution in the absorber with the radial solar flux distribution.

Design of solar receivers for chemical energy storage and pyroheliometallurgy applications

A preliminary study of two different kinds of solar receivers (a rotating cavity receiver and a volumetric receiver) suitable to operate in the 1 kW solar facility at the University of Rome is presented. Possible applications of solar energy in the aluminum extraction from leucite and chemical storage by the CuO/Cu 2O cycle are presented and discussed.

Analysis of Catalytically Enhanced Solar Absorption Chemical Reactors: Part I—Basic Concepts and Numerical Model Description

A detailed numerical model is presented for high-temperature, catalytically enhanced, solar absorption chemical reactors. In these reactors, concentrated solar energy is volumetrically absorbed throughout a porous absorber matrix impregnated with a catalyst. The catalyst promotes heterogeneous reactions with fluid-phase reactant species flowing through the absorber. This paper presents a description of a numerical model and the basic concepts of reactor operation. The numerical model of the absorber includes solar and infrared radiation, heterogeneous chemical reactions, conduction in the solid phase, and convection between the fluid and solid phases. The model is nonlinear primarily due to both the radiative transfer and the heterogeneous chemistry occurring in the absorber. The nonlinear two-point boundary value problem is solved using superposition with orthonormalization and an adaptive solution point scheme. This technique preserves accuracy throughout the domain. The model can be modified for other chemical reactions and can be simplified to model volumetric air-heating receivers.

Testing of a porous ceramic absorber for a volumetric air receiver

A new absorber for a volumetric air receiver was designed, built, and tested on an existing volumetric receiver test bed (200 kW t) at the Plataforma Solar de Almeria test facility in Spain. Volumetric air receivers are currently being investigated for use in solar central receiver power plants because of their inherent simplicity. The volumetric air receiver is a unique type of solar central receiver that uses a porous absorber (heat exchanger), on which the solar energy is concentrated and absorbed within its volume. Air flows through the absorber, convectively transferring energy from the absorber to the medium. Volumetric receivers have applications in electricity production, industrial process heat, and chemical processing. We designed this new volumetric receiver absorber to use a porous ceramic material. This material was selected because of its structural strength, high-temperature capability, and the potential for using smaller pieces to build up an absorber. The ceramic absorber was tested at the Plataforma Solar de Almeria with a solar flux of up to 824 kW/m 2, and it produced outlet air temperatures of 730°C. The porous ceramic material has exhibited reasonable thermal efficiencies and excellent structural integrity in the high-flux, high-temperature solar environment. In this paper we summarize the design of and test results of the porous ceramic absorber.

The ceramic foil volumetric receiver

A test of a ceramic foil volumetric receiver, made from siliconized silicon carbide (SiSiC), in the volumetric receiver test bed on top of the SSPS-CRS tower of the Plataforma Solar de Almeria showed very promising results with an efficiency of about 60% at maximum air temperatures of nearly 800 ° C. Design, fabrication method as well as test results are explained.

Development and testing of a volumetric gas receiver for high-temperature applications

Feasibility tests with a closed-loop volumetric gas receiver developed by Atlantis Energy Ltd, were conducted on the solar tower of the Sandia National Laboratories, Albuquerque, New Mexico (USA), in April/May, 1990. The tests demonstrated that it is possible to build receivers which are based on a novel ceramic grid absorber concept for working temperatures in excess of 850°C. Theoretical and experimental data allow further to conclude that reasonable efficiencies (84–92%) can be achieved also at radiation levels above 900 kW/m 2 for both open-loop and closed-loop receiver configurations. Although the development of this technology was primarily aimed at providing receivers for solar driven chemistry, the near-term applications may be in the area of CRS power generation (or CRS cogeneration of power and heat - e.g. for seawater desalination). Atlantis started working on high solar radiation flux transfer problems back in 1978. A first volumetric receiver concept based on cascaded absorption of solar radiation with partially absorbing quartz glass elements was tested on a laboratory scale. It demonstrated also the feasibility of quartz glass as a transparent construction material - important e.g. for thermophotochemical processes. In 1988, a new volumetric ceramic grid absorber was conceived. Laboratory tests were conducted using a dish for high solar concentrations. Mean gas temperatures of 840°C were achieved at a solar flux of 1500 kW/m 2. In order to test the feasibility of the concept, a larger scale 500 kW test receiver was subsequently built for testing with a heliostat field. In order to gain experience for chemical applications, a closed-cycle receiver was chosen for the tests in Albuquerque. Crucial for the success of the testing at Sandia was the necessity to develop a radiation shield capable to protect receiver structural elements from the high-intensity incident solar radiation. The project was supported by the Swiss Energy Research Foundation, the Swiss Federal Office for Education and Science, and the U.S. Department of Energy for the tests at Sandia National Laboratories.

30 MW e PHOEBUS feasibility study: results of system engineering

Within the feasibility study Phase 1B of the 30 MW e PHOEBUS solar central receiver power plant project using an air-cooled volumetric receiver, the basic data and optimal overall system design characteristics were determined by system engineering. This paper summarizes briefly essential results and boundary conditions.

Advanced high-temperature two-slab selective volumetric receiver

Experimental results about two-slab high-temperature solar receivers for gas heating are presented. Data related to two systems are reported. For the first one, the irradiated front slab is composed of glass-beads; for the second this slab is made of silica honeycomb. Outlet air temperatures of about 500°C have been reached with the first while temperatures larger than 800°C were obtained with the second. The receiver efficiency is 0.89 and 0.78 for gas outlet temperature of 700°C and 800°C respectively.

Heat exchange in a multi-cavity volumetric solar receiver

The concept of a multi-cavity volumetric solar receiver is very attractive for the profitability of certain of its characteristics such as high efficiency and economy. The absorber is based on a pack of small ceramic cavities which intercept and absorb the inherent high solar flux reflected from an array of mirrors. Atmospheric air acts as a coolant medium when it is drawn through the pack. A model for an overall heat transfer performance of the receiver is given and numerically solved.

Heat Transfer Modeling of the IEA/SSPS Volumetric Receiver

During the summer and fall of 1987 in Almeria, Spain, a wire-pack receiver was tested by the International Energy Agency/Small Solar Power Systems (IEA/SSPS). The basic operation of the receiver is that: air is drawn through several layers of stainless steel wire screen; concentrated solar flux is directed on the face of the screen pack; the oxidized wires absorb the solar energy; and heat is transferred to the air flowing through the screen. Although the experiment goal was strictly proof-of-concept and was not receiver characterization, modeling efforts were initiated to help understand the experimental results. The steady-state performance of the receiver is modeled using the fact that the net solar and infrared radiative energy absorbed by each screen layer must be transferred to the air by convection. Basic performance trends and typical calculations of receiver efficiency are given. Model predictions and experimentally measured temperatures and flow rates are compared. Model predictions of receiver power and efficiency are generally higher than the test results (operational modifications of the receiver absorber as tested are believed to have produced nonideal conditions), but trends are consistent with experimental data.