Coupled Concentrating Optics, Heat Transfer, and Thermochemical Modeling of a 100-kWth High-Temperature Solar Reactor for the Thermal Dissociation of ZnO

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
W. Villasmil ◽  
T. Cooper ◽  
E. Koepf ◽  
A. Meier ◽  
A. Steinfeld
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Energy Conversion ◽  
Solar Flux ◽  
Solar Furnace ◽  
Solar Irradiation ◽  
Radiation Boundary Condition ◽  
Solar Reactor ◽  
Concentrated Solar Energy ◽  
Conversion Efficiencies

This work reports a numerical investigation of the transient operation of a 100-kWth solar reactor for performing the high-temperature step of the Zn/ZnO thermochemical cycle. This two-step redox cycle comprises (1) the endothermal dissociation of ZnO to Zn and O2 above 2000 K using concentrated solar energy, and (2) the subsequent oxidation of Zn with H2O/CO2 to produce H2/CO. The performance of the 100-kWth solar reactor is investigated using a dynamic numerical model consisting of two coupled submodels. The first is a Monte Carlo (MC) ray-tracing model applied to compute the spatial distribution maps of incident solar flux absorbed on the reactor surfaces when subjected to concentrated solar irradiation delivered by the PROMES-CNRS MegaWatt Solar Furnace (MWSF). The second is a heat transfer and thermochemical model that uses the computed maps of absorbed solar flux as radiation boundary condition to simulate the coupled processes of chemical reaction and heat transfer by radiation, convection, and conduction. Experimental validation of the solar reactor model is accomplished by comparing solar radiative power input, temperatures, and ZnO dissociation rates with measured data acquired with the 100-kWth solar reactor at the MWSF. Experimentally obtained solar-to-chemical energy conversion efficiencies are reported and the various energy flows are quantified. The model shows the prominent influence of reaction kinetics on the attainable energy conversion efficiencies, revealing the potential of achieving ηsolar-to-chemical = 16% provided the mass transport limitations on the ZnO reaction interface were overcome.

The Thermodynamic Evaluation and Optimization of Fuel Cell Systems

2006 ◽  
Vol 3 (2) ◽  
pp. 155-164 ◽  
Author(s):  
N. Woudstra ◽  
T. P. van der Stelt ◽  
K. Hemmes
Keyword(s):  
Heat Transfer ◽  
Fuel Cells ◽  
High Temperature ◽  
Fuel Cell ◽  
Energy Conversion ◽  
System Optimization ◽  
Fuel Conversion ◽  
Cell Systems ◽  
Electrochemical Conversion ◽  
Conversion Efficiencies

Energy conversion today is subject to high thermodynamic losses. About 50% to 90% of the exergy of primary fuels is lost during conversion into power or heat. The fast increasing world energy demand makes a further increase of conversion efficiencies inevitable. The substantial thermodynamic losses (exergy losses of 20% to 30%) of thermal fuel conversion will limit future improvements of power plant efficiencies. Electrochemical conversion of fuel enables fuel conversion with minimum losses. Various fuel cell systems have been investigated at the Delft University of Technology during the past 20 years. It appeared that exergy analyses can be very helpful in understanding the extent and causes of thermodynamic losses in fuel cell systems. More than 50% of the losses in high temperature fuel cell (molten carbonate fuel cell and solid oxide fuel cell) systems can be caused by heat transfer. Therefore system optimization must focus on reducing the need for heat transfer as well as improving the conditions for the unavoidable heat transfer. Various options for reducing the need for heat transfer are discussed in this paper. High temperature fuel cells, eventually integrated into gas turbine processes, can replace the combustion process in future power plants. High temperature fuel cells will be necessary to obtain conversion efficiencies up to 80% in the case of large scale electricity production in the future. The introduction of fuel cells is considered to be a first step in the integration of electrochemical conversion in future energy conversion systems.

Modeling of a Methane Fuelled Direct Carbon Fuel Cell System

2005 ◽  
Author(s):  
N. Woudstra ◽  
T. P. van der Stelt ◽  
K. Hemmes
Keyword(s):  
Heat Transfer ◽  
Fuel Cells ◽  
High Temperature ◽  
Fuel Cell ◽  
Energy Conversion ◽  
Fuel Conversion ◽  
Cell Systems ◽  
Electrochemical Conversion ◽  
Direct Carbon Fuel Cell ◽  
Conversion Efficiencies

Energy conversion today is subject to high thermodynamic losses. About 50 to 90 % of the exergy of primary fuels is lost during conversion into power or heat. The fast increasing world energy demand makes a further increase of conversion efficiencies inevitable. The substantial thermodynamic losses (exergy losses of 20 to 30 %) of thermal fuel conversion will limit future improvements of power plant efficiencies. Electrochemical conversion of fuel enables fuel conversion with minimum losses. Various fuel cell systems have been investigated at the Delft University of Technology during the past twenty years. It appeared that exergy analyses can be very helpful in understanding the extent and causes of thermodynamic losses in fuel cell systems. More than 50 % of the losses in high temperature fuel cell (MCFC and SOFC) systems can be caused by heat transfer. Therefore system optimisation must focus on reducing the need for heat transfer as well as improving the conditions for the unavoidable heat transfer. Various options for reducing the need for heat transfer are discussed in this paper. High temperature fuel cells, eventually integrated into gas turbine processes, can replace the combustion process in future power plants. High temperature fuel cells will be necessary to obtain conversion efficiencies up to 80 % in case of large scale electricity production in the future. The introduction of fuel cells is considered to be a first step in the integration of electrochemical conversion in future energy conversion systems.

scholarly journals Heat Transfer Simulation in a High Temperature Solar Reactor

2015 ◽  
Vol 69 ◽  
pp. 1810-1818 ◽  
Author(s):  
P. Parthasarathy ◽  
P. Le Clercq
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Solar Reactor ◽  
Heat Transfer Simulation

scholarly journals Experimental Evaluation of Indirect Heating Tubular Reactors for Solar Methane Pyrolysis

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Sylvain Rodat ◽  
Stéphane Abanades ◽  
Gilles Flamant
Keyword(s):  
Carbon Black ◽  
Plasma Heating ◽  
Solar Furnace ◽  
Solar Irradiation ◽  
Hydrogen Yield ◽  
Heating Source ◽  
Solar Reactor ◽  
Production Of Hydrogen ◽  
Carbon Black Production ◽  
Indirect Heating

Solar thermal pyrolysis of natural gas is studied for the co-production of hydrogen, a promising energy carrier, and Carbon Black, a high-value nano-material, with the bonus of zero CO2 emissions. A 10 kW multi-tubular solar reactor (SR10) based on the indirect heating concept was designed, constructed and tested. It is composed of an insulated cubic cavity receiver (20 cm side) that absorbs concentrated solar irradiation through a quartz window by a 9 cm-diameter aperture. The solar concentrating system is the 1 MW solar furnace of CNRS-PROMES laboratory. An argon-methane mixture flows inside four graphite tubular reaction zones each composed of two concentric tubes that are settled vertically inside the cavity. Experimental runs mainly showed the key influence of the residence time and temperature on the reaction extent. Since SR10 design presented a weak recovery of carbon black in the filter, a single tube configuration was tested with an external plasma heating source. Complete methane conversion and hydrogen yield beyond 80% were achieved at 2073K. Hydrogen and carbon mass balances showed that C2H2 intermediates affect drastically the carbon black production yield: about half of the initial carbon content in the CH4 was found as C2H2 in the outlet gas. Nevertheless, the carbon black recovery in the filtering device was improved with this new configuration. Data are extrapolated to predict the possible hydrogen and carbon production for a future 50 kW solar reactor. The expected production was estimated to be about 2.47 Nm3/h H2 and 386 g/h carbon black for 1.47 Nm3/h of CH4 injected.

Rapid High Temperature Solar Thermal Biomass Gasification in a Prototype Cavity Reactor

2010 ◽  
Vol 132 (1) ◽  
Author(s):  
Paul Lichty ◽  
Christopher Perkins ◽  
Bryan Woodruff ◽  
Carl Bingham ◽  
Alan Weimer
Keyword(s):  
High Temperature ◽  
Solar Energy ◽  
Gas Flow ◽  
Biomass Conversion ◽  
Biomass Gasification ◽  
Solar Furnace ◽  
Concentrated Solar Energy ◽  
Product Stream ◽  
Tar Reduction ◽  
Composition Ratios

High temperature biomass gasification has been performed in a prototype concentrated solar reactor. Gasification of biomass at high temperatures has many advantages compared with historical methods of producing fuels. Enhancements in overall conversion, product composition ratios, and tar reduction are achievable at temperatures greater than 1000°C. Furthermore, the utilization of concentrated solar energy to drive these reactions eliminates the need to consume a portion of the product stream for heating and some of the solar energy is stored as chemical energy in the product stream. Experiments to determine the effects of temperature, gas flow rate, and feed type were conducted at the high flux solar furnace at the National Renewable Energy Laboratory, Golden, CO. These experiments were conducted in a reflective cavity multitube prototype reactor. Biomass type was found to be the only significant factor within a 95% confidence interval. Biomass conversion as high as 68% was achieved on sun. Construction and design considerations of the prototype reactor are discussed as well as initial performance results.

Monte Carlo Radiative Transfer Modeling of a Solar Chemical Reactor for The Co-Production of Zinc and Syngas

2005 ◽  
Vol 127 (1) ◽  
pp. 102-108 ◽  
Author(s):  
Stefan Kra¨upl ◽  
Aldo Steinfeld
Keyword(s):  
Heat Transfer ◽  
Monte Carlo ◽  
Radiation Heat Transfer ◽  
Convection Heat Transfer ◽  
Chemical Reactor ◽  
Solar Furnace ◽  
Solar Irradiation ◽  
Power Flux ◽  
Zinc Production ◽  
Radiative Transfer Modeling

Radiation heat transfer within a solar chemical reactor for the co-production of zinc and syngas is analyzed by the Monte Carlo ray-tracing method. The reactor is treated as a 3D nonisothermal cavity-receiver lined with ZnO particles that are directly exposed to concentrated solar irradiation and undergo endothermic reduction by CH4 at above 1300 K. The analysis includes coupling to conduction/convection heat transfer and chemical kinetics. A calculation of the apparent absorptivity indicates the cavity’s approach to a blackbody absorber, for either diffuse or specular reflecting inner walls. Numerically calculated temperature distributions, zinc production rates, and thermal efficiencies are validated with experimental measurements in a solar furnace with a 5-kW prototype reactor. At 1600 K, the zinc production rate reached 0.12 mol/min and the reactor’s thermal efficiency exceeded 16%. Scaling up the reactor to power levels of up to 1 MW while keeping constant the relative geometrical dimensions and the solar power flux at 2000 suns results in thermal efficiencies of up to 54%.

scholarly journals A Pressurized High-Flux Solar Reactor for the Thermochemical Gasification of Charcoal Slurry—Two-Phase Flow and Heat Transfer Analysis

2019 ◽  
Vol 142 (5) ◽  
Author(s):  
F. Müller ◽  
A. Steinfeld
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Calculated Data ◽  
Heat Transfer Analysis ◽  
Phase Flow ◽  
Operational Parameters ◽  
Two Phase ◽  
Carbonaceous Particles ◽  
Solar Reactor ◽  
Concentrated Solar Energy

Abstract A pressurized solar reactor for effecting the thermochemical gasification of carbonaceous particles driven by concentrated solar energy is modeled by means of a reacting two-phase flow. The governing mass, momentum, and energy conservation equations are formulated and solved numerically by finite volume computational fluid dynamics (CFD) coupled to a Monte Carlo radiation solver for a nongray absorbing, emitting, and scattering participating medium. Implemented are Langmuir–Hinshelwood kinetic rate expressions and size-dependent properties for charcoal particles undergoing shrinkage as gasification progresses. Validation is accomplished by comparing the numerically calculated data with the experimentally measured temperatures in the range 1283–1546 K, chemical conversions in the range 32–94%, and syngas product H2:CO and CO2:CO molar ratios obtained from testing a 3 kW solar reactor prototype with up to 3718 suns concentrated radiation. The simulation model is applied to identify the predominant heat transfer mechanisms and to analyze the effect of the solar rector's geometry and operational parameters (namely: carbon feeding rate, inert gas flowrate, solar concentration ratio, and total pressure) on the solar reactor's performance indicators given by the carbon molar conversion and the solar-to-fuel energy efficiency. Under optimal conditions, these can reach 94% and 40%, respectively.

Manipulation of a Thermal Emission by Use of Micro- and Nanoscale Structures

2010 ◽  
Author(s):  
Erez Hasman ◽  
Vladimir Kleiner ◽  
Nir Dahan ◽  
Igal Balin
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Solar Energy ◽  
Energy Conversion ◽  
Surface Texture ◽  
High Efficiency ◽  
Thermal Emission ◽  
Photovoltaic Cells ◽  
Nanoscale Structures ◽  
Infrared Sources

In high temperature and vacuum applications, when heat transfer is predominantly by radiation, the material’s surface texture is of substantial importance. Several micro and nanostructures designs have been proposed to enhance a material’s emissivity and its radiative coherence, as control of thermal emission is of crucial concern in the design of infrared sources, in electronic chip coolants, in high-efficiency photovoltaic cells, and in solar energy conversion.

Experimental Evaluation of Particle Consumption in a Particle Seeded Solar Receiver

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Hanna Helena Klein ◽  
Rachamim Rubin ◽  
Jacob Karni
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Carbon Black ◽  
Wall Temperature ◽  
Air Flow ◽  
Operating Conditions ◽  
Working Fluid ◽  
Concentrated Solar Energy ◽  
Exit Temperature ◽  
Solar Receiver

This experimental study shows the behavior of a directly irradiated, high temperature, solar receiver seeded with a low concentration of carbon black particles as the radiation absorbing media in the presence of air or nitrogen as the working fluid. Experiments were conducted in the presence of highly concentrated solar energy with an energy flux of up to 3MW∕m2 at the aperture of the receiver. 99.9% of the particles had an equivalent diameter of <5μm, but the remaining larger agglomerates accounted for 51% of the overall projected surface area. The molar ratio of carbon to gas in the fluid entering the receiver was 0.004–0.008. The heat transfer from the solar radiation to the working gas was accomplished almost exclusively via the particles. The receiver behavior during steady-state operation was evaluated. The receiver gas exit temperatures achieved during the experiments were between 1000 and 1550°C. When nitrogen was used as working gas, its exit temperature exceeded the average wall temperature, whereas when air was used, its exit temperature was lower than the average wall temperature. The air flow may have been heated to some extent by the receiver walls, whereas in the case of nitrogen, the particle-to-gas heat transfer was dominant throughout the receiver. When the gas exit temperature was above 1200°C, the particle seeded nitrogen flow absorbed 12–20% more energy than particle seeded air flow under the same operating conditions (insolation, particle load, flow rate, close proximity in time). The air tests reached high exit temperatures despite the reduction of particle concentration due to combustion. This indicates that heat transfer mainly occurs over a relatively short time period after the particle seeded flow enters the cavity close to the receiver aperture, before significant particle burning takes place. The energy due to carbon combustion was 3–5% of total energy absorbed in the high temperature air experiments. The carbon particles’ oxidation rate in the presence of molecular oxygen was found to be significantly lower than values documented in the literature for high temperature carbon black combustion in air. The high solar flux, which promotes very high radiation→particle→gas heat transfer rate, might account for this retardation.

scholarly journals Modeling of a Multitube High-Temperature Solar Thermochemical Reactor for Hydrogen Production

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
S. Haussener ◽  
D. Hirsch ◽  
C. Perkins ◽  
A. Weimer ◽  
A. Lewandowski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Concentration Ratio ◽  
Energy Conversion Efficiency ◽  
Thermochemical Cycle ◽  
Governing Equations ◽  
Particulate Media ◽  
Solar Reactor ◽  
Concentrated Solar Energy ◽  
Reaction Extent ◽  
Flux Concentration

A solar reactor consisting of a cavity-receiver containing an array of tubular absorbers is considered for performing the ZnO-dissociation as part of a two-step H2O-splitting thermochemical cycle using concentrated solar energy. The continuity, momentum, and energy governing equations that couple the rate of heat transfer to the Arrhenius-type reaction kinetics are formulated for an absorbing-emitting-scattering particulate media and numerically solved using a computational fluid dynamics code. Parametric simulations were carried out to examine the influence of the solar flux concentration ratio (3000–6000 suns), number of tubes (1–10), ZnO mass flow rate (2–20 g/min per tube), and ZnO particle size (0.06–1 μm) on the reactor’s performance. The reaction extent reaches completion within 1 s residence time at above 2000 K, yielding a solar-to-chemical energy conversion efficiency of up to 29%.

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