Experimental Investigation of a Vortex-Flow Solar Chemical Reactor for the Combined ZnO-Reduction and CH4-Reforming

2001 ◽  
Author(s):  
Stefan Kräupl ◽  
Aldo Steinfeld
Keyword(s):  
Heat Transfer ◽  
Vortex Flow ◽  
Solar Power ◽  
Radiation Heat Transfer ◽  
Chemical Conversion ◽  
Chemical Reactor ◽  
Solar Furnace ◽  
Reaction Products ◽  
Ch4 Reforming ◽  
Reactor Operating

Abstract The co-production of Zn and synthesis gas by the combined reduction of ZnO and reforming of CH4 has been performed using a vortex-flow chemical reactor in a high-flux solar furnace. The reactor operating temperature ranged between 1032 and 1481 K for an input solar power of 2.3 to 4.6 kW and mean solar flux intensities of 810 to 1609 kW/m2. The performance of the reactor was determined by conducting a complete mass and energy balance for the chemical process. The chemical conversion ranged between 83–100%. The thermal efficiency, defined as the portion of input solar power absorbed as sensible and process heat, was in the range 11–28%. The exergy efficiency for the closed cycle, defined as the ratio of the maximum amount of work that the products leaving the reactor could produce if were re-combined to the input solar power, was in the range 0.3–3.1%. Major sources of energy loss are re-radiation heat transfer through the reactor aperture, conduction heat transfer through the reactor walls, and the quenching of the reaction products.

Experimental Investigation of a Vortex-Flow Solar Chemical Reactor for the Combined ZnO-Reduction and CH4-Reforming*

2001 ◽  
Vol 123 (3) ◽  
pp. 237-243 ◽  
Author(s):  
Stefan Kra¨upl ◽  
Aldo Steinfeld
Keyword(s):  
Heat Transfer ◽  
Vortex Flow ◽  
Solar Power ◽  
Radiation Heat Transfer ◽  
Chemical Conversion ◽  
Chemical Reactor ◽  
Solar Furnace ◽  
Reaction Products ◽  
Ch4 Reforming ◽  
Reactor Operating

The co-production of Zn and synthesis gas by the combined reduction of ZnO and reforming of CH4 has been performed using a vortex-flow chemical reactor in a high-flux solar furnace. The reactor operating temperature ranged between 1221 and 1481 K for an input solar power of 2.3 to 4.6 kW and mean solar flux intensities of 810 to 1609 kW/m2. The performance of the reactor was determined by conducting a complete mass and energy balance for the chemical process. The chemical conversion ranged between 83–100 percent. The thermal efficiency, defined as the portion of input solar power absorbed as sensible and process heat, was in the range 11–28 percent. The exergy efficiency for the closed cycle, defined as the ratio of the maximum amount of work that the products leaving the reactor could produce if were re-combined to the input solar power, was in the range 0.3–3.1 percent. Major sources of energy loss are re-radiation heat transfer through the reactor aperture, conduction heat transfer through the reactor walls, and the quenching of the reaction products.

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 Pulsed Gas Feeding for Stoichiometric Operation of a Gas-Solid Vortex Flow Solar Chemical Reactor

2001 ◽  
Author(s):  
Stefan Kräupl ◽  
Aldo Steinfeld
Keyword(s):  
Vortex Flow ◽  
Chemical Reactor ◽  
Thermal Conversion ◽  
Solar Furnace ◽  
Molar Ratio ◽  
Technical Solution ◽  
Molar Amount ◽  
Flux Concentration ◽  
Ch4 Reforming ◽  
Opening Up

Abstract The thermodynamic implications of conducting the solar combined ZnO-reduction and CH4-reforming under stoichiometric and non-stoichiometric conditions are examined. For a solar flux concentration ratio of 5000 and for a solar cavity-receiver operating at 1300 K, the solar thermal conversion efficiency is 55% for a stoichiometric molar ratio of ZnO and CH4, and decreases by 50% when using excess methane by a factor 10 over the stoichiometric molar amount. A technical solution for operating a gas-solid vortex-flow solar reactor under stoichiometric conditions was established by using a pulsed-feed of methane to carry out the particles of ZnO. Using this technique, nearly stoichiometric operation was demonstrated with a prototype reactor in a high-flux solar furnace, thereby opening up a means for efficient conversion of sunlight into chemical fuels.

Operational Performance of a 5-kW Solar Chemical Reactor for the Co-Production of Zinc and Syngas

2003 ◽  
Vol 125 (1) ◽  
pp. 124-126 ◽  
Author(s):  
Stefan Kra¨upl ◽  
Aldo Steinfeld
Keyword(s):  
Vortex Flow ◽  
Fossil Fuel ◽  
Chemical Conversion ◽  
Chemical Reactor ◽  
Energy Conversion Efficiency ◽  
Operational Performance ◽  
Residence Times ◽  
Direct Irradiation ◽  
Mean Residence Times ◽  
Ch4 Reforming

We report on the improved operational performance and energy conversion efficiency of a 5-kW solar chemical reactor for the combined ZnO-reduction and CH4-reforming SynMet process. The reactor features a pulsed vortex flow of CH4 laden with ZnO particles, which is confined to a cavity-receiver and directly exposed to solar power fluxes exceeding 2000kW/m2. Reactants were continuously fed at ambient temperature, heated by direct irradiation to above 1350°K, and converted to Zn and syngas during mean residence times of 10 seconds. Typical chemical conversion attained was 100% for ZnO and up to 96% for CH4. The thermal efficiency was in the 15–22% range; the exergy efficiency reached up to 7.7% and may be increased by recovering the sensible and latent heat of the products. The SynMet process avoids emissions of greenhouse-gases and other pollutant derived from the traditional fossil-fuel-based production of zinc and syngas, and further converts solar energy into storable and transportable chemical fuels.

Pulsed Gas Feeding for Stoichiometric Operation of a Gas-Solid Vortex Flow Solar Chemical Reactor

2000 ◽  
Vol 123 (2) ◽  
pp. 133-137 ◽  
Author(s):  
Stefan Kra¨upl ◽  
Aldo Steinfeld
Keyword(s):  
Vortex Flow ◽  
Chemical Reactor ◽  
Thermal Conversion ◽  
Solar Furnace ◽  
Molar Ratio ◽  
Technical Solution ◽  
Molar Amount ◽  
Flux Concentration ◽  
Ch4 Reforming ◽  
Opening Up

The thermodynamic implications of conducting the solar combined ZnO-reduction and CH4-reforming under stoichiometric and non-stoichiometric conditions are examined. For a solar flux concentration ratio of 5000 and for a solar cavity-receiver operating at 1300 K, the solar thermal conversion efficiency is 55 percent for a stoichiometric molar ratio of ZnO and CH4, and decreases by 50 percent when using excess methane by a factor 10 over the stoichiometric molar amount. A technical solution for operating a gas-solid vortex-flow solar reactor under stoichiometric conditions was established by using a pulsed-feed of methane to carry out the particles of ZnO. Using this technique, nearly stoichiometric operation was demonstrated with a prototype reactor in a high-flux solar furnace, thereby opening up a means for efficient conversion of sunlight into chemical fuels.

Operational Performance of a 5 kW Solar Chemical Reactor for the Co-Production of Zinc and Syngas

Solar Energy ◽  
2002 ◽  
Author(s):  
Stefan Kra¨upl ◽  
Aldo Steinfeld
Keyword(s):  
Vortex Flow ◽  
Fossil Fuel ◽  
Chemical Conversion ◽  
Chemical Reactor ◽  
Energy Conversion Efficiency ◽  
Operational Performance ◽  
Residence Times ◽  
Direct Irradiation ◽  
Mean Residence Times ◽  
Ch4 Reforming

We report on the improved operational performance and energy conversion efficiency of a 5 kW solar chemical reactor for the combined ZnO-reduction and CH4-reforming “SynMet” process. The reactor features a pulsed vortex flow of CH4 laden with ZnO particles, which is confined to a cavity-receiver and directly exposed to solar power fluxes exceeding 2000 kW/m2. Reactants were continuously fed at ambient temperature, heated by direct irradiation to above 1350 K, and converted to Zn(g) and syngas during mean residence times of 10 seconds. Typical chemical conversion attained was 100% to Zn and up to 96% to syngas. The thermal efficiency was in the 15–22% range; the exergy efficiency reached up to 7.7% and may be increased by recovering the sensible and latent heat of the products. The Synmet process avoids emissions of greenhouse-gases and other pollutant derived from the traditional fossil-fuel-based production of zinc and syngas, and further converts solar energy into storable and transportable chemical fuels.

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

Solar Energy ◽  
2004 ◽  
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 non-isothermal 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. 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%.

Design Studies for a Solar Reactor Based on a Simple Radiative Heat Exchange Model

2005 ◽  
Vol 127 (3) ◽  
pp. 425-429 ◽  
Author(s):  
C. Wieckert
Keyword(s):  
Heat Transfer ◽  
Solar Power ◽  
Radiation Heat Transfer ◽  
Heat Transfer Analysis ◽  
Physical Parameters ◽  
Concentrated Solar Power ◽  
Radiation Heat ◽  
Small Aperture ◽  
Lower Cavity ◽  
Solar Reactor

A high-temperature solar chemical reactor for the processing of solids is scaled up from a laboratory scale (5kW concentrated solar power input) to a pilot scale (200kW). The chosen design features two cavities in series: An upper cavity has a small aperture to let in concentrated solar power coming from the top. It serves as the solar receiver, radiant absorber, and radiant emitter to a lower cavity. The lower cavity is a well-insulated enclosure. It is subjected to thermal radiation from the upper cavity and serves in our application as the reaction chamber for a mixture of ZnO and carbon. Important insight for the definition of the geometrical parameters of the pilot reactor has been generated by a radiation heat transfer analysis based on the radiosity enclosure theory. The steady-state model accounts for radiation heat transfer within the solar reactor including reradiation losses through the reactor aperture, wall losses due to thermal conduction and heat consumption by the endothermic chemical reaction. Key results include temperatures of the different reactor walls and the thermal efficiency of the reactor as a function of the major geometrical and physical parameters. The model, hence, allows for a fast estimate of the influence of these parameters on the reactor performance.

Experimental Investigation of the Solar Carbothermic Reduction of ZnO Using a Two-cavity Solar Reactor

2004 ◽  
Vol 126 (1) ◽  
pp. 633-637 ◽  
Author(s):  
T. Osinga ◽  
U. Frommherz ◽  
A. Steinfeld ◽  
C. Wieckert
Keyword(s):  
Carbothermic Reduction ◽  
Chemical Conversion ◽  
Chemical Reactor ◽  
Reaction Chamber ◽  
Solar Furnace ◽  
Molar Ratio ◽  
Solar Simulator ◽  
Co2 Emission Reduction ◽  
In Series ◽  
Reduction Of Zno

Zinc production by solar carbothermic reduction of ZnO offers a CO2 emission reduction by a factor of 5 vis-a`-vis the conventional fossil-fuel-based electrolytic or Imperial Smelting processes. Zinc can serve as a fuel in Zn-air fuel cells or can be further reacted with H2O to form high-purity H2. In either case, the product ZnO is solar-recycled to Zn. We report on experimental results obtained with a 5 kW solar chemical reactor prototype that features two cavities in series, with the inner one functioning as the solar absorber and the outer one as the reaction chamber. The inner cavity is made of graphite and contains a windowed aperture to let in concentrated solar radiation. The outer cavity is well insulated and contains the ZnO-C mixture that is subjected to irradiation from the inner graphite cavity. With this arrangement, the inner cavity protects the window against particles and condensable gases and further serves as a thermal shock absorber. Tests were conducted at PSI’s Solar Furnace and ETH’s High-Flux Solar Simulator to investigate the effect of process temperature (range 1350-1600 K), reducing agent type (beech charcoal, activated charcoal, petcoke), and C:ZnO stoichiometric molar ratio (range 0.7–0.9) on the reactor’s performance and chemical conversion. In a typical 40-min solar experiment at 1500 K, 500 g of a ZnO-C mixture were processed into Zn(g), CO, and CO2. Thermal efficiencies of up to 20% were achieved.

Heat Transfer Analysis in a Blast Furnace Tuyere Nose

2005 ◽  
Author(s):  
David Roldan ◽  
Clifford Tetrault ◽  
Yongfu Zhao ◽  
Mark Atkinson ◽  
Chenn Q. Zhou
Keyword(s):  
Heat Transfer ◽  
Blast Furnace ◽  
Radiation Heat Transfer ◽  
Cooling Water ◽  
Chemical Reactor ◽  
Operating Conditions ◽  
Heat Transfer Analysis ◽  
Large Area ◽  
Fuel Gas ◽  
Hot Air

The Blast furnace process is a counter current moving bed chemical reactor to reduce iron oxides to iron for iron/steel making. In the process, tuyeres are used to introduce hot air (blast) and fuel (gas or pulverized coal) into the furnace for combustion. The nose of a tuyere, composed of copper material, that is exposed to a high temperature environment and a cooling water pipe is embedded to prevent melting of the material. In this work, heat transfer and temperature distributions have been analyzed using the computational fluid dynamics commercial software, FLUENT®. The computations have included the cooling water flow and conjugate heat transfer in the tuyere nose. Both convection and radiation heat transfer on the surfaces are included. Different geometry and operating conditions were considered. The results have indicated that insufficient cooling in a large area between the nose inlet and outlet pipe can cause failures of the tuyere nose.

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