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  • 1
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    Solar Upgrading of Fuels for Generation of Electricity (2001)
    American Society of Mechanical Engineers
    Details
    Publication Date: 2001-01-01
    Description: This paper presents a novel process comprising solar upgrading of hydrocarbons by steam reforming in solar specific receiver-reactors and utilizing the upgraded, hydrogen-rich fuel in high efficiency conversion systems, such as gas turbines or fuel cells. In comparison to conventionally heated processes about 30% of fuel can be saved with respect to the same specific output. Such processes can be used in small scale as a stand-alone system for off-grid markets as well as in large scale to be operated in connection with conventional combined-cycle plants. The complete reforming process will be demonstrated in the SOLASYS project, supported by the European Commission in the JOULE/THERMIE framework. The project has been started in June 1998. The SOLASYS plant is designed for 300 kWel output, it consists of the solar field, the solar reformer and a gas turbine, adjusted to operate with the reformed gas. The SOLASYS plant will be operated at the experimental solar test facility of the Weizmann Institute of Science in Israel. Start-up of the pilot plant is scheduled in April 2001. The midterm goal is to replace fossil fuels by renewable or non-conventional feedstock in order to increase the share of renewable energy and to establish processes with only minor or no CO2 emission. Examples might be upgrading of bio-gas from municipal solid waste as well as upgrading of weak gas resources.
    Print ISSN: 0199-6231
    Electronic ISSN: 1528-8986
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by American Society of Mechanical Engineers
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  • 2
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    Solar Gasification of Biomass: A Molten Salt Pyrolysis Study (2004)
    American Society of Mechanical Engineers
    Details
    Publication Date: 2004-07-19
    Description: A novel solar process and reactor for thermochemical conversion of biomass to synthesis gas is described. The concept is based on dispersion of biomass particles in a molten inorganic salt medium and, simultaneously, absorbing, storing and transferring solar energy needed to perform pyrolysis reactions in the high-temperature liquid phase. A lab-scale reactor filled with carbonates of potassium and sodium was set up to study the kinetics of fast pyrolysis and the characteristics of transient heat transfer for cellulose particles (few millimeters size) introduced into the molten salt medium. The operating conditions were reaction temperatures of 1073–1188 K and a particle peak-heating rate of 100 K/sec. The assessments performed for a commercial-scale solar reactor demonstrate that pyrolysis of biomass particles dispersed in a molten salt phase could be a feasible option for the continuous, round-the-clock production of syngas, using solar energy only.
    Print ISSN: 0199-6231
    Electronic ISSN: 1528-8986
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by American Society of Mechanical Engineers
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  • 3
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    Solar Fixation of Atmospheric Nitrogen (2004)
    American Society of Mechanical Engineers
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    Publication Date: 2004-02-01
    Description: The thermal fixation of atmospheric nitrogen is explored, using a recently developed concept of a particle-seeded solar receiver. The thermodynamics and the kinetics of the formation of nitric oxide (NO) in air at temperatures of about 2300 K are analyzed, and the required residence time and the time to reach the steady state of the reaction between nitrogen and oxygen are calculated. The novel particle-seeded receiver concept is briefly described. The adaptation of the particle-seeded receiver to the fixation reaction in terms of heating rate of the air and residence time is validated based on previous test results and complementary calculations. A proposed method where the solar receiver/reactor is simultaneously coupled with power production, using the exhausted hot air from the reactor to generate electricity, is described. This concept can definitely increase the economical benefit of the process and, thus, its potential attractiveness. Some illustrative figures for a commercial size system are provided.
    Print ISSN: 0199-6231
    Electronic ISSN: 1528-8986
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by American Society of Mechanical Engineers
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  • 4
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    Simulation of Thermal and Chemical Processes in Annular Layer of ZnO–C Mixtures (2004)
    American Society of Mechanical Engineers
    Details
    Publication Date: 2004-09-14
    Description: A special setup, electrically heated, enabling the simulation of the process conditions encountered in a solar chemical reactor, is described. The setup allows us to study the thermal and chemical processes in different solid (powder or granules) reactant layers from the beginning of the heating until the reaction is completed, in a heating condition typical for indirectly, externally heated solar reactors. The particular case of the ZnO carboreduction process is analyzed in this paper as an example. Tests were executed using different powder mixtures of ZnO–C to demonstrate the layer-wise nature of the process. The results show that the reactivity and the behavior of mixtures strongly depend on their components structures, impurities, and stoichiometry. This method can be generally applied for studying endothermic chemical reactions involving other solid reactants.
    Print ISSN: 0199-6231
    Electronic ISSN: 1528-8986
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by American Society of Mechanical Engineers
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  • 5
    Electronic Resource
    Electronic Resource
    Nitrogen cycling in the soil–plant system along a precipitation gradient in the Kalahari sands (2004)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Nitrogen (N) cycling was analyzed in the Kalahari region of southern Africa, where a strong precipitation gradient (from 978 to 230 mm mean annual precipitation) is the main variable affecting vegetation. The region is underlain by a homogeneous soil substrate, the Kalahari sands, and provides the opportunity to analyze climate effects on nutrient cycling. Soil and plant N pools, 15N natural abundance (δ15N), and soil NO emissions were measured to indicate patterns of N cycling along a precipitation gradient. The importance of biogenic N2 fixation associated with vascular plants was estimated with foliar δ15N and the basal area of leguminous plants. Soil and plant N was more 15N enriched in arid than in humid areas, and the relation was steeper in samples collected during wet than during dry years. This indicates a strong effect of annual precipitation variability on N cycling. Soil organic carbon and C/N decreased with aridity, and soil N was influenced by plant functional types. Biogenic N2 fixation associated with vascular plants was more important in humid areas. Nitrogen fixation associated with trees and shrubs was almost absent in arid areas, even though Mimosoideae species dominate. Soil NO emissions increased with temperature and moisture and were therefore estimated to be lower in drier areas. The isotopic pattern observed in the Kalahari (15N enrichment with aridity) agrees with the lower soil organic matter, soil C/N, and N2 fixation found in arid areas. However, the estimated NO emissions would cause an opposite pattern in δ15N, suggesting that other processes, such as internal recycling and ammonia volatilization, may also affect isotopic signatures. This study indicates that spatial, and mainly temporal, variability of precipitation play a key role on N cycling and isotopic signatures in the soil–plant system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.2003.00698.x
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  • 6
    Electronic Resource
    Electronic Resource
    Detecting changes in arctic tundra plant communities in response to warming over decadal time scales (2004)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Detecting the response of vegetation to climate forcing as distinct from spatial and temporal variability may be difficult, if not impossible, over the typical duration of most field studies. We analyzed the spatial and interannual variability of plant functional type biomass from field studies in low arctic tussock tundra and compared these to climate change simulations of plant community composition using a dynamic tundra vegetation model (ArcVeg). Spatial heterogeneity of peak season live aboveground biomass was estimated using field samples taken from low arctic tundra at Ivotuk, Alaska (68.5°N, 155.7°W) in 1999. Coefficients of variation for live aboveground biomass at the 1 m2 scale ranged from 14.6% for deciduous shrubs, 18.5% for graminoids and 25.3% for mosses to over 57% for forbs and lichens. Spatial heterogeneity in the ArcVeg dynamic vegetation model was simulated to be greater than the field data, ranging from 37.1% for deciduous shrubs to 107.9% for forbs. Disturbances in the model, such as caribou grazing and freezing–thawing of soil, as well as demographic stochasticity, led to the greater variability in the simulated results. Temporal variances of aboveground live biomass over a 19-year period using data from Toolik Lake, AK fell within the range of field and simulation spatial variances. However, simulations using ArcVeg suggest that temporal variability can be substantially less than site-scale spatial variability. Field data coupled with ArcVeg simulations of climate change scenarios indicate that some changes in plant community composition may be detectable within two decades following the onset of warming, and shrubs and mosses might be the key indicators of community change. Model simulations also project increasing landscape scale spatial heterogeneity (particularly of shrubs) with increasing temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1529-8817.2003.00810.x
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  • 7
    Electronic Resource
    Electronic Resource
    Aqueous silicate complexes in wheat, Triticum aestivum L. (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The chemical speciation of silicon in xylem exudate from wheat (Triticum aestivum L.) was examined by 29Si NMR spectroscopy. Wheat plants were grown to maturity in silicon-free nutrient medium, and then transferred to a solution containing 0.02 mm29Si-enriched silicic acid. After 30 min the shoots were excised and xylem exudate was collected. Within 10 min the Si concentration of the xylem exudate reached values greatly in excess of that of the starting nutrient solution, eventually reaching levels as high as 8 mm. Silicon-29 nuclear magnetic resonance spectra indicated the existence of only two Si-containing species in the xylem exudate, mono and disilicic acid (H4SiO4o and (HO)3Si(µ-O)Si(OH)3o) in a ratio of approximately 7 : 1. Significantly, there was no evidence of organosilicate complexes. Nevertheless, the efficiency by which the plant concentrates aqueous silicon indicates active mechanisms of silicon transport across root cell membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0016-8025.2003.01124.x
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