Modellierung der Gas- Feststoffverteilung in einer zirkulierenden Wirbelschicht mit CFD

Zsfassung in engl. SpracheDurch die kontinuierliche Weiterentwicklung der Strömungsmodelle und dem Anstieg der Rechenleistung können auch komplexe Strömungen, wie dies in einer zirkulierenden Wirbelschicht der Fall ist, dargestellt werden. In dieser Arbeit wurde untersucht, in wie weit das verwendete Strömungsmodell, welches die Sandfraktion als Fluid approximiert abbildet, das für zirkulierende Wirbelschichten typische Verhalten in Bezug auf Strömungsbilder, Druckverluste und Abscheidegrade darstellen kann. Als Referenzanlage wurde eine Modellanlage aus Plexiglas vom ITE der Technischen Universität Wien verwendet. Die Strömungsberechnungen wurden mit dem kommerziellen CFD Code FLUENT durchgeführt.Auf Grund der benötigten enormen Rechenleistung und den daraus resultierenden Verzögerungen wurde die Sandmasse nur halb so groß gewählt wie dies in der realen Modellanlage der Fall ist. Auf Grund der kleinen Sandmasse stellte sich ein pulsierender Betrieb ein. Es konnte festgestellt werden, dass die Simulation mit der Realität vergleichbare Ergebnisse lieferte. Sowohl das Strömungsregime im Steigrohr, als auch die Darstellung des fluidisierten Sandes im Rückführzweig wurde realitätsnahe wiedergegeben. Auch stellte sich der Abscheidegrad des Zyklons als im Rahmen des Erwartbaren heraus.Kritisch anzumerken ist die lange Rechenzeit im Bereich von drei Monaten und die fehlende Darstellung von Temperatureinflüssen, chemischen Vorgängen und Verbrennungen. Dies ist mit der derzeitigen Rechnerleistung in akzeptabler Zeit nicht durchführbar.Owing to continuing further developments in models of fluid dynamics and rising computing power, it is possible for the first time to solve more complex applications with computational fluid dynamics, like a circulating fluidized bed. This work investigates the possibilities of the taken model which describes the sand particles as a fluid. It focuses on the behaviour of this model in terms of the two phase flow, the pressure losses in the system and the separation behavior of the cyclone.As a reference model a facility made of acrylic glass has been taken from the ITE of the Technical University Vienna. The flow computation has been done with the commercial CFD Code FLUENT.Because of the enormous computation effort and the resulting delays, the mass of sand was halved compared to the reference model. Owing to the small amount of sand the model got in a pulsing state. It could be detected, that the results of the simulation match in most terms with the reality. Both the flow field in the riser and the fluidized particles in the feedback were described close to reality. Furthermore the result reflects the separation behaviour of the cyclone really realistic data. Critically viewed further simulation in this field has to add the missing energy equations and combustion models which is currently not possible because of too little computing power.8

Saline Cavern Adiabatic Compressed Air Energy Storage Using Sand as Heat Storage Material

Adiabatic compressed air energy storage systems offer large energy storage capacities and power outputs beyond 100 MWel. Salt production in Austria produces large caverns which are able to hold pressure up to 100 bar, thus providing low cost pressurized air storage reservoirs for adiabatic compressed air energy storage plants. In this paper the results of a feasibility study is presented, which was financed by the Austrian Research Promotion Agency, with the objective to determine the adiabatic compressed air energy storage potential of Austria’s salt caverns. The study contains designs of realisable plants with capacities between 10 and 50 MWel, applying a high temperature energy storage system currently developed at the Institute for Energy Systems and Thermodynamics in Vienna. It could be shown that the overall storage potential of Austria’s salt caverns exceeds a total of 4 GWhel in the year 2030 and, assuming an adequate performance of the heat exchanger, that a 10 MWel adiabatic compressed air energy storage plant in Upper Austria is currently feasible using state of the art thermal turbomachinery which is able to provide a compressor discharge temperature of 400 °C

Modeling the Atmospheric Transport and Deposition of PCDD/F to the Great Lakes

Atmospheric deposition is a significant loading pathway for polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxin) to the Great Lakes. An innovative approach using NOAA's HYSPLIT atmospheric fate and transport model was developed to estimate the 1996 dioxin contribution to each lake from each of 5700 point sources and 42 600 area sources in a U.S./Canadian air emissions inventory. These unusually detailed source-receptor modeling results show that deposition to each lake arises from a broad geographical region, with significant contributions from up to 2000 km away. The source categories contributing most significantly to 1996 dioxin deposition appear to be municipal waste incineration, iron sintering, medical waste incineration, and cement kilns burning hazardous waste. Model-predicted air concentrations and deposition fluxes were consistent with ambient measurement data, within the uncertainties in each, but there may be a moderate tendency toward underestimation using midrange emissions estimates. The most likely reason for this tendency appears to be missing or underestimated emissions sources, but in-situ atmospheric formation of octachlorinated dibenzo-p-dioxin (OCDD) and heptachlorinated dibenzo-p-dioxin (HpCDD) may have also contributed. Despite uncertainties, the findings regarding the relative importance of different sources types and source regions appear to be relatively robust and may be useful in prioritizing pollution prevention efforts

Results from a round robin test for the ecotoxicological evaluation of construction products using two leaching tests and an aquatic test battery

A European round robin test according to ISO 5725-2 was conceptually prepared, realised, and evaluated. The aim was to determine the inter-laboratory variability of the overall process for the ecotoxicological characterization of construction products in eluates and bioassays. To this end, two construction products BAM-G1 (granulate) and HSR-2 (roof sealing sheet), both made of EPDM polymers (rubber), were selected. The granular construction product was eluted in a one stage batch test, the planar product in the Dynamic Surface Leaching test (DSLT). A total of 17 laboratories from 5 countries participated in the round robin test: Germany (12), Austria (2), Belgium (1), Czech Republic (1) and France (1). A test battery of four standardised ecotoxicity tests with algae, daphnia, luminescent bacteria and zebrafish eggs was used. As toxicity measures, EC50 and LID values were calculated. All tests, except the fish egg test, were basically able to demonstrate toxic effects and the level of toxicity. The reproducibility of test results depended on the test specimens and the test organisms. Generally, the variability of the EC50 or LID values increased with the overall level of toxicity. For the very toxic BAM-G1 eluate a relative high variability of CV = 73%–110% was observed for EC50 in all biotests, while for the less toxic HSR-2 eluate the reproducibility of EC50 varied with sensitivity: it was very good (CV = 9.3%) for the daphnia test with the lowest sensitivity, followed by the algae test (CV = 36.4%). The luminescent bacteria test, being the most sensitive bioassay for HSR-2 Eluate, showed the highest variability (CV = 74.8%). When considering the complex overall process the reproducibility of bioassays with eluates from construction products was acceptable