04 Fakultät Energie-, Verfahrens- und Biotechnik

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Institute: search.filters.UBSInstitut.Institut für Feuerungs- und KraftwerkstechnikSubject: search.filters.subject.540

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    ItemOpen Access
    Untersuchungen zur Belagsbildung und Charakterisierung der Ascheablagerungen in steinkohlegefeuerten Kraftwerken
    (2016) Babat, Selahattin; Scheffknecht, Günter (Prof. Dr. techn.)
    Bei der Verfeuerung fester Brennstoffe in Kraftwerken kann es durch Ascheablagerungen auf Heizflächen (Membranwände, Überhitzer, Zwischenüberhitzer, etc.) zur Verminderung des Wärmetransports und zu Betriebsstörungen und Schädigungen an Anlagenteilen kommen. Verantwortlich für diese Ablagerungen sind die mineralischen Bestandteile der Kohle, die beim Verbrennungsprozess zu schmelzflüssigen Phasen umgewandelt werden können. In einem Heizkraftwerk (730 MWth) wird für drei Steinkohlen das Verbrennungsverhalten im Hinblick auf Asche- und Belagsbildung sowie Belagscharakterisierung untersucht. Ein Schwerpunkt ist die Untersuchung des Belagaufbaus auf gekühlten und ungekühlten Depositionssonden. Mit der gekühlten Sonde wird die Initialschicht, die sich unmittelbar auf den Kesselrohren bildet, untersucht, während mit der ungekühlten Sonde eine Untersuchung im Hinblick auf die Deckschicht durchgeführt wird. Die Initialschichten zeigen für alle drei untersuchten Steinkohlen eine Anreicherung an Eisen im Vergleich zur Deckschicht und des Flugstaubes. Ursächlich für diese eisenreiche Grundschicht ist nach bisherigen Erkenntnissen das Mineral Pyrit. Neben den experimentellen und analytischen Untersuchungen werden mit der Software FactSage Gleichgewichtsberechnungen unter Berücksichtigung der im Brennstoff enthaltenen Mineralien (Pyrit, Illit, Kaolinit und Quarz) und der Analyse von Aschepartikeln unter oxidierenden und reduzierenden Verbrennungsbedingungen durch-geführt. Der Einfluss der Feuerraumatmosphäre auf das Ascheschmelzverhalten und die daraus hervorgehenden Ablagerungen wird mit diesen Berechnungen beurteilt. Die Ergebnisse zeigen, dass die Ablagerung eines Aschepartikels erheblich durch die Partikelhistorie beeinflusst wird. Abgesehen von der Partikelzusammensetzung haben insbesondere die Temperatur und die jeweilige Atmosphäre, die ein Partikel auf seiner Flugbahn bis zum Auftreffen auf die Heizfläche durchläuft, großen Einfluss auf die Mineralumwandlung und das Anhaften des Partikels.
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    ItemOpen Access
    Evaluation of a low-cost dryer for a low-cost optical particle counter
    (2022) Chacón-Mateos, Miriam; Laquai, Bernd; Vogt, Ulrich; Stubenrauch, Cosima
    The use of low-cost sensors for air quality measurements has become very popular in the last few decades. Due to the detrimental effects of particulate matter (PM) on human health, PM sensors like photometers and optical particle counters (OPCs) are widespread and have been widely investigated. The negative effects of high relative humidity (RH) and fog events in the mass concentration readings of these types of sensors are well documented. In the literature, different solutions to these problems - like correction models based on the Köhler theory or machine learning algorithms - have been applied. In this work, an air pre-conditioning method based on a low-cost thermal dryer for a low-cost OPC is presented. This study was done in two parts. The first part of the study was conducted in the laboratory to test the low-cost dryer under two different scenarios. In one scenario, the drying efficiency of the low-cost dryer was investigated in the presence of fog. In the second scenario, experiments with hygroscopic aerosols were done to determine to which extent the low-cost dryer reverts the growth of hygroscopic particles. In the second part of the study, the PM10 and PM2.5 mass concentrations of an OPC with dryer were compared with the gravimetric measurements and a continuous federal equivalent method (FEM) instrument in the field. The feasibility of using univariate linear regression (ULR) to correct the PM data of an OPC with dryer during field measurement was also evaluated. Finally, comparison measurements between an OPC with dryer, an OPC without dryer, and a FEM instrument during a real fog event are also presented. The laboratory results show that the sensor with the low-cost dryer at its inlet measured an average of 64 % and 59 % less PM2.5 concentration compared with a sensor without the low-cost dryer during the experiments with fog and with hygroscopic particles, respectively. The outcomes of the PM2.5 concentrations of the low-cost sensor with dryer in laboratory conditions reveal, however, an excess of heating compared with the FEM instrument. This excess of heating is also demonstrated in a more in-depth study on the temperature profile inside the dryer. The correction of the PM10 concentrations of the sensor with dryer during field measurements by using ULR showed a reduction of the maximum absolute error (MAE) from 4.3 µg m-3 (raw data) to 2.4 µg m-3 (after correction). The results for PM2.5 make evident an increase in the MAE after correction: from 1.9 µg m−3 in the raw data to 3.2 µg m−3. In light of these results, a low-cost thermal dryer could be a cost-effective add-on that could revert the effect of the hygroscopic growth and the fog in the PM readings. However, special care is needed when designing a low-cost dryer for a PM sensor to produce FEM similar PM readings, as high temperatures may irreversibly change the sampled air by evaporating the most volatile particulate species and thus deliver underestimated PM readings. New versions of a low-cost dryer aiming at FEM measurements should focus on maintaining the RH at the sensor inlet at 50 % and avoid reaching temperatures higher than 40 ∘C in the drying system. Finally, we believe that low-cost dryers have a very promising future for the application of sensors in citizen science, sensor networks for supplemental monitoring, and epidemiological studies.
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    ItemOpen Access
    Application of source apportionment methods to identify emission sources with the help of ambient air quality measurements in six European cities
    (2019) Chacón-Mateos, Miriam
    The quantification of pollution sources' contributions is a crucial element for implementing the Directives on Air Quality (2008/50/EC and 2004/107/EC). Within the ICARUS project, the source apportionment of PM2.5 in six cities of Europe (Athens, Brno, Ljubljana, Madrid, Thessaloniki, and Stuttgart) was assessed using datasets of measurements made in two different seasons (summer and winter) and two modeling tools: the Lenschow approach and the Positive Matrix Factorization. In order to increase the reliability and robustness of the results, an inter-comparison exercise was carried out with two receptor models for the same datasets: the Principal Component Analysis and the Positive Matrix Factorization model run by a different institution. It was observed that the Lenschow approach does not show the same results as the receptor models and therefore cannot be used to design strategies for urban air quality planning but just as a qualitative method. The comparison of the receptor models led to the validation of the results. Five sources have been found to be the main sources of PM2.5 in all the participating cities, namely, traffic, secondary inorganic aerosols (nitrates and sulphates), resuspension of soil dust, heating systems (biomass burning and/or fuel oil combustion) and industry. Geographical and seasonal variations have been observed, especially for heating sources hence, air quality measures at a local scale should be designed for the abatement of air pollution.