Untersuchungen zum Verschmutzungsverhalten rheinischer Braunkohlen in Kohledampferzeugern

Schlüter, Annette

Dissertation / PhD Thesis/Book

Untersuchungen zum Verschmutzungsverhalten rheinischer Braunkohlen in Kohledampferzeugern

Schlüter, A. (Correspondung author)FZJ*

2008
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-89336-524-1

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich : Energie & Umwelt / Energy & Environment 7, 164 S. (2008) = Aachen, RWTH, Diss., 2008

Please use a persistent id in citations: http://hdl.handle.net/2128/3108

Abstract: In lignite-fired power plants high fouling in heat exchangers can be observed while firing Rhenish brown coals rich in sodium and poor in silicon content. These sulphatic and oxidic deposits reduce the heat transfer and can cause plant damage. It is assumed that fouling is caused by ash softening and partial melting of alkaline phases. The objective of this dissertation is to provide a better understanding of the fouling processes in lignite-fired boilers through experimental analysis using the ashes of different Rhenish brown coals and synthetic ash mixtures. In order to estimate the agglomeration potential of the brown coal ashes and synthetic ash mixtures, measurements of shear properties and impedance spectroscopy were performed. Furthermore, exposure tests in air and flue gas were conducted in the temperature range between 600 to 1,200 °C to evaluate the influence of different parameters on the crystalline phase compounds and microstructures of the brown coal ashes and synthetic ash mixtures. The exposed samples were compared among each other and with corresponding ash deposits produced in a micro combustion chamber. Another aim of this dissertation is to verify the occurrence of NaOH melt in fouling processes. For this purpose impedance spectroscopy with a special probe was performed in the pilot power plant Niederaußem while firing sodium enriched fouling coal. This research indicates the importance of non-silicate bonded sodium and calcium in fouling processes. The higher their contents are, the higher is the fouling potential of the brown coal. Although the occurrence of NaOH in the boiler can not be directly proven by impedance spectroscopy, the experimental results indicate that it plays an important role in fouling. However, this research shows that silicates reduce the fouling potential of the ashes. Shear property measurements, impedance spectroscopy and the calculation of Na/Si and Ca/Si ratios of 450°C-ashes are applicable methods to predict the fouling potential of brown coals. According to the findings resulting from this dissertation it is 450°C-ashes with an Na/Si ratio > 2 and a very high Ca/Si ratio that show fouling behaviour.

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