Hochtemperaturreaktionen in Veraschungsrückständen von Grenzbereichskohlen

Luhmer, René; Stanjek, Helge (Thesis advisor); Roth, Georg (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

Because adjacent sediments (sands and clays) will be partially excavated during the extraction of lignite in the rhenish district, the chemical and mineralogical compositions of steam coals and their combustion residues are changing. As a result it is possible that these contaminated lignites show other characteristics during combustion in relation to the tendency of forming unwanted accumulations in the boilers, like sinter or slacks. To investigate the differences of the behaviour during combustion between contaminated and pure lignites, different lignites from Garzweiler mine, Hambach mine and Inden mine were sampled from the border areas between lignite and sediments for laboratory experiments. The immediately adjacent sediments were also sampled. The chemical and mineralogical compositions as well as the ash conversion temperatures of all samples were determined. For temperature and time dependent experiments, lignite residues were homogeneous divided and partially mixed with the sediments, who were also incinerated before these experiments. The mixtures between lignite and sediment incineration residues are made to simulate contaminated lignites as if a bucket wheel excavator also digged a certain thickness (10 and 20 cm) of the adjacent sediment. Those mixtures were also used to run temperature and time dependent experiments.All 815 °C incineration residues contain quarz and anhydrite. With rising temperature the formation of cristobalite out of quartz is revealed. The amount of anhydrite decreases with increasing temperature and calcium is mostly used for the fomation of silicates. Quartz and other silicates can be considered as a source of silicon. Samples without notable amount of aluminium show the formation of ternesite. Is aluminium available the generation of anorthite is preferred. Other silicates, builded during the tempering experiments, are for example larnite, akermanite, diopside, wollastonite, pseudowollastonite and hauyne respectively nosean. Because of the addition of sediments either the content of quartz (for sands) or the amount of X-ray amorphous components (for clays) rises significantly. By adding sand either the content of cristobalite is increased at high temperature or the content of silicates at all. By adding clays the identifcation of mullite can be observed next to a high amount of amorphous constituents. With rising temperature the amount of mullite increases while the amorphous constituents decreases.The simulated decomposition reactions, solid-solid-reactions, liquid-solid-reactions up to completely melting from this study are able to reflect the analytical documented mineral reactions and the behaviour of the formation of deposits in lignite fueled boilers from RWE Power AG. Mineralreactions, taking place in dependence of the fired steam coals, could get assigned to particular temperatur ranges. Hereby, it is possible to deduce the formation temperature of deposits in boilers by knowing the sampling location.

Institutions

• Division of Earth Sciences and Geography [530000]
• Petrology and Fluid Processes Teaching and Research Unit [541320]