Book/Dissertation / PhD Thesis

FZJ-2017-08536

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Einfluss der Kristallisation auf das Fließverhalten oxidischer Schmelzen

Seebold, S. (Corresponding author)FZJ*

2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-268-9

Please use a persistent id in citations: http://hdl.handle.net/2128/16356

Abstract: Numerous technical applications in the energy and metallurgical industries demand a fundamental knowledge of the flow of slags. In particular, the operation of an entrained flow gasifier is challenging as the slag has to be reliably discharged. The slag consists of unburned inorganic matter, usually oxides. Crystallization in this oxide melt influences the flow behavior of the slag because of the occurring precipitates. In this study the mechanisms and impact of crystallization on the flow of oxide slags were investigated. For this purpose, isothermal viscosity measurements were conducted on fossil and renewable solid fuel slags in order to examine the rheological evolution over time caused by the crystallization. It has been demonstrated that the evolution of viscosity of a sub-liquidus melt depends strongly on time, as well as on temperature and composition. Using a rotational high-temperature viscometer, it was found that the crystallization during flow could be separated into three time regimes: a lag-time, in which the undercooled melt behaved as an Arrhenius-liquid; the kinetic-driven crystallization accompanied by an increase of the viscosity; and, finally, the rheological equilibrium that is represented by a constant viscosity. Furthermore, an increase of viscosity caused by crystallization was accompanied by a shift from Newtonian to non-Newtonian flow; here, shear thinning flow indicated the existence of precipitates. SEM was used to examine the crystalline precipitates. The evolution of flow was used to create time-temperature-transformation diagrams. It was observed that an increase of the degree of supercooling decreases the incubation as well as the crystallization period. The crystallization of the oxide melt follows the classical theory of crystallization. Moreover, it was shown that the change of viscosity might be used as morphological information to describe kinetic parameters. The conclusions from the experimental results regarding the influence of crystallization on the flow of oxide melts were transferred to an empirical model. The model considers the physical influence of the crystals and the chemical change of the bulk composition caused by the crystallization. Therefore, the concept of the resulting relative viscosity was introduced, in order to describe the physical and chemical effects of crystallization. The evolution of viscosity from the metastable to the equilibrium state was described by a kinetic theory. The results of the model correlate well with the experimental observations.

Note: RWTH Aachen, Diss., 2017

---

Contributing Institute(s):

1. Werkstoffstruktur und -eigenschaften (IEK-2)

Research Program(s):

1. 111 - Efficient and Flexible Power Plants (POF3-111) (POF3-111)

Appears in the scientific report 2017

---

Database coverage:
;

---