Experimental Investigation and Modeling of the Viscosity of Oxide Slag Systems

Numerous technical applications in the energy and metallurgical industries demand a fundamental knowledge of the flow of slags. Besides temperature and composition, which determine the internal structure of an oxide melt, crystallization in the slag significantly influences its flow behavior. Therefore, not only the temperature-dependent viscosity of fully liquid oxide melts was determined using a rotational high-temperature viscometer but also isothermal viscosity measurements were conducted, in order to examine the rheological evolution over time caused by crystallization. The crystallization behavior during flow can be separated into three time regimes: a lag-time, in which the undercooled melt behaves as an Arrhenius liquid; the kinetic-driven crystallization; and, finally, the rheological equilibrium that is represented by a time-invariant viscosity plateau. To model the viscosity of oxide slags, in a first step, a self-consistent thermodynamic database for the system SiO2–Al2O3–CaO–MgO–FeO x –K2O–Na2O–P2O5–SO x has been established. The Gibbs energy of the liquid phase has been modeled using a non-ideal associate solution description. In a second step, an Arrhenius-type model for the calculation of viscosities of fully molten slags has been developed. The model is based on the same structural units, i.e., the associates, as the one for the Gibbs energy of the melt. In a third step, the influence of crystallization, which not only transforms the liquid into dispersion but also usually changes the composition of the residual liquid, on the viscosity is considered

Numerical Modeling Capabilities for the Simulation of Toxic By-Products Formation in Combustion Processes

A collaborative research program has been initiated to study the emissions of a wide variety of chemical species from stationary combustion systems. These product species have been included in Clean Air act legislation and their emissions must be rigidly controlled, but there is a need for a much better understanding of the physical and chemical mechanisms that produce and consume them. We are using numerical modeling techniques to study the chemical reactions and fluid mechanical factors that occur in industrial burners. We are examining systems including perfectly-stirred and plug-flow reactors, and diffusion flames in these modeling studies to establish the major factors leading to emissions of these chemicals. © 1994, Taylor & Francis Group, LLC. All rights reserved