SUB-LIQUIDUS RHEOLOGY OF COAL SLAGS UNDER GASIFICATION CONDITIONS

摘要

Numerous technical applications in the energy and metallurgical industries demand arnfundamental knowledge of the flow of slags. Currently, the flow behavior of a fully molten slag isrndefined as a function of composition and temperature. In contrast, little is known about the changernin flow behavior caused by the crystallization of sub-liquidus melts. We have demonstrated that thernevolution of flow of a sub-liquidus melt depends strongly on time, as well as on temperature. Usingrna rotational high-temperature viscometer to investigate coal slags, we found that the crystallizationrnduring flow could be separated in three time regimes: a lag-time, in which the undercooled meltrnbehaved as an Arrhenius-liquid; the kinetic-driven crystallization; and, finally, the thermodynamicrnequilibrium that is represented by a constant viscosity. Furthermore, an increase of viscosity causedrnby crystallization was accompanied by a shift from Newtonian to non-Newtonian flow; here,rnpseudoplastic flow indicated the existence of precipitations. Our results demonstrate thatrntime-dependency should be considered for an accurate description of flow during crystallization.rnAdditionally, we have verified that thermodynamic methods can be used to describe the structure ofrnpartly-crystallized slags in equilibrium. We showed that precipitations strongly affect the flowrnbehavior of slags and isothermal experiments provided insight into the time effects.