|عنوان فارسی مقاله:||کنترل کوره انفجار با استفاده از درجه حرارت های مایع و ویسکوزیته پسماند ها با محاسبات تعادل فازی|
|عنوان انگلیسی مقاله:||Blast Furnace Control using Slag Viscosities and Liquidus Temperatures with Phase Equilibria Calculations|
|رشته های مرتبط:||مهندسی مکانیک، مهندسی مواد، شیمی و فیزیک، فیزیک کاربردی، فیزیک هسته ای، مکانیک سیالات و شیمی معدنی|
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Physicochemical properties of slag, such as viscosity, are important process variables of the blast furnace process, and of significance when studying the process and applying the knowledge in management and optimization. Slag viscosity is a transport property that relates to the reaction kinetics and the degree of reduction of the final slag1. Slag viscosity also determines the slag– metal separation efficiency, and subsequently the metal yield and impurity removal capacity. In operation, the slag viscosity is indicative of the ease with which slag could be tapped from the furnace, and therefore relates to the energy requirement and profitability of the process. The ability to predict the slag viscosity and liquidus temperature has the potential to optimize the analysis and decision-making control of blast furnaces, replacing the use of rules of thumb pertaining to slag compositions. Efforts have been made in the past to measure and model viscosities for different slag systems, of which the results of many can be found in published literature1,2. Some of these models correlate the effect of the different components very well, 310 but often do not consider the effect of the adjusted liquid slag composition, and precipitation of solids at lower temperatures. In the typical slag system of interest, an increase in basicity not only leads to a lower liquid viscosity due to broken silicate bonds, but also increases the likelihood of solids precipitation, thereby increasing the viscosity. Phase equilibrium calculations are used to firstly determine the liquidus temperature, and then to estimate the amount (if any) of precipitated solids. For multiphase slags, the predicted amount of solids is to be used to adjust the viscosity predicted by the liquid viscosity model. To optimize the process using the developed model, the first step would be to apply the models to historical data to generate a performance baseline and determine targets for improvement. In this work, the aim was to develop liquidus temperature and effective-viscosity models and application methodologies, to illustrate how they could be used for a blast furnace, to monitor performance and drive optimization.
Overview of slag viscosity and liquidus temperature
Molten slag can be classified as a Newtonian fluid with the shear viscosity being independent of the shear rate, and therefore named dynamic viscosity1. Viscosity is largely influenced by bonding and the degree of polymerisation2, with SiO2 and Al2O3 contributing to higher viscosities with their highly covalent bonds1. In contrast, monoxides such as CaO and MgO exhibit ionic behaviour, leading to the destruction of silicate chains and lowering the viscosity2. These arguments only hold for the liquid slag-phase system, and in the multiphase system, an increase in monoxides leads to higher activities of solid phases and possible solids precipitation, which would increase the effective (observed) viscosity. It should also be noted that, in the typical operation where it is possible to alter the slag composition, changes in the composition would have opposing effects. For example, the achievement of lower viscosity at higher basicities will likely be associated with the adverse effect of increased liquidus temperature. In addition to the effects on physicochemical properties, the slag basicity also influences the sulphur (and to some extent the phosphorus) removal capacity of the slag, and the silicon content of the hot metal; higher basicities lead to higher sulphur values in the slag and lower silicon values in the metal.
The models developed are based on phase equilibrium calculations, using thermodynamic data set up for specific metallurgical systems. To follow is the definition of the metallurgical system for the material of interest, considering the typical operating region of compositions and temperatures of blast furnace slags. 311 The viscosity and liquidus temperature models developed were configured and optimized specifically for blast furnace type slag. These slags contain predominantly SiO2, Al2O3, MgO, and CaO, with smaller amounts of FeO, MnO, TiO2, Na2O, K2O, and S that also influence the physicochemical properties. The temperature of the slag also influences the phase equilibria and subsequently the values of physicochemical properties. Table I lists typical ranges and values for the chemical composition and temperature of blast furnace slag. The slag temperature values are estimates based on the assumption that this type of slag is approximately 100°C hotter inside the furnace than the tapped metal temperature. These values listed here can vary greatly between plants due to variances in the feed material.