Influence of the properties of blast furnace slag on cast iron heating at pulverized coal injection

Maksym Kuznetsov,Natalia Valuyeva,Gennady Kryachko,Vladimir Polyetaev

doi:10.15587/1729-4061.2018.122970

Abstract

In the course of the studies at two industrial blast furnaces, we established a change in the characteristics of slag mode and cast iron heating, resulting from the transition to the pulverized coal fuel injection with a decrease in basicity of CaO/SiO 2 slag from 1.16 to 1.10 and from 1.20 to 1.12 units. It was shown that depending on a particular influence of alumina and magnesia in the slag composition, as well as on their ratio, a decrease in slag basicity can be accompanied by both an increase and a decrease in viscosity. During the research, the dependence between slag viscosity at the temperature of 1,400 °C and chemical heating of cast iron heating at the outlet was established. According to obtained data, an increase in slag viscosity by 0.1 Pа∙s was accompanied by an increase in silica concentration in cast iron by 0.08–0.1 %. The relation of physical heating of metal with slag basicity and stoichiometry was established. It was shown that a decrease in basicity of (CaO+MgO)/SiO 2 by 0.1 units led to a decrease in cast iron temperature by 30 °C. Such a substantial effect of basicity of metal heating indicates the need to take this influence into account not only to control the blast furnace process, but also to state the thermal balance of steel smelting. It was shown that in the studied range of slag compositions, the influence of magnesia on heating of cast iron is limited. A slight influence of MgO on physical heating of metal was pronounced at a magnitude of the ratio Al 2 O 3 /MgO that is close to unity. Results of present research could be used to improve control over blast furnace smelting in terms of taking into consideration slag influence on heating of cast iron.

Highlights

The transition of blast furnaces in Ukraine to the injection of pulverized coal fuel (PCF) was, as a rule, accompanied by a change in slug mode
We established a change in characteristics of slag practice and cast iron heating, resulting from the transition to injection of pulverized coal fuel with a decrease in slag basicity from 1.16 to 1.10 and from 1.12 to 1.20 units
An increase in slag viscosity by 0.1 Pа⋅s was accompanied by an increase in silica concentration in cast iron by 0.08–0.1 %

Summary

Introduction

The transition of blast furnaces in Ukraine to the injection of pulverized coal fuel (PCF) was, as a rule, accompanied by a change in slug mode Such a change was often characterized by a decrease in slag basicity both in relation to CaO/SiO2 (C/S) and to (CaO+MgO)/SiO2 (C+M)/S. As shown in paper [1], there was a shift in the slag mode in the direction of formation of semi-slags, with a decrease in temperature of the produced cast iron. In the course of analysis of changes in slag mode of the blast furnace with a volume of 1,386 m3 at Dneprovsky Me tallurgical Plant (DMP, Ukraine), it was shown that the transition to semi-slags was accompanied, due to the injection of PCF, by a decrease in melting temperatures of slag melts [1]. It should be recognized that the problem on enabling a rational slag mode at transition of furnaces to PCF injection still exists, thereby the search for the ways to solve it is important

Literature review and problem statement

The aim and objectives of the study

Findings

Conclusions