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Introduction

The sintering process represents a proven agglomeration technology for fine ores and iron containing recycling materials. The main challenge is a low cost and energy efficient treatment of raw materials and residuals for the production of a suitable input material for an iron production in the blast furnace process.

Project 1.1 focuses on the formation of air pollutants during the sintering process as well as on the utilization of metallurgical dusts and sludge’s concerning the influence on waste gas composition. In context with the pollutant entry, these aspects are very important in case of a waste gas recirculation on the sinter strand. Furthermore research activities from the prior K1-MET funding period showed the dependence of sinter cooling conditions and the cooling step respectively on physical sinter quality and process productivity. In this context, the main relations with sinter mineralogy will be analysed in the course of the current project.

Objectives and Motivation

  • The knowledge of pollutant formation mechanism in dependence on sinter operating conditions
  • A generation of emission control strategies for the sintering process
  • The context between mineralogy, petrography and physical properties in dependence on sinter cooling conditions
  • An assessment as well as a concept development of a sinter cooling air recirculation on the sinter strand

Methodology

Modelling activities will be applied to describe gas-solid interactions during the sintering process for a quantification of gas flow through the sinter bed. The information concerning bed permeability represents an important impact factor on energy release and pollutant formation in dependence on the operating conditions. A model evaluation will be performed by means of laboratory experiments supported by off-gas measurement campaigns at an industrial sinter plant.

Further research activities focus on lab-scale sintering experiments under usage of a sinter pot test rig representing a proven possibility to evaluate changing sinter process operating conditions concerning off gas formation and, to a certain extent, sinter quality and productivity. Beside this, a lab-scale pelletizing plant will be operated offering the possibility to cool down hot sinter in different ways to investigate the sinter cooling conditions.

The Chair of Geology and Economic Geology from the Montanuniversität Leoben uses the software package VisuMet for mineralogical investigations of microscopic sinter probe images. VisuMet detects the mineral phase’s limonite, hematite and magnetite as well as the glass content and the porosity of iron ore probes. It is believed that the glass composition as well as the sinter porosity have an influence on sinter strength and reducibility. The image processing software delivers cost-efficient important information concerning the sinter reduction properties. Standardised laboratory methods are used for a further investigation of sinter quality at the Montanuniversität Leoben (Chair of Ferrous Metallurgy). Specific parameters are determined such as tumbler strength, RDI (Reduction Degradative Index i.e. sinter decomposition due to a reducing treatment) as well as reducibility. In addition to this, the specific surface will be determined using the Brunauer-Emmett-Teller gas adsorption method. All these quality parameters should be correlated with the results of the above described petrographic investigations.

The sum of theoretical aspects, modelling and simulation activities, laboratory experiments and sinter pot tests in combination with real plant experiments represents an extensive investigation  with the final goal of a sinter process development.

Results and application

Fundamental knowledge concerning the pollutant formation during the sintering process are expected from the laboratory experiments and measurement campaigns at industrial plants with respect to changing operating conditions such as sinter mix composition (e.g. basicity, fuel content) and suction air humidity. This information should be used for a generation of process control measures and strategies for a reduction of emission release. The measures should be finally applied at a large industrial sinter plant.

Furthermore, it is expected that the results of the microscopic sinter probe analysis deliver correlations between mineralogy, petrography and physical sinter properties. The gained knowledge can be used to further develop the sintering process providing a basis for an evaluation of the cooling conditions concerning the sinter quality. This information can be applied for a better control of the cooling process step.

Beside this, a recirculation of cooling air on the sinter strand will be evaluated without causing negative effects on sinter quality or the process itself respectively. Such a recirculation step can represent an economic solution of waste air utilization for sinter plants without a cooling air dedusting system. Additionally the research results should be used for a sinter cooling optimization to develop an efficient cooling step with simultaneous maximised heat recovery.