• Pichler, Anton
• Hauzenberger, Franz
• Thaler, Christoph
• Schenk, Johannes
• Stocker, Hugo

Abstract

Alkali metals are generally known as harmful elements for ironmaking processes. Although a high ratio of the input is discharged by the slag during tapping, small amounts of potassium and sodium are evaporated into the furnace from the slag phase. Furthermore, the thermochemical and physical properties lead to an undesirable behavior. The formation of alkali compounds in the blast furnace is determined by the oxygen potential and the temperature. This two parameters change over the blast furnace height, consequently the alkali compounds undergo oxidation and reduction as well as melting, solidification, evaporation and condensing. This leads to the formation of a circulating movement of alkalis. Enrichment in specific zones of the blast furnace and further destructive consequences are direct results of this alkali circle: for instance the formation of scaffolds, an increase in the dust emission, higher coke consumption, higher abrasion of the refractory and significant changes in the process gas flow. Operators of blast furnaces have two methods to reduce the negative effects of alkalis. One way, which is common for most operations, is the use of input materials with a low content of K and Na. The allowable alkali load for modern blast furnaces in western countries is lower than 4 kg/t hot metal[1]. This is mainly achieved by high quality iron ores and coal grades with a low ash-content. Another way is the optimization of process parameters, especially of the blast furnace slag. Lower tapping temperature as well as a low slag basicity can lead to higher output ratios of alkalis by the slag phase. Also higher masses of slag lead to an increased discharged of alkalis by tapping[1]. Equally the amount of circulating alkalis is lowered and the harmful effects are reduced. To determine the specific effects of slag properties on the circulation and enrichment of potassium and sodium, an alkali model for ironmaking reactors was developed. It enables the correlation between slag basicity, temperature and further process parameters with the alkali flow in the reactor and helps to get knowledge about fundamental reactions of K and Na inside the blast furnace. Also a prediction of the alkali distribution and enrichment in connection with the variation of slag properties can be done.

Topics

• impedance spectroscopy
• compound
• phase
• Oxygen
• Sodium
• Potassium
• iron
• refractory
• evaporation
• solidification