Influence of multiple factors on the alkali metal enrichment in blast furnaces by a thermodynamic model

Abstract

Alkali metal circulation enrichment occurs in blast furnaces, which is harmful to the blast furnace. The amount of enrichment helps to quantify the effect of alkali metals on blast furnace production, but it is not possible to directly measure the actual alkali metal enrichment in blast furnaces for technical reasons. On the basis of a thermodynamic model, FactSage was used to calculate the effects of alkali loading, slag basicity, MgO content in the slag and Al 2 O 3 content in the slag on the alkali metal enrichment in the blast furnace. Quantitative relationships among various factors and the enrichment were obtained, and the degree of influence of various factors on the amount of enrichment was determined. The basicity B 2 of the slag was the key factor for enrichment. With an increase in the slag basicity of 0.1, the enrichment of K and Na increased by 5.3 and 1.6 kg/tHM, respectively.

The Quantitative Effect of Blast Furnace Slag Composition and Temperature on the Kinetics of Potassium Evaporation

“…On the other hand, analyses of materials in a chilled and dissected BF, with an inner volume of 128 m 3 , indicated that certain positions in the BF had 50 times higher alkali contents than the charged materials. [6] However, the reported circulating load of 23 kg alkali/tHM from a dissected commercial BF [18] indicates that, when considering positions other than the peak alkali analyses, the value of the circulating load resembles that presented by Geerdes et al [5] High circulating loads of alkalis in the BF may cause scaffolding, [2,9,12,[19][20][21] which reduces the working volume and circumference of the shaft. Furthermore, scaffolding may result in irregular burden descent and, in extreme scenarios, hanging of the burden and slips.…”

“…Similar observations have been reported, but specifically for the alkali content, in other publications as well. [2,6,11,12] This trend suggests that alkali loads may increase in the future. Another factor that drives the alkali load to higher levels is the increased recycling of in-plant residues.…”

“…Another detrimental effect of alkalis is the increasing refractory wear, [2,6,9,11,12,[19][20][21][22][25][26][27] which necessitates more frequent relining. More specifically, alkalis penetrate the carbon blocks and cause crack formation.…”

“…Due to the detrimental effects of high alkali loads in the BF, several strategies have been proposed and employed in order to mitigate accumulation in the BF. These strategies include (i) lowering the input of alkalis, [1,2,4,8,12,[20][21][22] (ii) maximizing the quality of sinter and coke, [20] (iii) charging coarse dunite as an alkali removal agent, [28] (iv) increasing the slag rate, [17,21] and (v) altering the slag composition. [4,[7][8][9]17,[19][20][21][22]29] In addition, less realistic suggestions for modern BF ironmaking have been proposed and operated, such as charging CaCl 2 as an alkali cleaner [20][21][22] and reducing in-plant recycling via the sinter.…”

“…[4,[7][8][9]17,[19][20][21][22]29] In addition, less realistic suggestions for modern BF ironmaking have been proposed and operated, such as charging CaCl 2 as an alkali cleaner [20][21][22] and reducing in-plant recycling via the sinter. [20] The effect of lowering the input of alkalis into the BF is significant, e.g., the thermodynamic model developed by Chen et al [12] suggested that increasing the potassium or sodium load by 1 kg/tHM results in an increased circulating load by 27.7 and 15.5 kg/tHM, respectively. Furthermore, Jiao et al [6] calculated that increasing the potassium and sodium load by 1 kg/tHM increases the coke rate by 13.99 and 6.25 kg/tHM, respectively.…”