Char Formation by Coal Injection and Its Behavior in the Blast Furnace

Abstract

Blast furnace (BF) coal injection became a routine practice among European BFs; roughly, 40% of total energy required for the process is covered by auxiliary reducing agents. Pulverized coal (PC) remains the most commonly used auxiliary reductant. The key trend is increasing PC injection rates; over 200 kg tHM À1 PC on an annual basis is no rarity any more. Despite numerous measures for intensifying the coal conversion in the raceway, [1] it is hardly possible to combust such a high amount of coal within a very short residence time of few tens of milliseconds. Recent computational fluid dynamics calculations showed that at PC injection rate of 240 kg tHM À1 , about 50% of the coal amount entering the raceway may leave it as so-called char. [2] Another theoretical study from 2011 calculated a maximum PC injection rate of 190-210 kg tHM À1 for some BFs, considering that no ash deposition nor change in the gas flow distribution due to unburnt coal fines trapped in the coke bed takes place. [3] The following types of coal residues appear depending on different conditions and stages of its formation (Figure 1): 1) devolatilized coal particles (after light gases and tar have been released); 2) pyrolyzed (partly or completely) particles (caused by the thermal decomposition of the organic matter); and 3) not completely gasified particles (residues). Char formation, transportation, and behavior outside the raceway may significantly affect the BF process both negatively with respect to process stability and positively by increasing the combustion efficiency by possible consumption of char. The knowledge on these phenomena was limited because the main efforts over the last few decades were focused on the complete conversion of PC within the raceway. A char morphology system was introduced for the characterization of char types. [4] However, few studies are devoted to the

A Comparison of Laboratory Coal Testing with the Blast Furnace Process and Coal Injection

“…Many furnaces achieve coal injection rates of 200 kg/tHM (kg/tonne of hot metal) [7]; however, the scale and nature of this process can result in variations in characteristics such as temperature and pressure [8]. The impact of this can be localised hot/cold spots, which can cause damage to the furnace lining or result in variations in the rate of raw material consumption.…”

Effect of Carbonaceous Residues on the Blast Furnace Operation Efficiency by PC Injection

“…Figure 9 shows exemplary three images of the temperature distribution at PC rate of 200 and 100 kg t HM −1 , and when injection was stopped. Processing the results of several measuring campaigns at one BF conducted at three tuyeres indicated an increase in temperature by 35–80 °C for different ROIs (regions of interest [ 3 ] ) when reducing pulverized coal injection (PCI) from 200 to 100 kg t HM −1 , and up to 210 °C when stopping the injection of 200 kg t HM −1 PC. [ 18 ] At another BF, the measured by the TVC temperature became in some cases by 50–80 °C higher when stopping the injection of 200 kg t HM −1 PC.…”

“…Left: coal accumulation in the cold model (dark polyethylene balls); right: char holdup calculated in Ref. [3] by the mathematical model assuming that char is transported by the gas flow and is chemically inert. Adapted under the terms of the EUR 29548 license, [ 3 ] Copyright 2019, European Commission.…”

“…[3] by the mathematical model assuming that char is transported by the gas flow and is chemically inert. Adapted under the terms of the EUR 29548 license, [ 3 ] Copyright 2019, European Commission.…”

“…[ 2 ] Concerning the second reason, the mathematical modeling showed that char accumulates mainly in cohesive zone, deadman, and hearth. [ 3 ] The effect of accumulation of unburnt PC on the specific pressure drop is examined experimentally in this work.…”