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

Abstract

Counter current flow reactors are the most efficient metallurgical vessels. This is why the blast furnace (BF) remains since more than 700 years No. 1 aggregate for primary metal production. It is anticipated that also in the future, shaft furnaces operating on this principle will dominate the direct reduction (DR) production. Consequently, the gas permeability is a crucial issue for shaft furnaces. In the BF, required gas permeability, as well as a drainage ability in the dripping zone, is ensured, primarily, by a certain amount and quality of coke.The injection of solid auxiliary reducing agents (ARA) may negatively affect the gas permeability and the drainage ability by two means: decrease of thickness of coke layers due to lower coke rates─and accumulation of unburnt injected particles outside the raceway─in dripping zone (DZ), cohesive zone (CZ), and shaft. Concerning the first reason, the burden-coke layer thickness ratio was increased, for example, from 0.93 for only coke operation to 1.54 while injecting 200 kg t HM À1 pulverized coal (PC) according to the calculations conducted. [1] Effects of layer thickness on the pressure drop in the BF "dry" zone and in the cohesive zone become apparent at increasing Reynolds number and flow rate. [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.Factors affecting the BF operation efficiency while injecting PC can be divided into four major groups: 1) characteristics and conversion behavior of coal and formed char; 2) characteristics of charged materials and liquid products, and their change caused by PC injection; 3) BF operation parameters; and 4) design of tuyere and injection lance.These factors are also considered vital important by the current trend of PC co-injection with hydrogen-containing gases such as coke oven gas [4,5] or pure hydrogen. [6] Chemical, physical, mechanical, and petrographic characteristics of injected coals and their effect on the conversion behavior in the raceway, reducing gas, and heat generation and, consequently, on the coke replacement ratio are well known and summarized in Ref. [7,8] This also applies to the effect of BF operation parameters such as blast temperature, oxygen