Dr. GS Mahobia

Abstract:

The iron and steel industry contributes about 7 % of the total carbon dioxide emission globally and about 35% of all CO₂ produced in the manufacturing sector[1, 2]. About 1.9 tons of CO₂ is produced per ton of crude steel [3, 4]. Carbon from coke or coal is the primary source of heat energy in blast furnaces and rotary hearth furnaces used worldwide. Carbon in the form of graphite electrodes is also used in electric arc furnaces. Thus, it is easy to comprehend that carbon is used extensively in the entire steel making route, making it a high contributor to global CO₂ production. Using hydrogen gas as a reductant in place of carbonaceous material offers significant advantages like zero greenhouse gas (GHG) emissions, faster reduction at lower temperatures, and the absence of a complicated boudouard (C-O) reaction. Most hydrogen reduction studies have been carried out on commercial-grade iron ores containing more than 65% Fe, and limited studies are available on the hydrogen reduction of low-grade ores containing less than 50% Fe [3, 5]. 

The hydrogen reducibility of pellets made from a low-grade multimetallic magnetite ore (Fe content ~45%) was investigated in the present study. Pellets were reduced in a horizontal tube furnace at temperatures ranging from 973 K to 1173 K for 1 to 60 minutes. Pure Hydrogen (H₂) gas (99.9%) at three flow rates of 0.25 L/min, 0.5 L/min, and 1 L/min were blown during the reduction process. A maximum reduction degree of 93.55%, metallization ratio of 0.925, and H₂ gas utilization of 8.92% were obtained at a temperature and a reduction time of 1173 K and 60 minutes, respectively. In order to optimize the hydrogen utilization, a reduction temperature of 1173 K, a reduction time of 45 minutes, and a gas flow rate of 0.25 L/min were selected, resulting in a reduction degree and metallization ratio of 89% and 0.86, respectively. The cold crushing strength (CCS) of the reduced pellets initially decreased and then increased slightly, exhibiting behavior similar to high-grade ores. SiO₂, Al₂O₃, and MgO are found to control the porosity of the pellets, which directly affected the CCS and reducibility of the pellets.