Hydrogen‐Based Direct Reduction of Iron Oxides Pellets Modeling

Abstract

The present study deals with the analyses of the direct reduction kinetics during the hydrogen reduction of industrial iron oxide pellets. Various types of pellets with different percentage of total iron content and metal oxides are examined. They are reduced at different temperatures and pressure (700–1100 °C and 1–6 bar) in hydrogen atmosphere. The reduction behavior is described in terms of time to reduction, rate of reduction, and kinetics constant. All the obtained results are analyzed through the employment of a commercial multiobjective optimization tool to precisely define the weight that each single parameter has on the reduction behavior. It is shown that from the point of view of the processing conditions, temperature is the main factor influencing the time to total reduction. From the point of view of the pellets properties, it is mainly influenced by the total iron percentage and then by porosity and basicity index. Also, the kinetics behavior is largely influenced by the reduction temperature even if it is mainly governed by the porosity and pores size from the point of view of the reduced pellets. The reduction rate is also mainly influenced by temperature and then by iron percentage, gas pressure, basicity index, and porosity.

Reduction of Iron‐Ore Pellets Using Different Gas Mixtures and Temperatures

“…It is well established that an increase of H 2 share in the reduction gas mixture leads to higher reduction rate of the iron oxides. [11,29,30] The same effect was reported for increases in temperature and partial pressure. [11,29] Higher porosity of the pellet improves the gas penetration into the unreacted core, and therefore it enhances reduction rate as well.…”

“…[11,29,30] The same effect was reported for increases in temperature and partial pressure. [11,29] Higher porosity of the pellet improves the gas penetration into the unreacted core, and therefore it enhances reduction rate as well. [11,31] Tortuosity is negatively affecting the reduction rate of the iron-ore pellet.…”

“…[11,31] Tortuosity is negatively affecting the reduction rate of the iron-ore pellet. [29,30] In the recent time, some studies were performed on the topic of iron-ore pellets structure evolution. Ma et al [32] studied microstructure evolution of commercial pellets reduced with hydrogen at 700 °C.…”

Critical analysis of variable atmosphere gaseous reduction of iron oxides pellets

“…In this view, it is easy to establish the real effect of hydrogen as a substitute for carbon monoxide in the direct reduction relating its usage to carbon consumption and carbon dioxide emissions reduction during ironmaking [17]. The hydrogen-based direct reduction process includes multiple types of chemical reactions, solid state, and defect-mediated diffusion (of oxygen and hydrogen species), several phase transformations, as well as massive volume shrinkage and mechanical stress buildup [18,19]. The volume expansion of the pellets is inevitable during the reduction, and the abnormal swelling would cause serious accidents, such as poor permeability, even collapse of the burden [20].…”

Characteristics and applications of iron oxide reduction processes

“…The formation of some hard reducible phases such as fayalite and ferrites, sintering effects as well as α-γ Fe phase transformation (912 o C) are the most signifi cant factors affecting rate minimum phenomena 20 . It has been reported that the Polish Journal of Chemical Technology, 25,4,[81][82][83][84][85][86][87][88][89][90][91][92]10.2478/pjct-2023-0041 The reduction temperature has a great infl uence on the structure of the produced iron and its lattice strain [21][22] . By decreasing the reduction temperature, the pore structure becomes fi ner.…”