(521et) Computational Fluid Dynamics Modeling of Industrial Scale Direct Reduced Iron Reforming Process

In the iron and steel-making process, the direct reduced iron (DRI) is the very first step that uses CO and H₂ to reduce iron ore and therefore contributes to fewer CO₂ emissions than the conventional blast furnace process. The CO and H₂ required for the DRI process are generated through the steam and natural gas reforming in reformer tubes filled with catalyst particles. The bottom-fired burners in the reformer undergo combustion and provide energy to the tubes by radiation and promote the endothermic reforming reactions to produce reducing gas (i.e., CO and H₂). These gases are transported to the shaft furnace for iron-ore reduction. Therefore, the DRI reforming process plays an essential role for DRI production in the shaft furnace by supplying reducing gases of desired compositions, flow rate and temperature. An understanding of the influence of (i) process operating conditions of burner and tube side and (ii) catalyst loading profile on the reduced gas quality and temperature is important to further improve the efficiency of the reforming process.

In the present work an integrated 3D-CFD model of the DRI reforming process: (i) burner and tube coupled model that includes multicomponent gas flow in burner and tubes, (ii) heat and mass transfer due to combustion and radiation on the burner side, and (iii) endothermic reforming reactions on the tube side is developed. Figure 1 (a) shows the reformer geometry considered in the present work. It consists of 6 reformer tubes and 3 main burners present at the bottom between the tubes (see Figure 1 (a)). On the burner side, fuel gas and combustion air are given as input and undergo combustion resulting in higher temperature and consumption of O₂ (see Figure 2 (a) and 2 (b)). In the tube, the presence of the catalyst particles influences the flow field and the pressure drop. A variable radial porosity profile is generated from rigid body simulations and mapped into the tube domain. The pressure drop on the tube-side due to the presence of catalyst is calculated through porous media approach. In the tube-side, due to steam-methane reforming the mole fractions of CH₄ and H₂O decreased and, CO and H₂ increased from bottom to the top of tube (see Figure 2 (c)-(f)). Further, the model predictions of the outlet mole fraction and temperature are validated with the plant data for different burner and tube inlet operating conditions. The developed CFD model can be used to further investigate the effects of the (i) process (tube and burner inlet operating conditions) and (ii) design conditions (tube dimensions, catalyst loading profiles) on the tube wall temperature and reduced gas quality.