CFD simulation of two-phase gas-particle flow in the Midrex shaft furnace: The effect of twin gas injection system on the performance of the reactor

In the present study a mathematical model is developed to examine the effect of dual gas injection system on the distribution of process variables and energy consumption in the Midrex shaft furnace. The developed model was constructed by considering the major chemical reactions and physical structures within the furnace and describes a counter-current moving bed reactor in which hematite pellets are reduced to sponge iron by pure hydrogen gas. Governing equations containing overall continuity, momentum, energy and mass equations are developed for both gas and solid phases in cylindrical coordinate system. Unreacted shrinking core model is implemented to simulate gas-solid reactions in the reactor. The complicated equations are solved by applying finite volume technique. The model is applied to simulate multiphase flow inside the reactor when it is equipped with one and two hydrogen gas intake ports to examine the impact of gas injection arrangement on the process variables. The radial and axial distributions of operational parameters including gas and solid temperature, fractional reduction of iron oxides and hydrogen and water vapor concentration are obtained for both cases. The results indicate that reduction degree and energy consumption are improved by utilizing dual gas injection system.