Theoretical evaluation on merits of the processes of gas-based shaft furnace with top gas recycling

To achieve the solution to inadequate utilization of chemical potential of the reducing gas in gas-based shaft furnace, the different innovative processes with top gas recycling and oxygen blowing are established and the energy efficiency and CO₂ emission of each process are numerically analyzed through a validated process model based on the conservations of mass and heat. The results show that in the proposed TGR1, TGR2, and TGR3 cases, the demand of the fresh hot reducing gas decreases by 63.77, 57.13, and 55.85%, respectively, meanwhile the requirement of the corresponding sensible heat shows the same tendency. However, the consumption of energy in each process increases by 14.04, 17.17, and 24.65%, respectively, because of the additional cost of the gas reforming and preheating. The emission of CO₂ for TGR1 decreases by 15.35% while the one for TGR2 and TGR3 increases by 0.16 and 3.15%, respectively. Therefore, the proposed top gas recycling technology for the gas-based shaft furnace process cannot lower the consumption of energy from the whole process view. In the case with oxygen blowing of 4.49 Nm³ tDRI^-1, the gas consumption decreases by 8.54% and the reduction potential of top gas decreases by 13.74%. Additionally, oxygen blowing process can essentially reduce both the CO₂ emission and energy consumption. To achieve the solution to inadequate utilization of reducing gas in gas-based shaft furnace, the different innovative processes with top gas recycling and oxygen blowing are analyzed through a process model. The results show that top gas recycling has a limited effect on improvement of furnace performance. The oxygen blowing technology can reduce both the CO₂ emission and energy consumption.