How blast rate variation affects dynamic in-furnace behaviours and energy consumption of an industrial-scale blast furnace: A transient-state CFD study

Blast rate is a key operating parameter affecting the stability and energy consumption of ironmaking blast furnaces (BFs). Understanding the transient in-furnace behaviours resulting from blast rate variations is crucial for optimising BF operations and enhancing energy efficiency in the steel industry. The unplanned change in blast rate may occur sometimes, for example, due to the mechanical failures of blast supply system. However, the time-dependent evolution of in-furnace phenomena due to blast rate variations remains poorly understood. This work employs a transient BF model to numerically investigate the dynamic in-furnace behaviours following blast rate changes and explores potential countermeasures, providing valuable insights for BF operators to maintain furnace stability and performance under varying conditions. First, the impact of blast rate changes on in-furnace phenomena and key performance indicators are studied. The results show that when the bosh gas index ψ decreases by 7 m/min, the top gas temperature decreases by ~67 K and the gas utilisation efficiency increases by 1.8 % within 20 h. If ψ increases by 3 m/min, the top gas temperature increases by 23 K, but the top gas utilisation efficiency decreases by 0.7 % in 20 h. Then, it is found that it takes nearly 20 h to recover the in-furnace phenomena after the blast rate is recovered from shortage and if blast rate is insufficient, increasing oxygen enrichment ratio from 1.5 % to 5 % improves the raceway temperature by 170 K in 40 h. • A transient blast furnace model is used to study the dynamic effects of blast rate change. • The in-furnace phenomena evolution after a change in the blast rate can be captured. • The time needed to reach new stable state when blast rate is changed can be predicted. • Two countermeasures to compensate for blast rate shortage are studied. • Fuel consumption and liquid iron productivity are compared under each situation.