NUMERICAL ANALYSIS ON BLAST FURNACE LOW CO_2 EMISSION OPERATION WITH COKE OVEN GAS INJECTION

摘要

In recent years, the iron and steel industry has been faced with more and more pressure in saving energy, reducing CO_2 emission and environmental burden. The process of injecting coke oven gas (COG) into blast furnace is one of the effective measures for the iron and steel industry to achieve low-carbon ironmaking, energy saving and emission reduction. Numerical simulations on the injection of COG into blast furnace through tuyere are performed in this study by means of raceway mathematical model, multi-fluid blast furnace model and exergy analytical model. With the increase of COG injection, the simulation results are shown as follows: (1) The bosh gas flow rate is increased, while raceway temperature is decreased. Through reducing blast flow rate and enhancing oxygen enrichment to do thermal compensation for raceway, the conditions of raceway can be sustained stable. Meanwhile the volume of raceway is decreased. (2) The in-furnace concentrations of CO and H_2 show increasing; the utilization rate of CO is enhanced, while the utilization rate of H_2 tends to decrease. But the proportion of H_2 in indirect reduction gives a raised tendency, and the reduction rate of burden is accelerated. Due to the location of cohesive zone moving down, the thickness getting thinner and the pressure drop reducing obviously, the permeability of blast furnace gets better. The productivity shows a remarkable increase, for 152.34 m~3/tHM COG injection, improves by 26.36%. The silicon content of the hot metal decreases, and the quality of the hot metal improves, for 152.34 m~3/tHM COG injection, the silicon content decreases from 0.26% to 0.05%. Coke rate, total reducing agent rate and carbon emission rate show a considerable decrease, for 152.34 m /tHM COG injection, decreases by 13.49%, 4.12% and 17.54%, respectively. (3) The internal and external exergy loss of furnace both are decreased. The thermodynamic perfection degree and exergy efficiency are increased, compared with no COG injection, which are increased from 90.23% to 92.65% and from 53.39% to 54.25% respectively. The chemical exergy of blast furnace top gas is increased, compared with no COG injection, which is increased from 4.60 GJ/tHM to 4.97 GJ/tHM. So, it is important to strengthen the recycling of top gas.