HMB-CFD study of oxygen-enriched pulverised coal combustion in an ironmaking blast furnace

Abstract

Pulverised coal injection (PCI) into blast furnace (BF) is a dominant technology for partial coke replacement and lowering production cost, and high oxygen enrichment is a recent promising technology for further increasing coal combustion and thus increasing pulverised coal rate (PCR) and lowering emissions. In this paper, a heat and mass balance (HMB) model and a three-dimensional computational fluid dynamics (CFD) model of pulverised coal flow and combustion in the lower part of the BF are combined to investigate the effect of oxygen enrichment on coal combustion in terms of operational feasibility and coal combustion efficiency, where the injection schemes such as blast volume, oxygen enrichment, PCR are designed using the HMB model; and the local detailed coal combustion is studied using the CFD model, including the effect of oxygen enrichment and PCR on in-furnace phenomena including gas-solid flow, temperature field and particularly, coal burnout. The CFD simulations reveal that the combustion efficiency is the result of the combined effects of oxygen enrichment and PCR. The high oxygen enrichment in the blast enhances gaseous combustion and coal combustion. The high PCR needs more time and distance for preheating and devolatilisation, which was detrimental to coal combustion near tuyere; on the other hand, more particles in combustion release more heat which is beneficial to the continued combustion of unburned particles. As a result of the combined effects, the inflection points could be found in some key phenomena, including gas temperature, particle temperature, O2 mass fraction, etc. This HMB-CFD study implies that it is highly necessary to consider both feasible operation windows and the detailed impacts of the oxygen enrichment on coal combustion under industrial BF conditions; and thus should be used in future PCI investigations.