Abstract
With the recent push towards high injection rate blast furnace operation for economic and environmental reasons, it has become desirable in North America to better understand the impacts of alternate injected gas fuels in comparison to the well-documented limitations of natural gas. The quenching effects of gas injection on the furnace present a functional limit on the maximum stable injection rate which can be utilized. With this in mind, researchers at Purdue University Northwest’s Center for Innovation through Visualization and Simulation utilized previously developed computational fluid dynamics (CFD) models of the blast furnace to explore the impacts of replacing natural gas with syngas in a blast furnace with a single auxiliary fuel supply. Simulations predicted that the syngas injection can indeed reduce coke consumption in the blast furnace at similar injection rates to natural gas while maintaining stable raceway flame and reducing gas temperatures. The coke rates predicted by modeling using similar injection rates indicated an improvement of 8 to 15 kg/thm compared to baseline conditions when using the syngas of various feedstocks. Additionally, syngas injection scenarios typically produced higher raceway flame temperatures than comparable natural gas injection cases, indicating potential headroom for reducing oxygen enrichment in the hot blast or providing an even higher total injection rate.
Highlights
The ironmaking blast furnace (BF) is responsible for 73% of pig iron production inNorth America and represents the largest consumer of energy in the entire mill [1]
The BF is a countercurrent packed bed chemical reactor, where iron ore and coke are charged into the top of the furnace in alternating layers, with the heated air—known as hot blast (HB)—and any auxiliary fuels—such as natural gas (NG) or pulverized coal (PCI)—are blown into the furnace through ports known as tuyeres
Given the limitations of natural gas preheating encountered with gas cracking, syngas injection was investigated as an alternative method of maintaining raceway temperatures while pushing higher injection rates, with the added benefit of serving to reduce carbon emissions from the BF
Summary
The ironmaking blast furnace (BF) is responsible for 73% of pig iron production in. North America and represents the largest consumer of energy in the entire mill [1]. For a furnace operating at high natural gas injection rates, the limited gas residence time in the raceway can result in the inability to combust all injected NG This un-combusted fuel enters the coke bed and decomposes into carbon and hydrogen in a high-temperature and low-oxygen environment, further quenching gas temperatures. Four sub-models were utilized in this study, namely a kinetics-based model for estimating the temperature and composition of syngas generated via various ratios of oxygen and feedstock gases; a CFD model using ANSYS Fluent to simulate hot blast and injected fuel combustion in the BF tuyere; an in-house CFD model to simulate combustion and chemical reactions in the BF raceway; and an in-house CFD model to simulate reduction reactions, cohesive zone formation, and outputs such as coke rate in the BF shaft.
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