Abstract
During recent years, there has been great interest in exploring the potential for high-rate natural gas (NG) injection in North American blast furnaces (BFs) due to the fuel’s relatively low cost, operational advantages, and reduced carbon footprint. However, it is well documented that increasing NG injection rates results in declining raceway flame temperatures (a quenching effect on the furnace, so to speak), with the end result of a functional limit on the maximum injection rate that can be used while maintaining stable operation. Computational fluid dynamics (CFD) models of the BF raceway and shaft regions developed by Purdue University Northwest’s (PNW) Center for Innovation through Visualization and Simulation (CIVS) have been applied to simulate multi-phase reacting flow in industry blast furnaces with the aim of exploring the use of pre-heated NG as a method of widening the BF operating window. Simulations predicted that pre-heated NG injection could increase the flow of sensible heat into the BF and promote complete gas combustion through increased injection velocity and improved turbulent mixing. Modeling also indicated that the quenching effects of a 15% increase in NG injection rate could be countered by a 300K NG pre-heat. This scenario maintained furnace raceway flame temperatures and top gas temperatures at levels similar to those observed in baseline (stable) operation, while reducing coke rate by 6.3%.
Highlights
Worldwide, auxiliary fuel injection serves as one of the key technologies by which blast furnace (BF) coke consumption rates are reduced
Using the Computational fluid dynamics (CFD) model, it is possible to generate a numerical value that can be compared to the raceway adiabatic flame temperature (RAFT) by taking a mass-weighted average of the gas temperature in all computational cells in the domain with less than 0.5% H2 O, CO2, and O2 content by volume
This corresponds to the theoretical definition of RAFT as the temperature of all gases once they have been reduced from fuel and oxidizer into CO and H2
Summary
Auxiliary fuel injection serves as one of the key technologies by which blast furnace (BF) coke consumption rates are reduced. Through the reduction of coke consumption and by the introduction of some hydrogen to the reduction process via fuels such as natural gas, injected fuels are one of the key levers by which operators can reduce carbon footprint and possibly make the blast furnace more efficient. These injected fuels typically present a significant economic incentive for their greater use, especially in the case of natural gas (NG) in North America. With high NG injection rates becoming more and more common in addition to, and sometimes in place of, pulverized coal injection (PCI) in North American BFs, it is increasingly important for Processes 2020, 8, 771; doi:10.3390/pr8070771 www.mdpi.com/journal/processes
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