Effect of Oxygen Enrichment on Flow Field, Temperature, and Gas Concentration Profile Inside a Pilot-Scale Rotary Hearth
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THE world steelmaking industry has been completely dependent on hot metal from blast furnace for steel making since the advent of the industrial revolution. However, the recent advances in EAF (Electric Arc Furnace) steelmaking that can handle any mix of scrap, hot metal, and direct reduced iron (DRI) have promoted the most desired coke-free DRI production globally.[1] Rotary Hearth Furnace (RHF) is one such coal-based DRI process where iron-bearing solid waste can be utilized to produce value-added sponge iron. RHF has a rotating hearth that carries the raw materials through different temperature regimes like the preheating zone, reduction zones in a circular path and finally discharges the reduced burden through the exit door next to the inlet door. The raw materials used are cold-bonded iron ore coal composite pellets/briquettes. Metallization of around 85 to 95 pct could be achieved within 15 to 25 minutes of reduction at 1573 K (1300ºC).Since the SOORAJ SALEEM and GOUR GOPAL ROY are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India. Contact e-mail: [email protected] Manuscript submitted May 31, 2020; accepted September 14, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
reductant remains inside, only heat is required to reduce such pellets, which is supplied by gaseous fuel burner in the circular channel and the hot gas moves countercurrent to the solid charge underneath. Although some studies have been carried out on kinetics of reduction in multi-layer bed RHF,[2–5] very few models have been developed that considers the gas dynamics and combustion in the freeboard above the hearth. Liu et al.[6,7] developed an integrated model combining CFD in the freeboard and solid reduction over hearth. They reported an increase in concentration of CO2 and CO in the furnace with an increase in C/O molar ratio of the pellet, while it marginally affected the distribution of temperature in the freeboard. Oxygen combustion mechanism is one of the most effective energy-saving technologies for combustion systems. In conventional air-fuel combustion, nitrogen dilutes the gas, reduces the peak temperature, and drains away a part of the energy as flue gas, subsequently reducing the overall fuel efficiency. Nitrogen, however, increases the heat capacity of the gas by increasing the volume, but it decreases the heat transfer potential of the gas due to reduced peak temperature. The oxygen combustion has several advantages as well; it is found to increase the thermal efficiency by lowering heat energy loss through flue gas.[8] Generally, oxygen burners are applied for high-temperature furnaces such as aluminum re-melting furnaces, ladle furnaces etc. The oxygen used
for these purposes is often in their purest form. The high cost of oxygen production limits the widespread utilization of oxygen combustion. Moreover, to apply this oxygen combustion to the existing combustion system, the furnace body and burners need to be retrofitted extensively
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