Effects of Particle Diameter and Coke Layer Thickness on Solid Flow and Stress Distribution in BF by 3D Discrete Element
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NTRODUCTION
A blast furnace (BF) is a complex counter-current reactor involving numerous physical processes, among which heat transfer, thermodynamics, chemical reactions, and solid and fluid transports are the major ones. However, high temperatures and pressures in BFs complicate dissection studies, in situ measurements, and physical experiments. Consequently, computer simulations have played a very important role in understanding the intricate phenomena occurring inside BFs.[1–13] In BFs, alternating charges of coke and ore form the burden layers. Coke serves as a heat source to melt iron ore,[14] a carbon source to carburize iron,[15,16] a reducing agent generating carbon monoxide,[14,17] and a means of developing permeability for gas flows.[18–22] Indeed, iron and steel manufacturers have been targeting reductions in the amounts of coke they consume to minimize production costs and carbon dioxide emissions by developing technologies such as hydrogen-enriched DEREJE DEGEFA GELETA and JOONHO LEE are with the Department of Materials Science and Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, Korea. Contact e-mail: [email protected] Manuscript submitted March 26, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
ironmaking.[23–26] However, minimizing coke consumption may result in thin coke layers, which in turn may lead to unstable situations such as the mixing of burden materials, yielding gas channeling problems, which greatly affect heat transfer from gas to solid burden and consequently decrease BF efficiency. Gas permeabilities, which may affect BF efficiencies, rely not only on burden layer thicknesses but also on particle shapes and diameters.[1,20] The average particle diameters of the coke and ore used as raw materials in BFs are in the ranges 45 to 55 and 15 to 25 mm, respectively.[27] Owing to this difference in diameters, the permeability of coke is five times greater than that of the ore. Therefore, it is essential to understand gas permeability in thinner coke layers. Currently, many iron and steel manufacturers use 5600-m3 or larger BFs to increase energy efficiency.[22,23] Increasing BF volume, however, disturbs the burden layer arrangements, average normal particle stresses, and particle velocity distributions, especially in the lower parts of BFs.[28] Several researchers have applied numerical simulations such as continuum computational fluid dynamics (CCFD)[29,30] and discrete element method (DEM)[31–33] models to BF studies. In recent years, DEM and CFD have even been coupled.[1,34–46] For example, Fan et al.[47] employed DEM using burden layer arrangement, particle velocity, and stress distribution as parameters to investigate the effect of cohesion-zone shape on solid flow. Jiang-Liang et al.[48] used
the same parameters to analyze the impacts of BF profiles such as shaft and bosh angles on burden flow. Natsui et al.[43,49,50] also studied the distributions of particle velocity, stress, drag, and pressure in BFs by applying the same technique. Keyser et al.[51] used the continuum
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