Charging Behavior and Gas Distribution Considering Blast Furnace Aerodynamics

Abstract

The transitional behavior of the burden and gas distribution in the blast furnace has been studied aerodynamically by a blast furnace model.
When ore is charged, the coke colume is formed in the central region, named the central coke column. The formation process of its column is modeled as the following three steps from the experimental observation.
1) With the progressive covering of the stack surface from the periphery to the center by ore, the furnace gas is concentrated in the central region.
2) The coke layer is expanded in the area where the gas velocity exceeds the minimum fluidization velocity of coke layer.
3) Some of the expanded coke is pushed into the central part by the charged ore.
The central coke column is easily formed at pellets charging rather than at sinter charging. The concentrated gas velocity in the central part is related to the ore thickness and the area of ore layer and the permeability ratio of ore to coke, and is expressed by the following equations
U_c/U_av=1/{A_C/A_T+(A_W/A_T)/(U_C/U_W)}……(1)
U_C/U_W=C₀{(H/R)·(K₁/K₂)^0.778·(A_C/A_T)^-0.483}ⁿ……(2)
where, A is the sectional area and U is the gas velocity, and suffix _C and _W express the central part without ore and the peripheral part with ore covered, respectively, and suffix T is the throat and av is the average. H is the ore thickness, R is the throat radius, K₁ and K₂ are the permeability indicies of coke and ore, respectively, and C₀ and n are constants.
The area of central coke column is estimated to be about 0.114 dimensionless radius from Eqs. (1) and (2).
The pressure drop in the stack of blast furnace is decreased by formation of central coke column, while the distribution of gas through the coke layers in the softening-melting zone hardly changes.