Desirable Blast Velocity from the View Point of Fine Coke Deposit around Blast Furnace Raceway

Abstract

Using a two-dimensional model of the lower part of a blast furnace and a raceway hot model, the formation of raceway and furnace core and the coke degradation have been studied to clarify the desirable blast velocity of a blast furnace. The results obtained are summarized as follows.
(1) The reliable raceway penetration DR(m) is derived as shown by the equation below, and it is estimated that the penetration in large blast furnaces is about 1.4 m.
D_R=5.00 D_t·u_t√(P_b+1)/{ρ_c·d_p·(T_b+273)}
In the equation, D_t, is tuyere diameter (m), u_t is blast velocity (m/s), P_b is blast pressure (kgf/cm², gage), ρ_c is apparent density of coke (kg/m³), d_p is mean size of coke (m), and T_b is blast temperature (°C).
(2) The amount of fine coke deposit in the raceway increases to a great extent and the temperature in the lower part of a blast furnace decreases when the raceway penetration exceeds 1.3 m.
(3) The upper limit of blast velocity u_t (m/s) is estimated by the equation under below any conditions of equipments and operations of a blast furnace. According to the calculation based on this equation, the decrease of blast velocity in about 30 m/s causes the reduction of the raceway penetration of 0.1 m, and blast velocity should be decreased in inverse proportion to productivity when productivity increases.
u_t≤920(804-M_b)·ρ_c·d_p·N_t·D_R²/(γ·v_p·V_i)
In this equation, M_b is blast moisture (g/Nm₃), ρ_c is apparent density of coke (kg/m³), dp is mean size of coke (m), N, is number of tuyeres (-), D_R is raceway penetration (m), γ is productivity (t·d^-1·m^-3), v_p is blast volume per ton of hot metal (Nm³/t), and V_i is inner volume of a blast furnace (m³).