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.
In the equation, Dt, is tuyere diameter (m), ut is blast velocity (m/s), Pb is blast pressure (kgf/cm2, gage), ρc is apparent density of coke (kg/m3), dp is mean size of coke (m), and Tb 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 ut (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.
In this equation, Mb is blast moisture (g/Nm3), ρc is apparent density of coke (kg/m3), dp is mean size of coke (m), N, is number of tuyeres (-), DR is raceway penetration (m), γ is productivity (t·d-1·m-3), vp is blast volume per ton of hot metal (Nm3/t), and Vi is inner volume of a blast furnace (m3).