Development Of Slot-bottom Powder Injection Device And Study On Characteristics Of Gas-Particle Flow In Bottom-Blowing Ladle

With good thermodynamics and kinetics conditions for injecting powder into molten bath, powder injection technology has been universally applied in hot-metal pretreatment and secondary refining ladle. A slot-bottom powder injection device, for bottom powder injection in refining ladle, was developed to overcome disadvantages of lance, such as high cost, reoxidation, absorbing nitrogen, introducing security accident, in existing powder injection technics. And the theoretical and experimental researches on gas/particle flow, in bottom powder injection, were carried out to study the new technology. The main contents and results achieved in this paper are as follows(1) The movement characteristics of gas/particle flow in slot were studied with numerical simulation, achieving the quantitative relationship of density, velocity, particle size and viscosity of air and particle, that is, (2ρp+ρg)dVp/dt=3aρg(Vp-Vg)2-k/(2dp)(dp/v)-k +2ρgg-2ρpg, (in which, a and k is coefficient; V is velocity, m/s; t is time, s;ρis density, kg/m3; d is diameter, m; v is viscosity, m2/s; subscript p and g represent particle and gas) and analytic formulas in different Reynolds number. The results show that small particles, only a very short time and distance, can be accelerated to 99 per cent of the movement terminal velocity(abbreviation Vp(T)), e.g. the time and distance required for movement, for diameter of 0.02 mm lime particle, are respectively 0.01 s and 1.04m, moreover, for diameter of 2.00 mm lime particle, are respectively 1.34 s and 167.21m; A slight increase in the speed required for the acceleration distance is a substantial increase after particle velocity reached 99% Vp(T), e.g. achieving 99.9% Vp(T) velocity, the distance required for 0.02mm and 2.00mm particles of lime are respectively 2.17m and 328.65m; Large-diameter particles achieve critical penetration velocity need less accelerating distance, e.g.0.20mm lime particle, accelerating 0.46 m, reaches the critical velocity, however,2.00mm lime particle, accelerating 0.21m, reaches the critical velocity; The movement distance is sequentially increasing for the same diameter of lime, MgO and Fe2O3 particle accelerating to 99% Vp(T), but the particles, accelerating to critical penetration velocity, are reversed.(2) Mechanism of liquid steel leakage and powder blocking in bottom powder injection ladle were investigated by theoretical research, cold test, hot test and 5 hours abrasion test. The results show that slot thickness of bottom powder injection device for anti-steel leakage follows the expression (d＜-4σcosθ/(ρlgh)). Conical angle of fluidized bed of bottom powder injection device for anti-powder blocking follows the expression (a＜180°—2φ). No leading angle of slot of bottom powder injection device can prevent powder blocking in slot.(3) The characteristics of homogeneous mixing of molten bath-in bottom powder injection ladle were investigated through physical simulation. Nozzle shape, slot thickness, the distance between the slots, positions and gas flow rates were also carried out to optimize the powder injection process. The results show that the mixing time of round nozzle is shorter than that of slot nozzle under gas flow rates (0.209Nl/s～0.523Nl/s). When single slot specifications in 0.15-0.30mm×15mm or 0.50-0.80mm×15mm, its thickness has no influence on mixing time of molten bath, when slot thickness increase to some degree, the mixing time increase significantly, e.g. The mixing time of molten bath increased 7.42s when slot thickness broadened from 0.30mm to 0.50mm in the experiments. The mixing time of the double-slot nozzle with the distance between the slots of 5 mm is slightly less than that of single-slot nozzle in the same cross-sectional area. Either single-slot or multi-slot nozzle, bath mixing time in 1/2L of centre is shortest and that in side injection is longest, the two largest margin of 17.60s.(4) The characteristics of penetration of powder in bottom powder injection ladle are investigated by physical simulation. Nozzle shape, slot thickness, the distance between the slots, positions and gas velocity were also carried out to study the powder injection process. The results show that powder penetration ratio of narrow slot nozzle is higher than that of wide slot nozzle, e.g. the narrow slot nozzles'powder penetration ratio is higher than the wide slot nozzle average 1.3% in the experiments. Powder penetration ratio of single-slot nozzle, at the bottom center and distance to the central 1/2 positions, are higher than that of round nozzle respectively 4.21% and 1.38% in gas velocity (10m/s-60m/s). Powder penetration ratio of single-slot nozzle, at side and distance to the central 1/2 positions, are higher than that of single-slot nozzle at the bottom center respectively 3.68% and 2.56% in gas velocity (10m/s-60m/s). In bottom powder injection through slot nozzle, powder penetration ratio increased firstly, and then decreased with the gas velocity increasing. And in which there was a gas velocity to be the best for powder penetration ratio, e.g. the best gas velocity for bottom powder injection and side powder injection were respectively 50m/s and 40m/s in the experiments.