The Study Of Hydromechanics Performance Of The Countercurrent Flow Of Gas And Liquid In The Lower Blast Furnace

High permeability of the lower blast furnace is a major factor for achieving stable furnace operation with high productivity. A hydromechanics experiment on the counter-current flow of gas and liquid simulating the flow conditions in the lower blast furnace had been carried out. A cold model of a packed bed with various packing materials and liquids was used to study liquid distribution, holdup of liquid, pressure drop, loading velocity and flooding velocity.The experimental results show that a stable liquid distribution would be established after flowing through a given height of packed bed whether the initial distribution is uniform or not. The shape factor is small and the diameter is large for the packing materials, liquid would flow outward pronouncedly. The bigger the density and the smaller the viscosity for the liquid, the harder the occurrence of bias-flow is. It can be expected from this finding that even without the influence of gas, slag is easy to flow towards the wall in a blast furnace.The liquid static holdup, h_s, is correlated with the modified Galileo number and modified capillary number by the least square method. Increasing viscosity and surface tension and reducing density of the liquid would cause h_s to increase. These factors are in the descending order of degree of influence are density, surface tension and viscosity. Reducing size, shape factor and porosity of packing makes h_s to increase. The bigger the h_s is, the bigger the total liquid holdup h_t is as u_l increases for all the combinations of liquids and packing materials, it is obvious from this that the factors affecting h_s are also those affecting dynamic liquid holdup h_d. Correlations for h_s and h_d in the absence of gas flow and for h_t in the counter-current gas-liquid two-phase flow were obtained. A good agreement is found between the calculated and experimental data.The effect of density on the gas velocity of the flooding point is properly accounted for by multiplying the flooding factor of the ordinate of Sherwood's diagram by the density correction coefficient and a new flooding diagram and a new correlation are proposed. The gas velocity of the loading point is about 0.75 times the gas velocity of the flooding point according to the experimental data.The observed value of pressure drop is bigger than that calculated by the modified Ergun equation at smaller gas Reynolds numbers due to the presence of the dead space. It is smaller at larger gas Reynolds numbers because interfacial viscous drag-force between gas and liquid is smaller. A new formula for the pressure drop was obtained based on the relationship between the resistance coefficient and gas Reynolds numbers resulted from experimental results. When the density of packing material is smaller than that of liquid, the packing material becomes less dense and expands before flooding. The pressure drop in an expanding packed bed can be calculated by modifying the porosity of the bed. The expansion rate is related to liquid flow rate, fluidization velocity and free descending velocity of the packing material. By comparing the fluidization velocity with the flooding velocity, a diagram was developed to distinguish flooding from fluidization under given flow conditions. The results show that, in the dropping zone of a blast furnace, it is flooding of the slag will occur and not fluidization of the coke bed.A simulation model of two-dimensional gas flow in a blast furnace has been developed withthe finite element method, considering simultaneously the effect of the dead man, raceway, cohesive zone, burden profile and particle size distribution of ore and coke layers, holdup of slag and molten iron, slag and molten iron distribution in the dripping zone on gas flow resistance. The model calculating results show hs is the determinant of the total holdup of molten materials in the absence of gas flow. The most important factor affecting hs is the size of coke particles in the blast furnace. When the coke size decreases by 5mm, hs increases by about 20%. The smaller the coke size is, the bigger the incremental ratio is. The vertical velocity of gas is bigger near the molten ore layer in the cohesive zone and the surface of the dead man. These local regions are liable to flooding. The top of the raceway is the important region limiting furnace productivity. Once the gas permeability in this region becomes bad, the local flooding may disseminate to the whole cross section of the bosh, and normal operation will be damaged.In regard of the counter-current flow of gas and slag on the top of the raceway, a productivity optimizing model was developed on the basis of the liquid holdup model, gas pressure drop model and simulation model of two-dimensional gas flow. The optimizing model reflects the connection between some important operational factors in the blast furnace and the maximum productivity. The calculated results show that as the coke size increases by 5mm productivity increases by about 20%; as the slag ratio decreases by lOOkg/t productivity increases by about 8%; as the slag viscosity decreases by 0.1 Pa s productivity increases by about 4%; as the top pressure increases by 50kPa productivity increases by about 6%; as oxygen enrichment increases by 1% or blast temperature increases by 100°C productivity increases by about 2%. With proper operational means in the upper zone of the blast furnace to improve the utilization efficiency of unburnt pulverized coal in the blast furnace, it is completely possible that the productivity increases up to 3.0t/m3d when a large amount of pulverized coal is injected into a large-scale blast furnace.