| Gas quenching blast furnace slag is a kind of dry slag granulation technology,which uses supersonic gas to impact,tear and break up the slag into droplets,and then they fly into a cooler for cooling to form solid slag particles.Gas quenching method can not only come true the resource utilization of slag,but also realize the waste heat recovery of slag.In the whole process,no water is consumed and no harmful gas is discharged.Therefore,it is the most promising technology to replace the traditional wet slag treatment.Under the action of gas jet,a series of complex deformation and heat transfer will be occurred.Therefore,the combination of thermal state experiment and numerical simulation is adopted to study the granulation process of slag in supersonic gas,the purpose is to reveal the granulation mechanism and heat transfer characteristics,and to master the influence mechanism of granulation and heat transfer.It provides theoretical basis and technical guidance for the application of gas quenching granulation technology.In the aspect of thermal state experiment,the macro understanding was obtained based on granulation performance and waste heat recovery rate.The effects of gas velocity,slag mass flow rate and slag viscosity on granulation performance and waste heat recovery were studied.The droplet diameter can be reduced by increasing gas velocity and decreasing slag mass flow and viscosity.The initial temperature of molten slag has no effect on droplet size.The particle size distribution is mainly concentrated in1?3 mm.The formation of fibers is related to the internal and external forces and cooling rate.At low slag mass flow rate,considering the influence of fiber mass fraction,the gas velocity can not increase infinitely.The higher waste heat recovery rate can be obtained with the smaller particle size and the lower the fiber mass fraction.In the aspect of numerical simulation,the granulation mechanism was deeply studied based on the capture of fine morphology changes of slag.The slag breakup process can be divided into three stages: film formation,film breakup and ligaments breakup.The film is formed due to flow deformation under the effects of air impingement,recirculation zone and pressure gradients.Due to the gas-liquid velocity difference,Kelvin Helmholtz(K-H)unstable wave is generated on the film surface,and small holes are generated at the trough of the K-H wave.The growing of the small holes leads to the film breakup,and the K-H unstable wave is the fundamental cause of the film breakup.The film breakup is typical perforation breakup.According to Weber number(We)and Reynolds number(Re),the film breakup belongs to Second Wind Induced breakup,aerodynamic force is the driving force of film breakup.The wavelength and thickness of film decrease with the increase of Weber number(We),and they first decrease and then increase with the increase of Reynolds number(Re),which is optimum in the range of 1068-1280.According to the simulation data,the empirical formula of ligament diameter is obtained,the ligament diameter decreases with the increase of gas velocity and slag density,and increases with the increase of slag mass flow and viscosity.Under the action of Rayleigh Taylor(R-T)unstable wave,the ligaments break up into near spherical droplets at the wave trough,which belongs to pinch breakup.According to the simulation data,the empirical formula of droplet diameter is obtained,the droplet diameter decreases with the increase of gas velocity and slag density,and increases with the increase of slag mass flow and viscosity.The initial temperature of slag has a certain inhibition on the fiber formation.The simulation results is consistent with the experimental results.The solid phase distribution in the solidification process is not uniform,and the solid phase thickness on the windward side is greater than that on the leeward side.The cooling rate decreases gradually from the outside to the inside.During the whole solidification process,the cooling rate of different positions at different times is greater than that of crystallization,which indicates that the slag particles are mainly glass phase.Decreasing droplet diameter and increasing air velocity can improve heat transfer coefficient,shorten solidification time and increase cooling rate.Decreasing initial droplet temperature can shorten solidification time and increase cooling rate,but the effect on heat transfer coefficient is unstable.The droplet diameter has the greatest influence on these heat transfer characteristics,followed by the relative velocity.Figure 91;Table 17;Reference 146... |
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