Numerical Investigation On Fluidization And Heat Transfer Characteristics Of Granulated BF Slag Particles In Bubbling Fluidized Bed

As the main waste heat resources that have not been effectively utilized in the steel industry,the blast furnace slag discharged at the temperature of about 1450-1550 oC belongs to high grade waste heat resources.So far,the water quenching process is still the main blast furnace slag treatment process,that is,plenty of water is utilized to cool down the high temperature slag with direct contact.Rapid cooling facilitates the formation of vitreous slag,which can be used as cement ingredients because of the cementitious activity.However,the water quenching process fails to recover high-grade waste heat in blast furnace slag,with huge water consumption,resulting in environmental pollution gas,such as H2 S,SO2.Besides,additional energy is needed for drying slag from water quenching process.In order to take into account the waste heat recovery and material utilization of blast furnace slag at the same time,and reducing the consumption of water resources and reducing the discharge of environmental pollutants,dry process has attracted the attention of scholars.The basic idea of dry process is to break the slag into fine particles,to increase the specific surface area of the slag,and use the air as cooling medium to cool the slag particles.Among a number of dry processes,centrifugal granulation heat recovery process by virtue of its simple structure,easy operation and other advantages,is considered as the most promising blast furnace slag treatment process.However,the thermal conductivity of blast furnace slag and air are low,and the formation of glass-phase blast furnace slag need to cooling quickly.Therefore,the rapid cooling of granulated blast furnace slag particles is the key to the realization of the whole process.The bubbling fluidized bed,by virtue of its excellent heat transfer efficiency and handling capacity,is considered to be an ideal device.Which is beneficial to the rapid cooling of granulated slag particles and the realization of waste heat recovery.However,there is a lack of research on the fluidization and heat transfer of granulated slag particles in bubbling fluidized bed.Therefore,based on the above problems,the numerical investigation on fluidization and heat transfer of granulated blast furnace slag particles in bubbling fluidized bed is carried out.The main contents and conclusions are as follows:(1)In order to study the fluidized behavior of granulated blast furnace slag particles in bubbling fluidized bed,the Euler-Euler two-fluid model was adopted to study the effects of fluidized air velocity,initial particle packed height on the particle concentration distribution,bubble characteristics and so on.The results show that the fluidization number N is greater than 1 and less than or equal to 3,the initial packed height ratio R is less than or equal to 2 is the suitable operating conditions for granulated particles in the bubbling fluidized bed.(2)Based on the above cold state study,the effects of fluidized air velocity,initial particle packed height and other factors on particle volume fraction distribution,inter-phase heat transfer coefficient and global particle cooling rate were investigated.The results show that the local inter-phase heat transfer coefficient is dominated by the particle volume fraction distribution,but beside the bubble,the local inter-phase heat transfer coefficient is dominated by the gas flow field.(3)Based on the above-mentioned cold state and warm state studies,the temperature dependent parameters during the actual cooling process,such as thermal conductivity and specific heat capacity are taken into account.Based on the user-defined function,the blast furnace slag particles the flow behavior in the fluidized bed is analyzed,and the effects of the operating conditions on the phase heat transfer coefficient and the particle cooling rate are analyzed.The results show that the cooling rate is increasing when the average temperature of the particles is about 1000 K;and the shallow fluidized bed is suitable for the rapid cooling and large-scale treatment of granulated slag particles.