| Top-blowing submerged bath smelting technology is one of the primary processes in modern intensive smelting of non-ferrous metals such as lead and tin.The lance is the critical component of the top-blown furnace,which has a built-in swirler with multiple helical vanes.During the lead/tin smelting process,an axial jet is entered from the top of the lance into the casing pipe of the lance and is guided by the helical vanes to form a swirling flow with a downward spiral motion.The high-velocity jet is injected into the high-temperature bath to agitate the melt and cause the latter to move in a disorderly manner,effectively increasing the rate of chemical reaction between phases in the furnace.Moreover,in the tin smelting process,the concentrated powder is entrained by the swirling flow and injected into the bath,which significantly suppresses the volatilization of metal sulfides,improves the efficiency of the smelting reaction,and inhibits the soot rate within the furnace.Nevertheless,the highintensity stirring behavior in the furnace exacerbates the scouring wear of the lance head and dramatically diminishes the service life of the lance.Thus,an in-depth investigation of the formation/decay characteristics of the swirling flow,the failure mechanism of the lance,the interphase interaction between the swirling flow and the particles,the stirring characteristics of the swirling flow to slag phase and corresponding influencing factors can provide a powerful theoretical basis for the design of the top-blowing smelting furnace and the optimization of the top-blowing process.Due to the high-temperature invisibility of the topblowing system in industrial production,the industrial-scale bath smelting furnace with a top-submerged lance is investigated.The numerical method employed to investigate the jet kinematics,gas-particle interactions,and gas-slag multiphase mixing properties in the furnace is constructed.The main conclusion can be drawn as follows:The formation,diffusion and decay characteristics of the swirling flow inside the lance are numerically analyzed.The major causes of lance breakage are elucidated,together with the discussion of the regulation characteristics of the swirling intensity.It is illustrated that the jet exists in the form of a weak swirl inside the lance,whereas the swirling intensity attenuates with the jet motion in the downstream region of the swirler.The formation and diffusion of the swirling flow lead to the friction coefficient of the annular pipe wall and the outer wall of the center pipe increasing significantly.This is one of the main reasons affecting the breakage of the lance,demonstrating the necessity of increasing the compressive strength of the lance pipe at the height of the swirler in industrial applications.Besides,the swirl number is introduced to characterize the swirling intensity inside the lance.The swirl number increases with the swirler diameter,the twist angle of the vanes,and the number of vanes,but decreases with the swirler height.Based on the coupled model of computational fluid dynamics and the discrete element method,the spiral dispersion behavior of powder particles under swirl-induced entrainment is revealed,and a control scheme for the entrainment intensity of particles by swirling flow is obtained.In the mixing zone,the particles spiral downward and disperse outward by the disturbance of the swirling flow.Increasing the vane angle and swirler diameter facilitates the dispersion of particles in the lance,while increasing the swirler height and installing position reduces the particle dispersion width.Notably,the particle distribution width is equal to the lance diameter(i.e.0.25 m)for vane angles of 90°,110°,130° and a swirler height of250 mm.At each height,the number of particles always follows a distribution trend of being more concentrated in the center and less so around the periphery.The variation of the relative slip velocity between the jet-particles results in the particle Reynolds number increasing and then decreasing with decreasing height.The computational fluid dynamics framework and the heat transfer submodule are coupled to take into account the heat transfer process between the lance walls.In line with the industrial measurements,the temperature of the pipe wall is set as a multi-segment linear distribution along the axial direction.The spatial and temporal multi-scale coupling characteristics of the swirl flow-particles thermodynamic transfer are investigated,and the effects of the swirler configuration structure,as well as the diameter/density of powder particles,on the thermophysical properties of the binary-size particle mixture are explored.The results indicated that the intrinsic properties of the swirling flow cause an inhomogeneous distribution of local thermal thickness in the vicinity of the pipe wall.The heat transfer performance of the coupling surfaces of the annular pipe solid domain and the annular region,the coupling surfaces of the central pipe solid domain and annular region,as well as the particles and swirling flow,are increased with the increase of the vane angle and the swirler diameter but decreased with the swirler height increasing.When the particles move to the mixing zone,the Nusselt number of the particles exhibits an initial increase followed by a decrease as the particles descend.The heat exchange performance between the binary mixed particles and the high-temperature jet is enhanced by smaller powder diameters and densities.The chaos-enhanced modulation of the top-blowing smelting process is analyzed from multiple aspects,including jet characteristics,bubble morphology,slag splashing behavior,and gas-slag stirring efficiency in the bath.It is revealed that the cylindrical top-blowing furnace exhibits higher stirring intensity,larger penetration depth and smaller lance shear stress than the rectangular and elliptical top-blowing furnaces,being more suitable for industrial application.The bubble velocity increases with the increase of the vane angle.Increasing the vane number suppresses the splashing intensity of the slag phase.The increase of the swirler diameter increases the aspect ratio of the bubbles,but insignificantly impacts the penetration depth of the jet.The specific surface area of the bubbles and the penetration depth of the jet are reduced and increased with the swirler height increasing,respectively.For the conditions of furnace-lance with a diameter ratio of 16,the time-averaged velocity of the slag phase is about 0.0485 m/s,which is only 55.9% of that at a diameter ratio of 8.The volume of the region where molten velocity is less than 0.1 m/s is about 1.18 times larger in the former than in the latter.Comprehensive consideration of the jet swirling intensity and the particle dispersion intensity in the lance,and the stirring dead zone volume,molten velocity,splashing intensity inside the furnace,as well as the force exerted on the swirler/lance,the optimized structural parameters of the top-blowing system are listed as follows: cylindrical top-blown furnace,16 of furnace-lance diameter ratio,90° of vane angle,12 of vane number,160 mm of swirler diameter,450 mm of swirler height and 900 mm of installation height. |
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