Study On Thermal Characteristics Of Distillation Corridor In The Production Of Titanium Sponge By Magnesium Thermal Metho

The vacuum distillation process is an important process for the production of titanium sponge by the Kroll process.On the one hand,the blockage of distillation channel in the operation process intensifies the discontinuity of the process,resulting in the increase of production cycle,operation intensity and energy consumption.On the other hand,it limits the distillation separation of Cl and Mg Impurities in titanium sponge to a great extent,which indirectly affects the quality of titanium sponge.Clarifying the energy loss and heat transfer characteristics of the fluid in the distillation channel is a necessary prerequisite to solve the blockage problem.However,the existing theoretical research is insufficient and focuses on the optimization of process parameters and equipment structure,so the understanding of blockage problem is at the process level.Therefore,this paper focuses on the vacuum distillation process,through theoretical analysis and experimental exploration,in order to clarify the thermal characteristics of the distillation channel in the vacuum distillation process.The energy loss of the fluid in the distillation channel was experimentally studied,and the energy loss and its variation law of the fluid in the channel in different operation conditions were clarified.It is found that the fluid energy loss increases with the increase of average velocity,and the local loss accounts for 59.5%～63.1%of the energy loss.When the pressure drop is constant,the fluid energy loss decreases gradually with the increase of temperature.When the temperature remains unchanged,the fluid energy loss shows a trend of increasing with the pressure drop.The average velocity of fluid ranges from 31.5 m/s to 67.6 m/s,the Reynolds number ranges from 4295.4 to 7757.9.Furthermore,the mathematical expression of pressure drop isΔp=1/di2(1.485μvdiRe+0.1582lμvRe0.75),and the mathematical relationship between fluid energy loss and pressure drop is hw=(λl/di+ξ)2gdiRe0.25Δp/(1.485ρdiRe0.25+ρl).Aiming at the problem of blockage in distillation channel,the energy loss of fluid in different distillation channels was studied.The results show that after optimizing the local structure of distillation channel,the fluid energy loss decreases by 15.6%～15.9%.Therefore,a bent tube is recommended instead of a right-angle tube to optimize the channel structure and reduce the local resistance loss coefficient,which can effectively reduce the fluid energy loss and reduce the blockage rate of distillation channel.Based on the heat conduction process of insulation layer and infrared imaging test of outer wall of the heater,the temperature field distribution of aisle heater is clarified.It is found that the surface heat loss accounts for only 8%of the heating power.The thermal resistance in the 0.5～1.5m section of the heater is relatively weak,and there is a lot of heat dissipation at both ends of the outer wall of the heater.Hence,it is suggested to optimize the insulation layer design,heater structure and heating regime.Taking the distillation channel as the research object,the flow and heat transfer characteristics in the distillation aisle were experimentally analyzed,and the comprehensive convective heat transfer characteristics in the distillation aisle in different operation conditions were studied.It is found that the comprehensive heat transfer coefficient of the inner wall surface of the distillation channel ranges from 59.95 W/m2·K to 200.29 W/m2·K,which increases with the increase of Reynolds number and temperature.The Nusselt number range of comprehensive convective heat transfer ranges from 134.79 to 407.32,which increases with the increase of Reynolds number.Prandtl number has no significant change,and the approximate treatment is 0.0205.The dimensionless correlation of Nusselt number of comprehensive convective heat transfer is Nu=6.62×10-5 Re1.72.