Research On Multiphase Flow Field Characteristics And Fermentation Performance In Fermenter Based On CFD

L-threonine is an indispensable amino acid in biological body,which has high market value and its demand increases rapidly.At the beginning of the design,the complex flow field dynamics characteristics in the tank were not understood in detail,which resulted in the poor mixing effect of the existing stirring equipment on enhancing the fluid mixing in the fermentation tank,making it difficult to improve the production of L-threonine.Therefore,this paper mainly uses CFD numerical simulation technology to study the characteristics of multiphase flow field under the design of a variety of mixing combinations.At the same time,combining with the actual fermentation experiment,the fermentation production of L-threonine was analyzed and compared from the physiological point of view,and the conclusion was verified with the flow field simulation analysis.On this basis,the characteristics of multiphase flow field in the fermentation tank under different working conditions were further studied.The research results can provide an important reference for the optimization and control of Lthreonine fermentation process and the design,scale up and optimization of mixing equipment in medium and large fermentation tanks.The main contents are as follows:(1)The numerical simulation method of gas-liquid two-phase flow,the treatment method of agitating blade,the calculation model of the force between gas-liquid two phases and the turbulence model were analyzed,and the numerical simulation method in this paper was formulated,and the reliability of the method was verified.(2)Three dimensional modeling was carried out for different mixing combinations designed.The gas-liquid two-phase flow was simulated by FLUENT,and the characteristics of flow field,such as velocity field,turbulent kinetic energy and gas holdup,were analyzed.The results show that in the gas-liquid mixing system,the upper and bottom impellers adopt the three-layer stirring combination F of radial flow type impeller,and the overall velocity distribution of the mixed flow field is uniform,the turbulent kinetic energy distribution is wide,the gas holdup distribution is uniform,and the ventilation and stirring power is large,which is conducive to gas-liquid mixing.(3)The fermentation performance of L-threonine under different mixing conditions was studied.From four batches of fermentation bacteria concentration,sugar consumption rate,and the comparison of acid production rate,stirring combination of F is found that optimal fermentation batch fermentation performance,the effect of mixing of mixing combinations F the flow field of the best,followed by mixing composite D and E,well validated of L-threonine fermentation tank inner flow field simulation analysis.(4)The gas-liquid two-phase flow simulation study of stirring combination F was carried out,and the variation of flow field characteristics in the fermentation tank under different working conditions was analyzed,which provided an important reference for the optimization and control of L-threonine fermentation process,and then improved the fermentation performance of L-threonine.The results show that if the stirring speed is too low,the gas velocity will affect the velocity distribution and gas phase distribution of the flow field.Increasing the stirring speed can enhance the gas-liquid mixing effect of the fluid in the far impeller area,but it has no obvious effect on the gas holdup in the far impeller area at the tank bottom.The liquid dead zone at the bottom of the tank can not be completely solved by increasing the ventilation rate alone,and the effect on improving the gas dispersion at the bottom of the tank is small.The liquid dead zone at the bottom of the tank can not be solved by changing the mounting height of the bottom paddle alone,and it has little effect on the fluid flow pattern in the tank.The lower the installation height of the bottom paddle,the higher the average gas holdup in the upper region of the fermenter,and the more uneven the gas distribution in the bottom region.The aerated agitation power increases with the increase of the stirring speed,but decreases with the increase of the ventilation rate.The installation height of the bottom impeller has little effect on the aerated agitation power.