Design And Numerical Simulation Of Energy-Saving Fermentation Apparatus Based On Swirl Atomization

Ventilation fermenters commonly used in the fermentation industry at home and abroad are mechanically agitated,airlifted,bubbling and self-priming.Among them,mechanical agitated aeration fermenters have always occupied a dominant position,accounting for 70%to 80%of the total number of fermenters.The mechanical agitation device commonly used in the pre-ventilation fermentation process has the disadvantages of high energy consumption,high initial cost,low oxidation efficiency.The energy consumption of the mechanical stirring device accounts for about half of the whole process of fermentation.With the continuous production of high-yield strains,current mechanical agitation devices have been difficult to meet the requirements for higher dissolved oxygen rate and energy-saving need.In view of the difficult problems in traditional fermentation industry,such as high production cost,large energy consumption,long production cycle and poor quality of mycelium,a set of highly efficient and energy-saving fermentation apparatus with low energy consumption,small shear and self-adaptive temperature control was designed and developed in this paper,using the patented technology of highly efficient swirl atomization and the idea of empty tower independently developed by our research group.The flow process in the original fermentation unit and the energy saving fermentation unit based on swirl atomization was numerically simulated by using computational fluid dynamics(CFD)software.In this paper,a 26 m~3 fermentation tank was simulated and calculated by Fluent software.The population equilibrium model(PBM)coupled two fluid model(TFM)was used to solve the dynamic evolution process of bubble clustering and breaking.The sliding mesh(SM)method was used to solve the flow field containing rotating machinery.According to the knowledge of two film theory involved in the process of oxygen dissolution,the source term of oxygen absorption was introduced by the user defined function(UDF),and the original fermentation device and the modified energy-saving fermentation device were simulated.The flow field characteristics,mass transfer characteristics and energy consumption of the new and old equipment were compared and analyzed.According to the installation position,gas-liquid ratio and number of atomizer of the modified energy-saving fermentation device,the optimization analysis is put forward.The results show that:(1)The energy-saving fermentation device based on swirl atomization can achieve the rotary mixing of gas-liquid phase in the tank without mechanical stirrer.(2)There is no dissolved oxygen dead zone in the original mechanical stirring fermentation device,but the energy-saving fermentation device based on swirl atomization has uniform gas phase distribution,and the average gas holdup and average volume mass transfer coefficient are higher.(3)The stirring motor power consumption of the original mechanical stirring and fermentation device is relatively large,and the energy-saving fermentation device based on swirl atomization can save about 85.5%of the power consumption.(4)The swirl atomizer layer should be arranged at a lower position as far as possible,but for technical reasons,the installation height should not be lower than 0.7m;(5)Improved aeration ratio can achieve better dissolved oxygen effect in the device,but when the ratio of swirling atomized gas-liquid exceeds 1.5:1,the average gas volume fraction and average volume oxygen transfer coefficient in the fermentation device tend to increase less and less with the increase of swirling atomized gas-liquid ratio.(6)The oxygen accumulation transfer coefficient and average gas volume fraction of the fermentation device increase first and then decrease with the number of swirling atomizers,and the dissolved oxygen effect is best when the number of swirling atomizers is 4.(7)For the calculation example set in this simulation,the installation height is 0.7 m,the gas-liquid ratio of swirl atomizer is 2:1,and the number of swirl atomizer is 4,which are the optimal design and operation parameters.The above research methods and conclusions have certain reference and guiding significance for the fields with aerated biochemical reaction kettle as the core equipment,such as fermentation industry.