Establishment And Application Of A Prediction Method Of Flocculation Rate Based On CFD And Matlab

Recently,petrochemical energy exhaustion bacame a serious environmental problem in the mordern society.Oleaginous yeast has been widely used in the production of microbial oils.Trichosporon fermentans can be used to treat refined soybean oil wastewater（RSOW）and produce microbial lipids.But the recovery of oleaginous yeast is the bottleneck that hindered the large-scale application of oleaginous yeast.Microbial flocculants produced by Paecilomyces spp.M2-1 can be used to harvest Trichospron fermentans which accumulated intracellular oils from RSOW,and pollution to microbial lipid and environment could be avoided.During the flocculation,hydrodynamic distribution and parameters in the reactor are important factors to characterize performance of yeast flocculation.In this study,Fluent was used to simulate the operation of flocculation device,and the optimum hydrodynamic conditions were determined in the 0.25 L flocculation beaker as follows:the strirring speed of was 100 rpm,the volume of the suspension was 100 m L and the size of the stirring blade was 55 mm.It was also found that the appropriate range of turbulence kinetic energy was within 0.00065～0.00073m~2/s~2,the dissipation rate was within 0.119～0.317 m~2/s~3,and the shear force was less than 0.433Pa.When the hydrodynamic parameters were in the above range,the flocculation rate（Fr）of Trichosporon fermentans reached more than 90%.The development of flocculation cannot be limited in small-scale research in the laboratory.The scale-up of the flocculation device is neccessary in the industrial application.In this study,an empirical formula relating hydrodynamic parameters and Fr was obtained by Matlab.The enlargement of flocculation device was carried out.The empirical formula showed an average relative error of less than 3.03%.Thus,a prediction method for Fr in stirred flocculation device with different volumes was established.In order to verify the applicability of the above prediction method in other types of flocculation reactors,a new conical draft tube airlift circulating reactor with 5 L volume for flocculation was designed according to the empirical formula.Based on Fluent simulation,the optimized reactor structure parameters and operating conditions were determined as follows:the height-diameter ratio of the outer barrel H₁:D₁=5.4,the distance between the guide barrel and the bottom H₄=20 mm,the diameter of the outlet of the guide barrel D₄=36 mm,the number of layers of internal components n=3,the radius of internal components r=38 mm,and intake air volume V₀=0.22 m~3/s.It was found that the rounded internals designed in this study effectively reduced the shear force without reducing the turbulent kinetic energy and dissipation rate.According to the design results,the conical draft tube airlift circulating reactor was established and operated in the laboratory,the experience value(Fr_exp)and the calculate value(Fr_cal)were compared.It was found that the average relative error was less than 4.81%,and Frexp reached91.3%.In this study,the Fr of Trichospron fermentans was predicted by hydrodynamic parameters in different type of flocculation reactor.Based on numerical simulation and fitting empirical formulas,the novel prediction method of Fr contributed to the design of industrial flocculation reactor for harvesting oleaginous yeast.