Flow Field Analysis And Process Study Of L-Threonine Fermentation

L-threonine is an essential amino acid,which has a very wide range of application value,and its demand is growing rapidly.The industrial production of threonine is carried out in large threonine fermentation tank.The equipment and fermentation process of large threonine fermentation tank are mostly designed by experience in the early stage of design,which will make the later stage of design need more cost to optimize and adjust the experiment.In this paper,the stirring flow field and fermentation process of threonine fermenter were studied.According to the theory of computational fluid dynamics,the stirring model of threonine fermenter was established.The stirring flow field of threonine fermenter was simulated by Fluent and other software.The simulation results were analyzed and the mixing impeller combination was optimized.At the same time,threonine fermentation experiments were carried out to further study the technological process of threonine fermentation.The simulation and experimental study provide theoretical calculation analysis and experimental basis for the design of large threonine fermentation tank equipment and fermentation process control.The details are as follows:Firstly,based on computational fluid dynamics theory and stirring fermentation model,the numerical simulation model of stirring flow field in threonine fermentation was established,and the simulation method and process of stirring flow field in threonine fermentation tank were given.Secondly,the stirring flow field in threonine fermentation tank was simulated under different stirring impeller combinations.Combining the technological parameters of threonine fermentation and the design experience of stirring impeller,the stirring impeller combinations were optimized and the size of the stirring impeller combinations was determined according to the parameters of flow field distribution,power and mixing time obtained by simulation.The optimized impeller combination consists of four-stage impeller.The upper three-stage impeller is a three-inclined straight-blade impeller.The diameter of the impeller is d1= d2= 2.30 m.The bottom impeller is a six-blade parabolic disk turbine,and the diameter of the impeller is d4=2.30 m.Then,the stirring flow field of optimized blade combination in threonine fermentation process under different conditions was simulated.The effects of liquid level,fermentation liquid density,agitator speed and aeration stirring on the stirring flow field distribution and stirring power in tank were studied.The results showed that when the liquid level was completely immersed in a stirring impeller,the stirring power of the liquid level continued to rise with little change.In the process of fermentation,the power of agitator will increase with the increase of solution density,and the change curve of the process is obtained.The power curve of agitator at different rotational speeds is given,which is consistent with the experience.In the simulation of gas-liquid two-phase flow,it is found that the power of agitator combination will decrease by 20.9% and the average gas content of the solution will stabilize at about 21.4%.It is reasonable to calculate that the initial loading level of the threonine fermenter should be about 6.3 m high.Finally,threonine fermentation experiments were carried out in a small fermentor,and the stirring flow field was simulated.The error between the simulated stirring power and the actual stirring power is less than 10%.By comparing the simulated flow field and related parameters between the test tank and the large tank,the design of the large tank is reasonable.The parameters of rotational speed and ventilation rate are given in the threonine fermentation experiment.The dissolved oxygen in the fermentation tank is maintained at about 30% by indirect control of rotational speed and ventilation rate,and a better acid production rate is obtained.It provides a basis for the design of fermentation technology of large fermentor.