CFD-based Analysis And Improvement For The Flow Field Of 1-4L Stirred Tank Reactor For Crystallization

Jacketed reactor is a commonly used reaction vessel in the process of crystallization.The flow field distribution of the reactor is an important criterion for the evaluation of mixing effect,which has been an important research topic in the chemical field.Because of the complexity of the internal structure of the reactor,there are obvious defects in the process of mixing,such as insufficient stirring,mixture distribution unevenness and dead zone.It is difficult to get good results by using the traditional experimental method as well as time-consuming and laborious.So advanced computational fluid dynamics methods have been appealed to overcome these deficiencies.In the crystallization reactor,impeller is usually used to get a uniform distribution of the mixing of the flow field to ensure that the material fully mixed and reacted.The computational fluid dynamics(CFD)method is adopted to analyze the flow field of 1L stirred tank reactor for crystallization.A popular CFD software named FLUENT is used to analyze the influence of a single layer turbine agitator on the flow field in a stirred tank reactor.The standard turbulence model of k-? is employed to simulate a three-dimensional single-phase flow field of water.Simulation results indicate that the simulated flow field is consistent with real distribution of the flow field,while it shows that uniform blending can be achieved in the lower and middle parts of 1L stirred tank reactor,but the flow field in the middle and upper part is not uniform.To solve the problem,dual impellers are proposed for stirring so as to maintain a uniform speed for both the lower and upper parts of the reactor.Simulation results show that the two flow fields generated by the dual impellers can be well connected,and the blending effect is obviously better than that of traditional single-impeller style.However,no matter whether the single layer turbine agitator or dual impellers are installed,a “dead zone” will be formed at the bottom of the reactor.To resolve the above problem,the baffles are designed to eliminate the “dead zone” at the reactor bottom.First of all,four vertical baffles are installed in the 1L crystallizer.The simulation results show that the phenomenon of “dead zone” is not improved by installing vertical baffles,at the same time,it will form another “dead zone” near the reactor wall.Then,four bottom baffles are installed in the 1L crystallizer.Simulation studies indicate that compared with the reactor without baffles,there is no “dead zone” at the reactor bottom.The flow velocity of the reactor bottom is obviously increased,more obvious spiral upward axial flow at the central part of the reactor bottom are formed.The axial velocity of the center of the lower portion of the impeller is greater than that of other sites.A loop is formed between upper impeller and lower impeller,and a circle will be formed in the reactor bottom.The velocity distribution of the flow field of the reactor is uniform.