Design Optimization And Simulation Of Stirred Reactor For Cellulose Nanocrystals

With the development of nanotechnology in various fields,biomass nanomaterials represented by nanocellulose have been widely concerned by scholars and business circles in the field of materials because of their unique structure and superior physical and chemical properties.Howe ver,the domestic research on the preparation direction of nanocellulose is still in the laboratory stage.In order to solve the high cost problem in the commercial production process and develop towards the direction of green,efficient and sustainable,the pilot-scale research has become particularly important.It mainly includes preparation process selection and production line design.Stirred tank as the core equipment of the whole pilot production line,it is a hot topic to optimize the structure of the stirred tank and improve the mixing efficiency of the material.Along with the development of computational fluid dynamics(CFD)in the research of mixing process in recent years,the characteristics of flow field in the tank are deeply explored,and the visualization of prediction results makes the selection and design of agitator is no longer completely dependent on experiment and experience,which greatly shortens the research time and improves the accuracy of experimental results.The main contents of this paper are as follows:(1)Pilot-scale production line of cellulose nanocrystals and its process designThe feasibility of preparation of cellulose nanocrystals by s equential oxidation of periodate was studied from the point of view of product yield,economy and environmental friendliness.The results show that the obtained cellulose nanocrystals by this method have high yield,low energy consumption,simple operating conditions(normal temperature).and environmentally friendly,so this method can be used for preparing cellulose nanocrystals.A pilot-scale production line of cellulose nanocrystals with a scale of 1 kg/d was designed.(2)Study on optimization design and numerical simulation of the model of stirred reactorAccording to the problems and experience in the small-scale experiment,it is found that the solid phase short rod cellulose particles will become viscous after absorbing water,and will be attached to the bottom,side wall and baffle of the reactor under the action of the thrust of the agitator during the stirring process.The large amount of residue accumulation will change the flow field shape in the reactor,and then affect the mixing quality of the raw materials.In order to solve the above problems,the tangential flow and low mixing efficiency still exist when the baffle-free design is adopted.In this study,a baffle-free spherical stirring reactor is designed instead of the shape structure of the traditional cylindrical stirring reactor.Combined with the basic theory of computational fluid dynamics,the solid-liquid mixing model in the stirred reactor during oxidation process was established by FLUENT software.The flow field characteristics of cylindrical stirred reactor and spherical stirred reactor were compared from four angles: solid particle volume fraction,solid particle velocity,solid particle axial velocity and turbulent kinetic energy distribution.According to the numerical simulation results,under the condition of the structure and the rotating speed n=500 rpm,the solid-liquid mixing effect in the spherical stirred reactor is significantly improved compared with that in the cylindrical stirred reactor,but the tangential flow and the raw material attached wall problems are not well solved.(3)Optimization of influencing factors for homogeneous mixing of solid and liquid in a spherical stirred reactorBy means of numerical simulation,the influences of the diameter of the agitator,the installation height of the agitator and the rotating speed of the agitator shaft on the flow field morphology in the spherical agitator were further studied,and the optimal parameter combination of the spherical agitator model structure was determined by using the control variable method.According to the numerical simulation results,the optimal blade diameter d=0.45 D,the installation height c=0.25 D or slightly greater than 0.25 D can be,the optimal speed of the stirring shaft n=650rpm.The problem of material attachment to the wall is effectively solved by the optimized spherical agitating reactor.(4)Structure design of spherical mixing deviceAccording to the above simulation results,the mechanical structure of the optimized spherical stirred reactor is designed.It mainly includes the selection of motor power model,the determination of shaft diameter and material,and design sliding device and cleaning device,the problem of material adhesion to tank wall and punching is solved thoroughly.The whole modeling process was completed on CATIA software,and combined with the DMU mot ion simulation of its knowledge engineering module and digital assembly module,the parametric design of the whole device was realized and the whole working process was simulated,which provided a reference for the design of the agitating reactor in the pilot-scale production line of cellulose nanocrystals prepared by sequential oxidation of periodatate.