| Spray freeze drying(SFD)combines the advantages of spray drying(SD)and freeze dryin g(FD).The powder products with controllable particle size produced by this technology have th e advantages of high biological activity and good solubility.This technology has attracted muc h attention in the fields of food,medicine,and material manufacturing and processing.Neverthe less,spray freeze drying is almost in the stage of laboratory research currently in China.The tra ditional equipment has high energy consumption and low efficiency,and there is lack of large-sc ale continuous production equipment,which limits the promotion and application of SFD in m any fields.In this paper,a dynamic spray freeze drying equipment was proposed to solve the pr oblem of low efficiency and hard to large-scale production of SFD.In order to improve the uniformity of flow and temperature fields inside the freezing chamber of dynamic spray freeze drying equipment,the key structure of the freezing chamber was optimized by simulation using computational fluid dynamics(CFD)method.The optimized structure size of the freezing chamber is as follows : the height is 2100 mm,the diameter is 800 mm,the diameter of the hole was 20 mm,and the number of holes is uniformly distributed 9 rows and 11 columns.The optimized freezing chamber structure was used as the physical model,the discrete phase model(DPM)was used to numerically simulate the freezing process of liquid nitrogen spray,and the simulation data were fitted the curve equation of the relationship between the final freezing temperature and droplet diameter and solution flow rate.It provides basic data for design of automatic control program of dynamic spray freeze drying and optimization of spray freeze drying process.Adopt for improving the dispersion uniformity of particle motion in the designed dynamic drying chamber.Numerical simulation of the dynamic drying process of particles was carried out by the discrete unit method,and the main structure of the drying chamber was optimized.When the length of drying chamber is 2600 mm and the diameter is 1500 mm,the optimal inclination angle of the copying plate is 5°,and the optimal number is 18.Through simulation analysis,it is concluded that the main factors affecting the movement of particle motion are the rotation speed,diameter and structure size of drying chamber;the main factors affecting the discharge rate are the curvature of the discharge blade and the rotation speed of the drying chamber.To verify the reliability of the simulation,the size of the drying silo was reduced in an equal proportion and the same simulation was performed.A small drying chamber equipped with 3D printing was used to carry out the loading experiment,the observed material movement was consistent with the simulation results.When the discharge speed of the drying silo is 80r/min,the experimental discharge rate is 0.601kg/min,and the simulated discharge rate is 0.576kg/min,with a relative error of 4.16%.For studying the heat transfer in the dynamic drying process,the heat transfer characteristics of the drying chamber under no-load condition were analyzed by transient heat solution,and the temperature field in the drying chamber at different heating temperatures was obtained.At the same time,it is found that the temperature difference between different positions in the warehouse is large,but because the material is in a moving state in the drying warehouse,the heating of the material is relatively uniform.The CFD-DEM coupling model was used to simulate the heat transfer process of the drying chamber under the condition of loading.The effects of heating temperature,vacuum degree of drying chamber,particle size of material,rotation speed of drying chamber and filling amount of drying chamber on the temperature of material particles in the drying process were studied and analyzed.The influence of particle size on the temperature change of material particles is the most significant.The above simulation results provide a good theoretical basis for improving the efficiency of spray freeze-drying and developing large-scale spray freeze-drying equipment.On this basis,according to the requirements of dynamic spray freeze-drying process flow and process parameter monitoring,the preliminary control scheme of dynamic spray freeze-drying equipment monitoring system was further proposed,and the system program structure was constructed.Using Siemens SIMATIC Win CC software,the human-computer interaction interface was developed by configuring and writing VB scripts.The communication between upper and lower computers was established by OPC communication protocol,which can realize the real-time monitoring function of the system. |
