Modeling,Optimization And Control Of Continuous Crystallization Process

Crystallization process plays an important role in chemical process.The quality of thecrystalline product,such as purity and crystal size distribution(CSD),affects the downstream operations including separation and purification directly.At present,the common crystallization mode is batch crystallization.However,the shortcomings of batch crystallization such as difficulty to control the consistency of the product and the high time cost urge the development of continuous crystallization.In the existing literature,it is common to design the continuous crystallizer to improve the product.In this thesis,based on a newly crystallizer,continuous oscillatory baffled crystallizer(COBC),the modeling,optimization and control have been studied.The main contributions are as follows:(1)A population balance model(PBM)is derived by combining the crystallization mechanism and the COBC structure characteristics.The method of characteristics and high resolution finite volume method can be applied to solve the model.The solution of the PBE can be used to characterize the CSD of any given position within the crystallizer.When simulating the crystallization process,according to the residence time distribution(RTD)of the solution in the COBC,the tanks-in-series model is used to determine the number of segments in the simulation,by which the simulation results can be closer to the actual results.(2)In order to obtain the desired CSD,the optimization model is established,by which the constant supersaturation can be obtained.Combining the heat exchange principle with energy balance derive the optimal inlet temperature of cooling water in jacket.With the above model and solution method,the temperature control value can be set more accurately in practical operation.Additionally,the model predictive control strategy is proposed.(3)Taking L-glutamic acid as the crystalline object,the simulation experiments on the crystallization process are made according to the proposed model and method.In addition,the optimal constant supersaturation is obtained with the optimization model.The corresponding solution temperature curve and the optimum inlet temperature for the cooling water in jacket are also calculated.The simulation results show that the optimization result is very close to the target CSD,which demonstrates the effectiveness of proposed method.