| Ethylene glycol(EG)is an important chemical raw material for the production of polyester fibers.With the continuous expansion of global fiber demand,the demand for ethylene glycol is gradually increasing.Due to the energy structure,the process of ethylene glycol from coal is an important route for the ethylene glycol industry in China.From these aspects of process route,energy saving and emission reduction and dynamic control,Aspen Plus was used to simulate the steady state and optimize the operation parameters of the methanol tower,the ester tower and the EG tower in the 100000 t/a coal-to-EG distillation section.The double-effect distillation process and extraction process were designed to reduce the energy consumption of the whole process and recycle the waste,which achieved the goal of energy saving and emission reduction.Using Aspen Dynamics to simulate dynamic process of the entire process,a reasonable control structure was chosen by analyzing the response to disturbance.The main components of the EG distillation section were methanol(MeOH)-EG,EG-butanediol(BDO)and EG-propanediol(PG).The area integral method was used to verify the reliability of the vapor-liquid phase equilibrium data in the thermodynamic consistency test.The binary interaction parameters of NRTL,Wilson and UNIQUAC these thermodynamic models were fitted by using Data Regression module in Aspen Plus.By comparing the calculated data with the experimental data,the data calculated by the NRTL model has the smallest deviation,which can describe these systems well.Based on this,the NRTL model was used to simulate the subsequent process.In order to achieve the goal of high purity and energy consumption reduction,when the methanol tower,ester tower and EG tower were simulated,single factor sensitivity analysis and multi-factor orthogonal test were carried out to optimize the process parameters.The results are as follows:theoretical plate number N of 50,35,100,feed stage NF of 33,14,56,reflux ratio R of 1.70?7.08?60,distillate to feed D/F of 0.5020,0.0462,0.0370.The purity of methanol is 0.9991 and the purity of EG is 0.99919,which meets the requirements of the industry.To solve the problem of high energy consumption of methanol tower,countercurrent double-effect distillation process is designed by analyzing distillation characteristics of methanol process.The parameters of the low-pressure and high-pressure towers are as follows:operating pressure of 0.061 MPa,0.162 MPa,N of 36,50,NF of 16,31,R of 1.62,2.50,D/F of 0.235,0.347.Compared with the original process,the total energy consumption is saved by 11528 kW,and total annual cost is reduced by 9.403 million yuan.For the problem of ethylene glycol waste discharge,toluene extraction process is applied to recover fusel.The purity of butanediol recovered by extraction is 0.985,which was in line with industry requirements.Ethylene glycol has a purity of more than 0.915 and can be used as a raw material for antifreeze.The process can not only reduce the discharge of waste,but also increase the annual income by 14.416 million yuan,and can achieve annual economic benefits of 18.852 million yuan.Due to the existence of abnormal operation conditions in the production process,four control schemes were designed for the methanol tower,and two schemes were designed for the ester tower and EG tower in Aspen Dynamics by determining the sensitive plate and size of the tower and auxiliary equipment.From the perspective of production and purity of the key components,the dynamic response of feed flow rate and component disturbance was analyzed.The ideal control scheme for each tower was obtained:the double temperature control scheme was selected for the low-pressure methanol column and ester column,and the constant reflux ratio control scheme was selected for the high-methanol column and EG tower. |
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