Experimental And Simulation Study Of 4-Product Divided Wall Column For Alcohols Separation

Divided-wall column(DWC)can be used to separate multi-component mixture.The Kaibel DWC and Agrawal DWC can achieve high purity separation of quaternary mixture,which has the advantage of energy saving and lower investment cost compared with the conventional process and has significant industrial application value.To verify the industrial application feasibility of KDWC,the distillation separation of a quaternary mixture of four acohols,including methanol,ethanol,n-propanol,and n-butanol(MEPB),is researched in this study.On the basis of the steady-state simulation,a lab-scale KDWC equipment was designed and built.The SIMATIC S7-300 and WinCC were used for PLC programming configuration.The temperature and pressure monitoring system and operation variable control system were established.The steady-state experiment was divided into three stages,including the total reflux ratio stage,the batch distillation stage and the continuous distillation stage.The experimental results agree well with simulation results that the quaternary mixture can be separated into four products with specified mole purity of 90%,and the composition of light and heavy impurities in side streams were slightly different.Dynamic experiments showed that,in face of ±20%feed composition disturbances,the KDWC can be smoothly controlled by the 4×4 temperature control structure with the mole purity of products ranging between 88.17%and 93.99%,and the purity deviation of the product can be controlled within a range of-2%?+4%.Subsequently,ADWC was simulated with the product purity set as 99mol.%,and the separation effect of ADWC in three different feedconditioning areas was investigated.The results were compared with KDWC,under the same separation,showed that all three kinds of ADWC were better than KDWC in energy consumption and total annual cost(TAC).Compared with KDWC,the reboiler duty of the best structure of ADWC can be reduced by 12.28%and the TAC is also reduced by about 7.41%.At last,the dynamic control scheme of ADWC was investigated according to the steady state characteristics.Composition control structure,temperature control structure and temperature-composition control structure with 5×5 control loops were established for ADWC in Aspen Dynamics.Results showed that all three kinds of control structure has good control effect.Among them,the temperature-composition control structure can not only avoid large purity deviation of the product,but also improve the ability to cope with the disturbance.It could handle±20%disturbances of flow rate and composition in feed.