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

Divided wall column(DWC)can realize efficient separation of multi-component mixture in one single column.A mixture could be sharply separated into four products in Kaibel Divided Wall column(KDWC)or five products in Extended Divided Wall column(EDWC).A 4-component mixture of methanol/ethanol/n-propanol/n-butanol was selected to be investigated in a KDWC arrangement.Four products with molar purity of 90%are specified.Rigorous distillation models in Aspen Plus were employed in simulations.Under the same targets of product purity and yield,the reboiler duty of KDWC was reduced by 40.8%compared to the conventional separation sequence.Subsequently,a lab-scale KDWC tower was built for studying the characteristics of KDWC based on steady-state rigorous simulation.A temperature and pressure monitoring system was designed with WinCC and STEP7 in Siemens S7-300.The start-up procedure was tested and it can be divided into three stages,including the total reflux ratio stage,the batch distillation stage and the continuous feeding stage.The simulated results agree well with the experimental results under the same conditions,but the content of methanol impurity in the upper side-stream and butanol in the lower side-stream had small deviations.After slightly increasing liquid split ratio,we can achieve a smooth product control of ±20%composition disturbances in feed with product purities ranging 88.6-92.6 mol.%.The second part of this work aims to separate a mixture of five alcohols with product molar purity of 99%in two arrangements of DWC.The first CKDWC arrangement consists of a conventional column and a KDWC.The reboiler duty of CKDWC arrangement could be reduced by 22.4%compared to conventional separation sequence.The EDWC arrangement has two vertical partitions,which could separate a 5-component mixture in one single column.It can reduce the reboiler duty by 38.6%compared to conventional separation sequence.In the EDWC,the split of propanol and butanol is carried out in the prefractionator;methanol and propanol is split in the middle column.Ethanol,propanol and butanol products could be collected from the three sidestreams of the main column,respectively.Finally,two kinds of composition control model of CKDWC and EDWC were set up by Aspen Dynamics.The simulation shows that it could handle ±10%disturbances of flow rate and composition in feed.The purity of products was between 98.80?99.08%in CKDWC and 98.88?99.10%in EDWC.