Design And Control Of Extractive Distillation For The Benzene/Isopropanol/Water Separation And Safety Analysis

A novel thermally integrated two side stream extractive distillation for separating benzene-isopropanol-water in ternary azeotropic system was proposed.Compared with the traditional scheme,the thermal integration scheme can further reduce TAC by 15.8%and CO₂emission by 18.88%.The dynamic controllability of the two processes was further studied,and the open-loop and closed-loop methods were applied to find the temperature control stages.A control structure（CS1）was designed for the traditional Distillation system.The control structure was further improved on the base of CS1,and a more robust control structure CS2 was proposed.For the thermally integrated double side line extractive distillation process,the bypass strategy and the strategy of adding additional small heat exchanger are applied to the dynamic control of the thermally integrated process,and the control structure CS3 is designed and developed.In order to reduce the shake of the system,a single auxiliary heat exchanger control structure CS4 and a hot end bypass control structure CS5 are developed on the basis of the control structure CS3.The performance of the proposed control structure was tested by adding±10%flow disturbance and±20%component disturbance.It was found that CS2 has good dynamic characteristics under feed flow disturbance and component disturbance.CS3,CS4 and CS5 were resistant to feed flow and component disturbances.By calculating the DPT and IAE,it was quantitatively compared that the control performance of CS2 and CS4 is the best.In order to avoid potential safety hazards in Distillation process,quantitative Hazard and Operability Study was carried out for side stream extractive Distillation process.The extraction process is divided into three nodes.In order to more accurately and reflect the real working state of Distillation column,rigorous modeling was carried out.Then some typical fault causes were selected for detailed analysis and explanation.The typical fault causes include:Large disturbance of feed flow,Large disturbance of feed composition,Large disturbance of feed temperature,Decrease of cooling medium flow,Increase of cooling medium flow,Excessive overhead cooling medium temperature,Increase of heating steam flow,The flow of heating stream decreasing and The drain valve blocked.When the fault occurs,the changes of reflux drum level,base level,product purity,product recovery,base temperature and the top pressure of C1 were given.Finally,the quantitative HAZOP table was drawn which was combined with Aspen dynamic simulation.And the corresponding improvement suggestions were put forward to ensure its feasibility in process safety and stable operation.