| As an important unit operation of chemical industry,rectification has a low energy efficiency in the production process,so some unnecessary energy consumption has appeared.Most alcohols,with their good solubility,can be used as solvents in industry,and it is their high solubility that makes it difficult to separate them from water in the production process.In this paper,the water/ethanol/n-pentanol azeotrope system was taken as the research object,and the special rectification and energy-saving design of the alcohol-water system were studied.With the lowest total annual cost(TAC)as the optimization target,the steady state flow design and optimization were carried out by using aspen software and the appropriate control scheme was proposed.Firstly,the separation of n-pentanol/water azeotrope system was studied,and the conventional two-column extractive distillation process was designed to optimize the process.The optimal TAC was 1.74×10~6$/year.On this basis,a conventional three-column extractive distillation separation scheme was proposed for water/ethanol/n-pentanol azeotrope system.By optimizing the process,the optimal TAC is 2.21×10~6$/year.Dynamic control of the optimal flow is studied.Firstly,a control structure with fixed reflux ratio and a dual-temperature control structure with Qr/F feedforward control are proposed.For this reason,a component control structure with Qr/F feedforward control is proposed.The disturbance results show that the anti-disturbance ability of each component is enhanced and the response is relatively fast,which is an ideal control scheme.Based on the conventional three-column extractive distillation process,the energy saving integrated process was further studied,and the integrated process of extractive distillation column and solvent recovery column(C5-C6 integration)and the integrated process of two extractive distillation columns(C7-C8 integration)was proposed.By optimizing the C5-C6 integration process,the optimal TAC was1.91×10~6$/year,which decreased by 13.3%compared with the conventional process.By optimizing the C7-C8 integration process,the optimal TAC is2.15×10~6$/year.Compared with the two integration processes,the C5-C6 integration process was more energy-saving than the C7-C8 process,and the TAC savings was about 10.81%.The more economical C5-C6 integration process is studied on the dynamic control,and the control scheme of dual temperature control of the main tower is proposed.However,the disturbance shows that the response time of the control scheme is long and the purity of the product is difficult to recover to the predetermined value.Therefore,a composite-temperature cascade control structure with Qr/F feedforward control is proposed.This control structure can make up for the poor stabilization effect of the temperature controller,and the product purity can be restored to the expected value after disturbance,achieving a relatively ideal control effect.The above research results are valuable for the optimization and dynamic control of energy saving separation of alcohol-water system. |
