Simulation Study On Energy Saving Scheme Of Three-component Distillation

Distillation is one of the important basic chemical unit operations,but energy consumption is at the forefront of chemical production process.As distillation technology is widely used in chemical plants,research on distillation and energy conservation is of great significance.In this paper,a three-component mixture of six separation index(ESI)was selected as the research object.The simulation process of direct,indirect and full thermal coupled distillation was established in Aspen plus software,and the simulation calculation was carried out under given operating conditions.The components in the mixture are divided into light component(A),intermediate component(B)and heavy component(C)according to the boiling point.The ratios are 0.4/0.2/0.4,0.3/0.4/0.0.3,0.25/0.5/0.25,0.2/0.6/0.2,0.1/0.8/0.1,respectively.The feed heat condition(q)is adjusted from 0 to 1,and the composition of the feed is taken.Firstly,according to the simple calculation,the number of plates in different rectification schemes is determined.The Radfrac module is strictly calculated after fixing the number of plates,the parameters are repeatedly adjusted,and the three-component mixture is found to be separated when the rectification requirements are met.The best operating parameters.Through the comparative analysis of the simulated data,factors affecting the energy consumption of the distillation are verified.The results show that the energy consumption of direct distillation is lower than that of indirect distillation in six systems with ESI>1,ESI=1 and ESI<1.The feed heat condition can affect the distillation energy consumption.For the three-component mixture system of different ESI,the bubble point feed energy consumption is the lowest.In the light and heavy component content,the distillation energy consumption increases with the rising of intermediate component.The separation index can not be completely used as a parameter to judge the energy consumption of distillation.The separation index,the relative volatility between components and the difference in boiling point can be combined to accurately determine the energy consumption of distillation.For fully thermally coupled distillation,key parameters affecting the energy consumption of the fully thermally coupled distillation column—gas phase reflux(V),liquid phase reflux(L),and feed heat condition(q)were studied.The simulation results show that they have a significant impact on the energy consumption of fully thermally coupled distillation.In the case where q is constant,when V(or L)is fixed in a certain value,there is the lowest value of L(or V)which minimizes the heat duty of the entire column condenser and the reboiler.By adjusting V(or L),you can find the lowest value of the full tower heat duty,i.e.the value under optimal operating conditions.When q changes,the position of minimum value also changes.From the perspective of energy saving,the total heat duty of fully thermally coupled distillation is the smallest when q=1.For the different separation index systems,under the optimal operating conditions,it is found that the separation of the three-component mixture,the more difficult the separation of components B and C,the higher the energy consumption of the fully thermally coupled distillation.When the separation of components B and C is equivalent,the separation of components A and B is more difficult,and the energy consumption is higher.Comparing the energy consumption of the three distillation schemes under the same conditions of the number of trays,it was found that not all systems are suitable for fully thermally coupled distillation.For systems suitable for full thermal coupled rectification,the energy efficiency can reach 9%-46% compared to the lowest energy consumption of the other two distillation schemes.For the system with ESI>1,the energy efficiency of fully thermally coupled distillation is not significant enough.The system performance of ESI<1 and ESI?1 is outstanding.For systems with different separation indexes,when the content of light and heavy components is equal,the higher the content of intermediate components,the higher the energy saving efficiency.