Simulation And Optimization Of The Methanol Distillation System

Methanol is widely used as basic organic chemical and has a bright prospect. Because of the energy consumption in distillation process accounted for20%of the methanol production process, it is very important to develop energy-saving process and improve the product quality of the distillation process. The chemical process simulation technology becoming mature in recent decades, can reduce production cost, improve the innovative and comprehensive competitiveness, and increase the economic benefit.At present, the two-column and three-column double-effect distillation systems of methanol were mainly used. Firstly, the two different systems were simulated and optimized respectively using the RadFrac module based on equilibrium stage model of the Aspen plus. Both of the systems are suitable for using the combined property method of WILSON and NRTL by analysis. The effects of feed stage, reflux ratio, pressure of column, bottom rate on the methanol distillation process were studied, which contributed to determine the optimized control scheme. The Aspen Process Evaluation was also used to evaluate these two different systems. Main results are as flows:(1) The three-column double-effect distillation system has advantage of high production, good quality and low energy consumption compared with the two-column scheme.(2) For the production scale of500,000tons/year:Compared with the two-column scheme, the three-column scheme is11.32%higher in term of the total cost,48.93%lower in respect of the total utilities cost, and also far less annual operating cost. Therefore, the three-column scheme will get more high benefits.In addition, the two-column system was simulated using the RateFrac module of rate-based non-equilibrium stage model. The effects of packing type and operating conditions on distillation process were studied in order to optimize the system. The mass transfer behavior of the non-equilibrium stage model was described by the mass and heat transfer rate equation, so the simulation results about the distribution of temperature, composition and flow rate in columns are closer to reality. The HETP of the real packing column is also calculated by the RateFrac module, providing a reference value for other design and study.